[Impeller] round up subpass coverage when it is close to (and smaller) than root pass size.

impeller/aiks/aiks_unittests.cc

@@ -3867,6 +3867,29 @@ TEST_P(AiksTest, GaussianBlurMipMapImageFilter) {
 #endif
 }
 
+TEST_P(AiksTest, SaveLayersCloseToRootPassSizeAreScaledUp) {
+  Canvas canvas;
+  canvas.SaveLayer(
+      {
+          .color = Color::Black().WithAlpha(0.5),
+      },
+      Rect::MakeSize(ISize(95, 95)));
+  canvas.DrawRect(Rect::MakeLTRB(0, 0, 100, 100), {.color = Color::Red()});
+  canvas.DrawRect(Rect::MakeLTRB(50, 50, 150, 150), {.color = Color::Blue()});
+  canvas.Restore();
+
+  Picture picture = canvas.EndRecordingAsPicture();
+  std::shared_ptr<RenderTargetCache> cache =
+      std::make_shared<RenderTargetCache>(GetContext()->GetResourceAllocator());
+  AiksContext aiks_context(GetContext(), nullptr, cache);
+  picture.ToImage(aiks_context, {100, 100});
+
+  for (auto it = cache->GetTextureDataBegin(); it != cache->GetTextureDataEnd();
+       ++it) {
+    EXPECT_EQ(it->texture->GetTextureDescriptor().size, ISize(100, 100));
+  }
+}
+
 TEST_P(AiksTest, ImageColorSourceEffectTransform) {
   // Compare with https://fiddle.skia.org/c/6cdc5aefb291fda3833b806ca347a885
 

impeller/entity/entity_pass.cc

@@ -618,6 +618,19 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
       return EntityPass::EntityResult::Skip();
     }
 
+    // When a subpass size is close to, but still smaller than the root pass
+    // size, we may scale it up to the root pass size. This will improve
+    // performance by improving the efficiency of the render target cache, as
+    // only textures with exactly the same sizes + descriptors can be recycled.
+    if (subpass_size.width < root_pass_size.width &&
+        subpass_size.height < root_pass_size.height &&
+        root_pass_size.width - subpass_size.width <=
+            (0.1 * subpass_size.width) &&
+        root_pass_size.height - subpass_size.height <=
+            (0.1 * subpass_size.height)) {
+      subpass_size = root_pass_size;
+    }
+
     auto subpass_target = CreateRenderTarget(
         renderer,      // renderer
         subpass_size,  // size