Reland ImageFiltered bounds fix (#17077)

Fix for https://github.com/flutter/flutter/issues/51978 to use the bounds of the filtered result as the layer's paint bounds.

flow/layers/image_filter_layer.cc

@@ -11,9 +11,22 @@ ImageFilterLayer::ImageFilterLayer(sk_sp<SkImageFilter> filter)
 
 void ImageFilterLayer::Preroll(PrerollContext* context,
                                const SkMatrix& matrix) {
+  TRACE_EVENT0("flutter", "ImageFilterLayer::Preroll");
+
   Layer::AutoPrerollSaveLayerState save =
       Layer::AutoPrerollSaveLayerState::Create(context);
-  ContainerLayer::Preroll(context, matrix);
+
+  child_paint_bounds_ = SkRect::MakeEmpty();
+  PrerollChildren(context, matrix, &child_paint_bounds_);
+  if (filter_) {
+    const SkIRect filter_input_bounds = child_paint_bounds_.roundOut();
+    SkIRect filter_output_bounds =
+        filter_->filterBounds(filter_input_bounds, SkMatrix::I(),
+                              SkImageFilter::kForward_MapDirection);
+    set_paint_bounds(SkRect::Make(filter_output_bounds));
+  } else {
+    set_paint_bounds(child_paint_bounds_);
+  }
 
   if (!context->has_platform_view && context->raster_cache &&
       SkRect::Intersects(context->cull_rect, paint_bounds())) {
@@ -48,8 +61,12 @@ void ImageFilterLayer::Paint(PaintContext& context) const {
   SkPaint paint;
   paint.setImageFilter(filter_);
 
+  // Normally a save_layer is sized to the current layer bounds, but in this
+  // case the bounds of the child may not be the same as the filtered version
+  // so we use the child_paint_bounds_ which were snapshotted from the
+  // Preroll on the children before we adjusted them based on the filter.
   Layer::AutoSaveLayer save_layer =
-      Layer::AutoSaveLayer::Create(context, paint_bounds(), &paint);
+      Layer::AutoSaveLayer::Create(context, child_paint_bounds_, &paint);
   PaintChildren(context);
 }
 

flow/layers/image_filter_layer.h

@@ -21,6 +21,7 @@ class ImageFilterLayer : public ContainerLayer {
 
  private:
   sk_sp<SkImageFilter> filter_;
+  SkRect child_paint_bounds_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ImageFilterLayer);
 };

flow/layers/image_filter_layer_unittests.cc

@@ -83,8 +83,47 @@ TEST_F(ImageFilterLayerTest, SimpleFilter) {
   auto layer = std::make_shared<ImageFilterLayer>(layer_filter);
   layer->Add(mock_layer);
 
+  const SkRect child_rounded_bounds =
+      SkRect::MakeLTRB(5.0f, 6.0f, 21.0f, 22.0f);
+
   layer->Preroll(preroll_context(), initial_transform);
-  EXPECT_EQ(layer->paint_bounds(), child_bounds);
+  EXPECT_EQ(layer->paint_bounds(), child_rounded_bounds);
+  EXPECT_TRUE(layer->needs_painting());
+  EXPECT_EQ(mock_layer->parent_matrix(), initial_transform);
+
+  SkPaint filter_paint;
+  filter_paint.setImageFilter(layer_filter);
+  layer->Paint(paint_context());
+  EXPECT_EQ(mock_canvas().draw_calls(),
+            std::vector({
+                MockCanvas::DrawCall{0, MockCanvas::SaveData{1}},
+                MockCanvas::DrawCall{1, MockCanvas::SetMatrixData{SkMatrix()}},
+                MockCanvas::DrawCall{
+                    1, MockCanvas::SaveLayerData{child_bounds, filter_paint,
+                                                 nullptr, 2}},
+                MockCanvas::DrawCall{
+                    2, MockCanvas::DrawPathData{child_path, child_paint}},
+                MockCanvas::DrawCall{2, MockCanvas::RestoreData{1}},
+                MockCanvas::DrawCall{1, MockCanvas::RestoreData{0}},
+            }));
+}
+
+TEST_F(ImageFilterLayerTest, SimpleFilterBounds) {
+  const SkMatrix initial_transform = SkMatrix::MakeTrans(0.5f, 1.0f);
+  const SkRect child_bounds = SkRect::MakeLTRB(5.0f, 6.0f, 20.5f, 21.5f);
+  const SkPath child_path = SkPath().addRect(child_bounds);
+  const SkPaint child_paint = SkPaint(SkColors::kYellow);
+  const SkMatrix filter_transform = SkMatrix::MakeScale(2.0, 2.0);
+  auto layer_filter = SkImageFilter::MakeMatrixFilter(
+      filter_transform, SkFilterQuality::kMedium_SkFilterQuality, nullptr);
+  auto mock_layer = std::make_shared<MockLayer>(child_path, child_paint);
+  auto layer = std::make_shared<ImageFilterLayer>(layer_filter);
+  layer->Add(mock_layer);
+
+  const SkRect filter_bounds = SkRect::MakeLTRB(10.0f, 12.0f, 42.0f, 44.0f);
+
+  layer->Preroll(preroll_context(), initial_transform);
+  EXPECT_EQ(layer->paint_bounds(), filter_bounds);
   EXPECT_TRUE(layer->needs_painting());
   EXPECT_EQ(mock_layer->parent_matrix(), initial_transform);
 
@@ -123,10 +162,12 @@ TEST_F(ImageFilterLayerTest, MultipleChildren) {
 
   SkRect children_bounds = child_path1.getBounds();
   children_bounds.join(child_path2.getBounds());
+  SkRect children_rounded_bounds = SkRect::Make(children_bounds.roundOut());
+
   layer->Preroll(preroll_context(), initial_transform);
   EXPECT_EQ(mock_layer1->paint_bounds(), child_path1.getBounds());
   EXPECT_EQ(mock_layer2->paint_bounds(), child_path2.getBounds());
-  EXPECT_EQ(layer->paint_bounds(), children_bounds);
+  EXPECT_EQ(layer->paint_bounds(), children_rounded_bounds);
   EXPECT_TRUE(mock_layer1->needs_painting());
   EXPECT_TRUE(mock_layer2->needs_painting());
   EXPECT_TRUE(layer->needs_painting());
@@ -172,12 +213,17 @@ TEST_F(ImageFilterLayerTest, Nested) {
   layer1->Add(layer2);
 
   SkRect children_bounds = child_path1.getBounds();
-  children_bounds.join(child_path2.getBounds());
+  children_bounds.join(SkRect::Make(child_path2.getBounds().roundOut()));
+  const SkRect children_rounded_bounds =
+      SkRect::Make(children_bounds.roundOut());
+  const SkRect mock_layer2_rounded_bounds =
+      SkRect::Make(child_path2.getBounds().roundOut());
+
   layer1->Preroll(preroll_context(), initial_transform);
   EXPECT_EQ(mock_layer1->paint_bounds(), child_path1.getBounds());
   EXPECT_EQ(mock_layer2->paint_bounds(), child_path2.getBounds());
-  EXPECT_EQ(layer1->paint_bounds(), children_bounds);
-  EXPECT_EQ(layer2->paint_bounds(), mock_layer2->paint_bounds());
+  EXPECT_EQ(layer1->paint_bounds(), children_rounded_bounds);
+  EXPECT_EQ(layer2->paint_bounds(), mock_layer2_rounded_bounds);
   EXPECT_TRUE(mock_layer1->needs_painting());
   EXPECT_TRUE(mock_layer2->needs_painting());
   EXPECT_TRUE(layer1->needs_painting());