Allow layers that need squashing to draw into the squashing layer in some cases.

Source/core/rendering/compositing/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 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 588 matching lines @@
     // to paint on top of the background, but below the layer's main contents. For now, because we always composite layers
     // when they have a composited negative z-index child, such layers will never need squashing so it is not yet an issue.
     if (compositedLayerUpdate == PutInSquashingLayer) {
         // A layer that is squashed with other layers cannot have its own CompositedLayerMapping.
         ASSERT(!layer->hasCompositedLayerMapping());
         ASSERT(squashingState.hasMostRecentMapping);
 
         LayoutPoint offsetFromTransformedAncestorForSquashedLayer = layer->computeOffsetFromTransformedAncestor();
 
         // Compute the offset of this layer from the squashing owner. This computation is correct only because layers are allowed to squash only if they
-        // share a transformed ancestor (see canSquashIntoCurrentSquashingOwner).
+        // share a transformed ancestor (see computeSquashingBehaviorWhenSquashingRequired).
         LayoutSize offsetFromSquashingCLM(offsetFromTransformedAncestorForSquashedLayer.x() - squashingState.offsetFromTransformedAncestorForSquashingCLM.x(),
             offsetFromTransformedAncestorForSquashedLayer.y() - squashingState.offsetFromTransformedAncestorForSquashingCLM.y());
 
         bool changedSquashingLayer =
             squashingState.mostRecentMapping->updateSquashingLayerAssignment(layer, offsetFromSquashingCLM, squashingState.nextSquashedLayerIndex);
         if (!changedSquashingLayer)
             return true;
 
         // If we've modified the collection of squashed layers, we must update
         // the graphics layer geometry.
@@ skipping 49 matching lines @@
 bool RenderLayerCompositor::squashingWouldExceedSparsityTolerance(const RenderLayer* candidate, const RenderLayerCompositor::SquashingState& squashingState)
 {
     IntRect bounds = candidate->ancestorDependentProperties().clippedAbsoluteBoundingBox;
     IntRect newBoundingRect = squashingState.boundingRect;
     newBoundingRect.unite(bounds);
     const uint64_t newBoundingRectArea = newBoundingRect.size().area();
     const uint64_t newSquashedArea = squashingState.totalAreaOfSquashedRects + bounds.size().area();
     return newBoundingRectArea > gSquashingSparsityTolerance * newSquashedArea;
 }
 
-bool RenderLayerCompositor::canSquashIntoCurrentSquashingOwner(const RenderLayer* layer, const RenderLayerCompositor::SquashingState& squashingState)
+RenderLayerCompositor::NeedsSquashingBehavior RenderLayerCompositor::computeSquashingBehaviorWhenSquashingRequired(const RenderLayer* layer, const RenderLayerCompositor::SquashingState& squashingState)
 {
     // FIXME: this special case for video exists only to deal with corner cases
     // where a RenderVideo does not report that it needs to be directly composited.
     // Video does not currently support sharing a backing, but this could be
     // generalized in the future. The following layout tests fail if we permit the
     // video to share a backing with other layers.
     //
     // compositing/video/video-controls-layer-creation.html
     // virtual/softwarecompositing/video/video-controls-layer-creation.html
     if (layer->renderer()->isVideo())
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
     if (squashingWouldExceedSparsityTolerance(layer, squashingState))
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
     // FIXME: this is not efficient, since it walks up the tree . We should store these values on the AncestorDependentPropertiesCache.
     ASSERT(squashingState.hasMostRecentMapping);
     const RenderLayer& squashingLayer = squashingState.mostRecentMapping->owningLayer();
 
-    if (layer->renderer()->clippingContainer() != squashingLayer.renderer()->clippingContainer())
-        return false;
-
     // Composited descendants need to be clipped by a child contianment graphics layer, which would not be available if the layer is squashed.
     if (clipsCompositingDescendants(layer))
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
     if (layer->scrollsWithRespectTo(&squashingLayer))
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
     const RenderLayer::AncestorDependentProperties& ancestorDependentProperties = layer->ancestorDependentProperties();
     const RenderLayer::AncestorDependentProperties& squashingLayerAncestorDependentProperties = squashingLayer.ancestorDependentProperties();
 
     if (ancestorDependentProperties.opacityAncestor != squashingLayerAncestorDependentProperties.opacityAncestor)
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
     if (ancestorDependentProperties.transformAncestor != squashingLayerAncestorDependentProperties.transformAncestor)
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
     if (ancestorDependentProperties.filterAncestor != squashingLayerAncestorDependentProperties.filterAncestor)
-        return false;
+        return ShouldPaintIntoOwnLayer;
 
