MultiFilter to merge filters (#559)

* Ensure copied filters have right size

* Create MultiFilter base implementation

* Working implementation with replaceAll hack

* Implement OneParameterFilter and TwoParameterFilter in MultiFilter

* Add docs

* Add tests

* Fix rotation issues

* Fix tests and cleanup

* Small improvements

cameraview/src/androidTest/java/com/otaliastudios/cameraview/filter/MultiFilterTest.java

@@ -0,0 +1,213 @@
+package com.otaliastudios.cameraview.filter;
+
+
+import android.opengl.GLES20;
+
+import androidx.annotation.NonNull;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import androidx.test.filters.SmallTest;
+
+import com.otaliastudios.cameraview.BaseEglTest;
+import com.otaliastudios.cameraview.filters.AutoFixFilter;
+import com.otaliastudios.cameraview.filters.BrightnessFilter;
+import com.otaliastudios.cameraview.filters.DuotoneFilter;
+import com.otaliastudios.cameraview.filters.VignetteFilter;
+import com.otaliastudios.cameraview.internal.GlUtils;
+import com.otaliastudios.cameraview.internal.egl.EglViewport;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.Mockito.atLeastOnce;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class MultiFilterTest extends BaseEglTest {
+
+    @Test
+    public void testConstructor1() {
+        MultiFilter multiFilter = new MultiFilter(
+                new DuotoneFilter(),
+                new AutoFixFilter()
+        );
+        assertEquals(2, multiFilter.filters.size());
+    }
+
+    @Test
+    public void testConstructor2() {
+        List<Filter> filters = new ArrayList<>();
+        filters.add(new DuotoneFilter());
+        filters.add(new AutoFixFilter());
+        MultiFilter multiFilter = new MultiFilter(filters);
+        assertEquals(2, multiFilter.filters.size());
+    }
+
+    @Test
+    public void testAddFilter() {
+        MultiFilter multiFilter = new MultiFilter();
+        assertEquals(0, multiFilter.filters.size());
+        multiFilter.addFilter(new DuotoneFilter());
+        assertEquals(1, multiFilter.filters.size());
+        multiFilter.addFilter(new AutoFixFilter());
+        assertEquals(2, multiFilter.filters.size());
+    }
+
+    @Test
+    public void testAddFilter_multi() {
+        MultiFilter multiFilter = new MultiFilter(new DuotoneFilter());
+        assertEquals(1, multiFilter.filters.size());
+        MultiFilter other = new MultiFilter(
+                new AutoFixFilter(),
+                new BrightnessFilter(),
+                new VignetteFilter());
+        multiFilter.addFilter(other);
+        assertEquals(4, multiFilter.filters.size());
+    }
+
+    @Test
+    public void testSetSize() {
+        DuotoneFilter filter = new DuotoneFilter();
+        MultiFilter multiFilter = new MultiFilter(filter);
+        MultiFilter.State state = multiFilter.states.get(filter);
+        assertNotNull(state);
+        assertNull(state.size);
+        multiFilter.setSize(WIDTH, HEIGHT);
+        assertNotNull(state.size);
+    }
+
+    @Test
+    public void testCopy() {
+        DuotoneFilter filter = spy(new DuotoneFilter());
+        MultiFilter multiFilter = new MultiFilter(filter);
+        MultiFilter multiFilterCopy = (MultiFilter) multiFilter.copy();
+        assertEquals(1, multiFilterCopy.filters.size());
+        verify(filter, times(1)).onCopy();
+    }
+
+    @Test
+    public void testParameter1() {
+        DuotoneFilter filter = new DuotoneFilter();
+        MultiFilter multiFilter = new MultiFilter(filter);
+        float desired = 0.21582F; // whatever
+        multiFilter.setParameter1(desired);
+        assertEquals(desired, multiFilter.getParameter1(), 0.001F);
+        assertEquals(desired, filter.getParameter1(), 0.001F);
+    }
+
+    @Test
+    public void testParameter2() {
+        DuotoneFilter filter = new DuotoneFilter();
