Support opacity layers for platform-views using hybrid-composition (flutter/engine#30264)

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/mutatorsstack/FlutterMutatorView.java

@@ -6,6 +6,7 @@ import android.annotation.SuppressLint;
 import android.content.Context;
 import android.graphics.Canvas;
 import android.graphics.Matrix;
+import android.graphics.Paint;
 import android.graphics.Path;
 import android.view.MotionEvent;
 import android.view.View;
@@ -28,6 +29,7 @@ public class FlutterMutatorView extends FrameLayout {
   private int top;
   private int prevLeft;
   private int prevTop;
+  private Paint paint;
 
   private final AndroidTouchProcessor androidTouchProcessor;
 
@@ -42,6 +44,7 @@ public class FlutterMutatorView extends FrameLayout {
     super(context, null);
     this.screenDensity = screenDensity;
     this.androidTouchProcessor = androidTouchProcessor;
+    this.paint = new Paint();
   }
 
   /** Initialize the FlutterMutatorView. */
@@ -142,6 +145,11 @@ public class FlutterMutatorView extends FrameLayout {
       pathCopy.offset(-left, -top);
       canvas.clipPath(pathCopy);
     }
+
+    // Apply the final opacity value on the parent canvas.
+    paint.setAlpha((int) (mutatorsStack.getFinalOpacity() * 255));
+    this.setLayerType(LAYER_TYPE_HARDWARE, paint);
+
     super.draw(canvas);
     canvas.restore();
   }

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/mutatorsstack/FlutterMutatorsStack.java

@@ -47,6 +47,7 @@ public class FlutterMutatorsStack {
     @Nullable private Rect rect;
     @Nullable private Path path;
     @Nullable private float[] radiis;
+    @Nullable private float opacity;
 
     private FlutterMutatorType type;
 
@@ -93,6 +94,16 @@ public class FlutterMutatorsStack {
       this.matrix = matrix;
     }
 
+    /**
+     * Initialize an opacity mutator.
+     *
+     * @param opacity the opacity to apply.
+     */
+    public FlutterMutator(float opacity) {
+      this.type = FlutterMutatorType.OPACITY;
+      this.opacity = opacity;
+    }
+
     /**
      * Get the mutator type.
      *
@@ -128,18 +139,29 @@ public class FlutterMutatorsStack {
     public Matrix getMatrix() {
       return matrix;
     }
+
+    /**
+     * Get the opacity of the mutator if {@link #getType()} returns FlutterMutatorType.OPACITY.
+     *
+     * @return the opacity if the type is FlutterMutatorType.OPACITY; otherwise null.
+     */
+    public float getOpacity() {
+      return opacity;
+    }
   }
 
   private @NonNull List<FlutterMutator> mutators;
 
   private List<Path> finalClippingPaths;
   private Matrix finalMatrix;
+  private float finalOpacity;
 
   /** Initialize the mutator stack. */
   public FlutterMutatorsStack() {
     this.mutators = new ArrayList<FlutterMutator>();
     finalMatrix = new Matrix();
     finalClippingPaths = new ArrayList<Path>();
+    finalOpacity = 1.f;
   }
 
   /**
@@ -187,6 +209,17 @@ public class FlutterMutatorsStack {
     finalClippingPaths.add(path);
   }
 
+  /**
+   * Push an opacity {@link FlutterMutatorsStack.FlutterMutator} to the stack.
+   *
+   * @param opacity the opacity value.
+   */
+  public void pushOpacity(float opacity) {
+    FlutterMutator mutator = new FlutterMutator(opacity);
+    mutators.add(mutator);
+    finalOpacity *= opacity;
+  }
+
   /**
    * Get a list of all the raw mutators. The 0 index of the returned list is the top of the stack.
    */
@@ -214,4 +247,9 @@ public class FlutterMutatorsStack {
   public Matrix getFinalMatrix() {
     return finalMatrix;
   }
+
+  /** Returns the final opacity value. Apply this value to the canvas of the view. */
+  public float getFinalOpacity() {
+    return finalOpacity;
+  }
 }

engine/src/flutter/shell/platform/android/platform_view_android_jni_impl.cc

@@ -121,6 +121,7 @@ static jmethodID g_mutators_stack_init_method = nullptr;
 static jmethodID g_mutators_stack_push_transform_method = nullptr;
 static jmethodID g_mutators_stack_push_cliprect_method = nullptr;
 static jmethodID g_mutators_stack_push_cliprrect_method = nullptr;
+static jmethodID g_mutators_stack_push_opacity_method = nullptr;
 
 // Called By Java
 static jlong AttachJNI(JNIEnv* env, jclass clazz, jobject flutterJNI) {
@@ -1019,6 +1020,14 @@ bool PlatformViewAndroid::Register(JNIEnv* env) {
     return false;
   }
 
