Fix sub-pixel handling of transparency layers

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1198 matching lines @@
 enum TransparencyClipBoxBehavior {
     PaintingTransparencyClipBox,
     HitTestingTransparencyClipBox
 };
 
 enum TransparencyClipBoxMode {
     DescendantsOfTransparencyClipBox,
     RootOfTransparencyClipBox
 };
 
-static LayoutRect transparencyClipBox(const RenderLayer*, const RenderLayer* rootLayer, TransparencyClipBoxBehavior, TransparencyClipBoxMode, PaintBehavior = 0);
+static LayoutRect transparencyClipBox(const RenderLayer*, const RenderLayer* rootLayer, TransparencyClipBoxBehavior, TransparencyClipBoxMode, const LayoutSize& subPixelAccumulation, PaintBehavior = 0);
 
 static void expandClipRectForDescendantsAndReflection(LayoutRect& clipRect, const RenderLayer* layer, const RenderLayer* rootLayer,
-    TransparencyClipBoxBehavior transparencyBehavior, PaintBehavior paintBehavior)
+    TransparencyClipBoxBehavior transparencyBehavior, const LayoutSize& subPixelAccumulation, PaintBehavior paintBehavior)
 {
     // If we have a mask, then the clip is limited to the border box area (and there is
     // no need to examine child layers).
     if (!layer->renderer()->hasMask()) {
         // Note: we don't have to walk z-order lists since transparent elements always establish
         // a stacking container. This means we can just walk the layer tree directly.
         for (RenderLayer* curr = layer->firstChild(); curr; curr = curr->nextSibling()) {
             if (!layer->reflectionInfo() || layer->reflectionInfo()->reflectionLayer() != curr)
-                clipRect.unite(transparencyClipBox(curr, rootLayer, transparencyBehavior, DescendantsOfTransparencyClipBox, paintBehavior));
+                clipRect.unite(transparencyClipBox(curr, rootLayer, transparencyBehavior, DescendantsOfTransparencyClipBox, subPixelAccumulation, paintBehavior));
         }
     }
 
     // If we have a reflection, then we need to account for that when we push the clip.  Reflect our entire
     // current transparencyClipBox to catch all child layers.
     // FIXME: Accelerated compositing will eventually want to do something smart here to avoid incorporating this
     // size into the parent layer.
     if (layer->renderer()->hasReflection()) {
         LayoutPoint delta;
         layer->convertToLayerCoords(rootLayer, delta);
         clipRect.move(-delta.x(), -delta.y());
         clipRect.unite(layer->renderBox()->reflectedRect(clipRect));
         clipRect.moveBy(delta);
     }
 }
 
 static LayoutRect transparencyClipBox(const RenderLayer* layer, const RenderLayer* rootLayer, TransparencyClipBoxBehavior transparencyBehavior,
-    TransparencyClipBoxMode transparencyMode, PaintBehavior paintBehavior)
+    TransparencyClipBoxMode transparencyMode, const LayoutSize& subPixelAccumulation, PaintBehavior paintBehavior)
 {
     // FIXME: Although this function completely ignores CSS-imposed clipping, we did already intersect with the
     // paintDirtyRect, and that should cut down on the amount we have to paint.  Still it
     // would be better to respect clips.
 
     if (rootLayer != layer && ((transparencyBehavior == PaintingTransparencyClipBox && layer->paintsWithTransform(paintBehavior))
         || (transparencyBehavior == HitTestingTransparencyClipBox && layer->hasTransform()))) {
         // The best we can do here is to use enclosed bounding boxes to establish a "fuzzy" enough clip to encompass
         // the transformed layer and all of its children.
         const RenderLayer* paginationLayer = transparencyMode == DescendantsOfTransparencyClipBox ? layer->enclosingPaginationLayer() : 0;
         const RenderLayer* rootLayerForTransform = paginationLayer ? paginationLayer : rootLayer;
         LayoutPoint delta;
         layer->convertToLayerCoords(rootLayerForTransform, delta);
 
+        delta.move(subPixelAccumulation);
+        IntPoint pixelSnappedDelta = roundedIntPoint(delta);
         TransformationMatrix transform;
-        transform.translate(delta.x(), delta.y());
+        transform.translate(pixelSnappedDelta.x(), pixelSnappedDelta.y());
         transform = transform * *layer->transform();
 
         // We don't use fragment boxes when collecting a transformed layer's bounding box, since it always
         // paints unfragmented.
         LayoutRect clipRect = layer->boundingBox(layer);
-        expandClipRectForDescendantsAndReflection(clipRect, layer, layer, transparencyBehavior, paintBehavior);
+        expandClipRectForDescendantsAndReflection(clipRect, layer, layer, transparencyBehavior, subPixelAccumulation, paintBehavior);
         layer->renderer()->style()->filterOutsets().expandRect(clipRect);
         LayoutRect result = transform.mapRect(clipRect);
         if (!paginationLayer)
             return result;
 