+        MultiFilter multiFilter = new MultiFilter(filter);
+        float desired = 0.21582F; // whatever
+        multiFilter.setParameter2(desired);
+        assertEquals(desired, multiFilter.getParameter2(), 0.001F);
+        assertEquals(desired, filter.getParameter2(), 0.001F);
+    }
+
+    @Test
+    public void testOnCreate_isLazy() {
+        DuotoneFilter filter = spy(new DuotoneFilter());
+        MultiFilter multiFilter = new MultiFilter(filter);
+
+        int program = GlUtils.createProgram(multiFilter.getVertexShader(),
+                multiFilter.getFragmentShader());
+        multiFilter.onCreate(program);
+        verify(filter, never()).onCreate(anyInt());
+
+        multiFilter.onDestroy();
+        GLES20.glDeleteProgram(program);
+        verify(filter, never()).onDestroy();
+    }
+
+    @Test
+    public void testDraw_simple() {
+        DuotoneFilter filter = spy(new DuotoneFilter());
+        MultiFilter multiFilter = new MultiFilter(filter);
+        multiFilter.setSize(WIDTH, HEIGHT);
+        EglViewport viewport = new EglViewport(multiFilter);
+        int texture = viewport.createTexture();
+        float[] matrix = new float[16];
+        viewport.drawFrame(texture, matrix);
+        viewport.release();
+
+        // The child should have experienced the whole lifecycle.
+        verify(filter, atLeastOnce()).getVertexShader();
+        verify(filter, atLeastOnce()).getFragmentShader();
+        verify(filter, atLeastOnce()).setSize(anyInt(), anyInt());
+        verify(filter, times(1)).onCreate(anyInt());
+        verify(filter, times(1)).draw(matrix);
+        verify(filter, times(1)).onDestroy();
+    }
+
+    @Test
+    public void testDraw_multi() {
+        // Want to test that when filter1 is drawn, the current framebuffer is a
+        // non-default one. When filter2 is drawn, the current framebuffer is 0.
+        final DuotoneFilter filter1 = spy(new DuotoneFilter());
+        final DuotoneFilter filter2 = spy(new DuotoneFilter());
+        final MultiFilter multiFilter = new MultiFilter(filter1, filter2);
+        multiFilter.setSize(WIDTH, HEIGHT);
+        float[] matrix = new float[16];
+        final int[] result = new int[1];
+
+        doAnswer(new Answer() {
+            @Override
+            public Object answer(InvocationOnMock invocation) {
+                MultiFilter.State state = multiFilter.states.get(filter1);
+                assertNotNull(state);
+                assertTrue(state.isCreated);
+                assertTrue(state.isFramebufferCreated);
+
+                GLES20.glGetIntegerv(GLES20.GL_FRAMEBUFFER_BINDING, result, 0);
+                assertTrue(result[0] != 0);
+                return null;
+            }
+        }).when(filter1).draw(matrix);
+
+        // Note: second filter is drawn with the identity matrix!
+        doAnswer(new Answer() {
+            @Override
+            public Object answer(InvocationOnMock invocation) {
+                // The last filter has no FBO / texture.
+                MultiFilter.State state = multiFilter.states.get(filter2);
+                assertNotNull(state);
+                assertTrue(state.isCreated);
+                assertFalse(state.isFramebufferCreated);
+
+                GLES20.glGetIntegerv(GLES20.GL_FRAMEBUFFER_BINDING, result, 0);
+                assertEquals(0, result[0]);
+                return null;
+
+            }
+        }).when(filter2).draw(any(float[].class));
+
+        EglViewport viewport = new EglViewport(multiFilter);
+        int texture = viewport.createTexture();
+        viewport.drawFrame(texture, matrix);
+        viewport.release();
+
+        // Verify that both are drawn.
+        verify(filter1, times(1)).draw(matrix);
+        verify(filter2, times(1)).draw(any(float[].class));
+    }
+
+}

