Implement a paint offset cache for slimming paint v2

Source/core/paint/BlockFlowPainter.cpp

 // 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.
 
 #include "config.h"
 #include "core/paint/BlockFlowPainter.h"
 
 #include "core/layout/FloatingObjects.h"
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/paint/ClipScope.h"
@@ skipping 46 matching lines @@
     LayoutUnit lastRight = m_layoutBlockFlow.logicalRightSelectionOffset(&m_layoutBlockFlow, lastTop);
 
     LayoutRect bounds;
     if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
         bounds = m_layoutBlockFlow.visualOverflowRect();
         bounds.moveBy(paintOffset);
     }
 
     // Only create a DrawingRecorder and ClipScope if skipRecording is false. This logic is needed
     // because selectionGaps(...) needs to be called even when we do not record.
-    bool skipRecording = LayoutObjectDrawingRecorder::useCachedDrawingIfPossible(*paintInfo.context, m_layoutBlockFlow, DisplayItem::SelectionGap);
-    Optional<DrawingRecorder> drawingRecorder;
+    bool skipRecording = LayoutObjectDrawingRecorder::useCachedDrawingIfPossible(*paintInfo.context, m_layoutBlockFlow, DisplayItem::SelectionGap, paintOffset);

[Xianzhu, 2015/08/27 17:20:10]

I remember your idea of DrawingParameters when adding
useCachedDrawingIfPossible. Perhaps it's time to use it?

[pdr., 2015/08/28 03:31:41]

I'm afraid I don't remember what DrawingParameters are. Can you expand on this
idea?

In any case, I did this specific change in a separate patch
(https://src.chromium.org/viewvc/blink?view=rev&revision=201284).

[Xianzhu, 2015/08/28 03:59:00]

It is actually DrawingRecorderCacheParameters which you mentioned in
https://codereview.chromium.org/1220583004/#msg4 :)

+    Optional<LayoutObjectDrawingRecorder> drawingRecorder;
     Optional<ClipScope> clipScope;
     if (!skipRecording) {
-        drawingRecorder.emplace(*paintInfo.context, m_layoutBlockFlow, DisplayItem::SelectionGap, FloatRect(bounds));
+        drawingRecorder.emplace(*paintInfo.context, m_layoutBlockFlow, DisplayItem::SelectionGap, FloatRect(bounds), paintOffset);
         clipScope.emplace(paintInfo.context);
     }
 
     LayoutRect gapRectsBounds = m_layoutBlockFlow.selectionGaps(&m_layoutBlockFlow, paintOffset, LayoutSize(), lastTop, lastLeft, lastRight,
         skipRecording ? nullptr : &paintInfo,
         skipRecording ? nullptr : &(*clipScope));
     // TODO(wkorman): Rework below to process paint invalidation rects during layout rather than paint.
     if (!gapRectsBounds.isEmpty()) {
         DeprecatedPaintLayer* layer = m_layoutBlockFlow.enclosingLayer();
         gapRectsBounds.moveBy(-paintOffset);
         if (!m_layoutBlockFlow.hasLayer()) {
             LayoutRect localBounds(gapRectsBounds);
             m_layoutBlockFlow.flipForWritingMode(localBounds);
             gapRectsBounds = LayoutRect(m_layoutBlockFlow.localToContainerQuad(FloatRect(localBounds), layer->layoutObject()).enclosingBoundingBox());
             if (layer->layoutObject()->hasOverflowClip())
                 gapRectsBounds.move(layer->layoutBox()->scrolledContentOffset());
         }
         layer->addBlockSelectionGapsBounds(gapRectsBounds);
     }
 }
 
 } // namespace blink