Only store previous clip rects for PaintLayers that support subsequences.

third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp

Index: third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
diff --git a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
index 53ebcc64224eea42f9f30b9f3b5b941acca85d57..c841a1b9d97e9d99b9ad75a20c86073f0f77c3b2 100644
--- a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
+++ b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
@@ -21,7 +21,8 @@ struct PrePaintTreeWalkContext {
             WTF::WrapUnique(new PaintPropertyTreeBuilderContext)),
         paint_invalidator_context(tree_builder_context.get()),
         ancestor_overflow_paint_layer(nullptr),
-        ancestor_transformed_or_root_paint_layer(nullptr) {}
+        ancestor_transformed_or_root_paint_layer(nullptr),
+        enclosing_paint_layer(nullptr) {}
 
   PrePaintTreeWalkContext(const PrePaintTreeWalkContext& parent_context,
                           bool needs_tree_builder_context)
@@ -35,7 +36,8 @@ struct PrePaintTreeWalkContext {
         ancestor_overflow_paint_layer(
             parent_context.ancestor_overflow_paint_layer),
         ancestor_transformed_or_root_paint_layer(
-            parent_context.ancestor_transformed_or_root_paint_layer) {
+            parent_context.ancestor_transformed_or_root_paint_layer),
+        enclosing_paint_layer(parent_context.enclosing_paint_layer) {
 #if DCHECK_IS_ON()
     if (needs_tree_builder_context)
       DCHECK(parent_context.tree_builder_context->is_actually_needed);
@@ -55,6 +57,7 @@ struct PrePaintTreeWalkContext {
   // block or stacking ancestor.
   PaintLayer* ancestor_overflow_paint_layer;
   PaintLayer* ancestor_transformed_or_root_paint_layer;
+  PaintLayer* enclosing_paint_layer;
 };
 
 void PrePaintTreeWalk::Walk(FrameView& root_frame) {
@@ -66,8 +69,9 @@ void PrePaintTreeWalk::Walk(FrameView& root_frame) {
       root_frame.GetLayoutView()->Layer();
 
   // GeometryMapper depends on paint properties.
-  if (NeedsTreeBuilderContextUpdate(root_frame, initial_context))
+  if (NeedsTreeBuilderContextUpdate(root_frame, initial_context)) {
     GeometryMapper::ClearCache();
+  }
 
   Walk(root_frame, initial_context);
   paint_invalidator_.ProcessPendingDelayedPaintInvalidations();
@@ -79,7 +83,6 @@ void PrePaintTreeWalk::Walk(FrameView& frame_view,
     // Skip the throttled frame. Will update it when it becomes unthrottled.
     return;
   }
-
   bool needs_tree_builder_context_update =
       this->NeedsTreeBuilderContextUpdate(frame_view, parent_context);
   PrePaintTreeWalkContext context(parent_context,
@@ -94,7 +97,19 @@ void PrePaintTreeWalk::Walk(FrameView& frame_view,
                                              context.paint_invalidator_context);
 
   if (LayoutView* view = frame_view.GetLayoutView()) {
-    Walk(*view, context);
+    bool ignored;
+    if (!ShouldEarlyOut(*view, context, ignored)) {
+      context.enclosing_paint_layer = view->Layer();
+      if (!context.tree_builder_context) {
+        context.tree_builder_context =
+            WTF::WrapUnique(new PaintPropertyTreeBuilderContext);

[chrishtr, 2017/04/12 17:31:41]

This is a little weird and awkward, let's discuss offline ways to improve this
code.

+      }
+#if DCHECK_IS_ON()
+      if (context.tree_builder_context)
+        context.tree_builder_context->is_actually_needed = true;
+#endif
+      Walk(*view, context);
+    }
 #if DCHECK_IS_ON()
     view->AssertSubtreeClearedPaintInvalidationFlags();
 #endif
@@ -126,6 +141,8 @@ static void UpdateAuxiliaryObjectProperties(const LayoutObject& object,
 
   if (paint_layer->IsRootLayer() || object.HasOverflowClip())
     context.ancestor_overflow_paint_layer = paint_layer;
+
+  context.enclosing_paint_layer = paint_layer;
 }
 
 void PrePaintTreeWalk::ComputeClipRectForContext(
@@ -148,6 +165,9 @@ void PrePaintTreeWalk::InvalidatePaintLayerOptimizationsIfNeeded(
     return;
 
   PaintLayer& paint_layer = *ToLayoutBoxModelObject(object).Layer();
+  if (!paint_layer.SupportsSubsequenceCaching())
+    return;
+
   if (object.StyleRef().HasTransform() ||
       &object ==
           context.paint_invalidator_context.paint_invalidation_container) {
@@ -246,16 +266,28 @@ bool PrePaintTreeWalk::NeedsTreeBuilderContextUpdate(
           parent_context.tree_builder_context->force_subtree_update) ||
          // If the object needs visual rect update, we should update tree
          // builder context which is needed by visual rect update.
-         parent_context.paint_invalidator_context.NeedsVisualRectUpdate(object);
+         parent_context.paint_invalidator_context.NeedsVisualRectUpdate(
+             object) ||
+         (parent_context.enclosing_paint_layer &&

[pdr., 2017/04/12 18:40:06]

Can enclosing_paint_layer ever be null here?

Do we actually need to track the enclosing paint layer or can we just track a
bool for HasDescendantThatSupportsSubsequenceCaching?

+          parent_context.enclosing_paint_layer
+              ->HasDescendantThatSupportsSubsequenceCaching());
 }
 
-void PrePaintTreeWalk::Walk(const LayoutObject& object,
-                            const PrePaintTreeWalkContext& parent_context) {
+bool PrePaintTreeWalk::ShouldEarlyOut(
+    const LayoutObject& object,
+    const PrePaintTreeWalkContext& parent_context,
+    bool& needs_tree_builder_context_update) {
   // Early out from the tree walk if possible.
-  bool needs_tree_builder_context_update =
+  needs_tree_builder_context_update =
       this->NeedsTreeBuilderContextUpdate(object, parent_context);
-  if (!needs_tree_builder_context_update &&
-      !object.ShouldCheckForPaintInvalidation())
+  return !needs_tree_builder_context_update &&
+         !object.ShouldCheckForPaintInvalidation();
+}
+
+void PrePaintTreeWalk::Walk(const LayoutObject& object,
+                            const PrePaintTreeWalkContext& parent_context) {
+  bool needs_tree_builder_context_update = false;
+  if (ShouldEarlyOut(object, parent_context, needs_tree_builder_context_update))
     return;
 
   PrePaintTreeWalkContext context(parent_context,