cameraview/src/main/java/com/otaliastudios/cameraview/filter/MultiFilter.java

@@ -0,0 +1,325 @@
+package com.otaliastudios.cameraview.filter;
+
+import android.opengl.GLES11Ext;
+import android.opengl.GLES20;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+
+import com.otaliastudios.cameraview.internal.GlUtils;
+import com.otaliastudios.cameraview.size.Size;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A {@link MultiFilter} is a special {@link Filter} that can group one or more filters together.
+ * When this happens, filters are applied in sequence:
+ * - the first filter reads from input frames
+ * - the second filters reads the output of the first
+ * And so on, until the last filter which will read from the previous and write to the real output.
+ *
+ * New filters can be added at any time through {@link #addFilter(Filter)}, but currently they
+ * can not be removed because we can not easily ensure that they would be correctly released.
+ *
+ * The {@link MultiFilter} does also implement {@link OneParameterFilter} and {@link TwoParameterFilter},
+ * dispatching all the parameter calls to child filters, assuming they support it.
+ *
+ * There are some important technical caveats when using {@link MultiFilter}:
+ * - each child filter requires the allocation of a GL framebuffer. Using a large number of filters
+ *   will likely cause memory issues (e.g. https://stackoverflow.com/q/6354208/4288782).
+ * - some of the children need to write into {@link GLES20#GL_TEXTURE_2D} instead of
+ *   {@link GLES11Ext#GL_TEXTURE_EXTERNAL_OES}! To achieve this, we replace samplerExternalOES
+ *   with sampler2D in your fragment shader code. This might cause issues for some shaders.
+ */
+@SuppressWarnings("unused")
+public class MultiFilter implements Filter, OneParameterFilter, TwoParameterFilter {
+
+    @VisibleForTesting
+    static class State {
+        @VisibleForTesting boolean isCreated = false;
+        @VisibleForTesting boolean isFramebufferCreated = false;
+        @VisibleForTesting Size size = null;
+
+        private int programHandle = -1;
+        private int framebufferId = -1;
+        private int textureId = -1;
+    }
+
+    @VisibleForTesting final List<Filter> filters = new ArrayList<>();
+    @VisibleForTesting final Map<Filter, State> states = new HashMap<>();
+    private final Object lock = new Object();
+    private Size size = null;
+    private float parameter1 = 0F;
+    private float parameter2 = 0F;
+
+    /**
+     * Creates a new group with the given filters.
+     * @param filters children
+     */
+    @SuppressWarnings("WeakerAccess")
+    public MultiFilter(@NonNull Filter... filters) {
+        this(Arrays.asList(filters));
+    }
+
+    /**
+     * Creates a new group with the given filters.
+     * @param filters children
+     */
+    @SuppressWarnings("WeakerAccess")
+    public MultiFilter(@NonNull Collection<Filter> filters) {
+        for (Filter filter : filters) {
+            addFilter(filter);
+        }
+    }
+
+    /**
+     * Adds a new filter. It will be used in the next frame.
+     * If the filter is a {@link MultiFilter}, we'll use its children instead.
+     *
+     * @param filter a new filter
+     */
+    @SuppressWarnings("WeakerAccess")
+    public void addFilter(@NonNull Filter filter) {
+        if (filter instanceof MultiFilter) {
+            MultiFilter multiFilter = (MultiFilter) filter;
+            for (Filter multiChild : multiFilter.filters) {
+                addFilter(multiChild);
+            }
+            return;
+        }
+        synchronized (lock) {
+            if (!filters.contains(filter)) {
+                filters.add(filter);
+                states.put(filter, new State());
+            }
+        }
+    }
+
+    // We don't offer a removeFilter method since that would cause issues
+    // with cleanup. Cleanup must happen on the GL thread so we'd have to wait
+    // for new rendering call (which might not even happen).
+
+    private void maybeCreate(@NonNull Filter filter, boolean isFirst) {
+        State state = states.get(filter);
+        //noinspection ConstantConditions
+        if (!state.isCreated) {
+            state.isCreated = true;
+            String shader = filter.getFragmentShader();
+            if (!isFirst) {
+                // The first shader actually reads from a OES texture, but the others
+                // will read from the 2d framebuffer texture. This is a dirty hack.
+                shader = shader.replace("samplerExternalOES ", "sampler2D ");
+            }
+            state.programHandle = GlUtils.createProgram(filter.getVertexShader(), shader);
+            filter.onCreate(state.programHandle);
+        }
+    }
+
+    private void maybeDestroy(@NonNull Filter filter) {
+        State state = states.get(filter);
+        //noinspection ConstantConditions
+        if (state.isCreated) {
+            state.isCreated = false;
+            filter.onDestroy();
+            GLES20.glDeleteProgram(state.programHandle);
+            state.programHandle = -1;
+        }
+    }
+
+    private void maybeCreateFramebuffer(@NonNull Filter filter, boolean isLast) {
+        if (isLast) return;
+        State state = states.get(filter);
+        //noinspection ConstantConditions
+        if (!state.isFramebufferCreated) {
+            state.isFramebufferCreated = true;
+
+            int[] framebufferArray = new int[1];
+            int[] textureArray = new int[1];
+            GLES20.glGenFramebuffers(1, framebufferArray, 0);
+            GLES20.glGenTextures(1, textureArray, 0);
+            state.framebufferId = framebufferArray[0];
+            state.textureId = textureArray[0];
+
+            GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, state.textureId);
+            GLES20.glTexImage2D(GLES20.GL_TEXTURE_2D, 0, GLES20.GL_RGBA, state.size.getWidth(), state.size.getHeight(), 0, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, null);
+            GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);
+            GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
