Metering APIs (#580)

* Add cameraPictureMetering and cameraPictureSnapshotMetering

* Adapt Meter and metering package to picture use

* Simplify Full2PictureRecorder, we'll use metering package instead

* Add doMetering parameter

* Implement cameraPictureMetering and cameraPictureSnapshotMetering in engine

* Add options in demo app

* Add better logs

* Add Snapshot2PictureRecorder

* Capture the correct frame based on timestamp

* Lock AE and AWB. Account for captureBuilder changes

* Fix runtime flash changes bug

* Small changes

* Flash support for metered snapshots

* Remove AE and AWB locks

* Lock AE/AWB/AF inside the snapshot recorder

* Small changes

* Fix AutoExposure metering

* Create Locker and locking.* parameters

* Implement Locker in Camera2Engine

* Implement reset delay in Camera2Engine instead of Meter

* Simplify Snapshot2PictureRecorder

* Fix success value

* Unlock inside Camera2Engine

* Do not lock for normal gestures

* Simplify logic

* Improve locking/AutoFocus

* Fix TORCH bug

* Small changes to locking and metering

* Remove AF and AWB for testing

* Create action package

* Create OneShotAction

* Create LogAction

* Revisit Full2VideoRecorder using actions

* Revisit Full2PictureRecorder using actions

* Enable missing functionality in Snapshot2PictureRecorder

* Move Snapshot2PictureRecorder using actions, rewrite lock package

* Add TimeoutAction

* Add comments to the action package

* Add meter package

* Remove old metering package

* Fix various bugs

* Add action.abort()

* Abort old MeterAction when running new ones

* Fix various bugs

* Add doc empty page

* Add documentation

* Fix tests

README.md

@@ -136,6 +136,8 @@ Using CameraView is extremely simple:
     app:cameraAutoFocusMarker="@string/cameraview_default_autofocus_marker"
     app:cameraUseDeviceOrientation="true|false"
     app:cameraFilter="@string/real_time_filter"
+    app:cameraPictureMetering="true|false"
+    app:cameraPictureSnapshotMetering="false|true"
     app:cameraExperimental="false|true">
     
     <!-- Watermark! -->

cameraview/build.gradle

@@ -240,9 +240,12 @@ task mergedCoverageReport(type: JacocoReport) {
         classFilter.add('**/com/otaliastudios/cameraview/engine/CameraEngine**.*')
         classFilter.add('**/com/otaliastudios/cameraview/engine/Camera1Engine**.*')
         classFilter.add('**/com/otaliastudios/cameraview/engine/Camera2Engine**.*')
+        classFilter.add('**/com/otaliastudios/cameraview/engine/action/**.*')
+        classFilter.add('**/com/otaliastudios/cameraview/engine/lock/**.*')
+        classFilter.add('**/com/otaliastudios/cameraview/engine/meter/**.*')
         classFilter.add('**/com/otaliastudios/cameraview/picture/**.*')
         classFilter.add('**/com/otaliastudios/cameraview/video/**.*')
-        // TODO these below could be testable ALSO outside of the integration tests
+        // TODO these below could be easily testable ALSO outside of the integration tests
         classFilter.add('**/com/otaliastudios/cameraview/video/encoding/**.*')
     }
     // We don't test OpenGL filters.

cameraview/src/androidTest/java/com/otaliastudios/cameraview/CameraViewTest.java

@@ -171,7 +171,10 @@ public class CameraViewTest extends BaseTest {
         // Self managed
         GestureParser gestures = new GestureParser(empty);
         assertEquals(cameraView.getPlaySounds(), CameraView.DEFAULT_PLAY_SOUNDS);
+        assertEquals(cameraView.getAutoFocusResetDelay(), CameraView.DEFAULT_AUTOFOCUS_RESET_DELAY_MILLIS);
         assertEquals(cameraView.getUseDeviceOrientation(), CameraView.DEFAULT_USE_DEVICE_ORIENTATION);
+        assertEquals(cameraView.getPictureMetering(), CameraView.DEFAULT_PICTURE_METERING);
+        assertEquals(cameraView.getPictureSnapshotMetering(), CameraView.DEFAULT_PICTURE_SNAPSHOT_METERING);
         assertEquals(cameraView.getGestureAction(Gesture.TAP), gestures.getTapAction());
         assertEquals(cameraView.getGestureAction(Gesture.LONG_TAP), gestures.getLongTapAction());
         assertEquals(cameraView.getGestureAction(Gesture.PINCH), gestures.getPinchAction());
@@ -649,6 +652,22 @@ public class CameraViewTest extends BaseTest {
         assertFalse(cameraView.getUseDeviceOrientation());
     }
 
+    @Test
+    public void testSetPictureMetering() {
+        cameraView.setPictureMetering(true);
+        assertTrue(cameraView.getPictureMetering());
+        cameraView.setPictureMetering(false);
+        assertFalse(cameraView.getPictureMetering());
+    }
+
+    @Test
+    public void testSetPictureSnapshotMetering() {
+        cameraView.setPictureSnapshotMetering(true);
+        assertTrue(cameraView.getPictureSnapshotMetering());
+        cameraView.setPictureSnapshotMetering(false);
+        assertFalse(cameraView.getPictureSnapshotMetering());
+    }
+
     @Test
     public void testSetFlash() {
         cameraView.set(Flash.TORCH);

cameraview/src/androidTest/java/com/otaliastudios/cameraview/engine/CameraIntegration2Test.java

@@ -1,7 +1,12 @@
 package com.otaliastudios.cameraview.engine;
 
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.TotalCaptureResult;
+
 import com.otaliastudios.cameraview.DoNotRunOnTravis;
 import com.otaliastudios.cameraview.controls.Engine;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
 
 import org.junit.Ignore;
 import org.junit.Test;
@@ -11,6 +16,8 @@ import androidx.annotation.NonNull;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.LargeTest;
 
+import java.util.concurrent.CountDownLatch;
+
 /**
  * These tests work great on real devices, and are the only way to test actual CameraEngine
  * implementation - we really need to open the camera device.
@@ -29,7 +36,23 @@ public class CameraIntegration2Test extends CameraIntegrationTest {
     }
 
     @Override
-    public void testFrameProcessing_afterVideo() throws Exception {
-        super.testFrameProcessing_afterVideo();
+    protected void onOpenSync() {
+        super.onOpenSync();
+        // Extra wait for the first frame to be dispatched.
+        // This is because various classes require getLastResult to be non-null
+        // and that's typically the case in a real app.
+        Camera2Engine engine = (Camera2Engine) controller;
+        final CountDownLatch latch = new CountDownLatch(1);
+        new BaseAction() {
+            @Override
+            public void onCaptureCompleted(@NonNull ActionHolder holder,
+                                           @NonNull CaptureRequest request,
+                                           @NonNull TotalCaptureResult result) {
+                super.onCaptureCompleted(holder, request, result);
+                latch.countDown();
+                setState(STATE_COMPLETED);
+            }
+        }.start(engine);
+        try { latch.await(); } catch (InterruptedException ignore) {}
     }
 }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/engine/CameraIntegrationTest.java

@@ -71,7 +71,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
     public ActivityTestRule<TestActivity> rule = new ActivityTestRule<>(TestActivity.class);
 
     private CameraView camera;
-    private CameraEngine controller;
+    protected CameraEngine controller;
     private CameraListener listener;
     private Op<Throwable> uiExceptionOp;
 
@@ -136,7 +136,6 @@ public abstract class CameraIntegrationTest extends BaseTest {
         }
     }
 
-    @SuppressWarnings("StatementWithEmptyBody")
     private CameraOptions openSync(boolean expectSuccess) {
         camera.open();
         final Op<CameraOptions> open = new Op<>(true);
@@ -144,15 +143,20 @@ public abstract class CameraIntegrationTest extends BaseTest {
         CameraOptions result = open.await(DELAY);
         if (expectSuccess) {
             assertNotNull("Can open", result);
+            onOpenSync();
+        } else {
+            assertNull("Should not open", result);
+        }
+        return result;
+    }
+
+    @SuppressWarnings("StatementWithEmptyBody")
+    protected void onOpenSync() {
         // Extra wait for the bind and preview state, so we run tests in a fully operational
         // state. If we didn't do so, we could have null values, for example, in getPictureSize
         // or in getSnapshotSize.
         while (controller.getBindState() != CameraEngine.STATE_STARTED) {}
         while (controller.getPreviewState() != CameraEngine.STATE_STARTED) {}
-        } else {
-            assertNull("Should not open", result);
-        }
-        return result;
     }
 
     private void closeSync(boolean expectSuccess) {

cameraview/src/androidTest/java/com/otaliastudios/cameraview/engine/MockCameraEngine.java

@@ -123,12 +123,12 @@ public class MockCameraEngine extends CameraEngine {
     }
 
     @Override
-    protected void onTakePicture(@NonNull PictureResult.Stub stub) {
+    protected void onTakePicture(@NonNull PictureResult.Stub stub, boolean doMetering) {
 
     }
 
     @Override
-    protected void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio) {
+    protected void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio, boolean doMetering) {
 
     }
 

cameraview/src/main/java/com/otaliastudios/cameraview/CameraListener.java

@@ -81,8 +81,9 @@ public abstract class CameraListener {
 
 
     /**
-     * Notifies that user interacted with the screen and started focus with a gesture,
-     * and the autofocus is trying to focus around that area. This can be used to draw things on screen.
+     * Notifies that user interacted with the screen and started metering with a gesture,
+     * and touch metering routine is trying to focus around that area.
+     * This callback can be used to draw things on screen.
      * Can also be triggered by {@link CameraView#startAutoFocus(float, float)}.
      *
      * @param point coordinates with respect to CameraView.getWidth() and CameraView.getHeight()
@@ -92,12 +93,12 @@ public abstract class CameraListener {
 
 
     /**
-     * Notifies that a gesture focus event just ended, and the camera converged
-     * to a new focus (and possibly exposure and white balance).
+     * Notifies that a touch metering event just ended, and the camera converged
+     * to a new focus, exposure and possibly white balance.
      * This might succeed or not.
      * Can also be triggered by {@link CameraView#startAutoFocus(float, float)}.
      *
-     * @param successful whether camera succeeded
+     * @param successful whether metering succeeded
      * @param point coordinates with respect to CameraView.getWidth() and CameraView.getHeight()
      */
     @UiThread
@@ -105,7 +106,7 @@ public abstract class CameraListener {
 
 
     /**
-     * Noitifies that a finger gesture just caused the camera zoom
+     * Notifies that a finger gesture just caused the camera zoom
      * to be changed. This can be used to draw, for example, a seek bar.
      *
      * @param newValue the new zoom value

cameraview/src/main/java/com/otaliastudios/cameraview/CameraOptions.java

@@ -427,7 +427,7 @@ public class CameraOptions {
 
 
     /**
-     * Whether auto focus (metering with respect to a specific region of the screen) is
+     * Whether touch metering (metering with respect to a specific region of the screen) is
      * supported. If it is, you can map gestures to {@link GestureAction#AUTO_FOCUS}
      * and metering will change on tap.
      *

cameraview/src/main/java/com/otaliastudios/cameraview/CameraView.java

@@ -107,6 +107,8 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
     final static long DEFAULT_AUTOFOCUS_RESET_DELAY_MILLIS = 3000;
     final static boolean DEFAULT_PLAY_SOUNDS = true;
     final static boolean DEFAULT_USE_DEVICE_ORIENTATION = true;
+    final static boolean DEFAULT_PICTURE_METERING = true;
+    final static boolean DEFAULT_PICTURE_SNAPSHOT_METERING = false;
 
     // Self managed parameters
     private boolean mPlaySounds;
@@ -182,6 +184,8 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         int videoBitRate = a.getInteger(R.styleable.CameraView_cameraVideoBitRate, 0);
         int audioBitRate = a.getInteger(R.styleable.CameraView_cameraAudioBitRate, 0);
         long autoFocusResetDelay = (long) a.getInteger(R.styleable.CameraView_cameraAutoFocusResetDelay, (int) DEFAULT_AUTOFOCUS_RESET_DELAY_MILLIS);
+        boolean pictureMetering = a.getBoolean(R.styleable.CameraView_cameraPictureMetering, DEFAULT_PICTURE_METERING);
+        boolean pictureSnapshotMetering = a.getBoolean(R.styleable.CameraView_cameraPictureSnapshotMetering, DEFAULT_PICTURE_SNAPSHOT_METERING);
 
         // Size selectors and gestures
         SizeSelectorParser sizeSelectors = new SizeSelectorParser(a);
@@ -228,6 +232,8 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         setAudio(controls.getAudio());
         setAudioBitRate(audioBitRate);
         setPictureSize(sizeSelectors.getPictureSizeSelector());
+        setPictureMetering(pictureMetering);
+        setPictureSnapshotMetering(pictureSnapshotMetering);
         setVideoSize(sizeSelectors.getVideoSizeSelector());
         setVideoCodec(controls.getVideoCodec());
         setVideoMaxSize(videoMaxSize);
@@ -280,7 +286,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Instantiates the camera engine.
      *
@@ -547,7 +552,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return false;
     }
 
-
     /**
      * Clears any action mapped to the given gesture.
      * @param gesture which gesture to clear
@@ -556,7 +560,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mapGesture(gesture, GestureAction.NONE);
     }
 
-
     /**
      * Returns the action currently mapped to the given gesture.
      *
@@ -569,13 +572,11 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mGestureMap.get(gesture);
     }
 
-
     @Override
     public boolean onInterceptTouchEvent(MotionEvent ev) {
         return true; // Steal our own events.
     }
 
-
     @SuppressLint("ClickableViewAccessibility")
     @Override
     public boolean onTouchEvent(MotionEvent event) {
@@ -598,7 +599,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return true;
     }
 
-
     // Some gesture layout detected a gesture. It's not known at this moment:
     // (1) if it was mapped to some action (we check here)
     // (2) if it's supported by the camera (CameraEngine checks)
@@ -691,7 +691,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mLifecycle.addObserver(this);
     }
 
-
     /**
      * Starts the camera preview, if not started already.
      * This should be called onResume(), or when you are ready with permissions.
@@ -708,7 +707,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Checks that we have appropriate permissions.
      * This means checking that we have audio permissions if audio = Audio.ON.
@@ -736,7 +734,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return true;
     }
 
-
     /**
      * If audio is on we will ask for RECORD_AUDIO permission.
      * If the developer did not add this to its manifest, throw and fire warnings.
@@ -760,7 +757,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Stops the current preview, if any was started.
      * This should be called onPause().
@@ -772,7 +768,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         if (mCameraPreview != null) mCameraPreview.onPause();
     }
 
-
     /**
      * Destroys this instance, releasing immediately
      * the camera resource.
@@ -865,7 +860,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Controls the preview engine. Should only be called
      * if this CameraView was never added to any window
@@ -959,7 +953,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getCameraOptions();
     }
 
-
     /**
      * Sets exposure adjustment, in EV stops. A positive value will mean brighter picture.
      *
@@ -985,7 +978,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Returns the current exposure correction value, typically 0
      * at start-up.
@@ -995,7 +987,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getExposureCorrectionValue();
     }
 
-
     /**
      * Sets a zoom value. This is not guaranteed to be supported by the current device,
      * but you can take a look at {@link CameraOptions#isZoomSupported()}.
@@ -1012,7 +1003,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setZoom(zoom, null, false);
     }
 
-
     /**
      * Returns the current zoom value, something between 0 and 1.
      * @return the current zoom value
@@ -1021,7 +1011,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getZoomValue();
     }
 
-
     /**
      * Controls the grids to be drawn over the current layout.
      *
@@ -1036,7 +1025,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mGridLinesLayout.setGridMode(gridMode);
     }
 
-
     /**
      * Gets the current grid mode.
      * @return the current grid mode
@@ -1046,7 +1034,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mGridLinesLayout.getGridMode();
     }
 
-
     /**
      * Controls the color of the grid lines that will be drawn
      * over the current layout.
@@ -1077,7 +1064,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setHdr(hdr);
     }
 
-
     /**
      * Gets the current hdr value.
      * @return the current hdr value
@@ -1087,7 +1073,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getHdr();
     }
 
-
     /**
      * Set location coordinates to be found later in the EXIF header
      *
@@ -1103,7 +1088,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setLocation(location);
     }
 
-
     /**
      * Set location values to be found later in the EXIF header
      *
@@ -1113,7 +1097,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setLocation(location);
     }
 
-
     /**
      * Retrieves the location previously applied with setLocation().
      *
@@ -1124,7 +1107,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getLocation();
     }
 
-
     /**
      * Sets desired white balance to current camera session.
      *
@@ -1140,7 +1122,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setWhiteBalance(whiteBalance);
     }
 
-
     /**
      * Returns the current white balance behavior.
      * @return white balance value.
@@ -1150,7 +1131,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getWhiteBalance();
     }
 
-
     /**
      * Sets which camera sensor should be used.
      *
@@ -1163,7 +1143,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setFacing(facing);
     }
 
-
     /**
      * Gets the facing camera currently being used.
      * @return a facing value.
@@ -1173,7 +1152,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getFacing();
     }
 
-
     /**
      * Toggles the facing value between {@link Facing#BACK}
      * and {@link Facing#FRONT}.
@@ -1195,7 +1173,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getFacing();
     }
 
-
     /**
      * Sets the flash mode.
      *
@@ -1210,7 +1187,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setFlash(flash);
     }
 
-
     /**
      * Gets the current flash mode.
      * @return a flash mode
@@ -1220,7 +1196,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getFlash();
     }
 
-
     /**
      * Controls the audio mode.
      *
@@ -1250,7 +1225,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Gets the current audio value.
      * @return the current audio value
@@ -1260,9 +1234,8 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getAudio();
     }
 
-
     /**
-     * Sets an {@link AutoFocusMarker} to be notified of autofocus start, end and fail events
+     * Sets an {@link AutoFocusMarker} to be notified of metering start, end and fail events
      * so that it can draw elements on screen.
      *
      * @param autoFocusMarker the marker, or null
@@ -1272,29 +1245,27 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mMarkerLayout.onMarker(MarkerLayout.TYPE_AUTOFOCUS, autoFocusMarker);
     }
 
-
     /**
-     * Sets the current delay in milliseconds to reset the focus after an autofocus process.
+     * Sets the current delay in milliseconds to reset the focus after a metering event.
      *
      * @param delayMillis desired delay (in milliseconds). If the delay
      *                    is less than or equal to 0 or equal to Long.MAX_VALUE,
-     *                    the autofocus will not be reset.
+     *                    the values will not be reset.
      */
     public void setAutoFocusResetDelay(long delayMillis) {
         mCameraEngine.setAutoFocusResetDelay(delayMillis);
     }
 
-
     /**
-     * Returns the current delay in milliseconds to reset the focus after an autofocus process.
-     * @return the current autofocus reset delay in milliseconds.
+     * Returns the current delay in milliseconds to reset the focus after a metering event.
+     *
+     * @return the current reset delay in milliseconds
      */
     @SuppressWarnings("unused")
     public long getAutoFocusResetDelay() { return mCameraEngine.getAutoFocusResetDelay(); }
 
-
     /**
-     * Starts an autofocus process at the given coordinates, with respect
+     * Starts a 3A touch metering process at the given coordinates, with respect
      * to the view width and height.
      *
      * @param x should be between 0 and getWidth()
@@ -1306,7 +1277,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.startAutoFocus(null, new PointF(x, y));
     }
 
-
     /**
      * <strong>ADVANCED FEATURE</strong> - sets a size selector for the preview stream.
      * The {@link SizeSelector} will be invoked with the list of available sizes, and the first
@@ -1328,7 +1298,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setPreviewStreamSizeSelector(selector);
     }
 
-
     /**
      * Set the current session type to either picture or video.
      *
@@ -1341,7 +1310,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setMode(mode);
     }
 
-
     /**
      * Gets the current mode.
      * @return the current mode
@@ -1351,7 +1319,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getMode();
     }
 
-
     /**
      * Sets a capture size selector for picture mode.
      * The {@link SizeSelector} will be invoked with the list of available sizes, and the first
@@ -1364,6 +1331,61 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setPictureSizeSelector(selector);
     }
 
+    /**
+     * Whether the engine should perform a metering sequence before taking pictures requested
+     * with {@link #takePicture()}. A metering sequence includes adjusting focus, exposure
+     * and white balance to ensure a good quality of the result.
+     *
+     * When this parameter is true, the quality of the picture increases, but the latency
+     * increases as well. Defaults to true.
+     *
+     * This is a CAMERA2 only API. On CAMERA1, picture metering is always enabled.
+     *
+     * @see #setPictureSnapshotMetering(boolean)
+     * @param enable true to enable
+     */
+    public void setPictureMetering(boolean enable) {
+        mCameraEngine.setPictureMetering(enable);
+    }
+
+    /**
+     * Whether the engine should perform a metering sequence before taking pictures requested
+     * with {@link #takePicture()}. See {@link #setPictureMetering(boolean)}.
+     *
+     * @see #setPictureMetering(boolean)
+     * @return true if picture metering is enabled
+     */
+    public boolean getPictureMetering() {
+        return mCameraEngine.getPictureMetering();
+    }
+
+    /**
+     * Whether the engine should perform a metering sequence before taking pictures requested
+     * with {@link #takePictureSnapshot()}. A metering sequence includes adjusting focus,
+     * exposure and white balance to ensure a good quality of the result.
+     *
+     * When this parameter is true, the quality of the picture increases, but the latency
+     * increases as well. To keep snapshots fast, this defaults to false.
+     *
+     * This is a CAMERA2 only API. On CAMERA1, picture snapshot metering is always disabled.
+     *
+     * @see #setPictureMetering(boolean)
+     * @param enable true to enable
+     */
+    public void setPictureSnapshotMetering(boolean enable) {
+        mCameraEngine.setPictureSnapshotMetering(enable);
+    }
+
+    /**
+     * Whether the engine should perform a metering sequence before taking pictures requested
+     * with {@link #takePictureSnapshot()}. See {@link #setPictureSnapshotMetering(boolean)}.
+     *
+     * @see #setPictureSnapshotMetering(boolean)
+     * @return true if picture metering is enabled
+     */
+    public boolean getPictureSnapshotMetering() {
+        return mCameraEngine.getPictureSnapshotMetering();
+    }
 
     /**
      * Sets a capture size selector for video mode.
@@ -1425,7 +1447,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mListeners.add(cameraListener);
     }
 
-
     /**
      * Remove a {@link CameraListener} that was previously registered.
      *
@@ -1435,7 +1456,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mListeners.remove(cameraListener);
     }
 
-
     /**
      * Clears the list of {@link CameraListener} that are registered
      * to camera events.
@@ -1444,7 +1464,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mListeners.clear();
     }
 
-
     /**
      * Adds a {@link FrameProcessor} instance to be notified of
      * new frames in the preview stream.
@@ -1460,7 +1479,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Remove a {@link FrameProcessor} that was previously registered.
      *
@@ -1475,7 +1493,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Clears the list of {@link FrameProcessor} that have been registered
      * to preview frames.
@@ -1488,7 +1505,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Asks the camera to capture an image of the current scene.
      * This will trigger {@link CameraListener#onPictureTaken(PictureResult)} if a listener
@@ -1504,7 +1520,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.takePicture(stub);
     }
 
-
     /**
      * Asks the camera to capture a snapshot of the current preview.
      * This eventually triggers {@link CameraListener#onPictureTaken(PictureResult)} if a listener
@@ -1520,7 +1535,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.takePictureSnapshot(stub);
     }
 
-
     /**
      * Starts recording a video. Video will be written to the given file,
      * so callers should ensure they have appropriate permissions to write to the file.
@@ -1560,7 +1574,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         });
     }
 
-
     /**
      * Starts recording a video. Video will be written to the given file,
      * so callers should ensure they have appropriate permissions to write to the file.
@@ -1628,10 +1641,8 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         takeVideoSnapshot(file);
     }
 
-
     // TODO: pauseVideo and resumeVideo? There is mediarecorder.pause(), but API 24...
 
