Fix pixel snapping of stacked sub-pixel composited layers

Source/core/rendering/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 548 matching lines @@
         result.intersect(renderer->clipRect(LayoutPoint()));
 
     return pixelSnappedIntRect(result);
 }
 
 void CompositedLayerMapping::adjustBoundsForSubPixelAccumulation(const RenderLayer* compositedAncestor, IntRect& localBounds, IntRect& relativeBounds, IntPoint& delta)
 {
     LayoutRect localRawCompositingBounds = compositedBounds();
     LayoutPoint rawDelta;
     m_owningLayer.convertToLayerCoords(compositedAncestor, rawDelta);
+    if (compositedAncestor)
+        rawDelta.move(compositedAncestor->compositedLayerMapping()->subpixelAccumulation());
     delta = flooredIntPoint(rawDelta);
     m_subpixelAccumulation = toLayoutSize(rawDelta).fraction();
     RELEASE_ASSERT(m_subpixelAccumulation.width() < 1 && m_subpixelAccumulation.height() < 1);
 
     // Move the bounds by the subpixel accumulation so that it pixel-snaps relative to absolute pixels instead of local coordinates.
     localRawCompositingBounds.move(m_subpixelAccumulation);
     localBounds = pixelSnappedIntRect(localRawCompositingBounds);
 
     relativeBounds = localBounds;
     relativeBounds.moveBy(delta);
@@ skipping 82 matching lines @@
 
     RenderStyle* style = renderer()->style();
     m_graphicsLayer->setBackfaceVisibility(style->backfaceVisibility() == BackfaceVisibilityVisible);
 
     RenderLayer* compAncestor = m_owningLayer.ancestorCompositingLayer();
 
     // We compute everything relative to the enclosing compositing layer.
     IntRect ancestorCompositingBounds;
     if (compAncestor) {
         ASSERT(compAncestor->hasCompositedLayerMapping());
-        ancestorCompositingBounds = pixelSnappedIntRect(compAncestor->compositedLayerMapping()->compositedBounds());
+        ancestorCompositingBounds = compAncestor->compositedLayerMapping()->pixelSnappedCompositedBounds();
     }
 
     IntRect localCompositingBounds;
     IntRect relativeCompositingBounds;
     IntPoint delta;
     adjustBoundsForSubPixelAccumulation(compAncestor, localCompositingBounds, relativeCompositingBounds, delta);
 
     IntPoint graphicsLayerParentLocation;
     if (compAncestor && compAncestor->compositedLayerMapping()->hasClippingLayer()) {
         // If the compositing ancestor has a layer to clip children, we parent in that, and therefore
@@ skipping 55 matching lines @@
     if (m_maskLayer) {
         if (m_maskLayer->size() != m_graphicsLayer->size()) {
             m_maskLayer->setSize(m_graphicsLayer->size());
             m_maskLayer->setNeedsDisplay();
         }
         m_maskLayer->setPosition(FloatPoint());
         m_maskLayer->setOffsetFromRenderer(m_graphicsLayer->offsetFromRenderer());
     }
 
     if (m_owningLayer.hasTransform()) {
-        const IntRect borderBox = toRenderBox(renderer())->pixelSnappedBorderBoxRect();
+        const LayoutRect borderBox = toRenderBox(renderer())->borderBoxRect();
 
         // Get layout bounds in the coords of compAncestor to match relativeCompositingBounds.
-        IntRect layerBounds(delta + roundedIntSize(m_subpixelAccumulation), borderBox.size());
+        IntRect layerBounds = pixelSnappedIntRect(toLayoutPoint(m_subpixelAccumulation), borderBox.size());
+        layerBounds.moveBy(delta);
 
         // Update properties that depend on layer dimensions
-        FloatPoint3D transformOrigin = computeTransformOrigin(borderBox);
+        FloatPoint3D transformOrigin = computeTransformOrigin(IntRect(IntPoint(), layerBounds.size()));
         // Compute the anchor point, which is in the center of the renderer box unless transform-origin is set.
         FloatPoint3D anchor(
             relativeCompositingBounds.width() ? (layerBounds.x() - relativeCompositingBounds.x() + transformOrigin.x()) / relativeCompositingBounds.width()  : 0.5f,
             relativeCompositingBounds.height() ? (layerBounds.y() - relativeCompositingBounds.y() + transformOrigin.y()) / relativeCompositingBounds.height() : 0.5f,
             transformOrigin.z());
         m_graphicsLayer->setAnchorPoint(anchor);
     } else {
         m_graphicsLayer->setAnchorPoint(FloatPoint3D(0.5f, 0.5f, 0));
     }
 
@@ skipping 1258 matching lines @@
 {
     ASSERT(!renderer()->frame()->page() || !renderer()->frame()->page()->isPainting());
 }
 #endif
 
 void CompositedLayerMapping::notifyAnimationStarted(const GraphicsLayer*, double monotonicTime)
 {
     renderer()->node()->document().cssPendingAnimations().notifyCompositorAnimationStarted(monotonicTime);
 }
 
-LayoutRect CompositedLayerMapping::compositedBounds() const
+IntRect CompositedLayerMapping::pixelSnappedCompositedBounds() const
 {
-    return m_compositedBounds;
+    LayoutRect bounds = m_compositedBounds;
+    bounds.move(m_subpixelAccumulation);
+    return pixelSnappedIntRect(bounds);
 }
 
 void CompositedLayerMapping::setCompositedBounds(const LayoutRect& bounds)
 {
     m_compositedBounds = bounds;
 }
 
 bool CompositedLayerMapping::updateSquashingLayerAssignment(RenderLayer* layer, IntSize offsetFromSquashingCLM, size_t nextSquashedLayerIndex)
 {
     ASSERT(compositor()->layerSquashingEnabled());
@@ skipping 82 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore