Skip paint property update and visual rect update if no geometry change

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h

 // 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.
 
 #ifndef PaintPropertyTreeBuilder_h
 #define PaintPropertyTreeBuilder_h
 
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 class FrameView;
 class LayoutBoxModelObject;
 class LayoutObject;
 
 // The context for PaintPropertyTreeBuilder.
 // It's responsible for bookkeeping tree state in other order, for example, the
 // most recent position container seen.
 struct PaintPropertyTreeBuilderContext {
   USING_FAST_MALLOC(PaintPropertyTreeBuilderContext);
 
  public:
+  // Initializes all property tree nodes to the roots.
+  PaintPropertyTreeBuilderContext();
+
   // State that propagates on the containing block chain (and so is adjusted
   // when an absolute or fixed position object is encountered).
   struct ContainingBlockContext {
     // The combination of a transform and paint offset describes a linear space.
     // When a layout object recur to its children, the main context is expected
     // to refer the object's border box, then the callee will derive its own
     // border box by translating the space with its own layout location.
     const TransformPaintPropertyNode* transform = nullptr;
     LayoutPoint paintOffset;
     // Whether newly created children should flatten their inherited transform
@@ skipping 45 matching lines @@
   // clip. The cull rect for its input shall be derived from its output clip.
   // This variable represents the input cull of current effect, also serves as
   // output clip of child effects that don't have a hard clip.
   const ClipPaintPropertyNode* inputClipOfCurrentEffect;
 
   // True if a change has forced all properties in a subtree to be updated. This
   // can be set due to paint offset changes or when the structure of the
   // property tree changes (i.e., a node is added or removed).
   bool forceSubtreeUpdate;
 
-  // Initializes all property tree nodes to the roots.
-  PaintPropertyTreeBuilderContext();
+#if DCHECK_IS_ON()
+  // When DCHECK_IS_ON() we create PaintPropertyTreeBuilderContext even if not
+  // needed. See FindPaintOffsetAndVisualRectNeedingUpdate.h.
+  bool isActuallyNeeded = true;
+#endif
 };
 
 // Creates paint property tree nodes for special things in the layout tree.
 // Special things include but not limit to: overflow clip, transform, fixed-pos,
 // animation, mask, filter, ... etc.
 // It expects to be invoked for each layout tree node in DOM order during
 // InPrePaint phase.
 class PaintPropertyTreeBuilder {
  public:
   // Update the paint properties for a frame and ensure the context is up to
@@ skipping 48 matching lines @@
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
   ALWAYS_INLINE static void updateOutOfFlowContext(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
 };
 
 }  // namespace blink
 
 #endif  // PaintPropertyTreeBuilder_h