-
     /**
      * Stops capturing video or video snapshots being recorded, if there was any.
      * This will fire {@link CameraListener#onVideoTaken(VideoResult)}.
@@ -1699,7 +1710,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Returns the size used for pictures taken with {@link #takePicture()},
      * or null if it hasn't been computed (for example if the surface is not ready),
@@ -1714,7 +1724,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getPictureSize(Reference.OUTPUT);
     }
 
-
     /**
      * Returns the size used for videos taken with {@link #takeVideo(File)},
      * or null if it hasn't been computed (for example if the surface is not ready),
@@ -1729,7 +1738,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getVideoSize(Reference.OUTPUT);
     }
 
-
     // If we end up here, we're in M.
     @TargetApi(Build.VERSION_CODES.M)
     private void requestPermissions(boolean requestCamera, boolean requestAudio) {
@@ -1751,7 +1759,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     @SuppressLint("NewApi")
     private void playSound(int soundType) {
         if (mPlaySounds) {
@@ -1760,7 +1767,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
     }
 
-
     /**
      * Controls whether CameraView should play sound effects on certain
      * events (picture taken, focus complete). Note that:
@@ -1774,7 +1780,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setPlaySounds(playSounds);
     }
 
-
     /**
      * Gets the current sound effect behavior.
      *
@@ -1821,7 +1826,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setVideoCodec(codec);
     }
 
-
     /**
      * Gets the current encoder for video recordings.
      * @return the current video codec
@@ -1831,7 +1835,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getVideoCodec();
     }
 
-
     /**
      * Sets the maximum size in bytes for recorded video files.
      * Once this size is reached, the recording will automatically stop.
@@ -1843,7 +1846,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setVideoMaxSize(videoMaxSizeInBytes);
     }
 
-
     /**
      * Returns the maximum size in bytes for recorded video files, or 0
      * if no size was set.
@@ -1855,7 +1857,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getVideoMaxSize();
     }
 
-
     /**
      * Sets the maximum duration in milliseconds for video recordings.
      * Once this duration is reached, the recording will automatically stop.
@@ -1867,7 +1868,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraEngine.setVideoMaxDuration(videoMaxDurationMillis);
     }
 
-
     /**
      * Returns the maximum duration in milliseconds for video recordings, or 0
      * if no limit was set.
@@ -1879,7 +1879,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.getVideoMaxDuration();
     }
 
-
     /**
      * Returns true if the camera is currently recording a video
      * @return boolean indicating if the camera is recording a video
@@ -1888,7 +1887,6 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         return mCameraEngine.isTakingVideo();
     }
 
-
     /**
      * Returns true if the camera is currently capturing a picture
      * @return boolean indicating if the camera is capturing a picture

cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera1Engine.java

@@ -297,7 +297,7 @@ public class Camera1Engine extends CameraEngine implements
 
     @WorkerThread
     @Override
-    protected void onTakePicture(@NonNull PictureResult.Stub stub) {
+    protected void onTakePicture(@NonNull PictureResult.Stub stub, boolean doMetering) {
         stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT, Axis.RELATIVE_TO_SENSOR);
         stub.size = getPictureSize(Reference.OUTPUT);
         mPictureRecorder = new Full1PictureRecorder(stub, Camera1Engine.this, mCamera);
@@ -306,12 +306,12 @@ public class Camera1Engine extends CameraEngine implements
 
     @WorkerThread
     @Override
-    protected void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio) {
+    protected void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio, boolean doMetering) {
         stub.size = getUncroppedSnapshotSize(Reference.OUTPUT); // Not the real size: it will be cropped to match the view ratio
         stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT, Axis.RELATIVE_TO_SENSOR); // Actually it will be rotated and set to 0.
 
         if (mPreview instanceof GlCameraPreview && Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
-            mPictureRecorder = new SnapshotGlPictureRecorder(stub, this, (GlCameraPreview) mPreview, outputRatio, getOverlay());
+            mPictureRecorder = new SnapshotGlPictureRecorder(stub, this, (GlCameraPreview) mPreview, outputRatio);
         } else {
             mPictureRecorder = new Snapshot1PictureRecorder(stub, this, mCamera, outputRatio);
         }

cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera2Engine.java

@@ -42,7 +42,14 @@ import com.otaliastudios.cameraview.controls.Flash;
 import com.otaliastudios.cameraview.controls.Hdr;
 import com.otaliastudios.cameraview.controls.Mode;
 import com.otaliastudios.cameraview.controls.WhiteBalance;
+import com.otaliastudios.cameraview.engine.action.Action;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.Actions;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+import com.otaliastudios.cameraview.engine.action.CompletionCallback;
 import com.otaliastudios.cameraview.engine.mappers.Camera2Mapper;
+import com.otaliastudios.cameraview.engine.meter.MeterAction;
+import com.otaliastudios.cameraview.engine.meter.MeterResetAction;
 import com.otaliastudios.cameraview.engine.offset.Axis;
 import com.otaliastudios.cameraview.engine.offset.Reference;
 import com.otaliastudios.cameraview.frame.Frame;
@@ -52,7 +59,7 @@ import com.otaliastudios.cameraview.internal.utils.CropHelper;
 import com.otaliastudios.cameraview.internal.utils.ImageHelper;
 import com.otaliastudios.cameraview.internal.utils.WorkerHandler;
 import com.otaliastudios.cameraview.picture.Full2PictureRecorder;
-import com.otaliastudios.cameraview.picture.SnapshotGlPictureRecorder;
+import com.otaliastudios.cameraview.picture.Snapshot2PictureRecorder;
 import com.otaliastudios.cameraview.preview.GlCameraPreview;
 import com.otaliastudios.cameraview.size.AspectRatio;
 import com.otaliastudios.cameraview.size.Size;
@@ -64,16 +71,17 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 @RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAvailableListener, Meter.Callback {
+public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAvailableListener,
+        ActionHolder {
 
     private static final String TAG = Camera2Engine.class.getSimpleName();
     private static final CameraLogger LOG = CameraLogger.create(TAG);
 
     private static final int FRAME_PROCESSING_FORMAT = ImageFormat.NV21;
     private static final int FRAME_PROCESSING_INPUT_FORMAT = ImageFormat.YUV_420_888;
+    private static final long METER_TIMEOUT = 2500;
 
     private final CameraManager mManager;
     private String mCameraId;
@@ -81,8 +89,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     private CameraCharacteristics mCameraCharacteristics;
     private CameraCaptureSession mSession;
     private CaptureRequest.Builder mRepeatingRequestBuilder;
-    private CaptureRequest mRepeatingRequest;
-    private CameraCaptureSession.CaptureCallback mRepeatingRequestCallback;
+    private TotalCaptureResult mLastRepeatingResult;
     private final Camera2Mapper mMapper = Camera2Mapper.get();
 
     // Frame processing
@@ -101,13 +108,15 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     private ImageReader mPictureReader;
     private final boolean mPictureCaptureStopsPreview = false; // can make configurable at some point
 
-    // 3A metering
-    private Meter mMeter;
+    // Actions
+    private final List<Action> mActions = new ArrayList<>();
+    private MeterAction mMeterAction;
 
     public Camera2Engine(Callback callback) {
         super(callback);
         mManager = (CameraManager) mCallback.getContext().getSystemService(Context.CAMERA_SERVICE);
         mFrameConversionHandler = WorkerHandler.get("CameraFrameConversion");
+        new LogAction().start(this);
     }
 
     //region Utilities
@@ -126,6 +135,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return value == null ? fallback : value;
     }
 
+    @SuppressWarnings("DuplicateBranchesInSwitch")
     @NonNull
     private CameraException createCameraException(@NonNull CameraAccessException exception) {
         int reason;
@@ -140,6 +150,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return new CameraException(exception, reason);
     }
 
+    @SuppressWarnings("DuplicateBranchesInSwitch")
     @NonNull
     private CameraException createCameraException(int stateCallbackError) {
         int reason;
@@ -163,9 +174,10 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     @SuppressWarnings("UnusedReturnValue")
     @NonNull
     private CaptureRequest.Builder createRepeatingRequestBuilder(int template) throws CameraAccessException {
+        CaptureRequest.Builder oldBuilder = mRepeatingRequestBuilder;
         mRepeatingRequestBuilder = mCamera.createCaptureRequest(template);
         mRepeatingRequestBuilder.setTag(template);
-        applyAllParameters(mRepeatingRequestBuilder);
+        applyAllParameters(mRepeatingRequestBuilder, oldBuilder);
         return mRepeatingRequestBuilder;
     }
 
@@ -197,6 +209,17 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         }
     }
 
+    private void applyRepeatingRequestBuilderAsSingle() {
+        if (getPreviewState() == STATE_STARTED) {
+            try {
+                mSession.capture(mRepeatingRequestBuilder.build(),
+                        mRepeatingRequestCallback, null);
+            } catch (CameraAccessException e) {
+                throw createCameraException(e);
+            }
+        }
+    }
+
     /**
      * Applies the repeating request builder to the preview, assuming we actually have a preview
      * running. Can be called after changing parameters to the builder.
@@ -206,55 +229,52 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
      * {@link #createRepeatingRequestBuilder(int)}.
      */
     private void applyRepeatingRequestBuilder() {
-        applyRepeatingRequestBuilder(true, CameraException.REASON_DISCONNECTED, null);
+        applyRepeatingRequestBuilder(true, CameraException.REASON_DISCONNECTED);
     }
 
-    private void applyRepeatingRequestBuilder(boolean checkStarted, int errorReason, @Nullable final Runnable onFirstFrame) {
-        if (!checkStarted || getPreviewState() == STATE_STARTED) {
+    private void applyRepeatingRequestBuilder(boolean checkStarted, int errorReason) {
+        if (getPreviewState() == STATE_STARTED || !checkStarted) {
             try {
-                mRepeatingRequest = mRepeatingRequestBuilder.build();
-                final AtomicBoolean firstFrame = new AtomicBoolean(false);
-                mRepeatingRequestCallback = new CameraCaptureSession.CaptureCallback() {
-                    @Override
-                    public void onCaptureStarted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, long timestamp, long frameNumber) {
-                        super.onCaptureStarted(session, request, timestamp, frameNumber);
-                        if (firstFrame.compareAndSet(false, true) && onFirstFrame != null) {
-                            onFirstFrame.run();
+                mSession.setRepeatingRequest(mRepeatingRequestBuilder.build(),
+                        mRepeatingRequestCallback, null);
+            } catch (CameraAccessException e) {
+                throw new CameraException(e, errorReason);
             }
-                        if (mPictureRecorder instanceof Full2PictureRecorder) {
-                            ((Full2PictureRecorder) mPictureRecorder).onCaptureStarted(request);
         }
     }
 
+    private final CameraCaptureSession.CaptureCallback mRepeatingRequestCallback
+            = new CameraCaptureSession.CaptureCallback() {
         @Override
-                    public void onCaptureProgressed(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull CaptureResult partialResult) {
-                        super.onCaptureProgressed(session, request, partialResult);
-                        if (mPictureRecorder instanceof Full2PictureRecorder) {
-                            ((Full2PictureRecorder) mPictureRecorder).onCaptureProgressed(partialResult);
-                        }
-                        if (mMeter != null && mMeter.isMetering()) {
-                            mMeter.onCapture(partialResult);
+        public void onCaptureStarted(@NonNull CameraCaptureSession session,
+                                     @NonNull CaptureRequest request,
+                                     long timestamp,
+                                     long frameNumber) {
+            for (Action action : mActions) {
+                action.onCaptureStarted(Camera2Engine.this, request);
             }
         }
 
         @Override
-                    public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
-                        super.onCaptureCompleted(session, request, result);
-                        if (mPictureRecorder instanceof Full2PictureRecorder) {
-                            ((Full2PictureRecorder) mPictureRecorder).onCaptureCompleted(result);
-                        }
-                        if (mMeter != null && mMeter.isMetering()) {
-                            mMeter.onCapture(result);
+        public void onCaptureProgressed(@NonNull CameraCaptureSession session,
+                                        @NonNull CaptureRequest request,
+                                        @NonNull CaptureResult partialResult) {
+            for (Action action : mActions) {
+                action.onCaptureProgressed(Camera2Engine.this, request, partialResult);
             }
         }
 
-                };
-                mSession.setRepeatingRequest(mRepeatingRequest, mRepeatingRequestCallback, null);
-            } catch (CameraAccessException e) {
-                throw new CameraException(e, errorReason);
-            }
+        @Override
+        public void onCaptureCompleted(@NonNull CameraCaptureSession session,
+                                       @NonNull CaptureRequest request,
+                                       @NonNull TotalCaptureResult result) {
+            mLastRepeatingResult = result;
+            for (Action action : mActions) {
+                action.onCaptureCompleted(Camera2Engine.this, request, result);
             }
         }
+    };
+
     //endregion
 
     //region Protected APIs
@@ -265,10 +285,11 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         try {
             CameraCharacteristics characteristics = mManager.getCameraCharacteristics(mCameraId);
             StreamConfigurationMap streamMap = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
-            if (streamMap == null)
+            if (streamMap == null) {
                 throw new RuntimeException("StreamConfigurationMap is null. Should not happen.");
-            // This works because our previews return either a SurfaceTexture or a SurfaceHolder, which are
-            // accepted class types by the getOutputSizes method.
+            }
+            // This works because our previews return either a SurfaceTexture or a SurfaceHolder,
+            // which are accepted class types by the getOutputSizes method.
             android.util.Size[] sizes = streamMap.getOutputSizes(mPreview.getOutputClass());
             List<Size> candidates = new ArrayList<>(sizes.length);
             for (android.util.Size size : sizes) {
@@ -298,13 +319,16 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
             // However, let's launch an unrecoverable exception.
             throw createCameraException(e);
         }
-        LOG.i("collectCameraInfo", "Facing:", facing, "Internal:", internalFacing, "Cameras:", cameraIds.length);
+        LOG.i("collectCameraInfo", "Facing:", facing,
+                "Internal:", internalFacing,
+                "Cameras:", cameraIds.length);
         for (String cameraId : cameraIds) {
             try {
                 CameraCharacteristics characteristics = mManager.getCameraCharacteristics(cameraId);
                 if (internalFacing == readCharacteristic(characteristics, CameraCharacteristics.LENS_FACING, -99)) {
                     mCameraId = cameraId;
-                    int sensorOffset = readCharacteristic(characteristics, CameraCharacteristics.SENSOR_ORIENTATION, 0);
+                    int sensorOffset = readCharacteristic(characteristics,
+                            CameraCharacteristics.SENSOR_ORIENTATION, 0);
                     getAngles().setSensorOffset(facing, sensorOffset);
                     return true;
                 }
@@ -352,8 +376,8 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                     // However, using trySetException should address this problem - it will only trigger
                     // if the task has no result.
                     //
-                    // Docs say to release this camera instance, however, since we throw an unrecoverable CameraException,
-                    // this will trigger a stop() through the exception handler.
+                    // Docs say to release this camera instance, however, since we throw an unrecoverable
+                    // CameraException, this will trigger a stop() through the exception handler.
                     task.trySetException(new CameraException(CameraException.REASON_DISCONNECTED));
                 }
 
@@ -505,7 +529,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
         LOG.i("onStartPreview", "Starting preview.");
         addRepeatingRequestBuilderSurfaces();
-        applyRepeatingRequestBuilder(false, CameraException.REASON_FAILED_TO_START_PREVIEW, null);
+        applyRepeatingRequestBuilder(false, CameraException.REASON_FAILED_TO_START_PREVIEW);
         LOG.i("onStartPreview", "Started preview.");
 
         // Start delayed video if needed.
@@ -555,8 +579,6 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
             throw createCameraException(e);
         }
         removeRepeatingRequestBuilderSurfaces();
-        mRepeatingRequest = null;
-        mMeter = null;
         LOG.i("onStopPreview:", "Returning.");
         return Tasks.forResult(null);
     }
@@ -611,46 +633,84 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     @WorkerThread
     @Override
-    protected void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio) {
-        stub.size = getUncroppedSnapshotSize(Reference.OUTPUT); // Not the real size: it will be cropped to match the view ratio
-        stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT, Axis.RELATIVE_TO_SENSOR); // Actually it will be rotated and set to 0.
-        if (mPreview instanceof GlCameraPreview) {
-            mPictureRecorder = new SnapshotGlPictureRecorder(stub, this, (GlCameraPreview) mPreview, outputRatio, getOverlay());
+    protected void onTakePictureSnapshot(@NonNull final PictureResult.Stub stub, @NonNull final AspectRatio outputRatio, boolean doMetering) {
+        if (doMetering) {
+            LOG.i("onTakePictureSnapshot:", "doMetering is true. Delaying.");
+            Action action = Actions.timeout(METER_TIMEOUT, createMeterAction(null));
+            action.addCallback(new CompletionCallback() {
+                @Override
+                protected void onActionCompleted(@NonNull Action action) {
+                    onTakePictureSnapshot(stub, outputRatio, false);
+                }
+            });
+            action.start(this);
         } else {
-            throw new RuntimeException("takePictureSnapshot with Camera2 is only supported with Preview.GL_SURFACE");
+            LOG.i("onTakePictureSnapshot:", "doMetering is false. Performing.");
+            if (!(mPreview instanceof GlCameraPreview)) {
+                throw new RuntimeException("takePictureSnapshot with Camera2 is only " +
+                        "supported with Preview.GL_SURFACE");
             }
+            // stub.size is not the real size: it will be cropped to the given ratio
+            // stub.rotation will be set to 0 - we rotate the texture instead.
+            stub.size = getUncroppedSnapshotSize(Reference.OUTPUT);
+            stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT, Axis.RELATIVE_TO_SENSOR);
+            mPictureRecorder = new Snapshot2PictureRecorder(stub, this,
+                    (GlCameraPreview) mPreview, outputRatio);
             mPictureRecorder.take();
         }
+    }
 
     @Override
-    protected void onTakePicture(@NonNull PictureResult.Stub stub) {
+    protected void onTakePicture(@NonNull final PictureResult.Stub stub, boolean doMetering) {
+        if (doMetering) {
+            LOG.i("onTakePicture:", "doMetering is true. Delaying.");
+            Action action = Actions.timeout(METER_TIMEOUT, createMeterAction(null));
+            action.addCallback(new CompletionCallback() {
+                @Override
+                protected void onActionCompleted(@NonNull Action action) {
+                    onTakePicture(stub, false);
+                }
+            });
+            action.start(this);
+        } else {
+            LOG.i("onTakePicture:", "doMetering is false. Performing.");
             stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT, Axis.RELATIVE_TO_SENSOR);
             stub.size = getPictureSize(Reference.OUTPUT);
             try {
+                if (mPictureCaptureStopsPreview) {
+                    // These two are present in official samples and are probably meant to speed things up?
+                    // But from my tests, they actually make everything slower. So this is disabled by default
+                    // with a boolean flag. Maybe in the future we can make this configurable as some
+                    // people might want to stop the preview while picture is being taken even if it
+                    // increases the latency.
+                    mSession.stopRepeating();
+                    mSession.abortCaptures();
+                }
                 CaptureRequest.Builder builder = mCamera.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
-            applyAllParameters(builder);
-            mPictureRecorder = new Full2PictureRecorder(stub, this,
-                    mCameraCharacteristics,
-                    mSession,
-                    mRepeatingRequestBuilder,
-                    mRepeatingRequestCallback,
-                    builder,
-                    mPictureReader,
-                    mPictureCaptureStopsPreview);
+                applyAllParameters(builder, mRepeatingRequestBuilder);
+                mPictureRecorder = new Full2PictureRecorder(stub, this, builder, mPictureReader);
                 mPictureRecorder.take();
             } catch (CameraAccessException e) {
                 throw createCameraException(e);
             }
         }
+    }
 
     @Override
     public void onPictureResult(@Nullable PictureResult.Stub result, @Nullable Exception error) {
         boolean fullPicture = mPictureRecorder instanceof Full2PictureRecorder;
         super.onPictureResult(result, error);
         if (fullPicture && mPictureCaptureStopsPreview) {
-            // See comments in Full2PictureRecorder.
             applyRepeatingRequestBuilder();
         }
+
+        // Some picture recorders might lock metering, and we usually run a metering sequence
+        // before running the recorders. So, run an unlock/reset sequence if needed.
+        boolean unlock = (fullPicture && getPictureMetering())
+                || (!fullPicture && getPictureSnapshotMetering());
+        if (unlock) {
+            unlockAndResetMetering();
+        }
     }
 
     //endregion
@@ -672,18 +732,15 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     private void doTakeVideo(@NonNull final VideoResult.Stub stub) {
         if (!(mVideoRecorder instanceof Full2VideoRecorder)) {
-            throw new IllegalStateException("doTakeVideo called, but video recorder is not a Full2VideoRecorder! " + mVideoRecorder);
+            throw new IllegalStateException("doTakeVideo called, but video recorder " +
+                    "is not a Full2VideoRecorder! " + mVideoRecorder);
         }
         Full2VideoRecorder recorder = (Full2VideoRecorder) mVideoRecorder;
         try {
             createRepeatingRequestBuilder(CameraDevice.TEMPLATE_RECORD);
             addRepeatingRequestBuilderSurfaces(recorder.getInputSurface());
-            applyRepeatingRequestBuilder(true, CameraException.REASON_DISCONNECTED, new Runnable() {
-                @Override
-                public void run() {
+            applyRepeatingRequestBuilder(true, CameraException.REASON_DISCONNECTED);
             mVideoRecorder.start(stub);
-                }
-            });
         } catch (CameraAccessException e) {
             onVideoResult(null, e);
             throw createCameraException(e);
@@ -757,7 +814,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
      * the {@link #createRepeatingRequestBuilder(int)} method.
      */
     private void maybeRestorePreviewTemplateAfterVideo() {
-        int template = (int) mRepeatingRequest.getTag();
+        int template = (int) mRepeatingRequestBuilder.build().getTag();
         if (template != CameraDevice.TEMPLATE_PREVIEW) {
             try {
                 createRepeatingRequestBuilder(CameraDevice.TEMPLATE_PREVIEW);
@@ -773,7 +830,9 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     //region Parameters
 
-    private void applyAllParameters(@NonNull CaptureRequest.Builder builder) {
+    private void applyAllParameters(@NonNull CaptureRequest.Builder builder,
+                                    @Nullable CaptureRequest.Builder oldBuilder) {
+        LOG.i("applyAllParameters:", "called for tag", builder.build().getTag());
         builder.set(CaptureRequest.CONTROL_MODE, CaptureRequest.CONTROL_MODE_AUTO);
         applyDefaultFocus(builder);
         applyFlash(builder, Flash.OFF);
@@ -782,6 +841,17 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         applyHdr(builder, Hdr.OFF);
         applyZoom(builder, 0F);
         applyExposureCorrection(builder, 0F);
+
+        if (oldBuilder != null) {
+            // We might be in a metering operation, or the old builder might have some special
+            // metering parameters. Copy these special keys over to the new builder.
+            // These are the keys changed by metering.Parameters, or by us in applyFocusForMetering.
+            builder.set(CaptureRequest.CONTROL_AF_REGIONS, oldBuilder.get(CaptureRequest.CONTROL_AF_REGIONS));
+            builder.set(CaptureRequest.CONTROL_AE_REGIONS, oldBuilder.get(CaptureRequest.CONTROL_AE_REGIONS));
+            builder.set(CaptureRequest.CONTROL_AWB_REGIONS, oldBuilder.get(CaptureRequest.CONTROL_AWB_REGIONS));
+            builder.set(CaptureRequest.CONTROL_AF_MODE, oldBuilder.get(CaptureRequest.CONTROL_AF_MODE));
+            // Do NOT copy exposure or focus triggers!
+        }
     }
 
     private void applyDefaultFocus(@NonNull CaptureRequest.Builder builder) {
@@ -836,14 +906,31 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     }
 
     @Override
-    public void setFlash(@NonNull Flash flash) {
+    public void setFlash(@NonNull final Flash flash) {
         final Flash old = mFlash;
         mFlash = flash;
         mHandler.run(new Runnable() {
             @Override
             public void run() {
                 if (getEngineState() == STATE_STARTED) {
-                    if (applyFlash(mRepeatingRequestBuilder, old)) {
+                    boolean shouldApply = applyFlash(mRepeatingRequestBuilder, old);
+                    boolean needsWorkaround = getPreviewState() == STATE_STARTED;
+                    if (needsWorkaround) {
+                        // Runtime changes to the flash value are not correctly handled by the driver.
+                        // See https://stackoverflow.com/q/53003383/4288782 for example.
+                        // For this reason, we go back to OFF, capture once, then go to the new one.
+                        mFlash = Flash.OFF;
+                        applyFlash(mRepeatingRequestBuilder, old);
+                        try {
+                            mSession.capture(mRepeatingRequestBuilder.build(), null, null);
+                        } catch (CameraAccessException e) {
+                            throw createCameraException(e);
+                        }
+                        mFlash = flash;
+                        applyFlash(mRepeatingRequestBuilder, old);
+                        applyRepeatingRequestBuilder();
+
+                    } else if (shouldApply) {
                         applyRepeatingRequestBuilder();
                     }
                 }
@@ -884,12 +971,6 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                     LOG.i("applyFlash: setting FLASH_MODE to", pair.second);
                     builder.set(CaptureRequest.CONTROL_AE_MODE, pair.first);
                     builder.set(CaptureRequest.FLASH_MODE, pair.second);
-
-                    // On some devices, switching from TORCH/OFF to AUTO/ON is not immediately
-                    // reflected (for example, torch stays active) unless we do as follows.
-                    // It's just a way to wake up the AE routine.
-                    builder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
-                            CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
                     return true;
                 }
             }
@@ -1139,29 +1220,42 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     @Override
     public void startAutoFocus(@Nullable final Gesture gesture, @NonNull final PointF point) {
-        // TODO Should change this name at some point, and deprecate AF methods
-        startMetering(gesture, point);
-    }
-
-    private void startMetering(@Nullable final Gesture gesture, @NonNull final PointF point) {
-        LOG.i("startMetering", "dispatching. Gesture:", gesture);
+        LOG.i("startAutoFocus", "dispatching. Gesture:", gesture);
         mHandler.run(new Runnable() {
             @Override
             public void run() {
-                LOG.i("startMetering", "executing. Preview state:", getPreviewState());
+                LOG.i("startAutoFocus", "executing. Preview state:", getPreviewState());
                 // This will only work when we have a preview, since it launches the preview in the end.
                 // Even without this it would need the bind state at least, since we need the preview size.
                 if (getPreviewState() < STATE_STARTED) return;
 
                 // The camera options API still has the auto focus API but it really
-                // refers to 3A metering.
+                // refers to "3A metering to a specific point". Since we have a point, check.
                 if (!mCameraOptions.isAutoFocusSupported()) return;
 
-                // Reset the old meter if present.
-                if (mMeter != null) {
-                    mMeter.resetMetering();
+                // Create the meter and start.
+                mCallback.dispatchOnFocusStart(gesture, point);
+                final MeterAction action = createMeterAction(point);
+                Action wrapper = Actions.timeout(METER_TIMEOUT, action);
+                wrapper.start(Camera2Engine.this);
+                wrapper.addCallback(new CompletionCallback() {
+                    @Override
+                    protected void onActionCompleted(@NonNull Action a) {
+                        mCallback.dispatchOnFocusEnd(gesture, action.isSuccessful(), point);
+                        mHandler.remove(mUnlockAndResetMeteringRunnable);
+                        if (shouldResetAutoFocus()) {
+                            mHandler.post(getAutoFocusResetDelay(), mUnlockAndResetMeteringRunnable);
+                        }
+                    }
+                });
+            }
+        });
     }
 
+    @NonNull
+    private MeterAction createMeterAction(@Nullable PointF point) {
+        // Before creating any new meter action, abort the old one.
+        if (mMeterAction != null) mMeterAction.abort(this);
         // The meter will check the current configuration to see if AF/AE/AWB should run.
         // - AE should be on CONTROL_AE_MODE_ON*    (this depends on setFlash())
         // - AWB should be on CONTROL_AWB_MODE_AUTO (this depends on setWhiteBalance())
@@ -1169,65 +1263,93 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         // The last one is under our control because the library has no focus API.
         // So let's set a good af mode here. This operation is reverted during onMeteringReset().
         applyFocusForMetering(mRepeatingRequestBuilder);
+        mMeterAction = new MeterAction(Camera2Engine.this, point, point == null);
+        return mMeterAction;
+    }
 
-                // Create the meter and start.
-                mMeter = new Meter(Camera2Engine.this,
-                        mRepeatingRequestBuilder,
-                        mCameraCharacteristics,
-                        Camera2Engine.this);
-                mMeter.startMetering(point, gesture);
+    private final Runnable mUnlockAndResetMeteringRunnable = new Runnable() {
+        @Override
+        public void run() {
+            unlockAndResetMetering();
+        }
+    };
+
+    private void unlockAndResetMetering() {
+        if (getEngineState() == STATE_STARTED) {
+            Actions.sequence(
+                    new BaseAction() {
+                        @Override
+                        protected void onStart(@NonNull ActionHolder holder) {
+                            super.onStart(holder);
+                            applyDefaultFocus(holder.getBuilder(this));
+                            holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_LOCK, false);
+                            holder.getBuilder(this).set(CaptureRequest.CONTROL_AWB_LOCK, false);
+                            holder.applyBuilder(this);
+                            setState(STATE_COMPLETED);
+                            // TODO should wait results?
+                        }
+                    },
+                    new MeterResetAction()
+            ).start(Camera2Engine.this);
+        }
+    }
+
+    //endregion
+
+    //region Actions
+
+    @Override
+    public void addAction(final @NonNull Action action) {
+        // This is likely to be called during a Capture callback while we iterate
+        // on the actions list, or worse, from other threads. We must use mHandler.post.
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                if (!mActions.contains(action)) {
+                    mActions.add(action);
+                }
             }
         });
     }
 
-    /**
-     * Called by {@link Meter} when the metering process has started.
-     * We are currently exposing an auto focus API so that's what we dispatch.
-     * @param point point
-     * @param gesture gesture
-     */
     @Override
-    public void onMeteringStarted(@NonNull PointF point, @Nullable Gesture gesture) {
-        LOG.w("onMeteringStarted - point:", point, "gesture:", gesture);
-        mCallback.dispatchOnFocusStart(gesture, point);
-        applyRepeatingRequestBuilder();
+    public void removeAction(final @NonNull Action action) {
+        // This is likely to be called during a Capture callback while we iterate
+        // on the actions list, or worse, from other threads. We must use mHandler.post.
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                mActions.remove(action);
+            }
+        });
     }
 
-    /**
-     * Called by {@link Meter} when the metering process has ended.
-     * We are currently exposing an auto focus API so that's what we dispatch.
-     * @param point point
-     * @param gesture gesture
-     * @param success success
-     */
+    @NonNull
     @Override
-    public void onMeteringEnd(@NonNull PointF point, @Nullable Gesture gesture, boolean success) {
-        LOG.w("onMeteringEnd - point:", point, "gesture:", gesture, "success:", success);
-        mCallback.dispatchOnFocusEnd(gesture, success, point);
+    public CameraCharacteristics getCharacteristics(@NonNull Action action) {
+        return mCameraCharacteristics;
     }
 
-    /**
-     * When metering is reset, we're not sure that the engine is still alive.
-     * We should check this here.
-     * @param point point
-     * @param gesture gesture
-     * @return true if metering can be reset
-     */
+    @NonNull
     @Override
-    public boolean canResetMetering(@NonNull PointF point, @Nullable Gesture gesture) {
-        return getEngineState() == STATE_STARTED;
+    public TotalCaptureResult getLastResult(@NonNull Action action) {
+        return mLastRepeatingResult;
+    }
+
+    @NonNull
+    @Override
+    public CaptureRequest.Builder getBuilder(@NonNull Action action) {
+        return mRepeatingRequestBuilder;
+    }
+
+    @Override
+    public void applyBuilder(@NonNull Action source) {
+        applyRepeatingRequestBuilder();
     }
 
-    /**
-     * Called by {@link Meter} after resetting the metering parameters.
-     * We should apply them, and also go back to default focus.
-     * @param point point
-     * @param gesture gesture
-     */
     @Override
-    public void onMeteringReset(@NonNull PointF point, @Nullable Gesture gesture) {
-        applyDefaultFocus(mRepeatingRequestBuilder);
-        applyRepeatingRequestBuilder(); // only if preview started already
+    public void applyBuilder(@NonNull Action source, @NonNull CaptureRequest.Builder builder) throws CameraAccessException {
+        mSession.capture(builder.build(), mRepeatingRequestCallback, null);
     }
 
     //endregion

cameraview/src/main/java/com/otaliastudios/cameraview/engine/CameraEngine.java

@@ -167,6 +167,8 @@ public abstract class CameraEngine implements
     @SuppressWarnings("WeakerAccess") protected float mZoomValue;
     @SuppressWarnings("WeakerAccess") protected float mExposureCorrectionValue;
     @SuppressWarnings("WeakerAccess") protected boolean mPlaySounds;
+    @SuppressWarnings("WeakerAccess") protected boolean mPictureMetering;
+    @SuppressWarnings("WeakerAccess") protected boolean mPictureSnapshotMetering;
 
     // Can be private
     @VisibleForTesting Handler mCrashHandler;
@@ -225,6 +227,11 @@ public abstract class CameraEngine implements
         mPreview.setSurfaceCallback(this);
     }
 
+    @NonNull
+    public CameraPreview getPreview() {
+        return mPreview;
+    }
+
     //region Error handling
 
     /**
@@ -1008,6 +1015,22 @@ public abstract class CameraEngine implements
         return mAutoFocusResetDelayMillis > 0 && mAutoFocusResetDelayMillis != Long.MAX_VALUE;
     }
 
+    public final void setPictureMetering(boolean enable) {
+        mPictureMetering = enable;
+    }
+
+    public final boolean getPictureMetering() {
+        return mPictureMetering;
+    }
+
+    public final void setPictureSnapshotMetering(boolean enable) {
+        mPictureSnapshotMetering = enable;
+    }
+
+    public final boolean getPictureSnapshotMetering() {
+        return mPictureSnapshotMetering;
+    }
+
     //endregion
 
     //region Abstract setters and APIs
@@ -1070,7 +1093,6 @@ public abstract class CameraEngine implements
             public void run() {
                 LOG.v("takePicture", "performing. BindState:", getBindState(), "isTakingPicture:", isTakingPicture());
                 if (mMode == Mode.VIDEO) {
-                    // Could redirect to takePictureSnapshot, but it's better if people know what they are doing.
                     throw new IllegalStateException("Can't take hq pictures while in VIDEO mode");
                 }
                 if (getBindState() < STATE_STARTED) return;
@@ -1078,7 +1100,7 @@ public abstract class CameraEngine implements
                 stub.isSnapshot = false;
                 stub.location = mLocation;
                 stub.facing = mFacing;
-                onTakePicture(stub);
+                onTakePicture(stub, mPictureMetering);
             }
         });
     }
@@ -1102,7 +1124,7 @@ public abstract class CameraEngine implements
                 // Leave the other parameters to subclasses.
                 //noinspection ConstantConditions
                 AspectRatio ratio = AspectRatio.of(getPreviewSurfaceSize(Reference.OUTPUT));
-                onTakePictureSnapshot(stub, ratio);
+                onTakePictureSnapshot(stub, ratio, mPictureSnapshotMetering);
             }
         });
     }
@@ -1223,10 +1245,10 @@ public abstract class CameraEngine implements
     }
 
     @WorkerThread
-    protected abstract void onTakePicture(@NonNull PictureResult.Stub stub);
+    protected abstract void onTakePicture(@NonNull PictureResult.Stub stub, boolean doMetering);
 
     @WorkerThread
-    protected abstract void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio);
+    protected abstract void onTakePictureSnapshot(@NonNull PictureResult.Stub stub, @NonNull AspectRatio outputRatio, boolean doMetering);
 
     @WorkerThread
     protected abstract void onTakeVideoSnapshot(@NonNull VideoResult.Stub stub, @NonNull AspectRatio outputRatio);

cameraview/src/main/java/com/otaliastudios/cameraview/engine/LogAction.java

@@ -0,0 +1,62 @@
+package com.otaliastudios.cameraview.engine;
+
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+class LogAction extends BaseAction {
+
+    private final static CameraLogger LOG = CameraLogger.create(Camera2Engine.class.getSimpleName());
+
+    private String lastLog;
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer aeMode = result.get(CaptureResult.CONTROL_AE_MODE);
+        Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
+        Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
+        Boolean aeLock = result.get(CaptureResult.CONTROL_AE_LOCK);
+        Integer aeTriggerState = result.get(CaptureResult.CONTROL_AE_PRECAPTURE_TRIGGER);
+        Integer afTriggerState = result.get(CaptureResult.CONTROL_AF_TRIGGER);
+        String log = "aeMode: " + aeMode + " aeLock: " + aeLock +
+                " aeState: " + aeState + " aeTriggerState: " + aeTriggerState +
+                " afState: " + afState + " afTriggerState: " + afTriggerState;
+        if (!log.equals(lastLog)) {
+            lastLog = log;
+            LOG.w(log);
+        }
+
+        // START
+        // aeMode: 3 aeLock: false aeState: 4 aeTriggerState: 0 afState: 2 afTriggerState: 0
+        //
+        // DURING metering (focus skips)
+        // aeMode: 3 aeLock: false aeState: 4 aeTriggerState: 0 afState: 0 afTriggerState: 0
+        // aeMode: 3 aeLock: false aeState: 5 aeTriggerState: 1 afState: 0 afTriggerState: 0
+        //
+        // DURING locking (focus skips)
+        // aeMode: 3 aeLock: false aeState: 4 aeTriggerState: 1 afState: 0 afTriggerState: 0
+        // aeMode: 3 aeLock: true aeState: 5 aeTriggerState: 1 afState: 0 afTriggerState: 0
+        //
+        // AFTER locked
+        // aeMode: 3 aeLock: true aeState: 3 aeTriggerState: 1 afState: 0 afTriggerState: 0
+        //
+        // AFTER super.take() called
+        // aeMode: 1 aeLock: true aeState: 5 aeTriggerState: 1 afState: 0 afTriggerState: 0
+        // aeMode: 1 aeLock: true aeState: 3 aeTriggerState: 1 afState: 0 afTriggerState: 0
+        //
+        // Reverting flash changes + reset lock + reset metering
+        // aeMode: 3 aeLock: false aeState: 4 aeTriggerState: 2(1 now) afState: 2 afTriggerState: 0
+        // aeMode: 3 aeLock: false aeState: 1 aeTriggerState: 2(1 now) afState: 2 afTriggerState: 0
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/Meter.java

@@ -1,380 +0,0 @@
-package com.otaliastudios.cameraview.engine;
-
-import android.graphics.PointF;
-import android.graphics.Rect;
-import android.hardware.camera2.CameraCharacteristics;
-import android.hardware.camera2.CaptureRequest;
-import android.hardware.camera2.CaptureResult;
-import android.hardware.camera2.TotalCaptureResult;
-import android.hardware.camera2.params.MeteringRectangle;
-import android.os.Build;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
-import androidx.annotation.RequiresApi;
-
-import com.otaliastudios.cameraview.CameraLogger;
-import com.otaliastudios.cameraview.engine.metering.AutoExposure;
-import com.otaliastudios.cameraview.engine.metering.AutoFocus;
-import com.otaliastudios.cameraview.engine.metering.AutoWhiteBalance;
-import com.otaliastudios.cameraview.engine.metering.MeteringParameter;
-import com.otaliastudios.cameraview.engine.offset.Axis;
-import com.otaliastudios.cameraview.engine.offset.Reference;
-import com.otaliastudios.cameraview.gesture.Gesture;
-import com.otaliastudios.cameraview.size.AspectRatio;
-import com.otaliastudios.cameraview.size.Size;
-
-import java.util.Arrays;
-import java.util.List;
-
-/**
- * Helps Camera2-based engines to perform 3A (auto focus, auto exposure and auto white balance)
- * metering. Users are required to:
- *
- * - Call {@link #startMetering(PointF, Gesture)} to start
- * - Call {@link #onCapture(CaptureResult)} when they have partial or total results, as long as the
- *   meter is still in a metering operation, which can be checked through {@link #isMetering()}
- * - Call {@link #resetMetering()} to reset the metering parameters if needed. This is done automatically
- *   by the meter based on the reset delay configuration in the engine, but can be called explicitly
- *   for example when we have multiple meter requests and want to cancel the old one.
- */
-@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-public class Meter {
-
-    /**
-     * The meter callback.
-     */
-    public interface Callback {
-
-        /**
-         * Notifies that metering has started. At this point implementors should apply
-         * the builder onto the preview.
-         * @param point point
-         * @param gesture gesture
-         */
-        void onMeteringStarted(@NonNull PointF point, @Nullable Gesture gesture);
-
-        /**
-         * Notifies that metering has ended. No action is required for implementors.
-         * From now on, {@link #isMetering()} will return false so the meter should not
-         * be passed capture results anymore.
-         * @param point point
-         * @param gesture gesture
-         * @param success success
-         */
-        void onMeteringEnd(@NonNull PointF point, @Nullable Gesture gesture, boolean success);
-
-        /**
-         * Notifies that metering has been reset. From now on, this meter instance
-         * is done, although in theory it could be reused by calling
-         * {@link #startMetering(PointF, Gesture)} again.
-         * @param point point
-         * @param gesture gesture
-         */
-        void onMeteringReset(@NonNull PointF point, @Nullable Gesture gesture);
-
-        /**
-         * Whether metering can be reset. Since it happens at a future time, this should
-         * return true if the engine is still in a legit state for this operation.
-         * @param point point
-         * @param gesture gesture
-         * @return true if can reset
-         */
-        // TODO is this useful? engine could do its checks onMeteringReset()
-        boolean canResetMetering(@NonNull PointF point, @Nullable Gesture gesture);
-    }
-
-    private static final String TAG = Meter.class.getSimpleName();
-    private static final CameraLogger LOG = CameraLogger.create(TAG);
-    private static final int FORCED_END_DELAY = 2500;
-
-    private final CameraEngine mEngine;
-    private final CaptureRequest.Builder mBuilder;
-    private final CameraCharacteristics mCharacteristics;
-    private final Callback mCallback;
-    private PointF mPoint;
-    private Gesture mGesture;
-
-    private boolean mIsMetering;
-    private long mMeteringStartTime;
-    private MeteringParameter mAutoFocus = new AutoFocus();
-    private MeteringParameter mAutoWhiteBalance = new AutoWhiteBalance();
-    private MeteringParameter mAutoExposure = new AutoExposure();
-
-    /**
-     * Creates a new meter.
-     * @param engine the engine
-     * @param builder a capture builder
-     * @param characteristics the camera characteristics
-     * @param callback the callback
-     */
-    @SuppressWarnings("WeakerAccess")
-    public Meter(@NonNull CameraEngine engine,
-                 @NonNull CaptureRequest.Builder builder,
-                 @NonNull CameraCharacteristics characteristics,
-                 @NonNull Callback callback) {
-        mEngine = engine;
-        mBuilder = builder;
-        mCharacteristics = characteristics;
-        mCallback = callback;
-    }
-
-    /**
-     * Starts a metering sequence.
-     * @param point point
-     * @param gesture gesture
-     */
-    @SuppressWarnings("WeakerAccess")
-    public void startMetering(@NonNull PointF point, @Nullable Gesture gesture) {
-        mPoint = point;
-        mGesture = gesture;
-        mIsMetering = true;
-
-        // This is a good Q/A. https://stackoverflow.com/a/33181620/4288782
-        // At first, the point is relative to the View system and does not account our own cropping.
-        // Will keep updating these two below.
-        final PointF referencePoint = new PointF(mPoint.x, mPoint.y);
-        Size referenceSize = mEngine.mPreview.getSurfaceSize();
-
-        // 1. Account for cropping.
-        // This will enlarge the preview size so that aspect ratio matches.
-        referenceSize = applyPreviewCropping(referenceSize, referencePoint);
-
-        // 2. Scale to the preview stream coordinates.
-        // This will move to the preview stream coordinates by scaling.
-        referenceSize = applyPreviewScale(referenceSize, referencePoint);
-
-        // 3. Rotate to the stream coordinate system.
-        // This leaves us with sensor stream coordinates.
-        referenceSize = applyPreviewToSensorRotation(referenceSize, referencePoint);
-
-        // 4. Move to the crop region coordinate system.
-        // The crop region is the union of all currently active streams.
-        referenceSize = applyCropRegionCoordinates(referenceSize, referencePoint);
-
-        // 5. Move to the active array coordinate system.
-        referenceSize = applyActiveArrayCoordinates(referenceSize, referencePoint);
-
-        // 6. Now we can compute the metering regions.
-        // We want to define them as a fraction of the visible size which (apart from cropping)
-        // can be obtained through the SENSOR rotated preview stream size.
-        Size visibleSize = mEngine.getPreviewStreamSize(Reference.SENSOR);
-        //noinspection ConstantConditions
-        MeteringRectangle area1 = createMeteringRectangle(referenceSize, referencePoint, visibleSize, 0.05F, 1000);
-        MeteringRectangle area2 = createMeteringRectangle(referenceSize, referencePoint, visibleSize, 0.1F, 100);
-        List<MeteringRectangle> areas = Arrays.asList(area1, area2);
-
-        // 7. And finally dispatch everything
-        mAutoFocus.startMetering(mCharacteristics, mBuilder, areas);
-        mAutoWhiteBalance.startMetering(mCharacteristics, mBuilder, areas);
-        mAutoExposure.startMetering(mCharacteristics, mBuilder, areas);
-
-        // Dispatch to callback
-        mCallback.onMeteringStarted(mPoint, mGesture);
-        mMeteringStartTime = System.currentTimeMillis();
-    }
-
-    @SuppressWarnings("UnnecessaryLocalVariable")
-    @NonNull
-    private Size applyPreviewCropping(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
-        Size previewStreamSize = mEngine.getPreviewStreamSize(Reference.VIEW);
-        Size previewSurfaceSize = referenceSize;
-        if (previewStreamSize == null) {
-            throw new IllegalStateException("getPreviewStreamSize should not be null at this point.");
-        }
-        int referenceWidth = previewSurfaceSize.getWidth();
-        int referenceHeight = previewSurfaceSize.getHeight();
-        AspectRatio previewStreamAspectRatio = AspectRatio.of(previewStreamSize);
-        AspectRatio previewSurfaceAspectRatio = AspectRatio.of(previewSurfaceSize);
-        if (mEngine.mPreview.isCropping()) {
-            if (previewStreamAspectRatio.toFloat() > previewSurfaceAspectRatio.toFloat()) {
-                // Stream is larger. The x coordinate must be increased: a touch on the left side
-                // of the surface is not on the left size of stream (it's more to the right).
-                float scale = previewStreamAspectRatio.toFloat() / previewSurfaceAspectRatio.toFloat();
-                referencePoint.x += previewSurfaceSize.getWidth() * (scale - 1F) / 2F;
-                referenceWidth = Math.round(previewSurfaceSize.getWidth() * scale);
-            } else {
-                // Stream is taller. The y coordinate must be increased: a touch on the top side
-                // of the surface is not on the top size of stream (it's a bit lower).
-                float scale = previewSurfaceAspectRatio.toFloat() / previewStreamAspectRatio.toFloat();
-                referencePoint.y += previewSurfaceSize.getHeight() * (scale - 1F) / 2F;
-                referenceHeight = Math.round(previewSurfaceSize.getHeight() * scale);
-            }
-        }
-        return new Size(referenceWidth, referenceHeight);
-    }
-
-    @SuppressWarnings("ConstantConditions")
-    @NonNull
-    private Size applyPreviewScale(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
-        // The referenceSize how has the same aspect ratio of the previewStreamSize, but they
-        // can still have different size (that is, a scale operation is needed).
-        Size previewStreamSize = mEngine.getPreviewStreamSize(Reference.VIEW);
-        referencePoint.x *= (float) previewStreamSize.getWidth() / referenceSize.getWidth();
-        referencePoint.y *= (float) previewStreamSize.getHeight() / referenceSize.getHeight();
-        return previewStreamSize;
-    }
-
-    @SuppressWarnings("SuspiciousNameCombination")
-    @NonNull
-    private Size applyPreviewToSensorRotation(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
-        // Not elegant, but the sin/cos way was failing for some reason.
-        int angle = mEngine.getAngles().offset(Reference.SENSOR, Reference.VIEW, Axis.ABSOLUTE);
-        boolean flip = angle % 180 != 0;
-        float tempX = referencePoint.x;
-        float tempY = referencePoint.y;
-        if (angle == 0) {
-            referencePoint.x = tempX;
-            referencePoint.y = tempY;
-        } else if (angle == 90) {
-            referencePoint.x = tempY;
-            referencePoint.y = referenceSize.getWidth() - tempX;
-        } else if (angle == 180) {
-            referencePoint.x = referenceSize.getWidth() - tempX;
-            referencePoint.y = referenceSize.getHeight() - tempY;
-        } else if (angle == 270) {
-            referencePoint.x = referenceSize.getHeight() - tempY;
-            referencePoint.y = tempX;
-        } else {
-            throw new IllegalStateException("Unexpected angle " + angle);
-        }
-        return flip ? referenceSize.flip() : referenceSize;
-    }
-
-    @NonNull
-    private Size applyCropRegionCoordinates(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
-        // The input point and size refer to the stream rect.
-        // The stream rect is part of the 'crop region', as described below.
-        // https://source.android.com/devices/camera/camera3_crop_reprocess.html
-        Rect cropRect = mBuilder.get(CaptureRequest.SCALER_CROP_REGION);
-        // For now, we don't care about x and y position. Rect should be non-null, but let's be safe.
-        int cropRectWidth = cropRect == null ? referenceSize.getWidth() : cropRect.width();
-        int cropRectHeight = cropRect == null ? referenceSize.getHeight() : cropRect.height();
-        // The stream is always centered inside the crop region, and one of the dimensions
-        // should always match. We just increase the other one.
-        referencePoint.x += (cropRectWidth - referenceSize.getWidth()) / 2F;
-        referencePoint.y += (cropRectHeight - referenceSize.getHeight()) / 2F;
-        return new Size(cropRectWidth, cropRectHeight);
-    }
-
-    @NonNull
-    private Size applyActiveArrayCoordinates(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
-        // The input point and size refer to the scaler crop region.
-        // We can query for the crop region position inside the active array, so this is easy.
-        Rect cropRect = mBuilder.get(CaptureRequest.SCALER_CROP_REGION);
-        referencePoint.x += cropRect == null ? 0 : cropRect.left;
-        referencePoint.y += cropRect == null ? 0 : cropRect.top;
-        // Finally, get the active rect width and height from characteristics.
-        Rect activeRect = mCharacteristics.get(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE);
-        if (activeRect == null) { // Should never happen
-            activeRect = new Rect(0, 0, referenceSize.getWidth(), referenceSize.getHeight());
-        }
-        return new Size(activeRect.width(), activeRect.height());
-    }
-
-    /**
-     * Creates a metering rectangle around the center point.
-     * The rectangle will have a size that's a factor of the visible width and height.
-     * The rectangle will also be constrained to be inside the given boundaries,
-     * so we don't exceed them in case the center point is exactly on one side for example.
-     * @return a new rectangle
-     */
-    @NonNull
-    private MeteringRectangle createMeteringRectangle(
-            @NonNull Size boundaries,
-            @NonNull PointF center,
-            @NonNull Size visibleSize,
-            float factor,
-            int weight) {
-        float rectangleWidth = factor * visibleSize.getWidth();
-        float rectangleHeight = factor * visibleSize.getHeight();
-        float rectangleLeft = center.x - rectangleWidth / 2F;
-        float rectangleTop = center.y - rectangleHeight / 2F;
-        // Respect boundaries
-        if (rectangleLeft < 0) rectangleLeft = 0;
-        if (rectangleTop < 0) rectangleTop = 0;
-        if (rectangleLeft + rectangleWidth > boundaries.getWidth()) {
-            rectangleWidth = boundaries.getWidth() - rectangleLeft;
-        }
-        if (rectangleTop + rectangleHeight > boundaries.getHeight()) {
-            rectangleHeight = boundaries.getHeight() - rectangleTop;
-        }
-        return new MeteringRectangle(
-                (int) rectangleLeft,
-                (int) rectangleTop,
-                (int) rectangleWidth,
-                (int) rectangleHeight,
-                weight
-        );
-    }
-
-    /**
-     * True if we're metering. False if we're not, for example if we're waiting for
-     * a reset call, or if {@link #startMetering(PointF, Gesture)} was never called.
-     * @return true if metering
-     */
-    @SuppressWarnings("WeakerAccess")
-    public boolean isMetering() {
-        return mIsMetering;
-    }
-
-    /**
-     * Should be called when we have partial or total CaptureResults,
-     * but only while {@link #isMetering()} returns true.
-     * @param result result
-     */
-    @SuppressWarnings("WeakerAccess")
-    public void onCapture(@NonNull CaptureResult result) {
-        if (!mIsMetering) return; // We're not interested in results anymore
-        if (!(result instanceof TotalCaptureResult)) return; // Let's ignore these, contents are missing/wrong
-        
-        if (!mAutoFocus.isMetered()) mAutoFocus.onCapture(result);
-        if (!mAutoExposure.isMetered()) mAutoExposure.onCapture(result);
-        if (!mAutoWhiteBalance.isMetered()) mAutoWhiteBalance.onCapture(result);
-        if (mAutoFocus.isMetered() && mAutoExposure.isMetered() && mAutoWhiteBalance.isMetered()) {
-            LOG.i("onCapture:", "all MeteringParameters have converged. Dispatching onMeteringEnd");
-            boolean success = mAutoFocus.isSuccessful()
-                    && mAutoExposure.isSuccessful()
-                    && mAutoWhiteBalance.isSuccessful();
-            onMeteringEnd(success);
-        } else if (System.currentTimeMillis() - mMeteringStartTime >= FORCED_END_DELAY) {
-            LOG.i("onCapture:", "FORCED_END_DELAY was reached. Some MeteringParameter is stuck. Forcing end.");
-            onMeteringEnd(false);
-        }
-    }
-    
-    private void onMeteringEnd(boolean success) {
-        mCallback.onMeteringEnd(mPoint, mGesture, success);
-        mIsMetering = false;
-        mEngine.mHandler.remove(mResetRunnable);
-        if (mEngine.shouldResetAutoFocus()) {
-            mEngine.mHandler.post(mEngine.getAutoFocusResetDelay(), mResetRunnable);
-        }
-    }
-
-    /**
-     * Can be called to perform the reset at a time different than the one
-     * specified by the {@link CameraEngine} reset delay.
-     */
-    @SuppressWarnings("WeakerAccess")
-    public void resetMetering() {
-        mEngine.mHandler.remove(mResetRunnable);
-        if (mCallback.canResetMetering(mPoint, mGesture)) {
-            LOG.i("Resetting the meter parameters.");
-            Rect whole = mCharacteristics.get(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE);
-            if (whole == null) whole = new Rect();
-            MeteringRectangle rectangle = new MeteringRectangle(whole, MeteringRectangle.METERING_WEIGHT_DONT_CARE);
-            mAutoFocus.resetMetering(mCharacteristics, mBuilder, rectangle);
-            mAutoWhiteBalance.resetMetering(mCharacteristics, mBuilder, rectangle);
-            mAutoExposure.resetMetering(mCharacteristics, mBuilder, rectangle);
-            mCallback.onMeteringReset(mPoint, mGesture);
-        }
-    }
-
-    private Runnable mResetRunnable = new Runnable() {
-        @Override
-        public void run() {
-            resetMetering();
-        }
-    };
-}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/Action.java