         // We have to break up the transformed extent across our columns.
         // Split our box up into the actual fragment boxes that render in the columns/pages and unite those together to
         // get our true bounding box.
         RenderFlowThread* enclosingFlowThread = toRenderFlowThread(paginationLayer->renderer());
         result = enclosingFlowThread->fragmentsBoundingBox(result);
 
         LayoutPoint rootLayerDelta;
         paginationLayer->convertToLayerCoords(rootLayer, rootLayerDelta);
         result.moveBy(rootLayerDelta);
         return result;
     }
 
     LayoutRect clipRect = layer->boundingBox(rootLayer, RenderLayer::UseFragmentBoxes);
-    expandClipRectForDescendantsAndReflection(clipRect, layer, rootLayer, transparencyBehavior, paintBehavior);
+    expandClipRectForDescendantsAndReflection(clipRect, layer, rootLayer, transparencyBehavior, subPixelAccumulation, paintBehavior);
     layer->renderer()->style()->filterOutsets().expandRect(clipRect);
+    clipRect.move(subPixelAccumulation);
     return clipRect;
 }
 
-LayoutRect RenderLayer::paintingExtent(const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, PaintBehavior paintBehavior)
+LayoutRect RenderLayer::paintingExtent(const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, const LayoutSize& subPixelAccumulation, PaintBehavior paintBehavior)
 {
-    return intersection(transparencyClipBox(this, rootLayer, PaintingTransparencyClipBox, RootOfTransparencyClipBox, paintBehavior), paintDirtyRect);
+    return intersection(transparencyClipBox(this, rootLayer, PaintingTransparencyClipBox, RootOfTransparencyClipBox, subPixelAccumulation, paintBehavior), paintDirtyRect);
 }
 
-void RenderLayer::beginTransparencyLayers(GraphicsContext* context, const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, PaintBehavior paintBehavior)
+void RenderLayer::beginTransparencyLayers(GraphicsContext* context, const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, const LayoutSize& subPixelAccumulation, PaintBehavior paintBehavior)
 {
     bool createTransparencyLayerForBlendMode = m_stackingNode->isStackingContext() && m_blendInfo.childLayerHasBlendMode();
     if (context->paintingDisabled() || ((paintsWithTransparency(paintBehavior) || paintsWithBlendMode() || createTransparencyLayerForBlendMode) && m_usedTransparency))
         return;
 
     RenderLayer* ancestor = transparentPaintingAncestor();
     if (ancestor)
-        ancestor->beginTransparencyLayers(context, rootLayer, paintDirtyRect, paintBehavior);
+        ancestor->beginTransparencyLayers(context, rootLayer, paintDirtyRect, subPixelAccumulation, paintBehavior);
 
     if (paintsWithTransparency(paintBehavior) || paintsWithBlendMode() || createTransparencyLayerForBlendMode) {
         m_usedTransparency = true;
         context->save();
-        LayoutRect clipRect = paintingExtent(rootLayer, paintDirtyRect, paintBehavior);
+        LayoutRect clipRect = paintingExtent(rootLayer, paintDirtyRect, subPixelAccumulation, paintBehavior);
         context->clip(clipRect);
 
         if (paintsWithBlendMode())
             context->setCompositeOperation(context->compositeOperation(), m_blendInfo.blendMode());
 
         context->beginTransparencyLayer(renderer()->opacity());
 
         if (paintsWithBlendMode())
             context->setCompositeOperation(context->compositeOperation(), blink::WebBlendModeNormal);
 #ifdef REVEAL_TRANSPARENCY_LAYERS
@@ skipping 566 matching lines @@
     if (paintsWithTransform(paintingInfo.paintBehavior) && !(paintFlags & PaintLayerAppliedTransform)) {
         TransformationMatrix layerTransform = renderableTransform(paintingInfo.paintBehavior);
         // If the transform can't be inverted, then don't paint anything.
         if (!layerTransform.isInvertible())
             return;
 
         // If we have a transparency layer enclosing us and we are the root of a transform, then we need to establish the transparency
         // layer from the parent now, assuming there is a parent
         if (paintFlags & PaintLayerHaveTransparency) {
             if (parent())
-                parent()->beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.paintBehavior);
+                parent()->beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.subPixelAccumulation, paintingInfo.paintBehavior);
             else
-                beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.paintBehavior);
+                beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.subPixelAccumulation, paintingInfo.paintBehavior);
         }
 
         if (enclosingPaginationLayer()) {
             paintTransformedLayerIntoFragments(context, paintingInfo, paintFlags);
             return;
         }
 
