Setup a paint pass delgate.

impeller/aiks/BUILD.gn

@@ -14,6 +14,8 @@ impeller_component("aiks") {
     "image.h",
     "paint.cc",
     "paint.h",
+    "paint_pass_delegate.cc",
+    "paint_pass_delegate.h",
     "picture.cc",
     "picture.h",
     "picture_recorder.cc",

impeller/aiks/aiks_unittests.cc

@@ -112,7 +112,7 @@ TEST_F(AiksTest, CanRenderGroupOpacity) {
   Paint red;
   red.color = Color::Red();
   Paint green;
-  green.color = Color::Green();
+  green.color = Color::Green().WithAlpha(0.5);
   Paint blue;
   blue.color = Color::Blue();
 

impeller/aiks/canvas.cc

@@ -7,6 +7,7 @@
 #include <algorithm>
 
 #include "flutter/fml/logging.h"
+#include "impeller/aiks/paint_pass_delegate.h"
 #include "impeller/geometry/path_builder.h"
 
 namespace impeller {
@@ -90,7 +91,9 @@ void Canvas::DrawPath(Path path, Paint paint) {
   GetCurrentPass().AddEntity(std::move(entity));
 }
 
-void Canvas::SaveLayer(const Paint& paint, std::optional<Rect> bounds) {
+void Canvas::SaveLayer(Paint paint, std::optional<Rect> bounds) {
+  GetCurrentPass().SetDelegate(
+      std::make_unique<PaintPassDelegate>(std::move(paint)));
   Save(true);
 }
 

impeller/aiks/canvas.h

@@ -31,7 +31,7 @@ class Canvas {
 
   void Save();
 
-  void SaveLayer(const Paint& paint, std::optional<Rect> bounds = std::nullopt);
+  void SaveLayer(Paint paint, std::optional<Rect> bounds = std::nullopt);
 
   bool Restore();
 

impeller/aiks/paint.h

@@ -18,7 +18,7 @@ struct Paint {
     kStroke,
   };
 
-  Color color;
+  Color color = Color::Black();
   Scalar stroke_width = 0.0;
   Style style = Style::kFill;
 

impeller/aiks/paint_pass_delegate.cc

@@ -0,0 +1,35 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "impeller/aiks/paint_pass_delegate.h"
+
+#include "impeller/entity/contents.h"
+
+namespace impeller {
+
+PaintPassDelegate::PaintPassDelegate(Paint paint) : paint_(std::move(paint)) {}
+
+// |EntityPassDelgate|
+PaintPassDelegate::~PaintPassDelegate() = default;
+
+// |EntityPassDelgate|
+bool PaintPassDelegate::CanCollapseIntoParentPass() {
+  if (paint_.color.IsOpaque()) {
+    return true;
+  }
+
+  return false;
+}
+
+// |EntityPassDelgate|
+std::shared_ptr<Contents> PaintPassDelegate::CreateContentsForSubpassTarget(
+    std::shared_ptr<Texture> target) {
+  auto contents = std::make_shared<TextureContents>();
+  contents->SetTexture(target);
+  contents->SetSourceRect(IRect::MakeSize(target->GetSize()));
+  contents->SetOpacity(paint_.color.alpha);
+  return contents;
+}
+
+}  // namespace impeller

impeller/aiks/paint_pass_delegate.h

@@ -0,0 +1,33 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#pragma once
+
+#include "flutter/fml/macros.h"
+#include "impeller/aiks/paint.h"
+#include "impeller/entity/entity_pass_delegate.h"
+
+namespace impeller {
+
+class PaintPassDelegate final : public EntityPassDelegate {
+ public:
+  PaintPassDelegate(Paint paint);
+
+  // |EntityPassDelgate|
+  ~PaintPassDelegate() override;
+
+  // |EntityPassDelgate|
+  bool CanCollapseIntoParentPass() override;
+
+  // |EntityPassDelgate|
+  std::shared_ptr<Contents> CreateContentsForSubpassTarget(
+      std::shared_ptr<Texture> target) override;
+
+ private:
+  const Paint paint_;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(PaintPassDelegate);
+};
+
+}  // namespace impeller

impeller/entity/contents.cc

@@ -184,6 +184,10 @@ std::shared_ptr<Texture> TextureContents::GetTexture() const {
   return texture_;
 }
 
+void TextureContents::SetOpacity(Scalar opacity) {
+  opacity_ = opacity;
+}
+
 bool TextureContents::Render(const ContentRenderer& renderer,
                              const Entity& entity,
                              RenderPass& pass) const {
@@ -233,6 +237,7 @@ bool TextureContents::Render(const ContentRenderer& renderer,
   VS::FrameInfo frame_info;
   frame_info.mvp = Matrix::MakeOrthographic(pass.GetRenderTargetSize()) *
                    entity.GetTransformation();
+  frame_info.alpha = opacity_;
 