@@ -0,0 +1,85 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CameraCaptureSession;
+import android.hardware.camera2.CameraCaptureSession.CaptureCallback;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+/**
+ * The Action class encapsulates logic for completing an action in a Camera2 environment.
+ * In this case, we are often interested in constantly receiving the {@link CaptureResult}
+ * and {@link CaptureRequest} callbacks, as well as applying changes to a {@link CaptureRequest.Builder}
+ * and having them applied to the sensor.
+ *
+ * The Action class receives the given callbacks and can operate over the engine
+ * through the {@link ActionHolder} object.
+ *
+ * Each Action operates on a given state in a given moment. This base class offers the
+ * {@link #STATE_COMPLETED} state which is common to all actions.
+ *
+ * See {@link BaseAction} for a base implementation.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public interface Action {
+
+    int STATE_COMPLETED = Integer.MAX_VALUE;
+
+    /**
+     * Returns the current state.
+     * @return the state
+     */
+    int getState();
+
+    /**
+     * Starts this action.
+     * @param holder the holder
+     */
+    void start(@NonNull ActionHolder holder);
+
+    /**
+     * Aborts this action.
+     * @param holder the holder
+     */
+    void abort(@NonNull ActionHolder holder);
+
+    /**
+     * Adds an {@link ActionCallback} to receive state
+     * change events.
+     * @param callback a callback
+     */
+    void addCallback(@NonNull ActionCallback callback);
+
+    /**
+     * Removes a previously added callback.
+     * @param callback a callback
+     */
+    void removeCallback(@NonNull ActionCallback callback);
+
+    /**
+     * Called from {@link CaptureCallback#onCaptureStarted(CameraCaptureSession, CaptureRequest, long, long)}.
+     * @param holder the holder
+     * @param request the request
+     */
+    void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request);
+
+    /**
+     * Called from {@link CaptureCallback#onCaptureProgressed(CameraCaptureSession, CaptureRequest, CaptureResult)}.
+     * @param holder the holder
+     * @param request the request
+     * @param result the result
+     */
+    void onCaptureProgressed(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull CaptureResult result);
+
+    /**
+     * Called from {@link CaptureCallback#onCaptureCompleted(CameraCaptureSession, CaptureRequest, TotalCaptureResult)}.
+     * @param holder the holder
+     * @param request the request
+     * @param result the result
+     */
+    void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result);
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/ActionCallback.java

@@ -0,0 +1,23 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+/**
+ * A callback for {@link Action} state changes.
+ * See the action class.
+ *
+ * See also {@link CompletionCallback}.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public interface ActionCallback {
+
+    /**
+     * Action state has just changed.
+     * @param action action
+     * @param state new state
+     */
+    void onActionStateChanged(@NonNull Action action, int state);
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/ActionHolder.java

@@ -0,0 +1,81 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CameraAccessException;
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+/**
+ * The holder of {@link Action}.
+ *
+ * This class should keep a list or set of currently running actions, and offers
+ * to them the base Camera2 objects that are needed to apply changes.
+ *
+ * This class, or an holder of it, should also forward the capture callbacks
+ * to all {@link Action}s. See {@link com.otaliastudios.cameraview.engine.Camera2Engine} for
+ * our implementation.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public interface ActionHolder {
+
+    /**
+     * Adds a new action
+     * @param action action
+     */
+    void addAction(@NonNull Action action);
+
+    /**
+     * Removes a previously added action
+     * @param action action
+     */
+    void removeAction(@NonNull Action action);
+
+    /**
+     * Returns the {@link CameraCharacteristics} of the current
+     * camera device.
+     * @param action action
+     * @return characteristics
+     */
+    @NonNull
+    CameraCharacteristics getCharacteristics(@NonNull Action action);
+
+    /**
+     * Returns the latest {@link TotalCaptureResult}. Can be used
+     * by actions to start querying the state before receiving their
+     * first frame.
+     * @param action action
+     * @return last result
+     */
+    @NonNull
+    TotalCaptureResult getLastResult(@NonNull Action action);
+
+    /**
+     * Returns the current {@link CaptureRequest.Builder} so that
+     * actions can apply changes to it and later submit them.
+     * @param action action
+     * @return the builder
+     */
+    @NonNull
+    CaptureRequest.Builder getBuilder(@NonNull Action action);
+
+    /**
+     * Applies the current builder (as per {@link #getBuilder(Action)})
+     * as a repeating request on the preview.
+     * @param source action
+     */
+    void applyBuilder(@NonNull Action source);
+
+    /**
+     * Applies the given builder as a single capture request.
+     * Callers can catch the exception and choose what to do.
+     * @param source action
+     * @param builder builder
+     * @throws CameraAccessException camera exception
+     */
+    void applyBuilder(@NonNull Action source, @NonNull CaptureRequest.Builder builder) throws CameraAccessException;
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/ActionWrapper.java

@@ -0,0 +1,63 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+/**
+ * A simple wrapper around a {@link BaseAction}.
+ * This can be used to add functionality around a base action.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class ActionWrapper extends BaseAction {
+
+    /**
+     * Should return the wrapped action.
+     * @return the wrapped action
+     */
+    @NonNull
+    public abstract BaseAction getAction();
+
+    @Override
+    protected void onStart(@NonNull ActionHolder holder) {
+        super.onStart(holder);
+        getAction().addCallback(new ActionCallback() {
+            @Override
+            public void onActionStateChanged(@NonNull Action action, int state) {
+                setState(state);
+                if (state == STATE_COMPLETED) {
+                    action.removeCallback(this);
+                }
+            }
+        });
+        getAction().onStart(holder);
+    }
+
+    @Override
+    protected void onAbort(@NonNull ActionHolder holder) {
+        super.onAbort(holder);
+        getAction().onAbort(holder);
+    }
+
+    @Override
+    public void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request) {
+        super.onCaptureStarted(holder, request);
+        getAction().onCaptureStarted(holder, request);
+    }
+
+    @Override
+    public void onCaptureProgressed(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull CaptureResult result) {
+        super.onCaptureProgressed(holder, request, result);
+        getAction().onCaptureProgressed(holder, request, result);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        getAction().onCaptureCompleted(holder, request, result);
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/Actions.java

@@ -0,0 +1,56 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import java.util.Arrays;
+
+/**
+ * Utilities for creating {@link Action} sequences.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class Actions {
+
+    /**
+     * Creates a {@link BaseAction} that executes all the child actions
+     * together, at the same time, and completes once all of them are
+     * completed.
+     *
+     * @param actions input actions
+     * @return a new action
+     */
+    @NonNull
+    public static BaseAction together(@NonNull BaseAction... actions) {
+        return new TogetherAction(Arrays.asList(actions));
+    }
+
+    /**
+     * Creates a {@link BaseAction} that executes all the child actions
+     * in sequence, waiting for the first to complete, then going on with
+     * the second and so on, finally completing when all are completed.
+     *
+     * @param actions input actions
+     * @return a new action
+     */
+    @NonNull
+    public static BaseAction sequence(@NonNull BaseAction... actions) {
+        return new SequenceAction(Arrays.asList(actions));
+    }
+
+    /**
+     * Creates a {@link BaseAction} that completes as normal, but is also
+     * forced to complete if the given timeout is reached, by calling
+     * {@link Action#abort(ActionHolder)}.
+     *
+     * @param timeoutMillis timeout in milliseconds
+     * @param action action
+     * @return a new action
+     */
+    @NonNull
+    public static BaseAction timeout(long timeoutMillis, @NonNull BaseAction action) {
+        return new TimeoutAction(timeoutMillis, action);
+    }
+
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/BaseAction.java

@@ -0,0 +1,160 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.CallSuper;
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * The base implementation of {@link Action} that should always be subclassed,
+ * instead of implementing the root interface itself.
+ *
+ * It holds a list of callbacks and dispatches events to them, plus it cares about
+ * its own lifecycle:
+ * - when {@link #start(ActionHolder)} is called, we add ourselves to the holder list
+ * - when {@link #STATE_COMPLETED} is reached, we remove ouverselves from the holder list
+ *
+ * This is very important in all cases.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class BaseAction implements Action {
+
+    private final List<ActionCallback> callbacks = new ArrayList<>();
+    private int state;
+    private ActionHolder holder;
+
+    @Override
+    public final int getState() {
+        return state;
+    }
+
+    @Override
+    public final void start(@NonNull ActionHolder holder) {
+        holder.addAction(this);
+        onStart(holder);
+    }
+
+    @Override
+    public final void abort(@NonNull ActionHolder holder) {
+        holder.removeAction(this);
+        if (!isCompleted()) {
+            onAbort(holder);
+            setState(STATE_COMPLETED);
+        }
+    }
+
+    /**
+     * Action was started and will soon receive events from the
+     * holder stream.
+     * @param holder holder
+     */
+    @CallSuper
+    protected void onStart(@NonNull ActionHolder holder) {
+        this.holder = holder; // must be here
+        // Overrideable
+    }
+
+    /**
+     * Action was aborted and will not receive events from the
+     * holder stream anymore. It will soon be marked as completed.
+     * @param holder holder
+     */
+    @SuppressWarnings("unused")
+    protected void onAbort(@NonNull ActionHolder holder) {
+        // Overrideable
+    }
+
+    @Override
+    public void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request) {
+        // Overrideable
+    }
+
+    @Override
+    public void onCaptureProgressed(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull CaptureResult result) {
+        // Overrideable
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
+        // Overrideable
+    }
+
+    /**
+     * Called by subclasses to notify of their state. If state is {@link #STATE_COMPLETED},
+     * this removes this action from the holder.
+     * @param newState new state
+     */
+    protected void setState(int newState) {
+        if (newState != state) {
+            state = newState;
+            for (ActionCallback callback : callbacks) {
+                callback.onActionStateChanged(this, state);
+            }
+            if (state == STATE_COMPLETED) {
+                holder.removeAction(this);
+                onCompleted(holder);
+            }
+        }
+    }
+
+    /**
+     * Whether this action has reached the completed state.
+     * @return true if completed
+     */
+    public boolean isCompleted() {
+        return state == STATE_COMPLETED;
+    }
+
+    /**
+     * Called when this action has completed (possibly aborted).
+     * @param holder holder
+     */
+    protected void onCompleted(@NonNull ActionHolder holder) {
+        // Overrideable
+    }
+
+    /**
+     * Returns the holder.
+     * @return the holder
+     */
+    @NonNull
+    protected ActionHolder getHolder() {
+        return holder;
+    }
+
+
+    /**
+     * Reads a characteristic with a fallback.
+     * @param key key
+     * @param fallback fallback
+     * @param <T> key type
+     * @return value or fallback
+     */
+    @NonNull
+    protected <T> T readCharacteristic(@NonNull CameraCharacteristics.Key<T> key,
+                                       @NonNull T fallback) {
+        T value = holder.getCharacteristics(this).get(key);
+        return value == null ? fallback : value;
+    }
+
+    @Override
+    public void addCallback(@NonNull ActionCallback callback) {
+        if (!callbacks.contains(callback)) {
+            callbacks.add(callback);
+            callback.onActionStateChanged(this, getState());
+        }
+    }
+
+    @Override
+    public void removeCallback(@NonNull ActionCallback callback) {
+        callbacks.remove(callback);
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/CompletionCallback.java

@@ -0,0 +1,27 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+/**
+ * A special {@link ActionCallback} that just checks for the
+ * completed state. Handy as an inner anonymous class.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class CompletionCallback implements ActionCallback {
+
+    @Override
+    public final void onActionStateChanged(@NonNull Action action, int state) {
+        if (state == Action.STATE_COMPLETED) {
+            onActionCompleted(action);
+        }
+    }
+
+    /**
+     * The given action has just reached the completed state.
+     * @param action action
+     */
+    protected abstract void onActionCompleted(@NonNull Action action);
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/SequenceAction.java

@@ -0,0 +1,94 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import java.util.List;
+
+/**
+ * Executes a list of actions in sequence, completing once
+ * the last of them has been completed.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+class SequenceAction extends BaseAction {
+    // Need to be BaseAction so we can call onStart() instead of start()
+    private final List<BaseAction> actions;
+    private int runningAction = -1;
+
+    SequenceAction(@NonNull List<BaseAction> actions) {
+        this.actions = actions;
+        increaseRunningAction();
+    }
+
+    private void increaseRunningAction() {
+        boolean first = runningAction == -1;
+        boolean last = runningAction == actions.size() - 1;
+        if (last) {
+            // This was the last action. We're done.
+            setState(STATE_COMPLETED);
+        } else {
+            runningAction++;
+            actions.get(runningAction).addCallback(new ActionCallback() {
+                @Override
+                public void onActionStateChanged(@NonNull Action action, int state) {
+                    if (state == STATE_COMPLETED) {
+                        action.removeCallback(this);
+                        increaseRunningAction();
+                    }
+                }
+            });
+            if (!first) {
+                actions.get(runningAction).onStart(getHolder());
+            }
+        }
+    }
+
+    @Override
+    protected void onStart(@NonNull ActionHolder holder) {
+        super.onStart(holder);
+        if (runningAction >= 0) {
+            actions.get(runningAction).onStart(holder);
+        }
+    }
+
+    @Override
+    protected void onAbort(@NonNull ActionHolder holder) {
+        super.onAbort(holder);
+        if (runningAction >= 0) {
+            // Previous actions have been completed already.
+            // Future actions will never start. So this is OK.
+            actions.get(runningAction).onAbort(holder);
+        }
+    }
+
+    @Override
+    public void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request) {
+        super.onCaptureStarted(holder, request);
+        if (runningAction >= 0) {
+            actions.get(runningAction).onCaptureStarted(holder, request);
+        }
+    }
+
+    @Override
+    public void onCaptureProgressed(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                    @NonNull CaptureResult result) {
+        super.onCaptureProgressed(holder, request, result);
+        if (runningAction >= 0) {
+            actions.get(runningAction).onCaptureProgressed(holder, request, result);
+        }
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        if (runningAction >= 0) {
+            actions.get(runningAction).onCaptureCompleted(holder, request, result);
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/TimeoutAction.java

@@ -0,0 +1,50 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+/**
+ * An {@link Action} that wraps another, and forces the completion
+ * after the given timeout in milliseconds is reached.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+class TimeoutAction extends ActionWrapper {
+
+    private long startMillis;
+    private long timeoutMillis;
+    private BaseAction action;
+
+    TimeoutAction(long timeoutMillis, @NonNull BaseAction action) {
+        this.timeoutMillis = timeoutMillis;
+        this.action = action;
+    }
+
+    @NonNull
+    @Override
+    public BaseAction getAction() {
+        return action;
+    }
+
+    @Override
+    protected void onStart(@NonNull ActionHolder holder) {
+        startMillis = System.currentTimeMillis();
+        super.onStart(holder);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder,
+                                   @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        if (!isCompleted()) {
+            if (System.currentTimeMillis() > startMillis + timeoutMillis) {
+                // This will set our state to COMPLETED and stop requests.
+                getAction().abort(holder);
+            }
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/TogetherAction.java

@@ -0,0 +1,84 @@
+package com.otaliastudios.cameraview.engine.action;
+
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Performs a list of actions together, completing
+ * once all of them have completed.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+class TogetherAction extends BaseAction {
+    // Need to be BaseAction so we can call onStart() instead of start()
+    private final List<BaseAction> actions;
+    private final List<BaseAction> runningActions;
+
+    TogetherAction(@NonNull final List<BaseAction> actions) {
+        this.actions = new ArrayList<>(actions);
+        this.runningActions = new ArrayList<>(actions);
+        for (BaseAction action : actions) {
+            action.addCallback(new ActionCallback() {
+                @Override
+                public void onActionStateChanged(@NonNull Action action, int state) {
+                    if (state == STATE_COMPLETED) {
+                        //noinspection SuspiciousMethodCalls
+                        runningActions.remove(action);
+                    }
+                    if (runningActions.isEmpty()) {
+                        setState(STATE_COMPLETED);
+                    }
+                }
+            });
+        }
+    }
+
+    @Override
+    protected void onStart(@NonNull ActionHolder holder) {
+        super.onStart(holder);
+        for (BaseAction action : actions) {
+            if (!action.isCompleted()) action.onStart(holder);
+        }
+    }
+
+    @Override
+    protected void onAbort(@NonNull ActionHolder holder) {
+        super.onAbort(holder);
+        for (BaseAction action : actions) {
+            if (!action.isCompleted()) action.onAbort(holder);
+        }
+    }
+
+    @Override
+    public void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request) {
+        super.onCaptureStarted(holder, request);
+        for (BaseAction action : actions) {
+            if (!action.isCompleted()) action.onCaptureStarted(holder, request);
+        }
+    }
+
+    @Override
+    public void onCaptureProgressed(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                    @NonNull CaptureResult result) {
+        super.onCaptureProgressed(holder, request, result);
+        for (BaseAction action : actions) {
+            if (!action.isCompleted()) action.onCaptureProgressed(holder, request, result);
+        }
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        for (BaseAction action : actions) {
+            if (!action.isCompleted()) action.onCaptureCompleted(holder, request, result);
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/BaseLock.java