+            GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
+            GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);
+            GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, state.framebufferId);
+            GLES20.glFramebufferTexture2D(GLES20.GL_FRAMEBUFFER,
+                    GLES20.GL_COLOR_ATTACHMENT0,
+                    GLES20.GL_TEXTURE_2D,
+                    state.textureId,
+                    0);
+
+            int status = GLES20.glCheckFramebufferStatus(GLES20.GL_FRAMEBUFFER);
+            if (status != GLES20.GL_FRAMEBUFFER_COMPLETE) {
+                throw new RuntimeException("Invalid framebuffer generation. Error:" + status);
+            }
+
+            GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
+            GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, 0);
+        }
+    }
+
+    private void maybeDestroyFramebuffer(@NonNull Filter filter) {
+        State state = states.get(filter);
+        //noinspection ConstantConditions
+        if (state.isFramebufferCreated) {
+            state.isFramebufferCreated = false;
+            GLES20.glDeleteFramebuffers(1, new int[]{state.framebufferId}, 0);
+            state.framebufferId = -1;
+            GLES20.glDeleteTextures(1, new int[]{state.textureId}, 0);
+            state.textureId = -1;
+        }
+    }
+
+    private void maybeSetSize(@NonNull Filter filter) {
+        State state = states.get(filter);
+        //noinspection ConstantConditions
+        if (size != null && !size.equals(state.size)) {
+            state.size = size;
+            filter.setSize(size.getWidth(), size.getHeight());
+        }
+    }
+
+    @NonNull
+    @Override
+    public String getVertexShader() {
+        // Whatever, we won't be using this.
+        return new NoFilter().getVertexShader();
+    }
+
+    @NonNull
+    @Override
+    public String getFragmentShader() {
+        // Whatever, we won't be using this.
+        return new NoFilter().getFragmentShader();
+    }
+
+    @Override
+    public void onCreate(int programHandle) {
+        // We'll create children during the draw() op, since some of them
+        // might have been added after this onCreate() is called.
+    }
+
+    @Override
+    public void onDestroy() {
+        synchronized (lock) {
+            for (Filter filter : filters) {
+                maybeDestroyFramebuffer(filter);
+                maybeDestroy(filter);
+            }
+        }
+    }
+
+    @Override
+    public void setSize(int width, int height) {
+        size = new Size(width, height);
+        synchronized (lock) {
+            for (Filter filter : filters) {
+                maybeSetSize(filter);
+            }
+        }
+    }
+
+    @Override
+    public void draw(float[] transformMatrix) {
+        synchronized (lock) {
+            for (int i = 0; i < filters.size(); i++) {
+                boolean isFirst = i == 0;
+                boolean isLast = i == filters.size() - 1;
+                Filter filter = filters.get(i);
+                State state = states.get(filter);
+                maybeSetSize(filter);
+                maybeCreate(filter, isFirst);
+                maybeCreateFramebuffer(filter, isLast);
+
+                //noinspection ConstantConditions
+                GLES20.glUseProgram(state.programHandle);
+
+                // Define the output framebuffer.
+                // Each filter outputs into its own framebuffer object, except the
+                // last filter, which outputs into the default framebuffer.
+                if (!isLast) {
+                    GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, state.framebufferId);
+                    GLES20.glClearColor(0, 0, 0, 0);
+                } else {
+                    GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, 0);
+                }
+
+                // Perform the actual drawing.
+                // The first filter should apply all the transformations. Then,
+                // since they are applied, we should use a no-op matrix.
+                if (isFirst) {
+                    filter.draw(transformMatrix);
+                } else {
+                    filter.draw(GlUtils.IDENTITY_MATRIX);
+                }
+
+                // Set the input for the next cycle:
+                // It is the framebuffer texture from this cycle. If this is the last
+                // filter, reset this value just to cleanup.
+                if (!isLast) {
+                    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, state.textureId);
+                } else {
+                    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
+                }
+
+                GLES20.glUseProgram(0);
+            }
+        }
+    }
+
+    @NonNull
+    @Override
+    public Filter copy() {
+        synchronized (lock) {
+            MultiFilter copy = new MultiFilter();
+            for (Filter filter : filters) {
+                copy.addFilter(filter.copy());
+            }
+            return copy;
+        }
+    }
+
+    @Override
+    public void setParameter1(float parameter1) {
+        this.parameter1 = parameter1;
+        synchronized (lock) {
+            for (Filter filter : filters) {
+                if (filter instanceof OneParameterFilter) {
+                    ((OneParameterFilter) filter).setParameter1(parameter1);
+                }
+            }
+        }
+    }
+
+    @Override
+    public void setParameter2(float parameter2) {
+        this.parameter2 = parameter2;
+        synchronized (lock) {
+            for (Filter filter : filters) {
+                if (filter instanceof TwoParameterFilter) {
+                    ((TwoParameterFilter) filter).setParameter2(parameter2);
+                }
+            }
+        }
+    }
+
+    @Override
+    public float getParameter1() {
+        return parameter1;
+    }
+
+    @Override
+    public float getParameter2() {
+        return parameter2;
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/internal/egl/EglViewport.java

