iOS platform view opacity (flutter#9667)

Author: Chris Yang

flow/embedded_views.cc

@@ -30,6 +30,11 @@ void MutatorsStack::PushTransform(const SkMatrix& matrix) {
   vector_.push_back(element);
 };
 
+void MutatorsStack::PushOpacity(const int& alpha) {
+  std::shared_ptr<Mutator> element = std::make_shared<Mutator>(alpha);
+  vector_.push_back(element);
+};
+
 void MutatorsStack::Pop() {
   vector_.pop_back();
 };

flow/embedded_views.h

@@ -17,7 +17,7 @@
 
 namespace flutter {
 
-enum MutatorType { clip_rect, clip_rrect, clip_path, transform };
+enum MutatorType { clip_rect, clip_rrect, clip_path, transform, opacity };
 
 // Stores mutation information like clipping or transform.
 //
@@ -42,6 +42,9 @@ class Mutator {
       case transform:
         matrix_ = other.matrix_;
         break;
+      case opacity:
+        alpha_ = other.alpha_;
+        break;
       default:
         break;
     }
@@ -53,12 +56,15 @@ class Mutator {
       : type_(clip_path), path_(new SkPath(path)) {}
   explicit Mutator(const SkMatrix& matrix)
       : type_(transform), matrix_(matrix) {}
+  explicit Mutator(const int& alpha) : type_(opacity), alpha_(alpha) {}
 
   const MutatorType& GetType() const { return type_; }
   const SkRect& GetRect() const { return rect_; }
   const SkRRect& GetRRect() const { return rrect_; }
   const SkPath& GetPath() const { return *path_; }
   const SkMatrix& GetMatrix() const { return matrix_; }
+  const int& GetAlpha() const { return alpha_; }
+  float GetAlphaFloat() const { return (alpha_ / 255.0); }
 
   bool operator==(const Mutator& other) const {
     if (type_ != other.type_) {
@@ -73,6 +79,8 @@ class Mutator {
         return *path_ == *other.path_;
       case transform:
         return matrix_ == other.matrix_;
+      case opacity:
+        return alpha_ == other.alpha_;
     }
 
     return false;
@@ -98,6 +106,7 @@ class Mutator {
     SkRRect rrect_;
     SkMatrix matrix_;
     SkPath* path_;
+    int alpha_;
   };
 
 };  // Mutator
@@ -119,6 +128,7 @@ class MutatorsStack {
   void PushClipRRect(const SkRRect& rrect);
   void PushClipPath(const SkPath& path);
   void PushTransform(const SkMatrix& matrix);
+  void PushOpacity(const int& alpha);
 
   // Removes the `Mutator` on the top of the stack
   // and destroys it.

flow/layers/opacity_layer.cc

@@ -37,7 +37,12 @@ void OpacityLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
   EnsureSingleChild();
   SkMatrix child_matrix = matrix;
   child_matrix.postTranslate(offset_.fX, offset_.fY);
+  context->mutators_stack.PushTransform(
+      SkMatrix::MakeTrans(offset_.fX, offset_.fY));
+  context->mutators_stack.PushOpacity(alpha_);
   ContainerLayer::Preroll(context, child_matrix);
+  context->mutators_stack.Pop();
+  context->mutators_stack.Pop();
   set_paint_bounds(paint_bounds().makeOffset(offset_.fX, offset_.fY));
   // See |EnsureSingleChild|.
   FML_DCHECK(layers().size() == 1);

flow/mutators_stack_unittests.cc

@@ -42,7 +42,7 @@ TEST(MutatorsStack, PushClipRRect) {
 }
 
 TEST(MutatorsStack, PushClipPath) {
-  flutter::MutatorsStack stack;
+  MutatorsStack stack;
   SkPath path;
   stack.PushClipPath(path);
   auto iter = stack.Bottom();
@@ -60,6 +60,15 @@ TEST(MutatorsStack, PushTransform) {
   ASSERT_TRUE(iter->get()->GetMatrix() == matrix);
 }
 