@@ -0,0 +1,32 @@
+package com.otaliastudios.cameraview.engine.lock;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class BaseLock extends BaseAction {
+
+    @Override
+    protected final void onStart(@NonNull ActionHolder holder) {
+        super.onStart(holder);
+        boolean isSkipped = checkShouldSkip(holder);
+        boolean isSupported = checkIsSupported(holder);
+        if (isSupported && !isSkipped) {
+            onStarted(holder);
+        } else {
+            setState(STATE_COMPLETED);
+        }
+    }
+
+    protected abstract void onStarted(@NonNull ActionHolder holder);
+
+    protected abstract boolean checkShouldSkip(@NonNull ActionHolder holder);
+
+    protected abstract boolean checkIsSupported(@NonNull ActionHolder holder);
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/ExposureLock.java

@@ -0,0 +1,78 @@
+package com.otaliastudios.cameraview.engine.lock;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class ExposureLock extends BaseLock {
+
+    private final static String TAG = ExposureLock.class.getSimpleName();
+    private final static CameraLogger LOG = CameraLogger.create(TAG);
+
+    @Override
+    protected boolean checkIsSupported(@NonNull ActionHolder holder) {
+        boolean isNotLegacy = readCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1)
+                != CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY;
+        // Not sure we should check aeMode as well, probably all aeModes support locking,
+        // but this should not be a big issue since we're not even using different AE modes.
+        Integer aeMode = holder.getBuilder(this).get(CaptureRequest.CONTROL_AE_MODE);
+        boolean isAEOn = aeMode != null &&
+                (aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON
+                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_ALWAYS_FLASH
+                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH
+                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH_REDEYE
+                        || aeMode == 5 /* CameraCharacteristics.CONTROL_AE_MODE_ON_EXTERNAL_FLASH, API 28 */);
+        boolean result = isNotLegacy && isAEOn;
+        LOG.i("checkIsSupported:", result);
+        return result;
+    }
+
+    @Override
+    protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
+        Integer aeState = holder.getLastResult(this).get(CaptureResult.CONTROL_AE_STATE);
+        boolean result = aeState != null && aeState == CaptureResult.CONTROL_AE_STATE_LOCKED;
+        LOG.i("checkShouldSkip:", result);
+        return result;
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder) {
+        int cancelTrigger = Build.VERSION.SDK_INT >= 23
+                ? CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_CANCEL
+                : CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_IDLE;
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER, cancelTrigger);
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_LOCK, true);
+        holder.applyBuilder(this);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
+        LOG.i("processCapture:", "aeState:", aeState);
+        if (aeState == null) return;
+        switch (aeState) {
+            case CaptureRequest.CONTROL_AE_STATE_LOCKED: {
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AE_STATE_PRECAPTURE:
+            case CaptureRequest.CONTROL_AE_STATE_CONVERGED:
+            case CaptureRequest.CONTROL_AE_STATE_INACTIVE:
+            case CaptureRequest.CONTROL_AE_STATE_SEARCHING:
+            case CaptureRequest.CONTROL_AE_STATE_FLASH_REQUIRED: {
+                // Wait...
+                break;
+            }
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/FocusLock.java

@@ -0,0 +1,82 @@
+package com.otaliastudios.cameraview.engine.lock;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class FocusLock extends BaseLock {
+
+    private final static String TAG = FocusLock.class.getSimpleName();
+    private final static CameraLogger LOG = CameraLogger.create(TAG);
+
+    @Override
+    protected boolean checkIsSupported(@NonNull ActionHolder holder) {
+        // We'll lock by changing the AF mode to AUTO.
+        // In that mode, AF won't change unless someone starts a trigger operation.
+        int[] modes = readCharacteristic(CameraCharacteristics.CONTROL_AF_AVAILABLE_MODES, new int[]{});
+        for (int mode : modes) {
+            if (mode == CameraCharacteristics.CONTROL_AF_MODE_AUTO) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    @Override
+    protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
+        CaptureResult lastResult = holder.getLastResult(this);
+        Integer afState = lastResult.get(CaptureResult.CONTROL_AF_STATE);
+        boolean afStateOk = afState != null &&
+                (afState == CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED
+                        || afState == CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED
+                        || afState == CaptureResult.CONTROL_AF_STATE_INACTIVE
+                        || afState == CaptureResult.CONTROL_AF_STATE_PASSIVE_FOCUSED
+                        || afState == CaptureResult.CONTROL_AF_STATE_PASSIVE_UNFOCUSED);
+        Integer afMode = lastResult.get(CaptureResult.CONTROL_AF_MODE);
+        boolean afModeOk = afMode != null && afMode == CaptureResult.CONTROL_AF_MODE_AUTO;
+        boolean result = afStateOk && afModeOk;
+        LOG.i("checkShouldSkip:", result);
+        return result;
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder) {
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_AUTO);
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_TRIGGER, CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);
+        holder.applyBuilder(this);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
+        Integer afMode = result.get(CaptureResult.CONTROL_AF_MODE);
+        LOG.i("onCapture:", "afState:", afState, "afMode:", afMode);
+        if (afState == null || afMode == null) return;
+        if (afMode != CaptureResult.CONTROL_AF_MODE_AUTO) return;
+        switch (afState) {
+            case CaptureRequest.CONTROL_AF_STATE_FOCUSED_LOCKED:
+            case CaptureRequest.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED:
+            case CaptureRequest.CONTROL_AF_STATE_INACTIVE:
+            case CaptureRequest.CONTROL_AF_STATE_PASSIVE_FOCUSED:
+            case CaptureRequest.CONTROL_AF_STATE_PASSIVE_UNFOCUSED: {
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AF_STATE_ACTIVE_SCAN:
+            case CaptureRequest.CONTROL_AF_STATE_PASSIVE_SCAN: {
+                // Wait...
+                break;
+            }
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/LockAction.java

@@ -0,0 +1,26 @@
+package com.otaliastudios.cameraview.engine.lock;
+
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.engine.action.ActionWrapper;
+import com.otaliastudios.cameraview.engine.action.Actions;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class LockAction extends ActionWrapper {
+
+    private final BaseAction action = Actions.together(
+            new ExposureLock(),
+            new FocusLock(),
+            new WhiteBalanceLock()
+    );
+
+    @NonNull
+    @Override
+    public BaseAction getAction() {
+        return action;
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/WhiteBalanceLock.java

@@ -0,0 +1,64 @@
+package com.otaliastudios.cameraview.engine.lock;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class WhiteBalanceLock extends BaseLock {
+
+    private final static String TAG = WhiteBalanceLock.class.getSimpleName();
+    private final static CameraLogger LOG = CameraLogger.create(TAG);
+
+    @Override
+    protected boolean checkIsSupported(@NonNull ActionHolder holder) {
+        boolean isNotLegacy = readCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1)
+                != CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY;
+        Integer awbMode = holder.getBuilder(this).get(CaptureRequest.CONTROL_AWB_MODE);
+        boolean result = isNotLegacy && awbMode != null && awbMode == CaptureRequest.CONTROL_AWB_MODE_AUTO;
+        LOG.i("checkIsSupported:", result);
+        return result;
+    }
+
+    @Override
+    protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
+        Integer awbState = holder.getLastResult(this).get(CaptureResult.CONTROL_AWB_STATE);
+        boolean result = awbState != null && awbState == CaptureRequest.CONTROL_AWB_STATE_LOCKED;
+        LOG.i("checkShouldSkip:", result);
+        return result;
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder) {
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AWB_LOCK, true);
+        holder.applyBuilder(this);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer awbState = result.get(CaptureResult.CONTROL_AWB_STATE);
+        LOG.i("processCapture:", "awbState:", awbState);
+        if (awbState == null) return;
+        switch (awbState) {
+            case CaptureRequest.CONTROL_AWB_STATE_LOCKED: {
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AWB_STATE_CONVERGED:
+            case CaptureRequest.CONTROL_AWB_STATE_INACTIVE:
+            case CaptureRequest.CONTROL_AWB_STATE_SEARCHING: {
+                // Wait...
+                break;
+            }
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/BaseMeter.java

@@ -0,0 +1,62 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class BaseMeter extends BaseAction {
+
+    private final static String TAG = BaseMeter.class.getSimpleName();
+    private final static CameraLogger LOG = CameraLogger.create(TAG);
+
+    private final List<MeteringRectangle> areas;
+    private boolean isSuccessful;
+    private boolean skipIfPossible;
+
+    @SuppressWarnings("WeakerAccess")
+    protected BaseMeter(@NonNull List<MeteringRectangle> areas, boolean skipIfPossible) {
+        this.areas = areas;
+        this.skipIfPossible = skipIfPossible;
+    }
+
+    @Override
+    protected final void onStart(@NonNull ActionHolder holder) {
+        super.onStart(holder);
+        boolean isSkipped = skipIfPossible && checkShouldSkip(holder);
+        boolean isSupported = checkIsSupported(holder);
+        if (isSupported && !isSkipped) {
+            LOG.i("onStart:", "supported and not skipped. Dispatching onStarted.");
+            onStarted(holder, areas);
+        } else {
+            LOG.i("onStart:", "not supported or skipped. Dispatching COMPLETED state.");
+            setSuccessful(true);
+            setState(STATE_COMPLETED);
+        }
+    }
+
+    protected abstract void onStarted(@NonNull ActionHolder holder,
+                                      @NonNull List<MeteringRectangle> areas);
+
+    protected abstract boolean checkShouldSkip(@NonNull ActionHolder holder);
+
+    protected abstract boolean checkIsSupported(@NonNull ActionHolder holder);
+
+    @SuppressWarnings("WeakerAccess")
+    protected void setSuccessful(boolean successful) {
+        isSuccessful = successful;
+    }
+
+    @SuppressWarnings("WeakerAccess")
+    public boolean isSuccessful() {
+        return isSuccessful;
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/BaseReset.java

@@ -0,0 +1,40 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.graphics.Rect;
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class BaseReset extends BaseAction {
+
+    private boolean resetArea;
+
+    @SuppressWarnings("WeakerAccess")
+    protected BaseReset(boolean resetArea) {
+        this.resetArea = resetArea;
+    }
+
+    @Override
+    protected final void onStart(@NonNull ActionHolder holder) {
+        super.onStart(holder);
+        MeteringRectangle area = null;
+        if (resetArea) {
+            Rect rect = readCharacteristic(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE, new Rect());
+            area = new MeteringRectangle(rect, MeteringRectangle.METERING_WEIGHT_DONT_CARE);
+        }
+        onStarted(holder, area);
+    }
+
+    protected abstract void onStarted(@NonNull ActionHolder holder,
+                                      @Nullable MeteringRectangle area);
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/ExposureMeter.java

@@ -0,0 +1,150 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class ExposureMeter extends BaseMeter {
+
+    private static final String TAG = ExposureMeter.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    private static final int STATE_WAITING_PRECAPTURE = 0;
+    private static final int STATE_WAITING_PRECAPTURE_END = 1;
+
+    @SuppressWarnings("WeakerAccess")
+    public ExposureMeter(@NonNull List<MeteringRectangle> areas, boolean skipIfPossible) {
+        super(areas, skipIfPossible);
+    }
+
+    @Override
+    protected boolean checkIsSupported(@NonNull ActionHolder holder) {
+        // In our case, this means checking if we support the AE precapture trigger.
+        boolean isNotLegacy = readCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1)
+                != CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY;
+        Integer aeMode = holder.getBuilder(this).get(CaptureRequest.CONTROL_AE_MODE);
+        boolean isAEOn = aeMode != null &&
+                (aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON
+                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_ALWAYS_FLASH
+                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH
+                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH_REDEYE
+                        || aeMode == 5 /* CameraCharacteristics.CONTROL_AE_MODE_ON_EXTERNAL_FLASH, API 28 */);
+        boolean result = isNotLegacy && isAEOn;
+        LOG.i("checkIsSupported:", result);
+        return result;
+    }
+
+    @Override
+    protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
+        Integer aeState = holder.getLastResult(this).get(CaptureResult.CONTROL_AE_STATE);
+        boolean result = aeState != null && aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED;
+        LOG.i("checkShouldSkip:", result);
+        return result;
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder, @NonNull List<MeteringRectangle> areas) {
+        LOG.i("onStarted:", "with areas:", areas);
+
+        // Launch the precapture trigger.
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
+                CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
+
+        // Check the regions.
+        int maxRegions = readCharacteristic(CameraCharacteristics.CONTROL_MAX_REGIONS_AE, 0);
+        if (!areas.isEmpty() && maxRegions > 0) {
+            int max = Math.min(maxRegions, areas.size());
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_REGIONS,
+                    areas.subList(0, max).toArray(new MeteringRectangle[]{}));
+        }
+
+        // Apply
+        holder.applyBuilder(this);
+        setState(STATE_WAITING_PRECAPTURE);
+    }
+
+    @Override
+    protected void onCompleted(@NonNull ActionHolder holder) {
+        super.onCompleted(holder);
+        // Remove (but not apply) the risky parameter so it is not included in new requests.
+        // Documentation about this key says that this should be allowed.
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER, null);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
+        Integer aeTriggerState = result.get(CaptureResult.CONTROL_AE_PRECAPTURE_TRIGGER);
+        LOG.i("onCaptureCompleted:", "aeState:", aeState, "aeTriggerState:", aeTriggerState);
+        if (aeState == null) return;
+
+        if (getState() == STATE_WAITING_PRECAPTURE) {
+            switch (aeState) {
+                case CaptureResult.CONTROL_AE_STATE_PRECAPTURE: {
+                    setState(STATE_WAITING_PRECAPTURE_END);
+                    break;
+                }
+                case CaptureResult.CONTROL_AE_STATE_CONVERGED:
+                case CaptureResult.CONTROL_AE_STATE_FLASH_REQUIRED: {
+                    // PRECAPTURE is a transient state. Being here might mean that precapture run
+                    // and was successful, OR that the trigger was not even received yet. To
+                    // distinguish, check the trigger state.
+                    if (aeTriggerState != null
+                            && aeTriggerState == CaptureResult.CONTROL_AE_PRECAPTURE_TRIGGER_START) {
+                        setSuccessful(true);
+                        setState(STATE_COMPLETED);
+                    }
+                    break;
+                }
+                case CaptureResult.CONTROL_AE_STATE_LOCKED: {
+                    // There's nothing we can do, AE was locked, triggers are ignored.
+                    setSuccessful(false);
+                    setState(STATE_COMPLETED);
+                    break;
+                }
+                case CaptureResult.CONTROL_AE_STATE_INACTIVE:
+                case CaptureResult.CONTROL_AE_STATE_SEARCHING: {
+                    // Wait...
+                    break;
+                }
+            }
+        }
+
+        if (getState() == STATE_WAITING_PRECAPTURE_END) {
+            switch (aeState) {
+                case CaptureResult.CONTROL_AE_STATE_CONVERGED:
+                case CaptureResult.CONTROL_AE_STATE_FLASH_REQUIRED: {
+                    setSuccessful(true);
+                    setState(STATE_COMPLETED);
+                    break;
+                }
+                case CaptureResult.CONTROL_AE_STATE_LOCKED: {
+                    // There's nothing we can do, AE was locked, triggers are ignored.
+                    setSuccessful(false);
+                    setState(STATE_COMPLETED);
+                    break;
+                }
+                case CaptureResult.CONTROL_AE_STATE_PRECAPTURE:
+                case CaptureResult.CONTROL_AE_STATE_INACTIVE:
+                case CaptureResult.CONTROL_AE_STATE_SEARCHING: {
+                    // Wait...
+                    break;
+                }
+            }
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/ExposureReset.java

@@ -0,0 +1,72 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class ExposureReset extends BaseReset {
+
+    private static final String TAG = ExposureReset.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    private static final int STATE_WAITING_LOCK = 0;
+
+    @SuppressWarnings("WeakerAccess")
+    public ExposureReset() {
+        super(true);
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder, @Nullable MeteringRectangle area) {
+        int maxRegions = readCharacteristic(CameraCharacteristics.CONTROL_MAX_REGIONS_AE, 0);
+        if (area != null && maxRegions > 0) {
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_REGIONS,
+                    new MeteringRectangle[]{area});
+        }
+
+        // NOTE: precapture might not be supported, in which case I think it will be ignored.
+        Integer trigger = holder.getLastResult(this).get(CaptureResult.CONTROL_AE_PRECAPTURE_TRIGGER);
+        LOG.i("onStarted:", "last precapture trigger is", trigger);
+        if (trigger != null && trigger == CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START) {
+            LOG.i("onStarted:", "canceling precapture.");
+            int newTrigger = Build.VERSION.SDK_INT >= 23
+                    ? CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_CANCEL
+                    : CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_IDLE;
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER, newTrigger);
+        }
+
+        // Documentation about CONTROL_AE_PRECAPTURE_TRIGGER says that, if it was started but not
+        // followed by a CAPTURE_INTENT_STILL_PICTURE request, the internal AE routine might remain
+        // locked unless we unlock manually.
+        // This is often the case for us, since the snapshot picture recorder does not use the intent
+        // and anyway we use the precapture sequence for touch metering as well.
+        // To reset, docs suggest the use of CONTROL_AE_PRECAPTURE_TRIGGER_CANCEL, which we do above,
+        // or the technique used below: locking then unlocking. This proved to be the ONLY method
+        // to unlock reliably, unlike the cancel trigger (which we'll run anyway).
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_LOCK, true);
+        holder.applyBuilder(this);
+        setState(STATE_WAITING_LOCK);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        if (getState() == STATE_WAITING_LOCK) {
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_LOCK, false);
+            holder.applyBuilder(this);
+            setState(STATE_COMPLETED);
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/FocusMeter.java

@@ -0,0 +1,96 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class FocusMeter extends BaseMeter {
+
+    private static final String TAG = FocusMeter.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    public FocusMeter(@NonNull List<MeteringRectangle> areas, boolean skipIfPossible) {
+        super(areas, skipIfPossible);
+    }
+
+    @Override
+    protected boolean checkIsSupported(@NonNull ActionHolder holder) {
+        // Exclude OFF and EDOF as per docs. These do no support the trigger.
+        Integer afMode = holder.getBuilder(this).get(CaptureRequest.CONTROL_AF_MODE);
+        boolean result = afMode != null &&
+                (afMode == CameraCharacteristics.CONTROL_AF_MODE_AUTO
+                        || afMode == CameraCharacteristics.CONTROL_AF_MODE_CONTINUOUS_PICTURE
+                        || afMode == CameraCharacteristics.CONTROL_AF_MODE_CONTINUOUS_VIDEO
+                        || afMode == CameraCharacteristics.CONTROL_AF_MODE_MACRO);
+        LOG.i("checkIsSupported:", result);
+        return result;
+    }
+
+    @Override
+    protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
+        Integer afState = holder.getLastResult(this).get(CaptureResult.CONTROL_AF_STATE);
+        boolean result = afState != null &&
+                (afState == CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED ||
+                        afState == CaptureResult.CONTROL_AF_STATE_PASSIVE_FOCUSED);
+        LOG.i("checkShouldSkip:", result);
+        return result;
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder, @NonNull List<MeteringRectangle> areas) {
+        LOG.i("onStarted:", "with areas:", areas);
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_TRIGGER,
+                CaptureRequest.CONTROL_AF_TRIGGER_START);
+        int maxRegions = readCharacteristic(CameraCharacteristics.CONTROL_MAX_REGIONS_AF, 0);
+        if (!areas.isEmpty() && maxRegions > 0) {
+            int max = Math.min(maxRegions, areas.size());
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_REGIONS,
+                    areas.subList(0, max).toArray(new MeteringRectangle[]{}));
+        }
+        holder.applyBuilder(this);
+    }
+
+    @Override
+    protected void onCompleted(@NonNull ActionHolder holder) {
+        super.onCompleted(holder);
+        // Remove (but not apply) the risky parameter so it is not included in new requests.
+        // Documentation about this key says that this should be allowed.
+        holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_TRIGGER, null);
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
+        LOG.i("onCaptureCompleted:", "afState:", afState);
+        if (afState == null) return;
+        switch (afState) {
+            case CaptureRequest.CONTROL_AF_STATE_FOCUSED_LOCKED: {
+                setSuccessful(true);
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED: {
+                setSuccessful(false);
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AF_STATE_INACTIVE: break;
+            case CaptureRequest.CONTROL_AF_STATE_ACTIVE_SCAN: break;
+            default: break;
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/FocusReset.java

@@ -0,0 +1,49 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class FocusReset extends BaseReset {
+
+    private static final String TAG = FocusReset.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    @SuppressWarnings("WeakerAccess")
+    public FocusReset() {
+        super(true);
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder, @Nullable MeteringRectangle area) {
+        boolean changed = false;
+        int maxRegions = readCharacteristic(CameraCharacteristics.CONTROL_MAX_REGIONS_AF, 0);
+        if (area != null && maxRegions > 0) {
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_REGIONS,
+                    new MeteringRectangle[]{area});
+            changed = true;
+        }
+
+        // NOTE: trigger might not be supported, in which case I think it will be ignored.
+        Integer trigger = holder.getLastResult(this).get(CaptureResult.CONTROL_AF_TRIGGER);
+        LOG.w("onStarted:", "last focus trigger is", trigger);
+        if (trigger != null && trigger == CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START) {
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_TRIGGER,
+                    CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);
+            changed = true;
+        }
+
+        if (changed) holder.applyBuilder(this);
+        setState(STATE_COMPLETED);
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/MeterAction.java