@@ -21,7 +21,7 @@ public class EglViewport {
     private int mTextureUnit;
 
     private Filter mFilter;
-    private boolean mFilterChanged = false;
+    private Filter mPendingFilter;
 
     public EglViewport() {
         this(new NoFilter());
@@ -35,7 +35,6 @@ public class EglViewport {
     }
 
     private void createProgram() {
-        release(); // Release old program if present.
         mProgramHandle = GlUtils.createProgram(mFilter.getVertexShader(), mFilter.getFragmentShader());
         mFilter.onCreate(mProgramHandle);
     }
@@ -67,15 +66,18 @@ public class EglViewport {
         return texId;
     }
 
-    public void setFilter(@NonNull Filter filter){
-        this.mFilter = filter;
-        mFilterChanged = true;
+    public void setFilter(@NonNull Filter filter) {
+        // TODO see if this is needed. If setFilter is always called from the correct GL thread,
+        // we don't need to wait for a new draw call (which might not even happen).
+        mPendingFilter = filter;
     }
 
     public void drawFrame(int textureId, float[] textureMatrix) {
-        if (mFilterChanged) {
+        if (mPendingFilter != null) {
+            release();
+            mFilter = mPendingFilter;
+            mPendingFilter = null;
             createProgram();
-            mFilterChanged = false;
         }
 
         GlUtils.checkError("draw start");

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

@@ -95,6 +95,12 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
                 SnapshotGlPictureRecorder.this.onRendererTextureCreated(textureId);
             }
 
+            @RendererThread
+            @Override
+            public void onRendererFilterChanged(@NonNull Filter filter) {
+                SnapshotGlPictureRecorder.this.onRendererFilterChanged(filter);
+            }
+
             @RendererThread
             @Override
             public void onRendererFrame(@NonNull SurfaceTexture surfaceTexture, final float scaleX, final float scaleY) {
@@ -102,10 +108,6 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
                 SnapshotGlPictureRecorder.this.onRendererFrame(surfaceTexture, scaleX, scaleY);
             }
 
-            @Override
-            public void onFilterChanged(@NonNull Filter filter) {
-                mViewport.setFilter(filter.copy());
-            }
         });
     }
 
@@ -125,6 +127,12 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
         }
     }
 
+    @RendererThread
+    @TargetApi(Build.VERSION_CODES.KITKAT)
+    private void onRendererFilterChanged(@NonNull Filter filter) {
+        mViewport.setFilter(filter.copy());
+    }
+
     /**
      * The tricky part here is the EGL surface creation.
      *
@@ -150,7 +158,9 @@ public class SnapshotGlPictureRecorder extends PictureRecorder {
      */
     @RendererThread
     @TargetApi(Build.VERSION_CODES.KITKAT)
-    private void onRendererFrame(final @NonNull SurfaceTexture surfaceTexture, final float scaleX, final float scaleY) {
+    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.

