[Impeller] fix clear color optimization for large subpasses.

impeller/aiks/aiks_unittests.cc

@@ -2134,9 +2134,12 @@ TEST_P(AiksTest, CanRenderClippedLayers) {
     canvas.DrawRect(Rect::MakeSize(Size{400, 400}), {.color = Color::White()});
     // Fill the layer with green, but do so with a color blend that can't be
     // collapsed into the parent pass.
+    // TODO(jonahwilliams): this blend mode was changed from color burn to
+    // hardlight to work around https://github.com/flutter/flutter/issues/136554
+    // .
     canvas.DrawRect(
         Rect::MakeSize(Size{400, 400}),
-        {.color = Color::Green(), .blend_mode = BlendMode::kColorBurn});
+        {.color = Color::Green(), .blend_mode = BlendMode::kHardLight});
   }
 
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
@@ -3664,5 +3667,25 @@ TEST_P(AiksTest,
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
 
+// This should be solid red, if you see a little red box this is broken.
+TEST_P(AiksTest, ClearColorOptimizationWhenSubpassIsBiggerThanParentPass) {
+  SetWindowSize({400, 400});
+  Canvas canvas;
+  canvas.Scale(GetContentScale());
+  canvas.DrawRect(Rect::MakeLTRB(200, 200, 300, 300), {.color = Color::Red()});
+  canvas.SaveLayer({
+      .image_filter = std::make_shared<MatrixImageFilter>(
+          Matrix::MakeScale({2, 2, 1}), SamplerDescriptor{}),
+  });
+  // Draw a rectangle that would fully cover the parent pass size, but not
+  // the subpass that it is rendered in.
+  canvas.DrawRect(Rect::MakeLTRB(0, 0, 400, 400), {.color = Color::Green()});
+  // Draw a bigger rectangle to force the subpass to be bigger.
+  canvas.DrawRect(Rect::MakeLTRB(0, 0, 800, 800), {.color = Color::Red()});
+  canvas.Restore();
+
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 }  // namespace testing
 }  // namespace impeller

impeller/entity/entity_pass.cc

@@ -726,9 +726,10 @@ bool EntityPass::OnRender(
     VALIDATION_LOG << SPrintF("Pass context invalid (Depth=%d)", pass_depth);
     return false;
   }
+  auto clear_color_size = pass_target.GetRenderTarget().GetRenderTargetSize();
 
   if (!collapsed_parent_pass &&
-      !GetClearColor(root_pass_size).IsTransparent()) {
+      !GetClearColor(clear_color_size).IsTransparent()) {
     // Force the pass context to create at least one new pass if the clear color
     // is present.
     pass_context.GetRenderPass(pass_depth);
@@ -897,7 +898,7 @@ bool EntityPass::OnRender(
     // Skip elements that are incorporated into the clear color.
     if (is_collapsing_clear_colors) {
       auto [entity_color, _] =
-          ElementAsBackgroundColor(element, root_pass_size);
+          ElementAsBackgroundColor(element, clear_color_size);
       if (entity_color.has_value()) {
         continue;
       }