@@ -0,0 +1,262 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.graphics.PointF;
+import android.graphics.Rect;
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.TotalCaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.CameraEngine;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.ActionWrapper;
+import com.otaliastudios.cameraview.engine.action.Actions;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+import com.otaliastudios.cameraview.engine.offset.Axis;
+import com.otaliastudios.cameraview.engine.offset.Reference;
+import com.otaliastudios.cameraview.size.AspectRatio;
+import com.otaliastudios.cameraview.size.Size;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class MeterAction extends ActionWrapper {
+
+    private final static String TAG = MeterAction.class.getSimpleName();
+    private final static CameraLogger LOG = CameraLogger.create(TAG);
+
+    private List<BaseMeter> meters;
+    private BaseAction action;
+    private ActionHolder holder;
+    private final PointF point;
+    private final CameraEngine engine;
+    private final boolean skipIfPossible;
+
+    public MeterAction(@NonNull CameraEngine engine, @Nullable PointF point,
+                       boolean skipIfPossible) {
+        this.point = point;
+        this.engine = engine;
+        this.skipIfPossible = skipIfPossible;
+    }
+
+    @NonNull
+    @Override
+    public BaseAction getAction() {
+        return action;
+    }
+
+    @Nullable
+    public PointF getPoint() {
+        return point;
+    }
+
+    public boolean isSuccessful() {
+        for (BaseMeter meter : meters) {
+            if (!meter.isSuccessful()) {
+                LOG.i("isSuccessful:", "returning false.");
+                return false;
+            }
+        }
+        LOG.i("isSuccessful:", "returning true.");
+        return true;
+    }
+
+    @Override
+    protected void onStart(@NonNull ActionHolder holder) {
+        LOG.w("onStart:", "initializing.");
+        initialize(holder);
+        LOG.w("onStart:", "initialized.");
+        super.onStart(holder);
+    }
+
+    private void initialize(@NonNull ActionHolder holder) {
+        this.holder = holder;
+        List<MeteringRectangle> areas = new ArrayList<>();
+        if (point != null) {
+            // This is a good Q/A. https://stackoverflow.com/a/33181620/4288782
+            // At first, the point is relative to the View system and does not account our own cropping.
+            // Will keep updating these two below.
+            final PointF referencePoint = new PointF(point.x, point.y);
+            Size referenceSize = engine.getPreview().getSurfaceSize();
+
+            // 1. Account for cropping.
+            // This will enlarge the preview size so that aspect ratio matches.
+            referenceSize = applyPreviewCropping(referenceSize, referencePoint);
+
+            // 2. Scale to the preview stream coordinates.
+            // This will move to the preview stream coordinates by scaling.
+            referenceSize = applyPreviewScale(referenceSize, referencePoint);
+
+            // 3. Rotate to the stream coordinate system.
+            // This leaves us with sensor stream coordinates.
+            referenceSize = applyPreviewToSensorRotation(referenceSize, referencePoint);
+
+            // 4. Move to the crop region coordinate system.
+            // The crop region is the union of all currently active streams.
+            referenceSize = applyCropRegionCoordinates(referenceSize, referencePoint);
+
+            // 5. Move to the active array coordinate system.
+            referenceSize = applyActiveArrayCoordinates(referenceSize, referencePoint);
+
+            // 6. Now we can compute the metering regions.
+            // We want to define them as a fraction of the visible size which (apart from cropping)
+            // can be obtained through the SENSOR rotated preview stream size.
+            Size visibleSize = engine.getPreviewStreamSize(Reference.SENSOR);
+            //noinspection ConstantConditions
+            MeteringRectangle area1 = createMeteringRectangle(referenceSize, referencePoint,
+                    visibleSize, 0.05F, 1000);
+            MeteringRectangle area2 = createMeteringRectangle(referenceSize, referencePoint,
+                    visibleSize, 0.1F, 100);
+            areas.add(area1);
+            areas.add(area2);
+        }
+
+        BaseMeter ae = new ExposureMeter(areas, skipIfPossible);
+        BaseMeter af = new FocusMeter(areas, skipIfPossible);
+        BaseMeter awb = new WhiteBalanceMeter(areas, skipIfPossible);
+        meters = Arrays.asList(ae, af, awb);
+        action = Actions.together(ae, af, awb);
+    }
+
+    @SuppressWarnings("UnnecessaryLocalVariable")
+    @NonNull
+    private Size applyPreviewCropping(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
+        Size previewStreamSize = engine.getPreviewStreamSize(Reference.VIEW);
+        Size previewSurfaceSize = referenceSize;
+        if (previewStreamSize == null) {
+            throw new IllegalStateException("getPreviewStreamSize should not be null at this point.");
+        }
+        int referenceWidth = previewSurfaceSize.getWidth();
+        int referenceHeight = previewSurfaceSize.getHeight();
+        AspectRatio previewStreamAspectRatio = AspectRatio.of(previewStreamSize);
+        AspectRatio previewSurfaceAspectRatio = AspectRatio.of(previewSurfaceSize);
+        if (engine.getPreview().isCropping()) {
+            if (previewStreamAspectRatio.toFloat() > previewSurfaceAspectRatio.toFloat()) {
+                // Stream is larger. The x coordinate must be increased: a touch on the left side
+                // of the surface is not on the left size of stream (it's more to the right).
+                float scale = previewStreamAspectRatio.toFloat() / previewSurfaceAspectRatio.toFloat();
+                referencePoint.x += previewSurfaceSize.getWidth() * (scale - 1F) / 2F;
+                referenceWidth = Math.round(previewSurfaceSize.getWidth() * scale);
+            } else {
+                // Stream is taller. The y coordinate must be increased: a touch on the top side
+                // of the surface is not on the top size of stream (it's a bit lower).
+                float scale = previewSurfaceAspectRatio.toFloat() / previewStreamAspectRatio.toFloat();
+                referencePoint.y += previewSurfaceSize.getHeight() * (scale - 1F) / 2F;
+                referenceHeight = Math.round(previewSurfaceSize.getHeight() * scale);
+            }
+        }
+        return new Size(referenceWidth, referenceHeight);
+    }
+
+    @SuppressWarnings("ConstantConditions")
+    @NonNull
+    private Size applyPreviewScale(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
+        // The referenceSize how has the same aspect ratio of the previewStreamSize, but they
+        // can still have different size (that is, a scale operation is needed).
+        Size previewStreamSize = engine.getPreviewStreamSize(Reference.VIEW);
+        referencePoint.x *= (float) previewStreamSize.getWidth() / referenceSize.getWidth();
+        referencePoint.y *= (float) previewStreamSize.getHeight() / referenceSize.getHeight();
+        return previewStreamSize;
+    }
+
+    @SuppressWarnings("SuspiciousNameCombination")
+    @NonNull
+    private Size applyPreviewToSensorRotation(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
+        // Not elegant, but the sin/cos way was failing for some reason.
+        int angle = engine.getAngles().offset(Reference.SENSOR, Reference.VIEW, Axis.ABSOLUTE);
+        boolean flip = angle % 180 != 0;
+        float tempX = referencePoint.x;
+        float tempY = referencePoint.y;
+        if (angle == 0) {
+            referencePoint.x = tempX;
+            referencePoint.y = tempY;
+        } else if (angle == 90) {
+            referencePoint.x = tempY;
+            referencePoint.y = referenceSize.getWidth() - tempX;
+        } else if (angle == 180) {
+            referencePoint.x = referenceSize.getWidth() - tempX;
+            referencePoint.y = referenceSize.getHeight() - tempY;
+        } else if (angle == 270) {
+            referencePoint.x = referenceSize.getHeight() - tempY;
+            referencePoint.y = tempX;
+        } else {
+            throw new IllegalStateException("Unexpected angle " + angle);
+        }
+        return flip ? referenceSize.flip() : referenceSize;
+    }
+
+    @NonNull
+    private Size applyCropRegionCoordinates(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
+        // The input point and size refer to the stream rect.
+        // The stream rect is part of the 'crop region', as described below.
+        // https://source.android.com/devices/camera/camera3_crop_reprocess.html
+        Rect cropRect = holder.getBuilder(this).get(CaptureRequest.SCALER_CROP_REGION);
+        // For now, we don't care about x and y position. Rect should be non-null, but let's be safe.
+        int cropRectWidth = cropRect == null ? referenceSize.getWidth() : cropRect.width();
+        int cropRectHeight = cropRect == null ? referenceSize.getHeight() : cropRect.height();
+        // The stream is always centered inside the crop region, and one of the dimensions
+        // should always match. We just increase the other one.
+        referencePoint.x += (cropRectWidth - referenceSize.getWidth()) / 2F;
+        referencePoint.y += (cropRectHeight - referenceSize.getHeight()) / 2F;
+        return new Size(cropRectWidth, cropRectHeight);
+    }
+
+    @NonNull
+    private Size applyActiveArrayCoordinates(@NonNull Size referenceSize, @NonNull PointF referencePoint) {
+        // The input point and size refer to the scaler crop region.
+        // We can query for the crop region position inside the active array, so this is easy.
+        Rect cropRect = holder.getBuilder(this).get(CaptureRequest.SCALER_CROP_REGION);
+        referencePoint.x += cropRect == null ? 0 : cropRect.left;
+        referencePoint.y += cropRect == null ? 0 : cropRect.top;
+        // Finally, get the active rect width and height from characteristics.
+        Rect activeRect = holder.getCharacteristics(this).get(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE);
+        if (activeRect == null) { // Should never happen
+            activeRect = new Rect(0, 0, referenceSize.getWidth(), referenceSize.getHeight());
+        }
+        return new Size(activeRect.width(), activeRect.height());
+    }
+
+    /**
+     * Creates a metering rectangle around the center point.
+     * The rectangle will have a size that's a factor of the visible width and height.
+     * The rectangle will also be constrained to be inside the given boundaries,
+     * so we don't exceed them in case the center point is exactly on one side for example.
+     * @return a new rectangle
+     */
+    @NonNull
+    private MeteringRectangle createMeteringRectangle(
+            @NonNull Size boundaries,
+            @NonNull PointF center,
+            @NonNull Size visibleSize,
+            float factor,
+            int weight) {
+        float rectangleWidth = factor * visibleSize.getWidth();
+        float rectangleHeight = factor * visibleSize.getHeight();
+        float rectangleLeft = center.x - rectangleWidth / 2F;
+        float rectangleTop = center.y - rectangleHeight / 2F;
+        // Respect boundaries
+        if (rectangleLeft < 0) rectangleLeft = 0;
+        if (rectangleTop < 0) rectangleTop = 0;
+        if (rectangleLeft + rectangleWidth > boundaries.getWidth()) {
+            rectangleWidth = boundaries.getWidth() - rectangleLeft;
+        }
+        if (rectangleTop + rectangleHeight > boundaries.getHeight()) {
+            rectangleHeight = boundaries.getHeight() - rectangleTop;
+        }
+        return new MeteringRectangle(
+                (int) rectangleLeft,
+                (int) rectangleTop,
+                (int) rectangleWidth,
+                (int) rectangleHeight,
+                weight
+        );
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/MeterResetAction.java

@@ -0,0 +1,34 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.ActionWrapper;
+import com.otaliastudios.cameraview.engine.action.Actions;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+import com.otaliastudios.cameraview.engine.lock.ExposureLock;
+import com.otaliastudios.cameraview.engine.lock.FocusLock;
+import com.otaliastudios.cameraview.engine.lock.WhiteBalanceLock;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class MeterResetAction extends ActionWrapper {
+
+    private final BaseAction action;
+
+    public MeterResetAction() {
+        this.action = Actions.together(
+                new ExposureReset(),
+                new FocusReset(),
+                new WhiteBalanceReset()
+        );
+    }
+
+    @NonNull
+    @Override
+    public BaseAction getAction() {
+        return action;
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/WhiteBalanceMeter.java

@@ -0,0 +1,85 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class WhiteBalanceMeter extends BaseMeter {
+
+    private static final String TAG = WhiteBalanceMeter.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    public WhiteBalanceMeter(@NonNull List<MeteringRectangle> areas, boolean skipIfPossible) {
+        super(areas, skipIfPossible);
+    }
+
+    @Override
+    protected boolean checkIsSupported(@NonNull ActionHolder holder) {
+        boolean isNotLegacy = readCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1)
+                != CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY;
+        Integer awbMode = holder.getBuilder(this).get(CaptureRequest.CONTROL_AWB_MODE);
+        boolean result = isNotLegacy && awbMode != null && awbMode == CaptureRequest.CONTROL_AWB_MODE_AUTO;
+        LOG.i("checkIsSupported:", result);
+        return result;
+    }
+
+    @Override
+    protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
+        Integer awbState = holder.getLastResult(this).get(CaptureResult.CONTROL_AWB_STATE);
+        boolean result = awbState != null && awbState == CaptureRequest.CONTROL_AWB_STATE_CONVERGED;
+        LOG.i("checkShouldSkip:", result);
+        return result;
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder, @NonNull List<MeteringRectangle> areas) {
+        LOG.i("onStarted:", "with areas:", areas);
+        int maxRegions = readCharacteristic(CameraCharacteristics.CONTROL_MAX_REGIONS_AWB, 0);
+        if (!areas.isEmpty() && maxRegions > 0) {
+            int max = Math.min(maxRegions, areas.size());
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AWB_REGIONS,
+                    areas.subList(0, max).toArray(new MeteringRectangle[]{}));
+            holder.applyBuilder(this);
+        }
+    }
+
+    @Override
+    public void onCaptureCompleted(@NonNull ActionHolder holder, @NonNull CaptureRequest request,
+                                   @NonNull TotalCaptureResult result) {
+        super.onCaptureCompleted(holder, request, result);
+        Integer awbState = result.get(CaptureResult.CONTROL_AWB_STATE);
+        LOG.i("onCaptureCompleted:", "awbState:", awbState);
+        if (awbState == null) return;
+
+        switch (awbState) {
+            case CaptureRequest.CONTROL_AWB_STATE_CONVERGED: {
+                setSuccessful(true);
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AWB_STATE_LOCKED: {
+                // Nothing we can do if AWB was locked.
+                setSuccessful(false);
+                setState(STATE_COMPLETED);
+                break;
+            }
+            case CaptureRequest.CONTROL_AWB_STATE_INACTIVE:
+            case CaptureRequest.CONTROL_AWB_STATE_SEARCHING: {
+                // Wait...
+                break;
+            }
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/WhiteBalanceReset.java

@@ -0,0 +1,40 @@
+package com.otaliastudios.cameraview.engine.meter;
+
+import android.hardware.camera2.CameraCharacteristics;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.hardware.camera2.params.MeteringRectangle;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+
+import java.util.List;
+
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class WhiteBalanceReset extends BaseReset {
+
+    private static final String TAG = WhiteBalanceReset.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    @SuppressWarnings("WeakerAccess")
+    public WhiteBalanceReset() {
+        super(true);
+    }
+
+    @Override
+    protected void onStarted(@NonNull ActionHolder holder, @Nullable MeteringRectangle area) {
+        LOG.w("onStarted:", "with area:", area);
+        int maxRegions = readCharacteristic(CameraCharacteristics.CONTROL_MAX_REGIONS_AWB, 0);
+        if (area != null && maxRegions > 0) {
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AWB_REGIONS, new MeteringRectangle[]{area});
+            holder.applyBuilder(this);
+        }
+        setState(STATE_COMPLETED);
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/metering/AutoExposure.java

@@ -1,101 +0,0 @@
-package com.otaliastudios.cameraview.engine.metering;
-
-import android.hardware.camera2.CameraCharacteristics;
-import android.hardware.camera2.CaptureRequest;
-import android.hardware.camera2.CaptureResult;
-import android.hardware.camera2.params.MeteringRectangle;
-import android.os.Build;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.RequiresApi;
-
-import com.otaliastudios.cameraview.CameraLogger;
-
-import java.util.List;
-
-@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-public class AutoExposure extends MeteringParameter {
-
-    private static final String TAG = AutoExposure.class.getSimpleName();
-    private static final CameraLogger LOG = CameraLogger.create(TAG);
-
-    private boolean isStarted;
-
-    @Override
-    public void startMetering(@NonNull CameraCharacteristics characteristics,
-                              @NonNull CaptureRequest.Builder builder,
-                              @NonNull List<MeteringRectangle> areas) {
-        isSuccessful = false;
-        isMetered = false;
-        isStarted = false;
-
-        boolean isNotLegacy = readCharacteristic(characteristics,
-                CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1) !=
-                CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY;
-        Integer aeMode = builder.get(CaptureRequest.CONTROL_AE_MODE);
-        boolean isAEOn = aeMode != null &&
-                (aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON
-                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_ALWAYS_FLASH
-                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH
-                        || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH_REDEYE
-                        || aeMode == 5 /* CameraCharacteristics.CONTROL_AE_MODE_ON_EXTERNAL_FLASH, API 28 */);
-        isSupported = isNotLegacy && isAEOn;
-
-        if (isSupported) {
-            builder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
-                    CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
-        }
-
-        // Even if precapture is not supported, check the regions anyway.
-        int maxRegions = readCharacteristic(characteristics,
-                CameraCharacteristics.CONTROL_MAX_REGIONS_AE, 0);
-        if (maxRegions > 0) {
-            int max = Math.min(maxRegions, areas.size());
-            builder.set(CaptureRequest.CONTROL_AE_REGIONS,
-                    areas.subList(0, max).toArray(new MeteringRectangle[]{}));
-        }
-    }
-
-    @Override
-    public void onCapture(@NonNull CaptureResult result) {
-        if (isMetered || !isSupported) return;
-        Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
-        LOG.i("onCapture:", "aeState:", aeState);
-        if (aeState == null) return;
-
-        if (!isStarted) {
-            if (aeState == CaptureRequest.CONTROL_AE_STATE_PRECAPTURE) {
-                isStarted = true;
-            } else if (aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED
-                    || aeState == CaptureResult.CONTROL_AE_STATE_FLASH_REQUIRED) {
-                // PRECAPTURE is a transient state, so also check for the final states.
-                isMetered = true;
-                isSuccessful = true;
-            }
-        } else {
-            if (aeState == CaptureRequest.CONTROL_AE_STATE_CONVERGED
-                    || aeState == CaptureRequest.CONTROL_AE_STATE_FLASH_REQUIRED) {
-                isMetered = true;
-                isSuccessful = true;
-            }
-        }
-    }
-
-    @Override
-    public void resetMetering(@NonNull CameraCharacteristics characteristics,
-                              @NonNull CaptureRequest.Builder builder,
-                              @NonNull MeteringRectangle area) {
-        int maxRegions = readCharacteristic(characteristics,
-                CameraCharacteristics.CONTROL_MAX_REGIONS_AE, 0);
-        if (maxRegions > 0) {
-            builder.set(CaptureRequest.CONTROL_AE_REGIONS, new MeteringRectangle[]{area});
-        }
-        if (isSupported) {
-            // Cleanup any precapture sequence.
-            if (Build.VERSION.SDK_INT >= 23) {
-                builder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
-                        CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_CANCEL);
-            }
-        }
-    }
-}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/metering/AutoFocus.java

@@ -1,87 +0,0 @@
-package com.otaliastudios.cameraview.engine.metering;
-
-import android.hardware.camera2.CameraCharacteristics;
-import android.hardware.camera2.CaptureRequest;
-import android.hardware.camera2.CaptureResult;
-import android.hardware.camera2.params.MeteringRectangle;
-import android.os.Build;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.RequiresApi;
-
-import com.otaliastudios.cameraview.CameraLogger;
-
-import java.util.List;
-
-@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-public class AutoFocus extends MeteringParameter {
-
-    private static final String TAG = AutoFocus.class.getSimpleName();
-    private static final CameraLogger LOG = CameraLogger.create(TAG);
-
-    @Override
-    public void startMetering(@NonNull CameraCharacteristics characteristics,
-                              @NonNull CaptureRequest.Builder builder,
-                              @NonNull List<MeteringRectangle> areas) {
-        isSuccessful = false;
-        isMetered = false;
-
-        Integer afMode = builder.get(CaptureRequest.CONTROL_AF_MODE);
-        // Exclude OFF and EDOF as per docs.
-        isSupported = afMode != null &&
-                (afMode == CameraCharacteristics.CONTROL_AF_MODE_AUTO
-                || afMode == CameraCharacteristics.CONTROL_AF_MODE_CONTINUOUS_PICTURE
-                || afMode == CameraCharacteristics.CONTROL_AF_MODE_CONTINUOUS_VIDEO
-                || afMode == CameraCharacteristics.CONTROL_AF_MODE_MACRO);
-        if (isSupported) {
-            builder.set(CaptureRequest.CONTROL_AF_TRIGGER, CaptureRequest.CONTROL_AF_TRIGGER_START);
-        }
-
-        // Even if auto is not supported, change the regions anyway.
-        int maxRegions = readCharacteristic(characteristics, CameraCharacteristics.CONTROL_MAX_REGIONS_AF, 0);
-        if (maxRegions > 0) {
-            int max = Math.min(maxRegions, areas.size());
-            builder.set(CaptureRequest.CONTROL_AF_REGIONS,
-                    areas.subList(0, max).toArray(new MeteringRectangle[]{}));
-        }
-
-    }
-
-    @Override
-    public void onCapture(@NonNull CaptureResult result) {
-        if (isMetered || !isSupported) return;
-        Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
-        LOG.i("onCapture:", "afState:", afState);
-        if (afState == null) return;
-        switch (afState) {
-            case CaptureRequest.CONTROL_AF_STATE_FOCUSED_LOCKED: {
-                isMetered = true;
-                isSuccessful = true;
-                break;
-            }
-            case CaptureRequest.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED: {
-                isMetered = true;
-                isSuccessful = false;
-                break;
-            }
-            case CaptureRequest.CONTROL_AF_STATE_INACTIVE: break;
-            case CaptureRequest.CONTROL_AF_STATE_ACTIVE_SCAN: break;
-            default: break;
-        }
-    }
-
-    @Override
-    public void resetMetering(@NonNull CameraCharacteristics characteristics,
-                              @NonNull CaptureRequest.Builder builder,
-                              @NonNull MeteringRectangle area) {
-        int maxRegions = readCharacteristic(characteristics,
-                CameraCharacteristics.CONTROL_MAX_REGIONS_AF, 0);
-        if (maxRegions > 0) {
-            builder.set(CaptureRequest.CONTROL_AF_REGIONS, new MeteringRectangle[]{area});
-        }
-
-        if (isSupported) { // Cleanup any trigger.
-            builder.set(CaptureRequest.CONTROL_AF_TRIGGER, CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);
-        }
-    }
-}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/metering/AutoWhiteBalance.java

@@ -1,81 +0,0 @@
-package com.otaliastudios.cameraview.engine.metering;
-
-import android.hardware.camera2.CameraCharacteristics;
-import android.hardware.camera2.CaptureRequest;
-import android.hardware.camera2.CaptureResult;
-import android.hardware.camera2.params.MeteringRectangle;
-import android.os.Build;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.RequiresApi;
-
-import com.otaliastudios.cameraview.CameraLogger;
-
-import java.util.List;
-
-@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-public class AutoWhiteBalance extends MeteringParameter {
-
-    private static final String TAG = AutoWhiteBalance.class.getSimpleName();
-    private static final CameraLogger LOG = CameraLogger.create(TAG);
-
-    @Override
-    public void startMetering(@NonNull CameraCharacteristics characteristics,
-                              @NonNull CaptureRequest.Builder builder,
-                              @NonNull List<MeteringRectangle> areas) {
-        isSuccessful = false;
-        isMetered = false;
-
-        boolean isNotLegacy = readCharacteristic(characteristics,
-                CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1) !=
-                CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY;
-        Integer awbMode = builder.get(CaptureRequest.CONTROL_AWB_MODE);
-        isSupported = isNotLegacy && awbMode != null && awbMode == CaptureRequest.CONTROL_AWB_MODE_AUTO;
-
-        if (isSupported) {
-            // Remove any lock. We're not setting any, but just in case.
-            builder.set(CaptureRequest.CONTROL_AWB_LOCK, false);
-        }
-
-        // Even if auto is not supported, change the regions anyway.
-        int maxRegions = readCharacteristic(characteristics,
-                CameraCharacteristics.CONTROL_MAX_REGIONS_AWB, 0);
-        if (maxRegions > 0) {
-            int max = Math.min(maxRegions, areas.size());
-            builder.set(CaptureRequest.CONTROL_AWB_REGIONS,
-                    areas.subList(0, max).toArray(new MeteringRectangle[]{}));
-        }
-
-    }
-
-    @Override
-    public void onCapture(@NonNull CaptureResult result) {
-        if (isMetered || !isSupported) return;
-        Integer awbState = result.get(CaptureResult.CONTROL_AWB_STATE);
-        LOG.i("onCapture:", "awbState:", awbState);
-        if (awbState == null) return;
-
-        switch (awbState) {
-            case CaptureRequest.CONTROL_AWB_STATE_CONVERGED: {
-                isMetered = true;
-                isSuccessful = true;
-                break;
-            }
-            case CaptureRequest.CONTROL_AWB_STATE_LOCKED: break;
-            case CaptureRequest.CONTROL_AWB_STATE_INACTIVE: break;
-            case CaptureRequest.CONTROL_AWB_STATE_SEARCHING: break;
-            default: break;
-        }
-    }
-
-    @Override
-    public void resetMetering(@NonNull CameraCharacteristics characteristics,
-                              @NonNull CaptureRequest.Builder builder,
-                              @NonNull MeteringRectangle area) {
-        int maxRegions = readCharacteristic(characteristics,
-                CameraCharacteristics.CONTROL_MAX_REGIONS_AWB, 0);
-        if (maxRegions > 0) {
-            builder.set(CaptureRequest.CONTROL_AWB_REGIONS, new MeteringRectangle[]{area});
-        }
-    }
-}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/metering/MeteringParameter.java

@@ -1,54 +0,0 @@
-package com.otaliastudios.cameraview.engine.metering;
-
-import android.hardware.camera2.CameraCharacteristics;
-import android.hardware.camera2.CaptureRequest;
-import android.hardware.camera2.CaptureResult;
-import android.hardware.camera2.params.MeteringRectangle;
-import android.os.Build;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.RequiresApi;
-
-import java.util.List;
-
-@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-public abstract class MeteringParameter {
-
-    @SuppressWarnings("WeakerAccess")
-    protected boolean isSupported;
-
-    @SuppressWarnings("WeakerAccess")
-    protected boolean isSuccessful;
-
-    @SuppressWarnings("WeakerAccess")
-    protected boolean isMetered;
-
-    @SuppressWarnings("WeakerAccess")
-    @NonNull
-    protected <T> T readCharacteristic(@NonNull CameraCharacteristics characteristics,
-                                       @NonNull CameraCharacteristics.Key<T> key,
-                                       @NonNull T fallback) {
-        T value = characteristics.get(key);
-        return value == null ? fallback : value;
-    }
-
-    public final boolean isMetered() {
-        // A non supported parameter should always appear as metered
-        return isMetered || !isSupported;
-    }
-
-    public final boolean isSuccessful() {
-        // A non supported parameter should always appear as successful
-        return isSuccessful || !isSupported;
-    }
-
-    public abstract void startMetering(@NonNull CameraCharacteristics characteristics,
-                       @NonNull CaptureRequest.Builder builder,
-                       @NonNull List<MeteringRectangle> areas);
-
-    public abstract void resetMetering(@NonNull CameraCharacteristics characteristics,
-                       @NonNull CaptureRequest.Builder builder,
-                       @NonNull MeteringRectangle area);
-
-    public abstract void onCapture(@NonNull CaptureResult result);
-}

cameraview/src/main/java/com/otaliastudios/cameraview/gesture/GestureAction.java

@@ -23,7 +23,7 @@ public enum GestureAction {
     NONE(0, GestureType.ONE_SHOT),
 
