Improve the compositing reasons when squashing fails

Source/core/rendering/compositing/CompositingLayerAssigner.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google 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
@@ skipping 93 matching lines @@
                 // since that requires walking the render layer tree.
                 update = PutInSquashingLayer;
             } else if (layer->groupedMapping() || layer->lostGroupedMapping()) {
                 update = RemoveFromSquashingLayer;
             }
         }
     }
     return update;
 }
 
-bool CompositingLayerAssigner::canSquashIntoCurrentSquashingOwner(const RenderLayer* layer, const CompositingLayerAssigner::SquashingState& squashingState)
+CompositingReasons CompositingLayerAssigner::getReasonsPreventingSquashing(const RenderLayer* layer, const CompositingLayerAssigner::SquashingState& squashingState)
 {
     if (!squashingState.haveAssignedBackingsToEntireSquashingLayerSubtree)
-        return false;
+        return CompositingReasonSquashingWouldBreakPaintOrder;
 
     // 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 CompositingReasonSquashingVideoIsDisallowed;
 
     if (squashingWouldExceedSparsityTolerance(layer, squashingState))
-        return false;
+        return CompositingReasonSquashingSparsityExceeded;
 
     // FIXME: this is not efficient, since it walks up the tree . We should store these values on the CompositingInputsCache.
     ASSERT(squashingState.hasMostRecentMapping);
     const RenderLayer& squashingLayer = squashingState.mostRecentMapping->owningLayer();
 
     if (layer->renderer()->clippingContainer() != squashingLayer.renderer()->clippingContainer()) {
         if (!squashingLayer.compositedLayerMapping()->containingSquashedLayer(layer->renderer()->clippingContainer()))
-            return false;
+            return CompositingReasonSquashingClippingContainerMismatch;
     }
 
-    // Composited descendants need to be clipped by a child contianment graphics layer, which would not be available if the layer is
+    // Composited descendants need to be clipped by a child containment graphics layer, which would not be available if the layer is
+    // squashed (and therefore has no CLM nor a child containment graphics layer).
     if (m_compositor->clipsCompositingDescendants(layer))
-        return false;
+        return CompositingReasonSquashedLayerClipsCompositingDescendants;
 
     if (layer->scrollsWithRespectTo(&squashingLayer))
-        return false;
+        return CompositingReasonScrollsWithRespectToSquashingLayer;
 
     const RenderLayer::CompositingInputs& compositingInputs = layer->compositingInputs();
     const RenderLayer::CompositingInputs& squashingLayerCompositingInputs = squashingLayer.compositingInputs();
 
     if (compositingInputs.opacityAncestor != squashingLayerCompositingInputs.opacityAncestor)
-        return false;
+        return CompositingReasonSquashingOpacityAncestorMismatch;
 
     if (compositingInputs.transformAncestor != squashingLayerCompositingInputs.transformAncestor)
-        return false;
+        return CompositingReasonSquashingTransformAncestorMismatch;
 
     if (compositingInputs.filterAncestor != squashingLayerCompositingInputs.filterAncestor)
-        return false;
+        return CompositingReasonSquashingFilterAncestorMismatch;
 
-    return true;
+    return CompositingReasonNone;
 }
 
 bool CompositingLayerAssigner::updateSquashingAssignment(RenderLayer* layer, SquashingState& squashingState, const CompositingStateTransitionType compositedLayerUpdate,
     Vector<RenderLayer*>& layersNeedingRepaint)
 {
     // NOTE: In the future as we generalize this, the background of this layer may need to be assigned to a different backing than
     // the squashed RenderLayer's own primary contents. This would happen when we have a composited negative z-index element that needs
     // 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) {
@@ skipping 43 matching lines @@
         layersChanged = true;
         m_compositor->allocateOrClearCompositedLayerMapping(reflectionLayer, compositedLayerUpdate);
     }
     m_compositor->updateDirectCompositingReasons(reflectionLayer);
     if (reflectionLayer->hasCompositedLayerMapping())
         reflectionLayer->compositedLayerMapping()->updateGraphicsLayerConfiguration(GraphicsLayerUpdater::ForceUpdate);
 }
 
 void CompositingLayerAssigner::assignLayersToBackingsInternal(RenderLayer* layer, SquashingState& squashingState, bool& layersChanged, Vector<RenderLayer*>& layersNeedingRepaint)
 {
-    if (m_layerSquashingEnabled && requiresSquashing(layer->compositingReasons()) && !canSquashIntoCurrentSquashingOwner(layer, squashingState))
-        layer->setCompositingReasons(layer->compositingReasons() | CompositingReasonNoSquashingTargetFound);
+    if (m_layerSquashingEnabled && requiresSquashing(layer->compositingReasons())) {
+        CompositingReasons reasonsPreventingSquashing = getReasonsPreventingSquashing(layer, squashingState);
+        if (reasonsPreventingSquashing)
+            layer->setCompositingReasons(layer->compositingReasons() | reasonsPreventingSquashing);
+    }
 
     CompositingStateTransitionType compositedLayerUpdate = computeCompositedLayerUpdate(layer);
 
     if (m_compositor->allocateOrClearCompositedLayerMapping(layer, compositedLayerUpdate)) {
         layersNeedingRepaint.append(layer);
         layersChanged = true;
     }
 
     // FIXME: special-casing reflection layers here is not right.
     if (layer->reflectionInfo())
@@ skipping 29 matching lines @@
 
     RenderLayerStackingNodeIterator iterator(*layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
     while (RenderLayerStackingNode* curNode = iterator.next())
         assignLayersToBackingsInternal(curNode->layer(), squashingState, layersChanged, layersNeedingRepaint);
 
     if (squashingState.hasMostRecentMapping && &squashingState.mostRecentMapping->owningLayer() == layer)
         squashingState.haveAssignedBackingsToEntireSquashingLayerSubtree = true;
 }
 
 }