+TEST(MutatorsStack, PushOpacity) {
+  MutatorsStack stack;
+  int alpha = 240;
+  stack.PushOpacity(alpha);
+  auto iter = stack.Bottom();
+  ASSERT_TRUE(iter->get()->GetType() == MutatorType::opacity);
+  ASSERT_TRUE(iter->get()->GetAlpha() == 240);
+}
+
 TEST(MutatorsStack, Pop) {
   MutatorsStack stack;
   SkMatrix matrix;
@@ -113,6 +122,8 @@ TEST(MutatorsStack, Equality) {
   stack.PushClipRRect(rrect);
   SkPath path;
   stack.PushClipPath(path);
+  int alpha = 240;
+  stack.PushOpacity(alpha);
 
   MutatorsStack stackOther;
   SkMatrix matrixOther = SkMatrix::MakeScale(1, 1);
@@ -123,6 +134,8 @@ TEST(MutatorsStack, Equality) {
   stackOther.PushClipRRect(rrectOther);
   SkPath otherPath;
   stackOther.PushClipPath(otherPath);
+  int otherAlpha = 240;
+  stackOther.PushOpacity(otherAlpha);
 
   ASSERT_TRUE(stack == stackOther);
 }
@@ -148,6 +161,10 @@ TEST(Mutator, Initialization) {
   Mutator mutator4 = Mutator(matrix);
   ASSERT_TRUE(mutator4.GetType() == MutatorType::transform);
   ASSERT_TRUE(mutator4.GetMatrix() == matrix);
+
+  int alpha = 240;
+  Mutator mutator5 = Mutator(alpha);
+  ASSERT_TRUE(mutator5.GetType() == MutatorType::opacity);
 }
 
 TEST(Mutator, CopyConstructor) {
@@ -171,6 +188,11 @@ TEST(Mutator, CopyConstructor) {
   Mutator mutator4 = Mutator(matrix);
   Mutator copy4 = Mutator(mutator4);
   ASSERT_TRUE(mutator4 == copy4);
+
+  int alpha = 240;
+  Mutator mutator5 = Mutator(alpha);
+  Mutator copy5 = Mutator(mutator5);
+  ASSERT_TRUE(mutator5 == copy5);
 }
 
 TEST(Mutator, Equality) {
@@ -195,6 +217,10 @@ TEST(Mutator, Equality) {
   flutter::Mutator otherMutator4 = flutter::Mutator(path);
   ASSERT_TRUE(mutator4 == otherMutator4);
   ASSERT_FALSE(mutator2 == mutator);
+  int alpha = 240;
+  Mutator mutator5 = Mutator(alpha);
+  Mutator otherMutator5 = Mutator(alpha);
+  ASSERT_TRUE(mutator5 == otherMutator5);
 }
 
 TEST(Mutator, UnEquality) {
@@ -204,6 +230,12 @@ TEST(Mutator, UnEquality) {
   matrix.setIdentity();
   Mutator notEqualMutator = Mutator(matrix);
   ASSERT_TRUE(notEqualMutator != mutator);
+
+  int alpha = 240;
+  int alpha2 = 241;
+  Mutator mutator2 = Mutator(alpha);
+  Mutator otherMutator2 = Mutator(alpha2);
+  ASSERT_TRUE(mutator2 != otherMutator2);
 }
 
 }  // namespace testing

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -278,6 +278,9 @@
         head = clipView;
         break;
       }
+      case opacity:
+        embedded_view.alpha = (*iter)->GetAlphaFloat() * embedded_view.alpha;
+        break;
     }
     ++iter;
   }
@@ -299,6 +302,7 @@
   UIView* touchInterceptor = touch_interceptors_[view_id].get();
   touchInterceptor.layer.transform = CATransform3DIdentity;
   touchInterceptor.frame = frame;
+  touchInterceptor.alpha = 1;
 
   int currentClippingCount = CountClips(params.mutatorsStack);
   int previousClippingCount = clip_count_[view_id];