         // Make sure the parent's clip rects have been calculated.
         ClipRect clipRect = paintingInfo.paintDirtyRect;
         if (parent()) {
@@ skipping 112 matching lines @@
                 }
             }
         }
     }
 
     // Blending operations must be performed only with the nearest ancestor stacking context.
     // Note that there is no need to create a transparency layer if we're painting the root.
     bool createTransparencyLayerForBlendMode = !renderer()->isRoot() && m_stackingNode->isStackingContext() && m_blendInfo.childLayerHasBlendMode();
 
     if (createTransparencyLayerForBlendMode)
-        beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.paintBehavior);
+        beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.subPixelAccumulation, paintingInfo.paintBehavior);
 
     LayerPaintingInfo localPaintingInfo(paintingInfo);
     FilterEffectRendererHelper filterPainter(filterRenderer() && paintsWithFilters());
     if (filterPainter.haveFilterEffect() && !context->paintingDisabled()) {
         RenderLayerFilterInfo* filterInfo = this->filterInfo();
         ASSERT(filterInfo);
         LayoutRect filterRepaintRect = filterInfo->dirtySourceRect();
         filterRepaintRect.move(offsetFromRoot.x(), offsetFromRoot.y());
 
         if (!rootRelativeBoundsComputed)
@@ skipping 15 matching lines @@
                 // If the filter needs the full source image, we need to avoid using the clip rectangles.
                 // Otherwise, if for example this layer has overflow:hidden, a drop shadow will not compute correctly.
                 // Note that we will still apply the clipping on the final rendering of the filter.
                 localPaintingInfo.clipToDirtyRect = !filterRenderer()->hasFilterThatMovesPixels();
             }
         }
     }
 
     if (filterPainter.hasStartedFilterEffect() && haveTransparency) {
         // If we have a filter and transparency, we have to eagerly start a transparency layer here, rather than risk a child layer lazily starts one with the wrong context.
-        beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, paintingInfo.paintDirtyRect, localPaintingInfo.paintBehavior);
+        beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.subPixelAccumulation, localPaintingInfo.paintBehavior);
     }
 
     // If this layer's renderer is a child of the paintingRoot, we render unconditionally, which
     // is done by passing a nil paintingRoot down to our renderer (as if no paintingRoot was ever set).
     // Else, our renderer tree may or may not contain the painting root, so we pass that root along
     // so it will be tested against as we descend through the renderers.
     RenderObject* paintingRootForRenderer = 0;
     if (localPaintingInfo.paintingRoot && !renderer()->isDescendantOf(localPaintingInfo.paintingRoot))
         paintingRootForRenderer = localPaintingInfo.paintingRoot;
 
@@ skipping 213 matching lines @@
             LayoutPoint newOffsetFromRoot = *offsetFromRoot + fragment.paginationOffset;
             fragment.shouldPaintContent &= intersectsDamageRect(fragment.layerBounds, fragment.backgroundRect.rect(), localPaintingInfo.rootLayer, &newOffsetFromRoot);
         }
     }
 }
 
 void RenderLayer::paintTransformedLayerIntoFragments(GraphicsContext* context, const LayerPaintingInfo& paintingInfo, PaintLayerFlags paintFlags)
 {
     LayerFragments enclosingPaginationFragments;
     LayoutPoint offsetOfPaginationLayerFromRoot;
-    LayoutRect transformedExtent = transparencyClipBox(this, enclosingPaginationLayer(), PaintingTransparencyClipBox, RootOfTransparencyClipBox, paintingInfo.paintBehavior);
+    LayoutRect transformedExtent = transparencyClipBox(this, enclosingPaginationLayer(), PaintingTransparencyClipBox, RootOfTransparencyClipBox, paintingInfo.subPixelAccumulation, paintingInfo.paintBehavior);
     enclosingPaginationLayer()->collectFragments(enclosingPaginationFragments, paintingInfo.rootLayer, paintingInfo.paintDirtyRect,
         (paintFlags & PaintLayerTemporaryClipRects) ? TemporaryClipRects : PaintingClipRects, IgnoreOverlayScrollbarSize,
         (paintFlags & PaintLayerPaintingOverflowContents) ? IgnoreOverflowClip : RespectOverflowClip, &offsetOfPaginationLayerFromRoot, paintingInfo.subPixelAccumulation, &transformedExtent);
 
     for (size_t i = 0; i < enclosingPaginationFragments.size(); ++i) {
         const LayerFragment& fragment = enclosingPaginationFragments.at(i);
 