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

@@ -141,7 +141,9 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
         @RendererThread
         @Override
         public void onSurfaceCreated(GL10 gl, EGLConfig config) {
-            if (mCurrentFilter == null) mCurrentFilter = new NoFilter();
+            if (mCurrentFilter == null) {
+                mCurrentFilter = new NoFilter();
+            }
             mOutputViewport = new EglViewport(mCurrentFilter);
             mOutputTextureId = mOutputViewport.createTexture();
             mInputSurfaceTexture = new SurfaceTexture(mOutputTextureId);
@@ -282,7 +284,7 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
             public void run() {
                 mRendererFrameCallbacks.add(callback);
                 if (mOutputTextureId != 0) callback.onRendererTextureCreated(mOutputTextureId);
-                callback.onFilterChanged(mCurrentFilter);
+                callback.onRendererFilterChanged(mCurrentFilter);
             }
         });
     }
@@ -325,11 +327,15 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
     }
 
     @Override
-    public void setFilter(@NonNull Filter filter) {
+    public void setFilter(final @NonNull Filter filter) {
+        mCurrentFilter = filter;
         if (hasSurface()) {
             filter.setSize(mOutputSurfaceWidth, mOutputSurfaceHeight);
         }
-        mCurrentFilter = filter;
+
+        getView().queueEvent(new Runnable() {
+            @Override
+            public void run() {
                 if (mOutputViewport != null) {
                     mOutputViewport.setFilter(filter);
                 }
@@ -337,8 +343,10 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
                 // Need to synchronize when iterating the Collections.synchronizedSet
                 synchronized (mRendererFrameCallbacks) {
                     for (RendererFrameCallback callback : mRendererFrameCallbacks) {
-                callback.onFilterChanged(filter);
+                        callback.onRendererFilterChanged(filter);
                     }
                 }
             }
+        });
+    }
 }

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

@@ -33,10 +33,11 @@ public interface RendererFrameCallback {
     void onRendererFrame(@NonNull SurfaceTexture surfaceTexture, float scaleX, float scaleY);
 
     /**
-     * Called on the change of shader filter
-     * We should update the EglViewPort once you receives this event
+     * Called when the renderer filter changes. This is guaranteed to be called at least once
+     * before the first {@link #onRendererFrame(SurfaceTexture, float, float)}.
      *
-     * @param filter the new filter applied
+     * @param filter the new filter
      */
-    void onFilterChanged(@NonNull Filter filter);
+    @RendererThread
+    void onRendererFilterChanged(@NonNull Filter filter);
 }

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

@@ -104,9 +104,10 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
     }
 
     @Override
-    public void onFilterChanged(@NonNull Filter filter) {
+    public void onRendererFilterChanged(@NonNull Filter filter) {
         mCurrentFilter = filter.copy();
         if (mEncoderEngine != null) {
+            mCurrentFilter.setSize(mResult.size.getWidth(), mResult.size.getHeight());
             mEncoderEngine.notify(TextureMediaEncoder.FILTER_EVENT, mCurrentFilter);
         }
     }
@@ -161,6 +162,10 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
             }
             TextureMediaEncoder videoEncoder = new TextureMediaEncoder(videoConfig);
 
+            // Adjustment
+            mResult.rotation = 0; // We will rotate the result instead.
+            mCurrentFilter.setSize(mResult.size.getWidth(), mResult.size.getWidth());
+
             // Audio
             AudioMediaEncoder audioEncoder = null;
             if (mResult.audio == Audio.ON || mResult.audio == Audio.MONO || mResult.audio == Audio.STEREO) {
@@ -181,7 +186,6 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
                     SnapshotVideoRecorder.this);
             mEncoderEngine.notify(TextureMediaEncoder.FILTER_EVENT, mCurrentFilter);
             mEncoderEngine.start();
-            mResult.rotation = 0; // We will rotate the result instead.
             mCurrentState = STATE_RECORDING;
         }
 

cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/TextureMediaEncoder.java

@@ -134,15 +134,23 @@ public class TextureMediaEncoder extends VideoMediaEncoder<TextureConfig> {
     @EncoderThread
     @Override
     protected void onEvent(@NonNull String event, @Nullable Object data) {
+        switch (event) {
+            case FILTER_EVENT:
+                //noinspection ConstantConditions
+                onFilter((Filter) data);
+                break;
+            case FRAME_EVENT:
+                //noinspection ConstantConditions
+                onFrame((Frame) data);
+                break;
+        }
+    }
 