     /**
-     * Auto focus control, typically assigned to the tap gesture.
+     * Touch metering control, typically assigned to the tap gesture.
      * This action can be mapped to one shot gestures:
      *
      * - {@link Gesture#TAP}

cameraview/src/main/java/com/otaliastudios/cameraview/picture/Full2PictureRecorder.java

@@ -1,18 +1,18 @@
 package com.otaliastudios.cameraview.picture;
 
 import android.hardware.camera2.CameraAccessException;
-import android.hardware.camera2.CameraCaptureSession;
-import android.hardware.camera2.CameraCharacteristics;
 import android.hardware.camera2.CameraDevice;
 import android.hardware.camera2.CaptureRequest;
-import android.hardware.camera2.CaptureResult;
-import android.hardware.camera2.TotalCaptureResult;
 import android.media.Image;
 import android.media.ImageReader;
 import android.os.Build;
 
 import com.otaliastudios.cameraview.CameraLogger;
 import com.otaliastudios.cameraview.PictureResult;
+import com.otaliastudios.cameraview.engine.Camera2Engine;
+import com.otaliastudios.cameraview.engine.action.Action;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
 import com.otaliastudios.cameraview.internal.utils.ExifHelper;
 import com.otaliastudios.cameraview.internal.utils.WorkerHandler;
 
@@ -21,7 +21,6 @@ import java.io.IOException;
 import java.nio.ByteBuffer;
 
 import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
 import androidx.exifinterface.media.ExifInterface;
 
@@ -34,133 +33,30 @@ public class Full2PictureRecorder extends PictureRecorder implements ImageReader
     private static final String TAG = Full2PictureRecorder.class.getSimpleName();
     private static final CameraLogger LOG = CameraLogger.create(TAG);
 
-    private static final int STATE_IDLE = 0;
-    private static final int STATE_WAITING_FIRST_FRAME = 1;
-    private static final int STATE_WAITING_AUTOFOCUS = 2;
-    private static final int STATE_WAITING_PRECAPTURE_START = 3;
-    private static final int STATE_WAITING_PRECAPTURE_END = 4;
-    private static final int STATE_WAITING_CAPTURE = 5;
-    private static final int STATE_WAITING_IMAGE = 6;
-
-    private static final int REQUEST_TAG = CameraDevice.TEMPLATE_STILL_CAPTURE;
-
-    private CameraCaptureSession mSession;
-    private CameraCharacteristics mCharacteristics;
-    private CaptureRequest.Builder mBuilder;
-    private CameraCaptureSession.CaptureCallback mCallback;
-    private ImageReader mPictureReader;
-    private CaptureRequest.Builder mPictureBuilder;
-    private boolean mStopPreviewBeforeCapture;
-    private int mState = STATE_IDLE;
+    private final ActionHolder mHolder;
+    private final Action mAction;
+    private final ImageReader mPictureReader;
+    private final CaptureRequest.Builder mPictureBuilder;
 
     public Full2PictureRecorder(@NonNull PictureResult.Stub stub,
-                                @Nullable PictureResultListener listener,
-                                @NonNull CameraCharacteristics characteristics,
-                                @NonNull CameraCaptureSession session,
-                                @NonNull CaptureRequest.Builder builder,
-                                @NonNull CameraCaptureSession.CaptureCallback callback,
+                                @NonNull Camera2Engine engine,
                                 @NonNull CaptureRequest.Builder pictureBuilder,
-                                @NonNull ImageReader pictureReader,
-                                boolean stopPreviewBeforeCapture) {
-        super(stub, listener);
-        mCharacteristics = characteristics;
-        mSession = session;
-        mBuilder = builder;
-        mCallback = callback;
+                                @NonNull ImageReader pictureReader) {
+        super(stub, engine);
+        mHolder = engine;
         mPictureBuilder = pictureBuilder;
-        mStopPreviewBeforeCapture = stopPreviewBeforeCapture;
         mPictureReader = pictureReader;
         mPictureReader.setOnImageAvailableListener(this, WorkerHandler.get().getHandler());
-    }
+        mAction = new BaseAction() {
 
             @Override
-    public void take() {
-        mState = STATE_WAITING_FIRST_FRAME;
-    }
-
-    private boolean supportsAutoFocus() {
-        //noinspection ConstantConditions
-        int afMode = mBuilder.get(CaptureRequest.CONTROL_AF_MODE);
-        // Exclude OFF and EDOF as per docs.
-        return afMode == CameraCharacteristics.CONTROL_AF_MODE_AUTO
-                || afMode == CameraCharacteristics.CONTROL_AF_MODE_CONTINUOUS_PICTURE
-                || afMode == CameraCharacteristics.CONTROL_AF_MODE_CONTINUOUS_VIDEO
-                || afMode == CameraCharacteristics.CONTROL_AF_MODE_MACRO;
-    }
-
-    private void runAutoFocus(@NonNull CaptureResult lastResult) {
-        Integer afState = lastResult.get(CaptureResult.CONTROL_AF_STATE);
-        boolean shouldSkip = afState != null && afState == CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED;
-        boolean supports = supportsAutoFocus();
-        LOG.i("runAutoFocus:", "supports:", supports, "shouldSkip:", shouldSkip, "afState:", afState);
-        if (supports && !shouldSkip) {
-            try {
-                mState = STATE_WAITING_AUTOFOCUS;
-                mBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, CaptureRequest.CONTROL_AF_TRIGGER_START);
-                mSession.capture(mBuilder.build(), mCallback, null);
-            } catch (CameraAccessException e) {
-                mResult = null;
-                mError = e;
-                dispatchResult();
-            }
-        } else {
-            LOG.w("Device does not support auto focus. Running precapture.");
-            runPrecapture(lastResult);
-        }
-    }
-
-    @SuppressWarnings("ConstantConditions")
-    private boolean supportsPrecapture() {
-        // Precapture is not supported on legacy devices.
-        int level = mCharacteristics.get(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL);
-        if (level == CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY) return false;
-        // We still have to check the current AE mode, see CaptureResult.CONTROL_AE_STATE.
-        int aeMode = mBuilder.get(CaptureRequest.CONTROL_AE_MODE);
-        return aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON
-                || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_ALWAYS_FLASH
-                || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH
-                || aeMode == CameraCharacteristics.CONTROL_AE_MODE_ON_AUTO_FLASH_REDEYE
-                || aeMode == 5 /* CameraCharacteristics.CONTROL_AE_MODE_ON_EXTERNAL_FLASH, API 28 */;
-    }
-
-    private void runPrecapture(@NonNull CaptureResult lastResult) {
-        Integer aeState = lastResult.get(CaptureResult.CONTROL_AE_STATE);
-        boolean shouldSkip = aeState != null && aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED;
-        boolean supports = supportsPrecapture();
-        LOG.i("runPrecapture:", "supports:", supports, "shouldSkip:", shouldSkip, "aeState:", aeState);
-        if (supports && !shouldSkip) {
-            try {
-                mState = STATE_WAITING_PRECAPTURE_START;
-                mBuilder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
-                        CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
-                mSession.capture(mBuilder.build(), mCallback, null);
-            } catch (CameraAccessException e) {
-                mResult = null;
-                mError = e;
-                dispatchResult();
-            }
-        } else {
-            LOG.w("Device does not support precapture. Running capture.");
-            runCapture();
-        }
-    }
-
-    private void runCapture() {
-        try {
-            mState = STATE_WAITING_CAPTURE;
-            mPictureBuilder.setTag(REQUEST_TAG);
+            protected void onStart(@NonNull ActionHolder holder) {
+                super.onStart(holder);
                 mPictureBuilder.addTarget(mPictureReader.getSurface());
                 mPictureBuilder.set(CaptureRequest.JPEG_ORIENTATION, mResult.rotation);
-            if (mStopPreviewBeforeCapture) {
-                // These two are present in official samples and are probably meant to speed things up?
-                // But from my tests, they actually make everything slower. So this is disabled by default
-                // with a boolean coming from the engine. Maybe in the future we can make this configurable
-                // as some people might want to stop the preview while picture is being taken even if it
-                // increases the latency.
-                mSession.stopRepeating();
-                mSession.abortCaptures();
-            }
-            mSession.capture(mPictureBuilder.build(), mCallback, null);
+                mPictureBuilder.setTag(CameraDevice.TEMPLATE_STILL_CAPTURE);
+                try {
+                    holder.applyBuilder(this, mPictureBuilder);
                 } catch (CameraAccessException e) {
                     mResult = null;
                     mError = e;
@@ -168,80 +64,26 @@ public class Full2PictureRecorder extends PictureRecorder implements ImageReader
                 }
             }
 
-    public void onCaptureStarted(@NonNull CaptureRequest request) {
-        if (request.getTag() == (Integer) REQUEST_TAG) {
+            @Override
+            public void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request) {
+                super.onCaptureStarted(holder, request);
+                if (request.getTag() == (Integer) CameraDevice.TEMPLATE_STILL_CAPTURE) {
+                    LOG.i("onCaptureStarted:", "Dispatching picture shutter.");
                     dispatchOnShutter(false);
+                    setState(STATE_COMPLETED);
                 }
             }
-
-    public void onCaptureProgressed(@NonNull CaptureResult result) {
-        // Let's ignore these. They often do not have good results.
-        // process(result);
-    }
-
-    public void onCaptureCompleted(@NonNull CaptureResult result) {
-        process(result);
+        };
     }
 
-    private void process(@NonNull CaptureResult result) {
-        switch (mState) {
-            case STATE_IDLE: break;
-            case STATE_WAITING_FIRST_FRAME: {
-                runAutoFocus(result);
-                break;
-            }
-            case STATE_WAITING_AUTOFOCUS: {
-                Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
-                if (afState == null
-                        || afState == CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED
-                        || afState == CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED) {
-                    runPrecapture(result);
-                }
-                break;
-            }
-            case STATE_WAITING_PRECAPTURE_START: {
-                Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
-                if (aeState == null
-                        || aeState == CaptureResult.CONTROL_AE_STATE_PRECAPTURE
-                        // The one above is a transient state, which means it might not be reported
-                        // by the camera. So in addition let's also check for the precature end states.
-                        || aeState == CaptureRequest.CONTROL_AE_STATE_CONVERGED
-                        || aeState == CaptureRequest.CONTROL_AE_STATE_FLASH_REQUIRED) {
-                    mState = STATE_WAITING_PRECAPTURE_END;
-                }
-                break;
-            }
-            case STATE_WAITING_PRECAPTURE_END: {
-                Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
-                if (aeState == null
-                        || aeState == CaptureRequest.CONTROL_AE_STATE_CONVERGED
-                        || aeState == CaptureRequest.CONTROL_AE_STATE_FLASH_REQUIRED
-                        // The two above are the correct states. However, just for safety, and
-                        // since we got STATE_WAITING_PRECAPTURE_START already, let's accept anything
-                        // other than the precapturing state. We don't want to get stuck here.
-                        || aeState == CaptureRequest.CONTROL_AE_STATE_SEARCHING // Camera is in normal AE routine. Should never happen.
-                        || aeState == CaptureRequest.CONTROL_AE_STATE_INACTIVE // AE is OFF. Should never happen.
-                        || aeState == CaptureResult.CONTROL_AE_STATE_LOCKED // AE has been locked. Should never happen.
-                ) {
-                    runCapture();
-                }
-                break;
-            }
-            case STATE_WAITING_CAPTURE: {
-                if (result instanceof TotalCaptureResult
-                        && result.getRequest().getTag() == (Integer) REQUEST_TAG) {
-                    mState = STATE_WAITING_IMAGE;
-                }
-                break;
-            }
-        }
+    @Override
+    public void take() {
+        mAction.start(mHolder);
     }
 
     @Override
     public void onImageAvailable(ImageReader reader) {
         LOG.i("onImageAvailable started.");
-        mState = STATE_IDLE;
-
         // Read the JPEG.
         Image image = null;
         //noinspection TryFinallyCanBeTryWithResources
@@ -266,29 +108,13 @@ public class Full2PictureRecorder extends PictureRecorder implements ImageReader
         mResult.rotation = 0;
         try {
             ExifInterface exif = new ExifInterface(new ByteArrayInputStream(mResult.data));
-            int exifOrientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
+            int exifOrientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION,
+                    ExifInterface.ORIENTATION_NORMAL);
             mResult.rotation = ExifHelper.readExifOrientation(exifOrientation);
         } catch (IOException ignore) { }
 
-        // Before leaving, unlock focus.
-        if (supportsAutoFocus()) {
-            try {
-                mBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
-                        CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);
-                mSession.capture(mBuilder.build(), mCallback, null);
-            } catch (CameraAccessException ignore) {
-            }
-        }
-
         // Leave.
         LOG.i("onImageAvailable ended.");
         dispatchResult();
     }
-
-
-    @Override
-    protected void dispatchResult() {
-        mState = STATE_IDLE;
-        super.dispatchResult();
-    }
 }

cameraview/src/main/java/com/otaliastudios/cameraview/picture/Snapshot2PictureRecorder.java

@@ -0,0 +1,139 @@
+package com.otaliastudios.cameraview.picture;
+
+import android.graphics.SurfaceTexture;
+import android.hardware.camera2.CameraAccessException;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.os.Build;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.PictureResult;
+import com.otaliastudios.cameraview.engine.Camera2Engine;
+import com.otaliastudios.cameraview.engine.action.Action;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.Actions;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+import com.otaliastudios.cameraview.engine.action.CompletionCallback;
+import com.otaliastudios.cameraview.engine.lock.LockAction;
+import com.otaliastudios.cameraview.preview.GlCameraPreview;
+import com.otaliastudios.cameraview.size.AspectRatio;
+
+/**
+ * Wraps {@link SnapshotGlPictureRecorder} for Camera2.
+ *
+ * Camera2 engine supports metering for snapshots and we expect for them to correctly fire flash as well.
+ * The first idea, and in theory, the most correct one, was to set {@link CaptureRequest#CONTROL_CAPTURE_INTENT}
+ * to {@link CaptureRequest#CONTROL_CAPTURE_INTENT_STILL_CAPTURE}.
+ *
+ * According to documentation, this will automatically trigger the flash if parameters says so.
+ * In fact this is what happens, but it is a very fast flash that only lasts for 1 or 2 frames.
+ * It's not easy to call super.take() at the exact time so that we capture the frame that was lit.
+ * I have tried by comparing {@link SurfaceTexture#getTimestamp()} and {@link CaptureResult#SENSOR_TIMESTAMP}
+ * to identify the correct frame. These timestamps match, but the frame is not the correct one.
+ *
+ * So what we do here is ignore the {@link CaptureRequest#CONTROL_CAPTURE_INTENT} and instead open the
+ * torch, if requested to do so. Then wait for exposure to settle again and finally take a snapshot.
+ * I'd still love to use the capture intent instead of this, but was not able yet.
+ */
+@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
+public class Snapshot2PictureRecorder extends SnapshotGlPictureRecorder {
+
+    private final static String TAG = Snapshot2PictureRecorder.class.getSimpleName();
+    private final static CameraLogger LOG = CameraLogger.create(TAG);
+    private final static long LOCK_TIMEOUT = 2500;
+
+    private static class FlashAction extends BaseAction {
+
+        @Override
+        protected void onStart(@NonNull ActionHolder holder) {
+            super.onStart(holder);
+            LOG.i("FlashAction:", "Parameters locked, opening torch.");
+            holder.getBuilder(this).set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_TORCH);
+            holder.getBuilder(this).set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON);
+            holder.applyBuilder(this);
+        }
+
+        @Override
+        public void onCaptureCompleted(@NonNull ActionHolder holder,
+                                       @NonNull CaptureRequest request,
+                                       @NonNull TotalCaptureResult result) {
+            super.onCaptureCompleted(holder, request, result);
+            Integer flashState = result.get(CaptureResult.FLASH_STATE);
+            if (flashState == null) {
+                LOG.w("FlashAction:", "Waiting flash, but flashState is null! Taking snapshot.");
+                setState(STATE_COMPLETED);
+            } else if (flashState == CaptureResult.FLASH_STATE_FIRED) {
+                LOG.i("FlashAction:", "Waiting flash and we have FIRED state! Taking snapshot.");
+                setState(STATE_COMPLETED);
+            } else {
+                LOG.i("FlashAction:", "Waiting flash but flashState is",
+                        flashState, ". Waiting...");
+            }
+        }
+    }
+
+    private final Action mAction;
+    private final ActionHolder mHolder;
+    private final boolean mActionNeeded;
+    private Integer mOriginalAeMode;
+    private Integer mOriginalFlashMode;
+
+    public Snapshot2PictureRecorder(@NonNull PictureResult.Stub stub,
+                                    @NonNull Camera2Engine engine,
+                                    @NonNull GlCameraPreview preview,
+                                    @NonNull AspectRatio outputRatio) {
+        super(stub, engine, preview, outputRatio);
+        mHolder = engine;
+
+        mAction = Actions.sequence(
+                Actions.timeout(LOCK_TIMEOUT, new LockAction()),
+                new FlashAction());
+        mAction.addCallback(new CompletionCallback() {
+            @Override
+            protected void onActionCompleted(@NonNull Action action) {
+                LOG.i("Taking picture with super.take().");
+                Snapshot2PictureRecorder.super.take();
+            }
+        });
+
+        Integer aeState = mHolder.getLastResult(mAction).get(CaptureResult.CONTROL_AE_STATE);
+        mActionNeeded = engine.getPictureSnapshotMetering()
+                && aeState != null
+                && aeState == CaptureResult.CONTROL_AE_STATE_FLASH_REQUIRED;
+        mOriginalAeMode = mHolder.getBuilder(mAction).get(CaptureRequest.CONTROL_AE_MODE);
+        mOriginalFlashMode = mHolder.getBuilder(mAction).get(CaptureRequest.FLASH_MODE);
+    }
+
+    @Override
+    public void take() {
+        if (!mActionNeeded) {
+            LOG.i("take:", "Engine does no metering or needs no flash, taking fast snapshot.");
+            super.take();
+        } else {
+            LOG.i("take:", "Engine needs flash. Starting action");
+            mAction.start(mHolder);
+        }
+    }
+
+    @Override
+    protected void dispatchResult() {
+        // Revert our changes.
+        LOG.i("dispatchResult:", "Reverting the flash changes.");
+        try {
+            // See Camera2Engine.setFlash() comments: turning TORCH off has bugs and we must do
+            // as follows.
+            CaptureRequest.Builder builder = mHolder.getBuilder(mAction);
+            builder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON);
+            builder.set(CaptureRequest.FLASH_MODE, CaptureResult.FLASH_MODE_OFF);
+            mHolder.applyBuilder(mAction, builder);
+            builder.set(CaptureRequest.CONTROL_AE_MODE, mOriginalAeMode);
+            builder.set(CaptureRequest.FLASH_MODE, mOriginalFlashMode);
+            mHolder.applyBuilder(mAction);
+        } catch (CameraAccessException ignore) {}
+        super.dispatchResult();
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/picture/SnapshotGlPictureRecorder.java

@@ -31,7 +31,7 @@ import com.otaliastudios.cameraview.size.AspectRatio;
 import com.otaliastudios.cameraview.size.Size;
 
 import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
+import androidx.annotation.WorkerThread;
 
 import android.view.Surface;
 
@@ -75,14 +75,13 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
             @NonNull PictureResult.Stub stub,
             @NonNull CameraEngine engine,
             @NonNull GlCameraPreview preview,
-            @NonNull AspectRatio outputRatio,
-            @Nullable Overlay overlay) {
+            @NonNull AspectRatio outputRatio) {
         super(stub, engine);
         mEngine = engine;
         mPreview = preview;
         mOutputRatio = outputRatio;
-        mOverlay = overlay;
-        mHasOverlay = overlay != null && overlay.drawsOn(Overlay.Target.PICTURE_SNAPSHOT);
+        mOverlay = engine.getOverlay();
+        mHasOverlay = mOverlay != null && mOverlay.drawsOn(Overlay.Target.PICTURE_SNAPSHOT);
     }
 
     @TargetApi(Build.VERSION_CODES.KITKAT)
@@ -113,7 +112,7 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
 
     @RendererThread
     @TargetApi(Build.VERSION_CODES.KITKAT)
-    private void onRendererTextureCreated(int textureId) {
+    protected void onRendererTextureCreated(int textureId) {
         mTextureId = textureId;
         mViewport = new EglViewport();
         // Need to crop the size.
@@ -129,10 +128,30 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
 
     @RendererThread
     @TargetApi(Build.VERSION_CODES.KITKAT)
-    private void onRendererFilterChanged(@NonNull Filter filter) {
+    protected void onRendererFilterChanged(@NonNull Filter filter) {
         mViewport.setFilter(filter.copy());
     }
 
+    @RendererThread
+    @TargetApi(Build.VERSION_CODES.KITKAT)
+    protected void onRendererFrame(@SuppressWarnings("unused") @NonNull final SurfaceTexture surfaceTexture,
+                                 final float scaleX,
+                                 final float scaleY) {
+        // Get egl context from the RendererThread, which is the one in which we have created
+        // the textureId and the overlayTextureId, managed by the GlSurfaceView.
+        // Next operations can then be performed on different threads using this handle.
+        final EGLContext eglContext = EGL14.eglGetCurrentContext();
+        // Calling this invalidates the rotation/scale logic below:
+        // surfaceTexture.getTransformMatrix(mTransform); // TODO activate and fix the logic.
+        WorkerHandler.execute(new Runnable() {
+            @Override
+            public void run() {
+                takeFrame(surfaceTexture, scaleX, scaleY, eglContext);
+
+            }
+        });
+    }
+
     /**
      * The tricky part here is the EGL surface creation.
      *
@@ -156,20 +175,10 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
      * @param scaleX frame scale x in {@link Reference#VIEW}
      * @param scaleY frame scale y in {@link Reference#VIEW}
      */
-    @RendererThread
+    @WorkerThread
     @TargetApi(Build.VERSION_CODES.KITKAT)
-    private void onRendererFrame(@SuppressWarnings("unused") @NonNull SurfaceTexture surfaceTexture,
-                                 final float scaleX,
-                                 final float scaleY) {
-        // Get egl context from the RendererThread, which is the one in which we have created
-        // the textureId and the overlayTextureId, managed by the GlSurfaceView.
-        // Next operations can then be performed on different threads using this handle.
-        final EGLContext eglContext = EGL14.eglGetCurrentContext();
-        // Calling this invalidates the rotation/scale logic below:
-        // surfaceTexture.getTransformMatrix(mTransform); // TODO activate and fix the logic.
-        WorkerHandler.execute(new Runnable() {
-            @Override
-            public void run() {
+    protected void takeFrame(@NonNull SurfaceTexture surfaceTexture, float scaleX, float scaleY, @NonNull EGLContext eglContext) {
+
         // 0. EGL window will need an output.
         // We create a fake one as explained in javadocs.
         final int fakeOutputTextureId = 9999;
@@ -214,6 +223,7 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
         }
 
         // 5. Draw and save
+        LOG.i("takeFrame:", "timestamp:", surfaceTexture.getTimestamp());
         mViewport.drawFrame(mTextureId, mTransform);
         if (mHasOverlay) mOverlayDrawer.render();
         mResult.format = PictureResult.FORMAT_JPEG;
@@ -227,8 +237,6 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
         core.release();
         dispatchResult();
     }
-        });
-    }
 
     @Override
     protected void dispatchResult() {

cameraview/src/main/java/com/otaliastudios/cameraview/preview/GlCameraPreview.java

