Enable fast/images with slimming paint

Source/core/paint/BoxPainter.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/BoxPainter.h"
 
 #include "core/HTMLNames.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/paint/BackgroundImageGeometry.h"
 #include "core/paint/BoxDecorationData.h"
 #include "core/paint/DrawingRecorder.h"
+#include "core/paint/TransparencyDisplayItem.h"
 #include "core/rendering/ImageQualityController.h"
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderBox.h"
 #include "core/rendering/RenderBoxModelObject.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderObject.h"
 #include "core/rendering/RenderTable.h"
 #include "core/rendering/RenderTheme.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/compositing/CompositedLayerMapping.h"
@@ skipping 484 matching lines @@
     if (!paintInfo.shouldPaintWithinRoot(&m_renderBox) || m_renderBox.style()->visibility() != VISIBLE || paintInfo.phase != PaintPhaseMask)
         return;
 
     LayoutRect paintRect = LayoutRect(paintOffset, m_renderBox.size());
     paintMaskImages(paintInfo, paintRect);
 }
 
 void BoxPainter::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& paintRect)
 {
     // Figure out if we need to push a transparency layer to render our mask.
-    bool pushTransparencyLayer = false;
+    OwnPtr<TransparencyRecorder> transparencyRecorder;
     bool compositedMask = m_renderBox.hasLayer() && m_renderBox.layer()->hasCompositedMask();
     bool flattenCompositingLayers = m_renderBox.view()->frameView() && m_renderBox.view()->frameView()->paintBehavior() & PaintBehaviorFlattenCompositingLayers;
     CompositeOperator compositeOp = CompositeSourceOver;
 
     bool allMaskImagesLoaded = true;
 
     if (!compositedMask || flattenCompositingLayers) {
-        pushTransparencyLayer = true;
         StyleImage* maskBoxImage = m_renderBox.style()->maskBoxImage().image();
         const FillLayer& maskLayers = m_renderBox.style()->maskLayers();
 
         // Don't render a masked element until all the mask images have loaded, to prevent a flash of unmasked content.
         if (maskBoxImage)
             allMaskImagesLoaded &= maskBoxImage->isLoaded();
 
         allMaskImagesLoaded &= maskLayers.imagesAreLoaded();
 
         paintInfo.context->setCompositeOperation(CompositeDestinationIn);
-        paintInfo.context->beginTransparencyLayer(1);
+
+        transparencyRecorder = adoptPtr(new TransparencyRecorder(paintInfo.context, &m_renderBox, DisplayItem::BeginTransparency, WebBlendModeNormal, 1));

[chrishtr, 2014/11/26 17:20:59]

On reflection, I think this was maybe wrong. The only reason to store separate
transparency display items is to separate pieces of painted state from the
current render object and its children, or if the transparency is a compositing
trigger. I don't think either is true in this case. Instead, we should allocate
a DrawingRecorder for the mask phase, in BoxPainter::paintMask(). I'm trying
this approach now.

+
         compositeOp = CompositeSourceOver;
     }
 
     if (allMaskImagesLoaded) {
         paintFillLayers(paintInfo, Color::transparent, m_renderBox.style()->maskLayers(), paintRect, BackgroundBleedNone, compositeOp);
         paintNinePieceImage(m_renderBox, paintInfo.context, paintRect, m_renderBox.style(), m_renderBox.style()->maskBoxImage(), compositeOp);
     }
-
-    if (pushTransparencyLayer)
-        paintInfo.context->endLayer();
 }
 
 void BoxPainter::paintClippingMask(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     if (!paintInfo.shouldPaintWithinRoot(&m_renderBox) || m_renderBox.style()->visibility() != VISIBLE || paintInfo.phase != PaintPhaseClippingMask)
         return;
 
     if (!m_renderBox.layer() || m_renderBox.layer()->compositingState() != PaintsIntoOwnBacking)
         return;
 
@@ skipping 1602 matching lines @@
 
     FloatPoint secondQuad[4];
     secondQuad[0] = quad[0];
     secondQuad[1] = FloatPoint(quad[0].x() - r1 * cx, quad[0].y() - r1 * cy);
     secondQuad[2] = quad[2];
     secondQuad[3] = quad[3];
     graphicsContext->clipPolygon(4, secondQuad, !secondEdgeMatches);
 }
 
 } // namespace blink