[BGPT] Omit synthetic mask layers that don't mask any content.

A synthetic mask layer is not needed if there is no content under
it which draws. This patch implements that optimization, and also
adds a new optimization to CompositedLayerMapping to set DrawsContent
to false for layers which have empty size.

The patch also removes one unused method from cc::Layer.

Bug: 947715

Change-Id: I7625fc251a3dc04ce5319edc56a9dc5fccf27564
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1566029
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#650514}

cc/layers/layer.h

@@ -231,7 +231,6 @@ class CC_EXPORT Layer : public base::RefCounted<Layer> {
   // for each matching pixel.
   void SetMaskLayer(PictureLayer* mask_layer);
   PictureLayer* mask_layer() { return inputs_.mask_layer.get(); }
-  const PictureLayer* mask_layer() const { return inputs_.mask_layer.get(); }
 
   // Marks the |dirty_rect| as being changed, which will cause a commit and
   // the compositor to submit a new frame with a damage rect that includes the

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.cc

@@ -2790,6 +2790,9 @@ bool CompositedLayerMapping::HasVisibleNonCompositingDescendant(
 }
 
 bool CompositedLayerMapping::ContainsPaintedContent() const {
+  if (CompositedBounds().IsEmpty())
+    return false;
+
   if (GetLayoutObject().IsImage() && IsDirectlyCompositedImage())
     return false;
 

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping_test.cc

@@ -2720,6 +2720,28 @@ TEST_F(CompositedLayerMappingTest, ContentsNotOpaqueWithForegroundLayer) {
   EXPECT_FALSE(mapping->MainGraphicsLayer()->ContentsOpaque());
 }
 
+TEST_F(CompositedLayerMappingTest, EmptyBoundsDoesntDrawContent) {
+  if (RuntimeEnabledFeatures::CompositeAfterPaintEnabled())
+    return;
+
+  SetHtmlInnerHTML(R"HTML(
+    <style>
+      div {
+        width: 100px;
+        height: 0px;
+        position: relative;
+        isolation: isolate;
+      }
+    </style>
+    <div id='target' style='will-change: transform; background: blue'>
+    </div>
+    )HTML");
+  PaintLayer* target_layer =
+      ToLayoutBoxModelObject(GetLayoutObjectByElementId("target"))->Layer();
+  CompositedLayerMapping* mapping = target_layer->GetCompositedLayerMapping();
+  EXPECT_FALSE(mapping->MainGraphicsLayer()->DrawsContent());
+}
+
 TEST_F(CompositedLayerMappingTest, TouchActionRectsWithoutContent) {
   if (RuntimeEnabledFeatures::CompositeAfterPaintEnabled())
     return;

third_party/blink/renderer/platform/graphics/compositing/paint_artifact_compositor.cc

@@ -286,6 +286,9 @@ PaintArtifactCompositor::CompositedLayerForPendingLayer(
   auto cc_layer = content_layer_client->UpdateCcPictureLayer(
       paint_artifact, paint_chunks, cc_combined_bounds,
       pending_layer.property_tree_state);
+  if (cc_combined_bounds.IsEmpty())
+    cc_layer->SetIsDrawable(false);
+
   new_content_layer_clients.push_back(std::move(content_layer_client));
   if (extra_data_for_testing_enabled_)
     extra_data_for_testing_->content_layers.push_back(cc_layer);
@@ -894,7 +897,7 @@ void PaintArtifactCompositor::Update(
     int clip_id = property_tree_manager_.EnsureCompositorClipNode(clip);
     int effect_id =
         property_tree_manager_.SwitchToEffectNodeWithSynthesizedClip(
-            property_state.Effect(), clip);
+            property_state.Effect(), clip, layer->DrawsContent());
     blink_effects.resize(effect_id + 1);
     blink_effects[effect_id] = &property_state.Effect();
     // The compositor scroll node is not directly stored in the property tree

third_party/blink/renderer/platform/graphics/compositing/paint_artifact_compositor_test.cc