+  g_mutators_stack_push_opacity_method =
+      env->GetMethodID(g_mutators_stack_class->obj(), "pushOpacity", "(F)V");
+  if (g_mutators_stack_push_opacity_method == nullptr) {
+    FML_LOG(ERROR)
+        << "Could not locate FlutterMutatorsStack.pushOpacity method";
+    return false;
+  }
+
   g_on_display_platform_view_method =
       env->GetMethodID(g_flutter_jni_class->obj(), "onDisplayPlatformView",
                        "(IIIIIIILio/flutter/embedding/engine/mutatorsstack/"
@@ -1453,10 +1462,15 @@ void PlatformViewAndroidJNIImpl::FlutterViewOnDisplayPlatformView(
             (int)rect.bottom(), radiisArray.obj());
         break;
       }
+      case opacity: {
+        float opacity = (*iter)->GetAlphaFloat();
+        env->CallVoidMethod(mutatorsStack, g_mutators_stack_push_opacity_method,
+                            opacity);
+        break;
+      }
       // TODO(cyanglaz): Implement other mutators.
       // https://github.com/flutter/flutter/issues/58426
       case clip_path:
-      case opacity:
         break;
     }
     ++iter;

engine/src/flutter/shell/platform/android/test/io/flutter/FlutterTestSuite.java

@@ -24,6 +24,7 @@ import io.flutter.embedding.engine.deferredcomponents.PlayStoreDeferredComponent
 import io.flutter.embedding.engine.loader.ApplicationInfoLoaderTest;
 import io.flutter.embedding.engine.loader.FlutterLoaderTest;
 import io.flutter.embedding.engine.mutatorsstack.FlutterMutatorViewTest;
+import io.flutter.embedding.engine.mutatorsstack.FlutterMutatorsStackTest;
 import io.flutter.embedding.engine.plugins.shim.ShimPluginRegistryTest;
 import io.flutter.embedding.engine.renderer.FlutterRendererTest;
 import io.flutter.embedding.engine.systemchannels.DeferredComponentChannelTest;
@@ -73,6 +74,7 @@ import test.io.flutter.embedding.engine.PluginComponentTest;
   FlutterJNITest.class,
   FlutterLaunchTests.class,
   FlutterLoaderTest.class,
+  FlutterMutatorsStackTest.class,
   FlutterMutatorViewTest.class,
   FlutterShellArgsTest.class,
   FlutterRendererTest.class,

engine/src/flutter/shell/platform/android/test/io/flutter/embedding/engine/mutatorsstack/FlutterMutatorViewTest.java

@@ -1,10 +1,13 @@
 package io.flutter.embedding.engine.mutatorsstack;
 
+import static android.view.View.LAYER_TYPE_HARDWARE;
 import static android.view.View.OnFocusChangeListener;
 import static junit.framework.TestCase.*;
 import static org.mockito.Mockito.*;
 
+import android.graphics.Canvas;
 import android.graphics.Matrix;
+import android.graphics.Paint;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.ViewGroup;
@@ -250,4 +253,20 @@ public class FlutterMutatorViewTest {
     view.unsetOnDescendantFocusChangeListener();
     verify(viewTreeObserver, times(1)).removeOnGlobalFocusChangeListener(activeFocusListener);
   }
+
+  @Test
+  public void draw_opacityApplied() {
+    final FlutterMutatorView view = new FlutterMutatorView(RuntimeEnvironment.systemContext);
+    final FlutterMutatorView spy = spy(view);
+
+    final FlutterMutatorsStack mutatorsStack = new FlutterMutatorsStack();
+    mutatorsStack.pushOpacity(.3f);
+
+    spy.readyToDisplay(mutatorsStack, /*left=*/ 1, /*top=*/ 2, /*width=*/ 0, /*height=*/ 0);
+    spy.draw(new Canvas());
+    verify(spy)
+        .setLayerType(
+            intThat((Integer layerType) -> layerType == LAYER_TYPE_HARDWARE),
+            argThat((Paint paint) -> paint.getAlpha() == (int) (.3f * 255)));
+  }
 }

engine/src/flutter/shell/platform/android/test/io/flutter/embedding/engine/mutatorsstack/FlutterMutatorsStackTest.java

@@ -0,0 +1,42 @@
+package io.flutter.embedding.engine.mutatorsstack;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+@Config(manifest = Config.NONE)
+@RunWith(RobolectricTestRunner.class)
+public class FlutterMutatorsStackTest {
+
+  @Test
+  public void pushOpacity() {
+    final FlutterMutatorsStack mutatorsStack = new FlutterMutatorsStack();
+    mutatorsStack.pushOpacity(.5f);
+
+    assertEquals(mutatorsStack.getMutators().size(), 1);
+    assertEquals(
+        mutatorsStack.getMutators().get(0).getType(),
+        FlutterMutatorsStack.FlutterMutatorType.OPACITY);
+    assertEquals(mutatorsStack.getMutators().get(0).getOpacity(), .5f, 0f);
+  }
+
+  @Test
+  public void defaultOpacity() {
+    final FlutterMutatorsStack mutatorsStack = new FlutterMutatorsStack();
+
+    assertEquals(1f, mutatorsStack.getFinalOpacity(), 0f);
+  }
+
+  @Test
+  public void layeredOpacity() {
+    final FlutterMutatorsStack mutatorsStack = new FlutterMutatorsStack();
+    mutatorsStack.pushOpacity(.5f);
+    mutatorsStack.pushOpacity(.6f);
+    mutatorsStack.pushOpacity(1f);
+
+    assertEquals(.3f, mutatorsStack.getFinalOpacity(), 1 / 255);
+  }
+}