-        if (event.equals(FILTER_EVENT)) {
-            Filter filter = (Filter) data;
+    private void onFilter(@NonNull Filter filter) {
         mViewport.setFilter(filter);
-        } else if (event.equals(FRAME_EVENT)) {
-            Frame frame = (Frame) data;
-            if (frame == null) {
-                throw new IllegalArgumentException("Got null frame for FRAME_EVENT.");
     }
+
+    private void onFrame(@NonNull Frame frame) {
         if (!shouldRenderFrame(frame.timestampUs())) {
             mFramePool.recycle(frame);
             return;
@@ -213,7 +221,6 @@ public class TextureMediaEncoder extends VideoMediaEncoder<TextureConfig> {
         mWindow.swapBuffers();
         mFramePool.recycle(frame);
     }
-    }
 
     @Override
     protected void onStopped() {

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

@@ -5,6 +5,7 @@ import android.content.Intent;
 import android.content.pm.PackageManager;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
+import android.graphics.Color;
 import android.graphics.ImageFormat;
 import android.graphics.Rect;
 import android.graphics.YuvImage;
@@ -28,7 +29,9 @@ import com.otaliastudios.cameraview.controls.Mode;
 import com.otaliastudios.cameraview.VideoResult;
 import com.otaliastudios.cameraview.controls.Preview;
 import com.otaliastudios.cameraview.filter.Filters;
+import com.otaliastudios.cameraview.filter.MultiFilter;
 import com.otaliastudios.cameraview.filters.BrightnessFilter;
+import com.otaliastudios.cameraview.filters.DuotoneFilter;
 import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.frame.FrameProcessor;
 
@@ -334,6 +337,12 @@ public class CameraActivity extends AppCompatActivity implements View.OnClickLis
         Filters filter = mAllFilters[mCurrentFilter];
         camera.setFilter(filter.newInstance());
         message(filter.toString(), false);
+
+        // To test MultiFilter:
+        // DuotoneFilter duotone = new DuotoneFilter();
+        // duotone.setFirstColor(Color.RED);
+        // duotone.setSecondColor(Color.GREEN);
+        // camera.setFilter(new MultiFilter(duotone, filter.newInstance()));
     }
 
     @Override

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

@@ -91,6 +91,27 @@ camera.mapGesture(Gesture.SCROLL_HORIZONTAL, GestureAction.FILTER_CONTROL_1);
 camera.mapGesture(Gesture.SCROLL_VERTICAL, GestureAction.FILTER_CONTROL_2);
 ```
 
+### MultiFilter
+
+CameraView provides a special filter called `MultiFilter` which can be used to group different filters
+together, and apply them in sequence to the input frame, in order to process it more than once.
+
+```java
+camera.setFilter(new MultiFilter(firstFilter, secondFilter, thirdFilter));
+```
+
+You can even add new filters to the group at any time, using `MultiFilter.addFilter()`.
+The `MultiFilter` will also try to dispatch [filter controls](#filters-controls) (e.g. from gestures) 
+to its children.
+
+There are some technical caveats when using a `MultiFilter`:
+
+- Using a large number of child filters can consume the available graphic memory
+- For [advanced users](#advanced-usage), child filters need to read from `GLES20.GL_TEXTURE_2D`
+  instead of the typical `GLES11Ext.GL_TEXTURE_EXTERNAL_OES`. To achieve this, we get your fragment 
+  shader String and replace any `"samplerExternalOES"` with `"sampler2D"`. This is a hack
+  that might cause issues with specific shader implementations.
+
 ### Advanced usage
 
 Advanced users with OpenGL experience can create their own filters by implementing the `Filter` interface