@@ -2619,6 +2619,49 @@ TEST_P(PaintArtifactCompositorTest, SynthesizedClipSimple) {
       *GetPropertyTrees().effect_tree.Node(mask_effect_0_id);
   ASSERT_EQ(mask_isolation_0_id, mask_effect_0.parent_id);
   EXPECT_EQ(SkBlendMode::kDstIn, mask_effect_0.blend_mode);
+
+  // The masks DrawsContent because it has content that it masks which also
+  // DrawsContent.
+  EXPECT_TRUE(clip_mask0->DrawsContent());
+}
+
+TEST_P(PaintArtifactCompositorTest, SynthesizedClipIsNotDrawable) {
+  // This tests the simplist case that a single layer needs to be clipped
+  // by a single composited rounded clip.
+  FloatSize corner(5, 5);
+  FloatRoundedRect rrect(FloatRect(50, 50, 300, 200), corner, corner, corner,
+                         corner);
+  auto c1 = CreateClip(c0(), t0(), rrect);
+
+  TestPaintArtifact artifact;
+  artifact.Chunk(t0(), *c1, e0())
+      .RectDrawing(FloatRect(0, 0, 0, 0), Color::kBlack);
+  Update(artifact.Build());
+
+  // Expectation in effect stack diagram:
+  //           l1
+  // [ mask_isolation_0 ]
+  // [        e0        ]
+  // One content layer, no clip mask (because layer doesn't draw content).
+  ASSERT_EQ(1u, RootLayer()->children().size());
+  ASSERT_EQ(1u, ContentLayerCount());
+  ASSERT_EQ(0u, SynthesizedClipLayerCount());
+
+  const cc::Layer* content0 = RootLayer()->children()[0].get();
+
+  constexpr int c0_id = 1;
+  constexpr int e0_id = 1;
+
+  EXPECT_EQ(ContentLayerAt(0), content0);
+  int c1_id = content0->clip_tree_index();
+  const cc::ClipNode& cc_c1 = *GetPropertyTrees().clip_tree.Node(c1_id);
+  EXPECT_EQ(gfx::RectF(50, 50, 300, 200), cc_c1.clip);
+  ASSERT_EQ(c0_id, cc_c1.parent_id);
+  int mask_isolation_0_id = content0->effect_tree_index();
+  const cc::EffectNode& mask_isolation_0 =
+      *GetPropertyTrees().effect_tree.Node(mask_isolation_0_id);
+  ASSERT_EQ(e0_id, mask_isolation_0.parent_id);
+  EXPECT_EQ(SkBlendMode::kSrcOver, mask_isolation_0.blend_mode);
 }
 
 TEST_P(PaintArtifactCompositorTest,

third_party/blink/renderer/platform/graphics/compositing/property_tree_manager.cc

@@ -504,12 +504,15 @@ int PropertyTreeManager::EnsureCompositorScrollNode(
 }
 
 void PropertyTreeManager::EmitClipMaskLayer() {
+  cc::EffectNode& mask_isolation = *GetEffectTree().Node(current_.effect_id);
+  if (pending_synthetic_mask_layers_.Contains(mask_isolation.id))
+    return;
+
   int clip_id = EnsureCompositorClipNode(*current_.clip);
   CompositorElementId mask_isolation_id, mask_effect_id;
   cc::Layer* mask_layer = client_.CreateOrReuseSynthesizedClipLayer(
       *current_.clip, mask_isolation_id, mask_effect_id);
 
-  cc::EffectNode& mask_isolation = *GetEffectTree().Node(current_.effect_id);
   // Assignment of mask_isolation.stable_id was delayed until now.
   // See PropertyTreeManager::SynthesizeCcEffectsForClipsIfNeeded().
   DCHECK_EQ(static_cast<uint64_t>(cc::EffectNode::INVALID_STABLE_ID),
@@ -557,6 +560,9 @@ void PropertyTreeManager::CloseCcEffect() {
   if (IsCurrentCcEffectSyntheticForNonTrivialClip())
     EmitClipMaskLayer();
 
+  if (IsCurrentCcEffectSynthetic())
+    pending_synthetic_mask_layers_.erase(current_.effect_id);
+
   current_ = previous_state;
   effect_stack_.pop_back();
 