   Command cmd;
   cmd.label = "TextureFill";

impeller/entity/contents.h

@@ -94,6 +94,8 @@ class TextureContents final : public Contents {
 
   void SetSourceRect(const IRect& source_rect);
 
+  void SetOpacity(Scalar opacity);
+
   const IRect& GetSourceRect() const;
 
   // |Contents|
@@ -104,6 +106,7 @@ class TextureContents final : public Contents {
  public:
   std::shared_ptr<Texture> texture_;
   IRect source_rect_;
+  Scalar opacity_ = 1.0f;
 
   FML_DISALLOW_COPY_AND_ASSIGN(TextureContents);
 };

impeller/entity/entity_pass.cc

@@ -11,15 +11,17 @@
 
 namespace impeller {
 
-EntityPass::EntityPass(std::unique_ptr<EntityPassDelegate> delegate)
-    : delegate_(std::move(delegate)) {
-  if (!delegate_) {
-    delegate_ = EntityPassDelegate::MakeDefault();
-  }
-}
+EntityPass::EntityPass() = default;
 
 EntityPass::~EntityPass() = default;
 
+void EntityPass::SetDelegate(std::unique_ptr<EntityPassDelegate> delegate) {
+  if (!delegate) {
+    return;
+  }
+  delegate_ = std::move(delegate);
+}
+
 void EntityPass::AddEntity(Entity entity) {
   entities_.emplace_back(std::move(entity));
 }
@@ -117,7 +119,7 @@ bool EntityPass::Render(ContentRenderer& renderer,
     }
 
     auto offscreen_texture_contents =
-        delegate_->CreateContentsForSubpassTarget(*subpass_texture);
+        delegate_->CreateContentsForSubpassTarget(subpass_texture);
 
     if (!offscreen_texture_contents) {
       // This is an error because the subpass delegate said the pass couldn't be

impeller/entity/entity_pass.h

@@ -23,10 +23,12 @@ class EntityPass {
   using Entities = std::vector<Entity>;
   using Subpasses = std::vector<std::unique_ptr<EntityPass>>;
 
-  EntityPass(std::unique_ptr<EntityPassDelegate> delegate = nullptr);
+  EntityPass();
 
   ~EntityPass();
 
+  void SetDelegate(std::unique_ptr<EntityPassDelegate> delgate);
+
   size_t GetSubpassesDepth() const;
 
   std::unique_ptr<EntityPass> Clone() const;
@@ -61,7 +63,8 @@ class EntityPass {
   EntityPass* superpass_ = nullptr;
   Matrix xformation_;
   size_t stencil_depth_ = 0u;
-  std::unique_ptr<EntityPassDelegate> delegate_;
+  std::unique_ptr<EntityPassDelegate> delegate_ =
+      EntityPassDelegate::MakeDefault();
 
   FML_DISALLOW_COPY_AND_ASSIGN(EntityPass);
 };

impeller/entity/entity_pass_delegate.cc

@@ -19,7 +19,7 @@ class DefaultEntityPassDelegate final : public EntityPassDelegate {
   bool CanCollapseIntoParentPass() override { return true; }
 
   std::shared_ptr<Contents> CreateContentsForSubpassTarget(
-      const Texture& target) override {
+      std::shared_ptr<Texture> target) override {
     // Not possible since this pass always collapses into its parent.
     FML_UNREACHABLE();
   }

impeller/entity/entity_pass_delegate.h

@@ -23,7 +23,7 @@ class EntityPassDelegate {
   virtual bool CanCollapseIntoParentPass() = 0;
 
   virtual std::shared_ptr<Contents> CreateContentsForSubpassTarget(
-      const Texture& target) = 0;
+      std::shared_ptr<Texture> target) = 0;
 
  private:
   FML_DISALLOW_COPY_AND_ASSIGN(EntityPassDelegate);

impeller/entity/shaders/texture_fill.frag

@@ -5,10 +5,12 @@
 uniform sampler2D texture_sampler;
 
 in vec2 v_texture_coords;
+in float v_alpha;
 
 out vec4 frag_color;
 
 void main() {
   vec4 sampled = texture(texture_sampler, v_texture_coords);
+  sampled.w *= v_alpha;
   frag_color = sampled;
 }

impeller/entity/shaders/texture_fill.vert

@@ -4,14 +4,17 @@
 
 uniform FrameInfo {
   mat4 mvp;
+  float alpha;
 } frame_info;
 
 in vec2 vertices;
 in vec2 texture_coords;
 
 out vec2 v_texture_coords;
+out float v_alpha;
 
 void main() {
   gl_Position = frame_info.mvp * vec4(vertices, 0.0, 1.0);
   v_texture_coords = texture_coords;
+  v_alpha = frame_info.alpha;
 }

impeller/geometry/color.h

@@ -644,6 +644,8 @@ struct Color {
   }
 
   constexpr bool IsTransparent() const { return alpha == 0.0; }
+
+  constexpr bool IsOpaque() const { return alpha == 1.0; }
 };
 
 /**