Setup canvas pass hierarchies.

impeller/aiks/aiks_renderer.cc

@@ -33,16 +33,10 @@ bool AiksRenderer::Render(const Picture& picture, RenderPass& parent_pass) {
     return false;
   }
 
-  for (const auto& entry : picture.entries) {
-    if (!entry.pass.has_value()) {
-      continue;
-      ;
-    }
-
-    if (!entry.pass->Render(*content_renderer_, parent_pass)) {
-      return false;
-    }
+  if (picture.pass) {
+    return picture.pass->Render(*content_renderer_, parent_pass);
   }
+
   return true;
 }
 

impeller/aiks/canvas.cc

@@ -12,11 +12,25 @@
 namespace impeller {
 
 Canvas::Canvas() {
-  Save(true);
+  Initialize();
 }
 
 Canvas::~Canvas() = default;
 
+void Canvas::Initialize() {
+  base_pass_ = std::make_unique<CanvasPass>();
+  current_pass_ = base_pass_.get();
+  xformation_stack_.emplace_back(CanvasStackEntry{});
+  FML_DCHECK(GetSaveCount() == 1u);
+  FML_DCHECK(base_pass_->GetDepth() == 1u);
+}
+
+void Canvas::Reset() {
+  base_pass_ = nullptr;
+  current_pass_ = nullptr;
+  xformation_stack_ = {};
+}
+
 void Canvas::Save() {
   Save(false);
 }
@@ -26,6 +40,10 @@ bool Canvas::Restore() {
   if (xformation_stack_.size() == 1) {
     return false;
   }
+  if (xformation_stack_.back().is_subpass) {
+    current_pass_ = GetCurrentPass().GetSuperpass();
+    FML_DCHECK(current_pass_);
+  }
   xformation_stack_.pop_back();
   return true;
 }
@@ -69,11 +87,11 @@ void Canvas::DrawPath(Path path, Paint paint) {
   entity.SetStencilDepth(GetStencilDepth());
   entity.SetContents(paint.CreateContentsForEntity());
 
-  GetCurrentPass().PushEntity(std::move(entity));
+  GetCurrentPass().AddEntity(std::move(entity));
 }
 
 void Canvas::SaveLayer(const Paint& paint, std::optional<Rect> bounds) {
-  Save();
+  Save(true);
 }
 
 void Canvas::ClipPath(Path path) {
@@ -85,23 +103,24 @@ void Canvas::ClipPath(Path path) {
   entity.SetContents(std::make_shared<ClipContents>());
   entity.SetStencilDepth(GetStencilDepth());
 
-  GetCurrentPass().PushEntity(std::move(entity));
+  GetCurrentPass().AddEntity(std::move(entity));
 }
 
 void Canvas::DrawShadow(Path path, Color color, Scalar elevation) {}
 
-void Canvas::DrawPicture(const Picture& picture) {
-  for (const auto& stack_entry : picture.entries) {
-    auto new_stack_entry = stack_entry;
-    if (auto pass = new_stack_entry.pass) {
-      for (auto entity : pass->GetEntities()) {
-        entity.IncrementStencilDepth(GetStencilDepth());
-        entity.SetTransformation(GetCurrentTransformation() *
-                                 entity.GetTransformation());
-      }
-    }
-    xformation_stack_.emplace_back(std::move(new_stack_entry));
+void Canvas::DrawPicture(Picture picture) {
+  if (!picture.pass) {
+    return;
   }
+  // Clone the base pass and account for the CTM updates.
+  auto pass = picture.pass->Clone();
+  pass->IterateAllEntities([&](auto& entity) -> bool {
+    entity.IncrementStencilDepth(GetStencilDepth());
+    entity.SetTransformation(GetCurrentTransformation() *
+                             entity.GetTransformation());
+    return true;
+  });
+  return;
 }
 
 void Canvas::DrawImage(std::shared_ptr<Image> image,
@@ -140,23 +159,23 @@ void Canvas::DrawImageRect(std::shared_ptr<Image> image,
   entity.SetPath(PathBuilder{}.AddRect(dest).CreatePath());
   entity.SetContents(contents);
   entity.SetTransformation(GetCurrentTransformation());
-  GetCurrentPass().PushEntity(std::move(entity));
+
+  GetCurrentPass().AddEntity(std::move(entity));
 }
 
 Picture Canvas::EndRecordingAsPicture() {
   Picture picture;
-  picture.entries = std::move(xformation_stack_);
+  picture.pass = std::move(base_pass_);
+
+  Reset();
+  Initialize();
+
   return picture;
 }
 
 CanvasPass& Canvas::GetCurrentPass() {
-  for (auto i = xformation_stack_.rbegin(), end = xformation_stack_.rend();
-       i < end; i++) {
-    if (i->pass.has_value()) {
-      return i->pass.value();
-    }
-  }
-  FML_UNREACHABLE();
+  FML_DCHECK(current_pass_ != nullptr);
+  return *current_pass_;
 }
 
 void Canvas::IncrementStencilDepth() {
@@ -172,21 +191,15 @@ void Canvas::DrawRect(Rect rect, Paint paint) {
 }
 
 void Canvas::Save(bool create_subpass) {
-  // Check if called from the ctor.
-  if (xformation_stack_.empty()) {
-    FML_DCHECK(create_subpass) << "Base entries must have a pass.";
-    CanvasStackEntry entry;
-    entry.pass = CanvasPass{};
-    xformation_stack_.emplace_back(std::move(entry));
-  }
-
   auto entry = CanvasStackEntry{};
-
   entry.xformation = xformation_stack_.back().xformation;
   entry.stencil_depth = xformation_stack_.back().stencil_depth;
+  entry.is_subpass = create_subpass;
+
   if (create_subpass) {
-    entry.pass = CanvasPass{};
+    current_pass_ = GetCurrentPass().AddSubpass(std::make_unique<CanvasPass>());
   }
+
   xformation_stack_.emplace_back(std::move(entry));
 }
 

impeller/aiks/canvas.h

@@ -64,13 +64,19 @@ class Canvas {
 
   void DrawShadow(Path path, Color color, Scalar elevation);
 