@@ -568,7 +574,8 @@ void PropertyTreeManager::CloseCcEffect() {
 
 int PropertyTreeManager::SwitchToEffectNodeWithSynthesizedClip(
     const EffectPaintPropertyNode& next_effect,
-    const ClipPaintPropertyNode& next_clip) {
+    const ClipPaintPropertyNode& next_clip,
+    bool layer_draws_content) {
   // This function is expected to be invoked right before emitting each layer.
   // It keeps track of the nesting of clip and effects, output a composited
   // effect node whenever an effect is entered, or a non-trivial clip is
@@ -623,6 +630,10 @@ int PropertyTreeManager::SwitchToEffectNodeWithSynthesizedClip(
 
   BuildEffectNodesRecursively(next_effect);
   SynthesizeCcEffectsForClipsIfNeeded(next_clip, SkBlendMode::kSrcOver);
+
+  if (layer_draws_content)
+    pending_synthetic_mask_layers_.clear();
+
   return current_.effect_id;
 }
 
@@ -745,6 +756,8 @@ SkBlendMode PropertyTreeManager::SynthesizeCcEffectsForClipsIfNeeded(
     synthetic_effect.transform_id = EnsureCompositorTransformNode(transform);
     synthetic_effect.double_sided = !transform.IsBackfaceHidden();
     synthetic_effect.has_render_surface = true;
+    pending_synthetic_mask_layers_.insert(synthetic_effect.id);
+
     // Clip and kDstIn do not commute. This shall never be reached because
     // kDstIn is only used internally to implement CSS clip-path and mask,
     // and there is never a difference between the output clip of the effect

third_party/blink/renderer/platform/graphics/compositing/property_tree_manager.h

@@ -114,7 +114,8 @@ class PropertyTreeManager {
   // effect, i.e. applying the clip as a mask.
   int SwitchToEffectNodeWithSynthesizedClip(
       const EffectPaintPropertyNode& next_effect,
-      const ClipPaintPropertyNode& next_clip);
+      const ClipPaintPropertyNode& next_clip,
+      bool layer_draws_content);
   // Expected to be invoked after emitting the last layer. This will exit all
   // effects on the effect stack, generating clip mask layers for all the
   // unclosed synthesized clips.
@@ -262,6 +263,10 @@ class PropertyTreeManager {
   // recent push.
   Vector<EffectState> effect_stack_;
 
+  // A set of synthetic clips masks which will be applied if a layer under them
+  // is encountered which draws content (and thus necessitates the mask).
+  HashSet<int> pending_synthetic_mask_layers_;
+
 #if DCHECK_IS_ON()
   HashSet<const EffectPaintPropertyNode*> effect_nodes_converted_;
   bool initialized_ = false;

third_party/blink/web_tests/compositing/layer-creation/fixed-position-change-out-of-view-in-view-expected.txt

@@ -29,6 +29,7 @@ Layer tree when the fixed elements are out-of-view (should have just a root laye
       "name": "LayoutBlockFlow (positioned) DIV id='fixed2'",
       "position": [100, 100],
       "contentsOpaque": true,
+      "drawsContent": false,
       "backgroundColor": "#C0C0C0"
     }
   ]
@@ -102,6 +103,7 @@ Layer tree when the fixed elements are out-of-view again (should have just a roo
       "name": "LayoutBlockFlow (positioned) DIV id='fixed2'",
       "position": [100, 100],
       "contentsOpaque": true,
+      "drawsContent": false,
       "backgroundColor": "#C0C0C0"
     }
   ]

third_party/blink/web_tests/compositing/squashing/do-not-squash-non-self-painting-layer-expected.txt

@@ -22,6 +22,7 @@ Item 1
       "name": "LayoutBlockFlow DIV id='composited-container'",
       "position": [8, 8],
       "contentsOpaque": true,
+      "drawsContent": false,
       "backfaceVisibility": "hidden"
     }
   ]

third_party/blink/web_tests/css3/blending/mix-blend-mode-composited-reason-children-expected.txt

@@ -26,6 +26,7 @@
       "name": "LayoutBlockFlow (positioned) DIV class='stacking-context'",
       "position": [8, 8],
       "contentsOpaque": true,
+      "drawsContent": false,
       "backgroundColor": "#FF0000"
     },
     {
@@ -51,7 +52,8 @@
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV class='stacking-context' (foreground) Layer",
-      "position": [8, 8]
+      "position": [8, 8],
+      "drawsContent": false
     },
     {
       "name": "LayoutBlockFlow HTML (foreground) Layer",

third_party/blink/web_tests/css3/blending/mix-blend-mode-isolation-2-stacking-contexts-expected.txt

@@ -26,6 +26,7 @@
       "name": "LayoutBlockFlow (positioned) DIV class='stacking-context'",
       "position": [8, 8],
       "contentsOpaque": true,
+      "drawsContent": false,
       "backgroundColor": "#FF0000"
     },
     {
@@ -45,11 +46,13 @@
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV class='stacking-context' (foreground) Layer",
-      "position": [8, 8]
+      "position": [8, 8],
+      "drawsContent": false
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV class='accelerated stacking-context'",
       "contentsOpaque": true,
+      "drawsContent": false,
       "backgroundColor": "#FF0000",
       "transform": 2
     },
@@ -70,6 +73,7 @@
     },
     {
       "name": "LayoutBlockFlow (positioned) DIV class='accelerated stacking-context' (foreground) Layer",
+      "drawsContent": false,
       "transform": 2
     },
     {

third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/paint/invalidation/compositing/composited-float-under-composited-inline-expected.txt

@@ -19,7 +19,8 @@
     },
     {
       "name": "LayoutInline (relative positioned) SPAN",
-      "position": [108, 108]
+      "position": [108, 108],
+      "drawsContent": false
     },
     {
       "name": "LayoutNGBlockFlow (relative positioned) (floating) DIV id='float'",

third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/paint/invalidation/compositing/composited-float-under-composited-inline-individual-expected.txt

@@ -19,7 +19,8 @@
     },
     {
       "name": "LayoutInline (relative positioned) SPAN",
-      "position": [108, 108]
+      "position": [108, 108],
+      "drawsContent": false
     },
     {
       "name": "LayoutNGBlockFlow (relative positioned) (floating) DIV id='float'",

third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/paint/invalidation/table/invalidate-cell-in-row-with-offset-expected.txt

@@ -20,6 +20,7 @@
     {
       "name": "LayoutTableRow TR",
       "position": [8, 18],
+      "drawsContent": false,
       "backgroundColor": "#0000FF"
     },
     {

third_party/blink/web_tests/paint/invalidation/compositing/composited-float-under-composited-inline-expected.txt

@@ -19,7 +19,8 @@
     },
     {
       "name": "LayoutInline (relative positioned) SPAN",
-      "position": [108, 108]
+      "position": [108, 108],
+      "drawsContent": false
     },
     {
       "name": "LayoutBlockFlow (relative positioned) (floating) DIV id='float'",

third_party/blink/web_tests/paint/invalidation/compositing/composited-float-under-composited-inline-individual-expected.txt

@@ -19,7 +19,8 @@
     },
     {
       "name": "LayoutInline (relative positioned) SPAN",
-      "position": [108, 108]
+      "position": [108, 108],
+      "drawsContent": false
     },
     {
       "name": "LayoutBlockFlow (relative positioned) (floating) DIV id='float'",

third_party/blink/web_tests/paint/invalidation/compositing/float-under-composited-inline-expected.txt

@@ -26,7 +26,8 @@
     },
     {
       "name": "LayoutInline (relative positioned) SPAN",
-      "position": [108, 108]
+      "position": [108, 108],
+      "drawsContent": false
     }
   ]
 }

third_party/blink/web_tests/paint/invalidation/table/invalidate-cell-in-row-with-offset-expected.txt

@@ -20,6 +20,7 @@
     {
       "name": "LayoutTableRow TR",
       "position": [8, 18],
+      "drawsContent": false,
       "backgroundColor": "#0000FF"
     },
     {