         // Apply the page/column clip for this fragment, as well as any clips established by layers in between us and
         // the enclosing pagination layer.
         LayoutRect clipRect = fragment.backgroundRect.rect();
@@ skipping 28 matching lines @@
     const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo& localPaintingInfo, PaintBehavior paintBehavior,
     RenderObject* paintingRootForRenderer)
 {
     for (size_t i = 0; i < layerFragments.size(); ++i) {
         const LayerFragment& fragment = layerFragments.at(i);
         if (!fragment.shouldPaintContent)
             continue;
 
         // Begin transparency layers lazily now that we know we have to paint something.
         if (haveTransparency || paintsWithBlendMode())
-            beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, transparencyPaintDirtyRect, localPaintingInfo.paintBehavior);
+            beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, transparencyPaintDirtyRect, localPaintingInfo.subPixelAccumulation, localPaintingInfo.paintBehavior);
 
         if (localPaintingInfo.clipToDirtyRect) {
             // Paint our background first, before painting any child layers.
             // Establish the clip used to paint our background.
             clipToRect(localPaintingInfo, context, fragment.backgroundRect, DoNotIncludeSelfForBorderRadius); // Background painting will handle clipping to self.
         }
 
         // Paint the background.
         // FIXME: Eventually we will collect the region from the fragment itself instead of just from the paint info.
         PaintInfo paintInfo(context, pixelSnappedIntRect(fragment.backgroundRect.rect()), PaintPhaseBlockBackground, paintBehavior, paintingRootForRenderer, 0, 0, localPaintingInfo.rootLayer->renderer());
         renderer()->paint(paintInfo, toPoint(fragment.layerBounds.location() - renderBoxLocation() + subPixelAccumulationIfNeeded(localPaintingInfo.subPixelAccumulation, compositingState())));
 
         if (localPaintingInfo.clipToDirtyRect)
             restoreClip(context, localPaintingInfo.paintDirtyRect, fragment.backgroundRect);
     }
 }
 
 void RenderLayer::paintForegroundForFragments(const LayerFragments& layerFragments, GraphicsContext* context, GraphicsContext* transparencyLayerContext,
     const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo& localPaintingInfo, PaintBehavior paintBehavior,
     RenderObject* paintingRootForRenderer, bool selectionOnly, bool forceBlackText)
 {
     // Begin transparency if we have something to paint.
     if (haveTransparency || paintsWithBlendMode()) {
         for (size_t i = 0; i < layerFragments.size(); ++i) {
             const LayerFragment& fragment = layerFragments.at(i);
             if (fragment.shouldPaintContent && !fragment.foregroundRect.isEmpty()) {
-                beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, transparencyPaintDirtyRect, localPaintingInfo.paintBehavior);
+                beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, transparencyPaintDirtyRect, localPaintingInfo.subPixelAccumulation, localPaintingInfo.paintBehavior);
                 break;
             }
         }
     }
 
     PaintBehavior localPaintBehavior = forceBlackText ? (PaintBehavior)PaintBehaviorForceBlackText : paintBehavior;
 
     // Optimize clipping for the single fragment case.
     bool shouldClip = localPaintingInfo.clipToDirtyRect && layerFragments.size() == 1 && layerFragments[0].shouldPaintContent && !layerFragments[0].foregroundRect.isEmpty();
     if (shouldClip)
@@ skipping 552 matching lines @@
     }
 
     return false;
 }
 
 RenderLayer* RenderLayer::hitTestTransformedLayerInFragments(RenderLayer* rootLayer, RenderLayer* containerLayer, const HitTestRequest& request, HitTestResult& result,
     const LayoutRect& hitTestRect, const HitTestLocation& hitTestLocation, const HitTestingTransformState* transformState, double* zOffset)
 {
     LayerFragments enclosingPaginationFragments;
     LayoutPoint offsetOfPaginationLayerFromRoot;
-    LayoutRect transformedExtent = transparencyClipBox(this, enclosingPaginationLayer(), HitTestingTransparencyClipBox, RootOfTransparencyClipBox);
+    // FIXME: We're missing a sub-pixel offset here crbug.com/348728
+    LayoutRect transformedExtent = transparencyClipBox(this, enclosingPaginationLayer(), HitTestingTransparencyClipBox, RootOfTransparencyClipBox, LayoutSize());
     enclosingPaginationLayer()->collectFragments(enclosingPaginationFragments, rootLayer, hitTestRect,
         RootRelativeClipRects, IncludeOverlayScrollbarSize, RespectOverflowClip, &offsetOfPaginationLayerFromRoot, LayoutSize(), &transformedExtent);
 
     for (int i = enclosingPaginationFragments.size() - 1; i >= 0; --i) {
         const LayerFragment& fragment = enclosingPaginationFragments.at(i);
 
         // Apply the page/column clip for this fragment, as well as any clips established by layers in between us and
         // the enclosing pagination layer.
         LayoutRect clipRect = fragment.backgroundRect.rect();
 
@@ skipping 1066 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif