Optimize ClipRects in the PrePaintTreeWalk

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PrePaintTreeWalk.h"
 
 #include "core/dom/DocumentLifecycle.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutMultiColumnSpannerPlaceholder.h"
@@ skipping 106 matching lines @@
     // sticky layer position, so we need to update it again here.
     // TODO(flackr): This should be refactored in the future to be clearer (i.e.
     // update layer position and ancestor inputs updates in the same walk).
     paintLayer->updateLayerPosition();
   }
 
   if (paintLayer->isRootLayer() || object.hasOverflowClip())
     context.ancestorOverflowPaintLayer = paintLayer;
 }
 
-// Returns whether |a| is an ancestor of or equal to |b|.
-static bool isAncestorOfOrEqualTo(const ClipPaintPropertyNode* a,
-                                  const ClipPaintPropertyNode* b) {
-  while (b && b != a) {
-    b = b->parent();
-  }
-  return b == a;
-}
-
 void PrePaintTreeWalk::computeClipRectForContext(
     const PaintPropertyTreeBuilderContext::ContainingBlockContext& context,
     const EffectPaintPropertyNode* effect,
     const PropertyTreeState& ancestorState,
     const LayoutPoint& ancestorPaintOffset,
-    bool& hasClip,
     FloatClipRect& clipRect) {
-  // Only return a non-infinite clip if clips differ, or the "ancestor" state is
-  // actually an ancestor clip. This ensures no accuracy issues due to
-  // transforms applied to infinite rects.
-  if (isAncestorOfOrEqualTo(context.clip, ancestorState.clip()))
-    clipRect = FloatClipRect();
-
-  hasClip = true;
   PropertyTreeState localState(context.transform, context.clip, effect);
 
   clipRect =
       m_geometryMapper.sourceToDestinationClipRect(localState, ancestorState);
   clipRect.moveBy(-FloatPoint(ancestorPaintOffset));
 }
 
 void PrePaintTreeWalk::invalidatePaintLayerOptimizationsIfNeeded(
     const LayoutObject& object,
     PrePaintTreeWalkContext& context) {
@@ skipping 24 matching lines @@
     }
   }
 
 #ifdef CHECK_CLIP_RECTS
   ClipRects& oldClipRects =
       paintLayer.clipper(PaintLayer::DoNotUseGeometryMapper)
           .paintingClipRects(&ancestorTransformedOrRootPaintLayer,
                              respectOverflowClip, LayoutSize());
 #endif
 
-  bool hasClip = false;
   RefPtr<ClipRects> clipRects = ClipRects::create();
   const LayoutPoint& ancestorPaintOffset =
       context.ancestorTransformedOrRootPaintLayer->layoutObject().paintOffset();
 
   FloatClipRect clipRect;
   const EffectPaintPropertyNode* effect =
       context.treeBuilderContext->currentEffect;
   computeClipRectForContext(context.treeBuilderContext->current, effect,
-                            ancestorState, ancestorPaintOffset, hasClip,
-                            clipRect);
+                            ancestorState, ancestorPaintOffset, clipRect);
   clipRects->setOverflowClipRect(clipRect);
 #ifdef CHECK_CLIP_RECTS
-  CHECK(!hasClip ||
-        clipRects->overflowClipRect() == oldClipRects.overflowClipRect())
+  CHECK(clipRects->overflowClipRect() == oldClipRects.overflowClipRect())
       << "rect= " << clipRects->overflowClipRect().toString();
 #endif
 
   computeClipRectForContext(context.treeBuilderContext->fixedPosition, effect,
-                            ancestorState, ancestorPaintOffset, hasClip,
-                            clipRect);
+                            ancestorState, ancestorPaintOffset, clipRect);
   clipRects->setFixedClipRect(clipRect);
 #ifdef CHECK_CLIP_RECTS
-  CHECK(hasClip || clipRects->fixedClipRect() == oldClipRects.fixedClipRect())
+  CHECK(clipRects->fixedClipRect() == oldClipRects.fixedClipRect())
       << " fixed=" << clipRects->fixedClipRect().toString();
 #endif
 
   computeClipRectForContext(context.treeBuilderContext->absolutePosition,
-                            effect, ancestorState, ancestorPaintOffset, hasClip,
+                            effect, ancestorState, ancestorPaintOffset,
                             clipRect);
   clipRects->setPosClipRect(clipRect);
 #ifdef CHECK_CLIP_RECTS
-  CHECK(!hasClip || clipRects->posClipRect() == oldClipRects.posClipRect())
+  CHECK(clipRects->posClipRect() == oldClipRects.posClipRect())
       << " abs=" << clipRects->posClipRect().toString();
 #endif
 
   ClipRects* previousClipRects = paintLayer.previousPaintingClipRects();
 
   if (!previousClipRects || *clipRects != *previousClipRects) {
     paintLayer.setNeedsRepaint();
     paintLayer.setPreviousPaintPhaseDescendantOutlinesEmpty(false);
     paintLayer.setPreviousPaintPhaseFloatEmpty(false);
     paintLayer.setPreviousPaintPhaseDescendantBlockBackgroundsEmpty(false);
@@ skipping 78 matching lines @@
       }
       walk(*toFrameView(frameViewBase), context);
     }
     // TODO(pdr): Investigate RemoteFrameView (crbug.com/579281).
   }
 
   object.getMutableForPainting().clearPaintFlags();
 }
 
 }  // namespace blink