@@ -2,6 +2,7 @@ package com.otaliastudios.cameraview.preview;
 
 import android.content.Context;
 import android.graphics.SurfaceTexture;
+import android.hardware.camera2.CaptureResult;
 import android.opengl.GLSurfaceView;
 import android.opengl.Matrix;
 import androidx.annotation.NonNull;
@@ -186,14 +187,17 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
         @Override
         public void onDrawFrame(GL10 gl) {
             if (mInputSurfaceTexture == null) return;
-            // Latch the latest frame.  If there isn't anything new,
-            // we'll just re-use whatever was there before.
-            mInputSurfaceTexture.updateTexImage();
             if (mInputStreamWidth <= 0 || mInputStreamHeight <= 0) {
                 // Skip drawing. Camera was not opened.
                 return;
             }
+
+            // Latch the latest frame. If there isn't anything new,
+            // we'll just re-use whatever was there before.
+            mInputSurfaceTexture.updateTexImage();
             mInputSurfaceTexture.getTransformMatrix(mTransformMatrix);
+            // LOG.v("onDrawFrame:", "timestamp:", mInputSurfaceTexture.getTimestamp());
+
 
             // For Camera2, apply the draw rotation.
             // See TextureCameraPreview.setDrawRotation() for info.

cameraview/src/main/java/com/otaliastudios/cameraview/video/Full2VideoRecorder.java

@@ -1,6 +1,9 @@
 package com.otaliastudios.cameraview.video;
 
 import android.annotation.SuppressLint;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
 import android.media.MediaRecorder;
 import android.os.Build;
 import android.view.Surface;
@@ -8,6 +11,11 @@ import android.view.Surface;
 import com.otaliastudios.cameraview.CameraLogger;
 import com.otaliastudios.cameraview.VideoResult;
 import com.otaliastudios.cameraview.engine.Camera2Engine;
+import com.otaliastudios.cameraview.engine.action.Action;
+import com.otaliastudios.cameraview.engine.action.ActionCallback;
+import com.otaliastudios.cameraview.engine.action.ActionHolder;
+import com.otaliastudios.cameraview.engine.action.BaseAction;
+import com.otaliastudios.cameraview.engine.action.CompletionCallback;
 import com.otaliastudios.cameraview.internal.utils.CamcorderProfiles;
 import com.otaliastudios.cameraview.size.Size;
 
@@ -25,15 +33,42 @@ public class Full2VideoRecorder extends FullVideoRecorder {
     private static final String TAG = Full2VideoRecorder.class.getSimpleName();
     private static final CameraLogger LOG = CameraLogger.create(TAG);
 
+    private ActionHolder mHolder;
     private final String mCameraId;
     private Surface mInputSurface;
 
-    public Full2VideoRecorder(@NonNull Camera2Engine engine,
-                              @NonNull String cameraId) {
+    public Full2VideoRecorder(@NonNull Camera2Engine engine, @NonNull String cameraId) {
         super(engine);
+        mHolder = engine;
         mCameraId = cameraId;
     }
 
+    @Override
+    protected void onStart() {
+        // Do not start now. Instead, wait for the first frame.
+        // Check that the request is the correct one, using the request tag.
+        // The engine might have been changing the request to add our surface lately,
+        // and we don't want to start on an old frame.
+        Action action = new BaseAction() {
+            @Override
+            public void onCaptureStarted(@NonNull ActionHolder holder, @NonNull CaptureRequest request) {
+                super.onCaptureStarted(holder, request);
+                Object tag = holder.getBuilder(this).build().getTag();
+                Object currentTag = request.getTag();
+                if (tag == null ? currentTag == null : tag.equals(currentTag)) {
+                    setState(STATE_COMPLETED);
+                }
+            }
+        };
+        action.addCallback(new CompletionCallback() {
+            @Override
+            protected void onActionCompleted(@NonNull Action action) {
+                Full2VideoRecorder.super.onStart();
+            }
+        });
+        action.start(mHolder);
+    }
+
     @SuppressLint("NewApi")
     @Override
     protected boolean onPrepareMediaRecorder(@NonNull VideoResult.Stub stub, @NonNull MediaRecorder mediaRecorder) {

cameraview/src/main/res/values/attrs.xml

@@ -141,6 +141,9 @@
 
         <attr name="cameraUseDeviceOrientation" format="boolean"/>
 
+        <attr name="cameraPictureMetering" format="boolean|reference"/>
+        <attr name="cameraPictureSnapshotMetering" format="boolean|reference"/>
+
         <attr name="cameraExperimental" format="boolean" />
 
     </declare-styleable>

demo/src/main/java/com/otaliastudios/cameraview/demo/CameraActivity.java

@@ -7,11 +7,14 @@ import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.graphics.Color;
 import android.graphics.ImageFormat;
+import android.graphics.PointF;
 import android.graphics.Rect;
 import android.graphics.YuvImage;
 import android.os.Bundle;
 import androidx.annotation.NonNull;
 import com.google.android.material.bottomsheet.BottomSheetBehavior;
+
+import androidx.annotation.Nullable;
 import androidx.appcompat.app.AppCompatActivity;
 
 import android.view.View;
@@ -111,6 +114,7 @@ public class CameraActivity extends AppCompatActivity implements View.OnClickLis
                 new Option.Mode(), new Option.Engine(), new Option.Preview(),
                 // Some controls
                 new Option.Flash(), new Option.WhiteBalance(), new Option.Hdr(),
+                new Option.PictureMetering(), new Option.PictureSnapshotMetering(),
                 // Video recording
                 new Option.VideoCodec(), new Option.Audio(),
                 // Gestures
@@ -126,7 +130,7 @@ public class CameraActivity extends AppCompatActivity implements View.OnClickLis
         List<Boolean> dividers = Arrays.asList(
                 false, true,
                 false, false, true,
-                false, false, true,
+                false, false, false, false, true,
                 false, true,
                 false, false, false, false, true,
                 false, false, true,
@@ -236,6 +240,18 @@ public class CameraActivity extends AppCompatActivity implements View.OnClickLis
             message("Video taken. Processing...", false);
             LOG.w("onVideoRecordingEnd!");
         }
+
+        @Override
+        public void onExposureCorrectionChanged(float newValue, @NonNull float[] bounds, @Nullable PointF[] fingers) {
+            super.onExposureCorrectionChanged(newValue, bounds, fingers);
+            message("Exposure correction:" + newValue, false);
+        }
+
+        @Override
+        public void onZoomChanged(float newValue, @NonNull float[] bounds, @Nullable PointF[] fingers) {
+            super.onZoomChanged(newValue, bounds, fingers);
+            message("Zoom:" + newValue, false);
+        }
     }
 
     @Override

demo/src/main/java/com/otaliastudios/cameraview/demo/Option.java

@@ -252,6 +252,54 @@ public abstract class Option<T> {
         }
     }
 
+    public static class PictureMetering extends Option<Boolean> {
+
+        public PictureMetering() {
+            super("Picture Metering");
+        }
+
+        @NonNull
+        @Override
+        public Boolean get(@NonNull CameraView view) {
+            return view.getPictureMetering();
+        }
+
+        @NonNull
+        @Override
+        public Collection<Boolean> getAll(@NonNull CameraView view, @NonNull CameraOptions options) {
+            return Arrays.asList(true, false);
+        }
+
+        @Override
+        public void set(@NonNull CameraView view, @NonNull Boolean value) {
+            view.setPictureMetering(value);
+        }
+    }
+
+    public static class PictureSnapshotMetering extends Option<Boolean> {
+
+        public PictureSnapshotMetering() {
+            super("Picture Snapshot Metering");
+        }
+
+        @NonNull
+        @Override
+        public Boolean get(@NonNull CameraView view) {
+            return view.getPictureSnapshotMetering();
+        }
+
+        @NonNull
+        @Override
+        public Collection<Boolean> getAll(@NonNull CameraView view, @NonNull CameraOptions options) {
+            return Arrays.asList(true, false);
+        }
+
+        @Override
+        public void set(@NonNull CameraView view, @NonNull Boolean value) {
+            view.setPictureSnapshotMetering(value);
+        }
+    }
+
     public static class VideoCodec extends ControlOption<com.otaliastudios.cameraview.controls.VideoCodec> {
         public VideoCodec() {
             super(com.otaliastudios.cameraview.controls.VideoCodec.class, "Video Codec");

docs/_posts/2018-12-20-capture-size.md

@@ -4,7 +4,7 @@ title: "Capture Size"
 subtitle: "Set size of output media"
 description: "Set size of output media"
 category: docs
-order: 8
+order: 9
 date: 2018-12-20 22:07:22
 disqus: 1
 ---

docs/_posts/2018-12-20-changelog.md

@@ -70,7 +70,7 @@ https://github.com/natario1/CameraView/compare/v2.0.0-beta06...v2.0.0-rc1
 
 If you were using `focus`, just switch to `autoFocus`.
 
-If you were using `focusWithMarker`, you can [add back the old marker](../docs/controls.html#cameraautofocusmarker).
+If you were using `focusWithMarker`, you can [add back the old marker](../docs/metering.html#touch-metering-markers).
 
 https://github.com/natario1/CameraView/compare/v2.0.0-beta05...v2.0.0-beta06
 

docs/_posts/2018-12-20-controls.md

@@ -143,76 +143,6 @@ cameraView.setVideoBitRate(0);
 cameraView.setVideoBitRate(4000000);
 ```
 
-### Auto Focus
-
-There are many ways to focus a CameraView engine:
-
-- Continuous autofocus is activated by default, where present
-- User can start focus with a [Gesture](gestures.html)
-- The developer can start focus with the `startAutoFocus(float, float)` API. This action needs
-  the coordinates of a point to focus, with respect to the view width and height.
-
-The last two actions will trigger the focus callbacks:
-
-```java
-cameraView.addCameraListener(new CameraListener() {
-    
-    @Override
-    public void onAutoFocusStart(@NonNull PointF point) {
-        // Auto focus was started by a gesture or by startAutoFocus(float, float).
-        // The camera is currently trying to focus around that area.
-        // This can be used to draw things on screen.
-    }
-
-    @Override
-    public void onAutoFocusEnd(boolean successful, @NonNull PointF point) {
-        // Auto focus operation just ended. If successful, the camera will have converged
-        // to a new focus point, and possibly changed exposure and white balance as well.
-        // The point is the same that was passed to onAutoFocusStart.
-    }
-});
-```
-
-Auto focus is not guaranteed to be supported: check the `CameraOptions` to be sure.
-
-```xml
-<com.otaliastudios.cameraview.CameraView
-    app:cameraAutoFocusMarker="@string/cameraview_default_autofocus_marker"
-    app:cameraAutoFocusResetDelay="3000"/>
-```
-
-##### cameraAutoFocusMarker
-
-Lets you set a marker for drawing on screen in response to auto focus events.
-In XML, you should pass the qualified class name of your marker.
-
-```java
-cameraView.setAutoFocusMarker(null);
-cameraView.setAutoFocusMarker(marker);
-```
-
-We offer a default marker (similar to the old `focusWithMarker` attribute in v1),
-which you can set in XML using the `@string/cameraview_default_autofocus_marker` resource,
-or programmatically:
-
-```java
-cameraView.setAutoFocusMarker(new DefaultAutoFocusMarker());
-```
-
-##### cameraAutoFocusResetDelay
-
-Lets you control how an auto-focus operation is reset after completed.
-Setting a value <= 0 or == Long.MAX_VALUE will not reset the auto-focus.
-This is useful for low end devices that have slow auto-focus capabilities.
-Defaults to 3 seconds.
-
-```java
-cameraView.setCameraAutoFocusResetDelay(1000);  // 1 second
-cameraView.setCameraAutoFocusResetDelay(0);  // NO reset
-cameraView.setCameraAutoFocusResetDelay(-1);  // NO reset
-cameraView.setCameraAutoFocusResetDelay(Long.MAX_VALUE);  // NO reset
-```
-
 ### Zoom
 
 There are two ways to control the zoom value:
@@ -235,28 +165,3 @@ cameraView.addCameraListener(new CameraListener() {
 ```
 
 Zoom is not guaranteed to be supported: check the `CameraOptions` to be sure.
-
-### Exposure correction
-
-There are two ways to control the exposure correction value:
-
-- User can change the exposure correction with a [Gesture](gestures.html)
-- The developer can change this value with the `setExposureCorrection(float)` API, passing in the EV
-  value, in camera stops. This value should be contained in the minimum and maximum supported values,
-  as returned by `CameraOptions`.
-
-Both actions will trigger the exposure correction callback, which can be used, for example, to draw a seek bar:
-
-```java
-cameraView.addCameraListener(new CameraListener() {
-    
-    @UiThread
-    public void onExposureCorrectionChanged(float newValue, @NonNull float[] bounds, @Nullable PointF[] fingers) {
-        // newValue: the new correction value
-        // bounds: min and max bounds for newValue, as returned by {@link CameraOptions}
-        // fingers: finger positions that caused the event, null if not caused by touch
-    }
-});
-```
-
-EV correction is not guaranteed to be supported: check the `CameraOptions` to be sure.

docs/_posts/2018-12-20-debugging.md

@@ -2,7 +2,7 @@
 layout: page
 title: "Debugging"
 category: docs
-order: 14
+order: 15
 date: 2018-12-20 20:02:38
 disqus: 1
 ---

docs/_posts/2018-12-20-error-handling.md

@@ -2,7 +2,7 @@
 layout: page
 title: "Error Handling"
 category: docs
-order: 13
+order: 14
 date: 2018-12-20 20:02:31
 disqus: 1
 ---

docs/_posts/2018-12-20-frame-processing.md

@@ -4,7 +4,7 @@ title: "Frame Processing"
 subtitle: "Process each frame in real time"
 description: "Process each frame in real time"
 category: docs
-order: 5
+order: 6
 date: 2018-12-20 20:45:42
 disqus: 1
 ---

docs/_posts/2018-12-20-gestures.md

@@ -4,7 +4,7 @@ title: "Gestures"
 subtitle: "Gestures control"
 description: "Gestures control"
 category: docs
-order: 4
+order: 5
 date: 2018-12-20 20:49:35
 disqus: 1
 ---
@@ -39,10 +39,10 @@ Looking at this from the other side:
 |Gesture action|Description|Can be mapped to|
 |--------------|-----------|----------------|
 |`NONE`|Disables this gesture.|`TAP` `LONG_TAP` `PINCH` `SCROLL_HORIZONTAL` `SCROLL_VERTICAL`|
-|`AUTO_FOCUS`|Launches an [auto-focus operation](controls.html#auto-focus) on the finger position.|`TAP` `LONG_TAP`|
+|`AUTO_FOCUS`|Launches a [touch metering operation](metering.html#touch-metering) on the finger position.|`TAP` `LONG_TAP`|
 |`TAKE_PICTURE`|Takes a picture using [takePicture](capturing-media.html).|`TAP` `LONG_TAP`|
 |`ZOOM`|[Zooms](controls.html#zoom) in or out.|`PINCH` `SCROLL_HORIZONTAL` `SCROLL_VERTICAL`|
-|`EXPOSURE_CORRECTION`|Controls the [exposure correction](controls.html#exposure-correction).|`PINCH` `SCROLL_HORIZONTAL` `SCROLL_VERTICAL`|
+|`EXPOSURE_CORRECTION`|Controls the [exposure correction](metering.html#exposure-correction).|`PINCH` `SCROLL_HORIZONTAL` `SCROLL_VERTICAL`|
 |`FILTER_CONTROL_1`|Controls the first parameter (if any) of a [real-time filter](filters.html).|`PINCH` `SCROLL_HORIZONTAL` `SCROLL_VERTICAL`|
 |`FILTER_CONTROL_2`|Controls the second parameter (if any) of a [real-time filter](filters.html).|`PINCH` `SCROLL_HORIZONTAL` `SCROLL_VERTICAL`|
 

docs/_posts/2018-12-20-more-features.md

@@ -4,7 +4,7 @@ title: "More features"
 subtitle: "Undocumented features & more"
 description: "Undocumented features & more"
 category: docs
-order: 15
+order: 16
 date: 2018-12-20 20:41:20
 disqus: 1
 ---

docs/_posts/2018-12-20-preview-size.md

@@ -4,7 +4,7 @@ title: "Preview Size"
 subtitle: "Measuring behavior"
 description: "Measuring behavior"
 category: docs
-order: 7
+order: 8
 date: 2018-12-20 22:07:17
 disqus: 1
 ---

docs/_posts/2018-12-20-previews.md

@@ -4,7 +4,7 @@ title: "Engine and Previews"
 subtitle: "Camera engine and preview implementations"
 description: "Camera engine and preview implementations"
 category: docs
-order: 6
+order: 7
 date: 2018-12-20 21:58:16
 disqus: 1
 ---

docs/_posts/2018-12-20-runtime-permissions.md

@@ -4,7 +4,7 @@ title: "Runtime Permissions"
 subtitle: "Permissions and Manifest setup"
 description: "Permissions and Manifest setup"
 category: docs
-order: 12
+order: 13
 date: 2018-12-20 20:03:03
 disqus: 1
 ---

docs/_posts/2019-02-24-snapshot-size.md

@@ -4,7 +4,7 @@ title: "Snapshot Size"
 subtitle: "Sizing the snapshots output"
 description: "Sizing the snapshots output"
 category: docs
-order: 9
+order: 10
 date: 2019-02-24 17:36:39
 disqus: 1
 ---

docs/_posts/2019-07-14-watermarks-and-overlays.md

@@ -4,7 +4,7 @@ title: "Watermarks and Overlays"
 subtitle: "Static and animated overlays"
 description: "Static and animated overlays"
 category: docs
-order: 10
+order: 11
 date: 2019-07-14 20:14:31
 disqus: 1
 ---

docs/_posts/2019-08-06-filters.md

@@ -4,7 +4,7 @@ title: "Real-time Filters"
 subtitle: "Apply filters to preview and snapshots"
 description: "Apply filters to preview and snapshots"
 category: docs
-order: 11
+order: 12
 date: 2019-08-06 17:10:17
 disqus: 1
 ---

docs/_posts/2019-09-04-metering.md

@@ -0,0 +1,158 @@
+---
+layout: page
+title: "Metering"
+subtitle: "Exposure and metering controls"
+description: "Exposure and metering controls"
+category: docs
+order: 4
+date: 2019-09-04 19:39:03
+disqus: 1
+---
+
+In CameraView grammar, metering is the act of measuring the scene brightness, colors and focus
+distance in order to automatically adapt the camera exposure, focus and white balance (AE, AF and AWB,
+often referred as 3A).
+
+We treat three different types on metering: [continuous metering](#continuous-metering), 
+[picture metering](#picture-metering) and [touch metering](#touch-metering).
+
+You can also apply adjustment to the metered exposure through the [exposure correction](#exposure-correction) control.
+
+### Continuous Metering
+
+By default, and if the device supports it, all three routines (AE, AF, AWB) are continuously metered
+as the device moves or the scene changes.
+
+- For AE, this is always enabled if supported
+- For AF, this is always enabled if supported
+- For AWB, this is enabled if the `WhiteBalance` parameter is set to `AUTO` [[docs]](#controls.html#camerawhitebalance)
+
+### Picture Metering
+
+*In Camera1, picture metering is always enabled for pictures, and always disabled for picture snapshots. 
+The following applies to Camera2 only.*
+
+The camera engine will try to trigger metering when a picture is requested, either with `takePicture()`
+or `takePictureSnapshot()`. This has two obvious consequences:
+
+- improves the picture quality
+- increases the latency, because metering takes time
+
+For these reasons, picture metering is **enabled** by default for HQ pictures and **disabled** by
+default for picture snapshots. However, the behavior can be changed with two flags and their
+respective XML attributes:
+
+```java
+cameraView.setPictureMetering(true); // Meter before takePicture()
+cameraView.setPictureMetering(false); // Don't
+cameraView.setPictureSnapshotMetering(true); // Meter before takePictureSnapshot()
+cameraView.setPictureSnapshotMetering(false); // Don't
+```
+
+### Touch Metering
+
+Touch metering is triggered by either a [Gesture](gestures.html) or by the developer itself, which
+can start touch metering on a specific point with the `startAutoFocus(float, float)` API.
+This action needs the coordinates of a point computed with respect to the view width and height.
+
+In both cases, the metering callbacks will be triggered:
+
+```java
+cameraView.addCameraListener(new CameraListener() {
+    
+    @Override
+    public void onAutoFocusStart(@NonNull PointF point) {
+        // Touch metering was started by a gesture or by startAutoFocus(float, float).
+        // The camera is currently trying to meter around that area.
+        // This can be used to draw things on screen.
+    }
+
+    @Override
+    public void onAutoFocusEnd(boolean successful, @NonNull PointF point) {
+        // Touch metering operation just ended. If successful, the camera will have converged
+        // to a new focus point, and possibly new exposure and white balance as well.
+        // The point is the same that was passed to onAutoFocusStart.
+    }
+});
+```
+
+Touch metering is not guaranteed to be supported: check the `CameraOptions` to be sure.
+
+##### Touch Metering Markers
+
+You can set a marker for drawing on screen in response to touch metering events.
+In XML, you should pass the qualified class name of your marker.
+
+```java
+cameraView.setAutoFocusMarker(null);
+cameraView.setAutoFocusMarker(marker);
+```
+
+We offer a default marker (similar to the old `focusWithMarker` attribute in v1),
+which you can set in XML using the `@string/cameraview_default_autofocus_marker` resource,
+or programmatically:
+
+```java
+cameraView.setAutoFocusMarker(new DefaultAutoFocusMarker());
+```
+
+##### Touch Metering Reset Delay
+
+You control control how a touch metering operation is reset after completed.
+Setting a value <= 0 or == Long.MAX_VALUE will not reset the metering values.
+This is useful for low end devices that have slow auto-focus capabilities.
+Defaults to 3 seconds.
+
+```java
+cameraView.setCameraAutoFocusResetDelay(1000);  // 1 second
+cameraView.setCameraAutoFocusResetDelay(0);  // NO reset
+cameraView.setCameraAutoFocusResetDelay(-1);  // NO reset
+cameraView.setCameraAutoFocusResetDelay(Long.MAX_VALUE);  // NO reset
+```
+
+### Exposure correction
+
+There are two ways to control the exposure correction value:
+
+- User can change the exposure correction with a [Gesture](gestures.html)
+- The developer can change this value with the `setExposureCorrection(float)` API, passing in the EV
+  value, in camera stops. This value should be contained in the minimum and maximum supported values,
+  as returned by `CameraOptions`.
+
+Both actions will trigger the exposure correction callback, which can be used, for example, to draw a seek bar:
+
+```java
+cameraView.addCameraListener(new CameraListener() {
+    
+    @UiThread
+    public void onExposureCorrectionChanged(float newValue, @NonNull float[] bounds, @Nullable PointF[] fingers) {
+        // newValue: the new correction value
+        // bounds: min and max bounds for newValue, as returned by CameraOptions
+        // fingers: finger positions that caused the event, null if not caused by touch
+    }
+});
+```
+
+EV correction is not guaranteed to be supported: check the `CameraOptions` to be sure.
+
+### Related XML Attributes
+
+```xml
+<com.otaliastudios.cameraview.CameraView
+    app:cameraPictureMetering="true|false"
+    app:cameraPictureSnapshotMetering="false|true"
+    app:cameraAutoFocusMarker="@string/cameraview_default_autofocus_marker"
+    app:cameraAutoFocusResetDelay="3000"/>
+```
+
+### Related APIs
+
+|Method|Description|
+|------|-----------|
+|`setPictureMetering(boolean)`|Whether the engine should trigger 3A metering when a picture is requested. Defaults to true.|
+|`setPictureSnapshotMetering(boolean)`|Whether the engine should trigger 3A metering when a picture snapshot is requested. Defaults to false.|
+|`startAutoFocus(float, float)`|Starts the 3A touch metering routine at the given coordinates, with respect to the view system.|
+|`CameraOptions.isAutoFocusSupported()`|Whether touch metering (metering with respect to a specific region of the screen) is supported.|
+|`setExposureCorrection(float)`|Changes the exposure adjustment, in EV stops. A positive value means a brighter picture.|
+|`CameraOptions.getExposureCorrectionMinValue()`|The minimum value of negative exposure correction, in EV stops.|
+|`CameraOptions.getExposureCorrectionMaxValue()`|The maximum value of positive exposure correction, in EV stops.|