Allow entity passes to be elided based on their contents.

Author: chinmaygarde

impeller/aiks/paint_pass_delegate.cc

@@ -14,12 +14,13 @@ PaintPassDelegate::PaintPassDelegate(Paint paint) : paint_(std::move(paint)) {}
 PaintPassDelegate::~PaintPassDelegate() = default;
 
 // |EntityPassDelgate|
-bool PaintPassDelegate::CanCollapseIntoParentPass() {
-  if (paint_.color.IsOpaque()) {
-    return true;
-  }
+bool PaintPassDelegate::CanElide() {
+  return paint_.color.IsTransparent();
+}
 
-  return false;
+// |EntityPassDelgate|
+bool PaintPassDelegate::CanCollapseIntoParentPass() {
+  return paint_.color.IsOpaque();
 }
 
 // |EntityPassDelgate|

impeller/aiks/paint_pass_delegate.h

@@ -17,6 +17,9 @@ class PaintPassDelegate final : public EntityPassDelegate {
   // |EntityPassDelgate|
   ~PaintPassDelegate() override;
 
+  // |EntityPassDelgate|
+  bool CanElide() override;
+
   // |EntityPassDelgate|
   bool CanCollapseIntoParentPass() override;
 

impeller/entity/entity_pass.cc

@@ -91,6 +91,10 @@ bool EntityPass::Render(ContentRenderer& renderer,
     }
   }
   for (const auto& subpass : subpasses_) {
+    if (delegate_->CanElide()) {
+      continue;
+    }
+
     if (delegate_->CanCollapseIntoParentPass()) {
       // Directly render into the parent pass and move on.
       if (!subpass->Render(renderer, parent_pass)) {

impeller/entity/entity_pass_delegate.cc

@@ -16,6 +16,8 @@ class DefaultEntityPassDelegate final : public EntityPassDelegate {
 
   ~DefaultEntityPassDelegate() override = default;
 
+  bool CanElide() override { return false; }
+
   bool CanCollapseIntoParentPass() override { return true; }
 
   std::shared_ptr<Contents> CreateContentsForSubpassTarget(

impeller/entity/entity_pass_delegate.h

@@ -20,6 +20,8 @@ class EntityPassDelegate {
 
   virtual ~EntityPassDelegate();
 
+  virtual bool CanElide() = 0;
+
   virtual bool CanCollapseIntoParentPass() = 0;
 
   virtual std::shared_ptr<Contents> CreateContentsForSubpassTarget(