From 36dbd47ad6bed4fd4510c0468553d0f025b002cf Mon Sep 17 00:00:00 2001
From: Aaron Clarke <aaclarke@google.com>
Date: Thu, 22 Jun 2023 10:30:32 -0700
Subject: [PATCH 1/3] [Impeller] fix and reland drawPaint collapsing
 optimization

---
 impeller/aiks/aiks_unittests.cc    | 12 ++++++++++++
 impeller/aiks/canvas.cc            |  8 ++++++++
 impeller/renderer/render_target.cc |  2 +-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/impeller/aiks/aiks_unittests.cc b/impeller/aiks/aiks_unittests.cc
index 464dc000216a2..37b13e5817971 100644
--- a/impeller/aiks/aiks_unittests.cc
+++ b/impeller/aiks/aiks_unittests.cc
@@ -1992,6 +1992,18 @@ TEST_P(AiksTest, OpacityPeepHoleApplicationTest) {
   ASSERT_TRUE(delegate->CanCollapseIntoParentPass(entity_pass.get()));
 }
 
+TEST_P(AiksTest, DrawPaintAbsorbsClears) {
+  Canvas canvas;
+  canvas.DrawPaint({.color = Color::Red(), .blend_mode = BlendMode::kSource});
+  canvas.DrawPaint(
+      {.color = Color::CornflowerBlue(), .blend_mode = BlendMode::kSource});
+
+  Picture picture = canvas.EndRecordingAsPicture();
+
+  ASSERT_EQ(picture.pass->GetElementCount(), 0u);
+  ASSERT_EQ(picture.pass->GetClearColor(), Color::CornflowerBlue());
+}
+
 TEST_P(AiksTest, ForegroundBlendSubpassCollapseOptimization) {
   Canvas canvas;
 
diff --git a/impeller/aiks/canvas.cc b/impeller/aiks/canvas.cc
index 3e2962ea18983..272c6c2770894 100644
--- a/impeller/aiks/canvas.cc
+++ b/impeller/aiks/canvas.cc
@@ -172,6 +172,14 @@ void Canvas::DrawPath(const Path& path, const Paint& paint) {
 }
 
 void Canvas::DrawPaint(const Paint& paint) {
+  if (xformation_stack_.size() == 1 &&  // If we're recording the root pass,
+      GetCurrentPass().GetElementCount() == 0 &&  // and this is the first item,
+      paint.blend_mode == BlendMode::kSourceOver && paint.color.alpha >= 1.0f) {
+    // Then we can absorb this drawPaint as the clear color of the pass.
+    GetCurrentPass().SetClearColor(paint.color);
+    return;
+  }
+
   Entity entity;
   entity.SetTransformation(GetCurrentTransformation());
   entity.SetStencilDepth(GetStencilDepth());
diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index 67c18d95386e6..55ce503b59291 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -303,7 +303,7 @@ RenderTarget RenderTarget::CreateOffscreenMSAA(
   // Color attachment.
 
   ColorAttachment color0;
-  color0.clear_color = Color::BlackTransparent();
+  color0.clear_color = color_attachment_config.clear_color;
   color0.load_action = color_attachment_config.load_action;
   color0.store_action = color_attachment_config.store_action;
   color0.texture = color0_msaa_tex;

From 7848976ef551705c9a768339b26e136877f8b289 Mon Sep 17 00:00:00 2001
From: Aaron Clarke <aaclarke@google.com>
Date: Thu, 22 Jun 2023 13:33:19 -0700
Subject: [PATCH 2/3] added kSource too

---
 impeller/aiks/canvas.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/impeller/aiks/canvas.cc b/impeller/aiks/canvas.cc
index 272c6c2770894..204f8425d4d31 100644
--- a/impeller/aiks/canvas.cc
+++ b/impeller/aiks/canvas.cc
@@ -174,7 +174,9 @@ void Canvas::DrawPath(const Path& path, const Paint& paint) {
 void Canvas::DrawPaint(const Paint& paint) {
   if (xformation_stack_.size() == 1 &&  // If we're recording the root pass,
       GetCurrentPass().GetElementCount() == 0 &&  // and this is the first item,
-      paint.blend_mode == BlendMode::kSourceOver && paint.color.alpha >= 1.0f) {
+      (paint.blend_mode == BlendMode::kSourceOver ||
+       paint.blend_mode == BlendMode::kSource) &&
+      paint.color.alpha >= 1.0f) {
     // Then we can absorb this drawPaint as the clear color of the pass.
     GetCurrentPass().SetClearColor(paint.color);
     return;

From 0362a950ad79dfa1326b41e200bf2c5dd3252003 Mon Sep 17 00:00:00 2001
From: Aaron Clarke <aaclarke@google.com>
Date: Thu, 22 Jun 2023 16:29:40 -0700
Subject: [PATCH 3/3] Made the clear color only apply to the top surface

---
 impeller/entity/entity_pass.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/impeller/entity/entity_pass.cc b/impeller/entity/entity_pass.cc
index ddb0d443a0a8a..b32bd6bd46332 100644
--- a/impeller/entity/entity_pass.cc
+++ b/impeller/entity/entity_pass.cc
@@ -477,7 +477,7 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
         renderer,                                  // renderer
         subpass_size,                              // size
         subpass->GetTotalPassReads(renderer) > 0,  // readable
-        clear_color_.Premultiply());               // clear_color
+        Color::BlackTransparent());                // clear_color
 
     if (!subpass_target.IsValid()) {
       VALIDATION_LOG << "Subpass render target is invalid.";