-    return true;
+    if (layer->renderer()->clippingContainer() != squashingLayer.renderer()->clippingContainer()) {
+        //layer->renderer()->showRenderObject();
+        const RenderLayer* parent = layer->renderer()->clippingContainer()->enclosingLayer()->containingGroupedLayer();
+        if (parent && squashingLayer.compositedLayerMapping().equals(parent->groupedMapping()))
+            return ShouldPaintIntoSameLayer;
+        printf("clipping: ShouldPaintIntoOwnLayer\n");
+        return ShouldPaintIntoOwnLayer;
+    }
+
+    return ShouldSquash;
 }
 
 RenderLayerCompositor::CompositingStateTransitionType RenderLayerCompositor::computeCompositedLayerUpdate(RenderLayer* layer)
 {
     CompositingStateTransitionType update = NoCompositingStateChange;
     if (!layer->subtreeIsInvisible() && needsOwnBacking(layer)) {
         if (!layer->hasCompositedLayerMapping()) {
             update = AllocateOwnCompositedLayerMapping;
         }
     } else {
@@ skipping 92 matching lines @@
 
     nextSquashedLayerIndex = 0;
     mostRecentMapping = newCompositedLayerMapping;
     hasMostRecentMapping = hasNewCompositedLayerMapping;
     offsetFromTransformedAncestorForSquashingCLM = newOffsetFromTransformedAncestorForSquashingCLM;
 }
 
 void RenderLayerCompositor::assignLayersToBackings(RenderLayer* updateRoot, bool& layersChanged)
 {
     SquashingState squashingState;
+    printf("RenderLayerCompositor::assignLayersToBackings()\n");
     assignLayersToBackingsInternal(updateRoot, squashingState, layersChanged);
     if (squashingState.hasMostRecentMapping)
         squashingState.mostRecentMapping->finishAccumulatingSquashingLayers(squashingState.nextSquashedLayerIndex);
 }
 
 void RenderLayerCompositor::assignLayersToBackingsForReflectionLayer(RenderLayer* reflectionLayer, bool& layersChanged)
 {
     CompositingStateTransitionType compositedLayerUpdate = computeCompositedLayerUpdate(reflectionLayer);
     if (compositedLayerUpdate != NoCompositingStateChange) {
         layersChanged = true;
         allocateOrClearCompositedLayerMapping(reflectionLayer, compositedLayerUpdate);
     }
     updateDirectCompositingReasons(reflectionLayer);
     if (reflectionLayer->hasCompositedLayerMapping())
         reflectionLayer->compositedLayerMapping()->updateGraphicsLayerConfiguration(GraphicsLayerUpdater::ForceUpdate);
 }
 
 void RenderLayerCompositor::assignLayersToBackingsInternal(RenderLayer* layer, SquashingState& squashingState, bool& layersChanged)
 {
-    if (layerSquashingEnabled() && requiresSquashing(layer->compositingReasons()) && !canSquashIntoCurrentSquashingOwner(layer, squashingState))
-        layer->setCompositingReasons(layer->compositingReasons() | CompositingReasonNoSquashingTargetFound);
+    if (layerSquashingEnabled() && requiresSquashing(layer->compositingReasons())) {
+        switch (computeSquashingBehaviorWhenSquashingRequired(layer, squashingState)) {
+        case ShouldPaintIntoOwnLayer: {
+                printf("assignLayersToBackingsInternal: ShouldPaintIntoOwnLayer\n");
+                layer->setCompositingReasons(layer->compositingReasons() | CompositingReasonNoSquashingTargetFound);
+            break;
+        }
+        case ShouldSquash:
+            break;
+        case ShouldPaintIntoSameLayer:
+            layer->setCompositingReasons(CompositingReasonNone);
+            break;
+        }
+    }
 
     CompositingStateTransitionType compositedLayerUpdate = computeCompositedLayerUpdate(layer);
 
     if (allocateOrClearCompositedLayerMapping(layer, compositedLayerUpdate))
         layersChanged = true;
 
     // FIXME: special-casing reflection layers here is not right.
     if (layer->reflectionInfo())
         assignLayersToBackingsForReflectionLayer(layer->reflectionInfo()->reflectionLayer(), layersChanged);
 
@@ skipping 840 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore