Calculate paint invalidation rect for scrollbars

third_party/WebKit/Source/core/layout/PaintInvalidationState.h

 // Copyright 2014 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 PaintInvalidationState_h
 #define PaintInvalidationState_h
 
 #include "platform/geometry/LayoutRect.h"
 #include "platform/transforms/AffineTransform.h"
 #include "wtf/Allocator.h"
@@ skipping 35 matching lines @@
 
     bool canMapToContainer(const LayoutBoxModelObject* container) const
     {
         return m_cachedOffsetsEnabled && container == &m_paintInvalidationContainer;
     }
 
     // Records |obj| as needing paint invalidation on the next frame. See the definition of PaintInvalidationDelayedFull for more details.
     void pushDelayedPaintInvalidationTarget(LayoutObject& obj) { m_pendingDelayedPaintInvalidations.append(&obj); }
     Vector<LayoutObject*>& pendingDelayedPaintInvalidationTargets() { return m_pendingDelayedPaintInvalidations; }
 
+    // Disable view clipping and scroll offset adjustment for paint invalidation of FrameView scrollbars.

[chrishtr, 2015/11/11 01:40:29]

Why? What goes wrong and why is it wrong now and not before?

[Xianzhu, 2015/11/11 19:29:57]

Now we calculate paint invalidation rect for frame scrollbars using
PaintLayer::mapRectToPaintInvalidationBacking(layoutView,
paintInvalidationContainer, PaintInvalidationState-created-for-LayoutView). This
will call LayoutView::mapRectToPaintInvalidationBacking() which previously
treated the rect in coordinates of scrolling contents which is not suitable for
frame scrollbars. The following code makes
LayoutView::mapRectToPaintInvalidationBacking() work for frame scrollbars.

This is temporary before we switch to root-layer-scrolls.

+    // TODO(wangxianzhu): Remove this for root-layer-scrolls.
+    bool viewClippingAndScrollOffsetDisabled() const { return m_viewClippingAndScrollOffsetDisabled; }
+    void setViewClippingAndScrollOffsetDisabled(bool b) { m_viewClippingAndScrollOffsetDisabled = b; }
+
 private:
     PaintInvalidationState(const LayoutView&, Vector<LayoutObject*>& pendingDelayedPaintInvalidations, PaintInvalidationState* ownerPaintInvalidationState);
 
     void applyClipIfNeeded(const LayoutObject&);
     void addClipRectRelativeToPaintOffset(const LayoutSize& clipSize);
 
     friend class ForceHorriblySlowRectMapping;
 
     bool m_clipped;
     mutable bool m_cachedOffsetsEnabled;
     bool m_forcedSubtreeInvalidationWithinContainer;
     bool m_forcedSubtreeInvalidationRectUpdateWithinContainer;
+    bool m_viewClippingAndScrollOffsetDisabled;
 
     LayoutRect m_clipRect;
 
     // x/y offset from paint invalidation container. Includes relative positioning and scroll offsets.
     LayoutSize m_paintOffset;
 
     const LayoutBoxModelObject& m_paintInvalidationContainer;
 
     // Transform from the initial viewport coordinate system of an outermost
     // SVG root to the userspace _before_ the relevant element. Combining this
     // with |m_paintOffset| yields the "final" offset.
     OwnPtr<AffineTransform> m_svgTransform;
 
     Vector<LayoutObject*>& m_pendingDelayedPaintInvalidations;
 };
 
 } // namespace blink
 
 #endif // PaintInvalidationState_h