Add offset to engine OpacityLayer

flow/layers/opacity_layer.cc

@@ -11,10 +11,12 @@ OpacityLayer::OpacityLayer() = default;
 OpacityLayer::~OpacityLayer() = default;
 
 void OpacityLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
-  ContainerLayer::Preroll(context, matrix);
+  SkMatrix child_matrix = matrix;
+  child_matrix.postTranslate(offset_.fX, offset_.fY);
+  ContainerLayer::Preroll(context, child_matrix);
   if (context->raster_cache && layers().size() == 1) {
     Layer* child = layers()[0].get();
-    SkMatrix ctm = matrix;
+    SkMatrix ctm = child_matrix;
 #ifndef SUPPORT_FRACTIONAL_TRANSLATION
     ctm = RasterCache::GetIntegralTransCTM(ctm);
 #endif
@@ -30,6 +32,7 @@ void OpacityLayer::Paint(PaintContext& context) const {
   paint.setAlpha(alpha_);
 
   SkAutoCanvasRestore save(&context.canvas, true);
+  context.canvas.translate(offset_.fX, offset_.fY);
 
 #ifndef SUPPORT_FRACTIONAL_TRANSLATION
   context.canvas.setMatrix(

flow/layers/opacity_layer.h

@@ -15,6 +15,7 @@ class OpacityLayer : public ContainerLayer {
   ~OpacityLayer() override;
 
   void set_alpha(int alpha) { alpha_ = alpha; }
+  void set_offset(const SkPoint& offset) { offset_ = offset; }
 
   void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
 
@@ -25,6 +26,7 @@ class OpacityLayer : public ContainerLayer {
 
  private:
   int alpha_;
+  SkPoint offset_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(OpacityLayer);
 };

lib/ui/compositing.dart

@@ -122,7 +122,10 @@ class SceneBuilder extends NativeFieldWrapperClass2 {
   /// opacity).
   ///
   /// See [pop] for details about the operation stack.
-  void pushOpacity(int alpha) native 'SceneBuilder_pushOpacity';
+  void pushOpacity(int alpha, {Offset offset = Offset.zero}) {
+    _pushOpacity(alpha, offset.dx, offset.dy);
+  }
+  void _pushOpacity(int alpha, double dx, double dy) native 'SceneBuilder_pushOpacity';
 
   /// Pushes a color filter operation onto the operation stack.
   ///

lib/ui/compositing/scene_builder.cc

@@ -118,9 +118,10 @@ void SceneBuilder::pushClipPath(const CanvasPath* path, int clipBehavior) {
   PushLayer(std::move(layer));
 }
 
-void SceneBuilder::pushOpacity(int alpha) {
+void SceneBuilder::pushOpacity(int alpha, double dx, double dy) {
   auto layer = std::make_unique<flow::OpacityLayer>();
   layer->set_alpha(alpha);
+  layer->set_offset(SkPoint::Make(dx, dy));
   PushLayer(std::move(layer));
 }
 

lib/ui/compositing/scene_builder.h

@@ -42,7 +42,7 @@ class SceneBuilder : public RefCountedDartWrappable<SceneBuilder> {
                     int clipBehavior);
   void pushClipRRect(const RRect& rrect, int clipBehavior);
   void pushClipPath(const CanvasPath* path, int clipBehavior);
-  void pushOpacity(int alpha);
+  void pushOpacity(int alpha, double dx = 0, double dy = 0);
   void pushColorFilter(int color, int blendMode);
   void pushBackdropFilter(ImageFilter* filter);
   void pushShaderMask(Shader* shader,