-  void DrawPicture(const Picture& picture);
+  void DrawPicture(Picture picture);
 
   Picture EndRecordingAsPicture();
 
  private:
+  std::unique_ptr<CanvasPass> base_pass_;
+  CanvasPass* current_pass_ = nullptr;
   std::deque<CanvasStackEntry> xformation_stack_;
 
+  void Initialize();
+
+  void Reset();
+
   CanvasPass& GetCurrentPass();
 
   void IncrementStencilDepth();

impeller/aiks/canvas_pass.cc

@@ -12,14 +12,26 @@ CanvasPass::CanvasPass() = default;
 
 CanvasPass::~CanvasPass() = default;
 
-void CanvasPass::PushEntity(Entity entity) {
+void CanvasPass::AddEntity(Entity entity) {
   entities_.emplace_back(std::move(entity));
 }
 
 const std::vector<Entity>& CanvasPass::GetEntities() const {
   return entities_;
 }
 
+void CanvasPass::SetEntities(Entities entities) {
+  entities_ = std::move(entities);
+}
+
+size_t CanvasPass::GetDepth() const {
+  size_t max_subpass_depth = 0u;
+  for (const auto& subpass : subpasses_) {
+    max_subpass_depth = std::max(max_subpass_depth, subpass->GetDepth());
+  }
+  return max_subpass_depth + 1u;
+}
+
 Rect CanvasPass::GetCoverageRect() const {
   std::optional<Point> min, max;
   for (const auto& entity : entities_) {
@@ -43,13 +55,21 @@ Rect CanvasPass::GetCoverageRect() const {
   return {min->x, min->y, diff.x, diff.y};
 }
 
+CanvasPass* CanvasPass::GetSuperpass() const {
+  return superpass_;
+}
+
 const CanvasPass::Subpasses& CanvasPass::GetSubpasses() const {
   return subpasses_;
 }
 
-bool CanvasPass::AddSubpass(CanvasPass pass) {
-  subpasses_.emplace_back(std::move(pass));
-  return true;
+CanvasPass* CanvasPass::AddSubpass(std::unique_ptr<CanvasPass> pass) {
+  if (!pass) {
+    return nullptr;
+  }
+  FML_DCHECK(pass->superpass_ == nullptr);
+  pass->superpass_ = this;
+  return subpasses_.emplace_back(std::move(pass)).get();
 }
 
 bool CanvasPass::Render(ContentRenderer& renderer,
@@ -59,7 +79,37 @@ bool CanvasPass::Render(ContentRenderer& renderer,
       return false;
     }
   }
+  for (const auto& subpass : subpasses_) {
+    if (!subpass->Render(renderer, parent_pass)) {
+      return false;
+    }
+  }
   return true;
 }
 
+void CanvasPass::IterateAllEntities(std::function<bool(Entity&)> iterator) {
+  if (!iterator) {
+    return;
+  }
+
+  for (auto& entity : entities_) {
+    if (!iterator(entity)) {
+      return;
+    }
+  }
+
+  for (auto& subpass : subpasses_) {
+    subpass->IterateAllEntities(iterator);
+  }
+}
+
+std::unique_ptr<CanvasPass> CanvasPass::Clone() const {
+  auto pass = std::make_unique<CanvasPass>();
+  pass->SetEntities(entities_);
+  for (const auto& subpass : subpasses_) {
+    pass->AddSubpass(subpass->Clone());
+  }
+  return pass;
+}
+
 }  // namespace impeller

impeller/aiks/canvas_pass.h

@@ -18,33 +18,47 @@ class ContentRenderer;
 
 class CanvasPass {
  public:
-  using Subpasses = std::vector<CanvasPass>;
+  using Entities = std::vector<Entity>;
+  using Subpasses = std::vector<std::unique_ptr<CanvasPass>>;
 
   CanvasPass();
 
   ~CanvasPass();
 
-  void PushEntity(Entity entity);
+  size_t GetDepth() const;
+
+  std::unique_ptr<CanvasPass> Clone() const;
 
   Rect GetCoverageRect() const;
 
+  void AddEntity(Entity entity);
+
+  void SetEntities(Entities entities);
+
   const std::vector<Entity>& GetEntities() const;
 
   const Subpasses& GetSubpasses() const;
 
-  bool AddSubpass(CanvasPass pass);
+  CanvasPass* AddSubpass(std::unique_ptr<CanvasPass> pass);
+
+  CanvasPass* GetSuperpass() const;
 
   bool Render(ContentRenderer& renderer, RenderPass& parent_pass) const;
 
+  void IterateAllEntities(std::function<bool(Entity&)> iterator);
+
  private:
-  std::vector<Entity> entities_;
+  Entities entities_;
   Subpasses subpasses_;
+  CanvasPass* superpass_ = nullptr;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(CanvasPass);
 };
 
 struct CanvasStackEntry {
   Matrix xformation;
   size_t stencil_depth = 0u;
-  std::optional<CanvasPass> pass;
+  bool is_subpass = false;
 };
 
 }  // namespace impeller

impeller/aiks/picture.h

@@ -14,7 +14,7 @@
 namespace impeller {
 
 struct Picture {
-  std::deque<CanvasStackEntry> entries;
+  std::unique_ptr<CanvasPass> pass;
 };
 
 }  // namespace impeller