Fix unexpected blurry text caused by combination of skew and promotion

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.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 136 matching lines @@
         m_subtreeIsCompositing(false),
         m_hasUnisolatedCompositedBlendingDescendant(false),
         m_testingOverlap(true),
         m_hasCompositedScrollingAncestor(false) {}
 
   PaintLayer* m_compositingAncestor;
   bool m_subtreeIsCompositing;
   bool m_hasUnisolatedCompositedBlendingDescendant;
   bool m_testingOverlap;
   bool m_hasCompositedScrollingAncestor;
+  Vector<PaintLayer*>& layersNeedingPostProcessing() {
+    return m_layersNeedingPostProcessing;
+  }
+
+ private:
+  Vector<PaintLayer*> m_layersNeedingPostProcessing;
 };
 
 static bool requiresCompositingOrSquashing(CompositingReasons reasons) {
 #if DCHECK_IS_ON()
   bool fastAnswer = reasons != CompositingReasonNone;
   bool slowAnswer = requiresCompositing(reasons) || requiresSquashing(reasons);
   DCHECK_EQ(slowAnswer, fastAnswer);
 #endif
   return reasons != CompositingReasonNone;
 }
@@ skipping 343 matching lines @@
     }
 
     if (willBeCompositedOrSquashed &&
         layer->layoutObject().style()->hasBlendMode())
       currentRecursionData.m_hasUnisolatedCompositedBlendingDescendant = true;
 
     // Tell the parent it has compositing descendants.
     if (willBeCompositedOrSquashed)
       currentRecursionData.m_subtreeIsCompositing = true;
 
+    // Track non-composited skewed elements
+    if (!willBeCompositedOrSquashed && canBeComposited &&
+        layer->layoutObject().styleRef().hasTransform() &&
+        layer->layoutObject().styleRef().transform().hasSkew()) {
+      currentRecursionData.layersNeedingPostProcessing().push_back(layer);
+    }
+
+    // Promote skewed elements within a promoted skewed element to improve
+    // output quality.
+    if (willBeCompositedOrSquashed &&
+        !childRecursionData.layersNeedingPostProcessing().isEmpty()) {
+      // If an skewed element is composited due to its descendants, we have to
+      // update the uncomposited skewed descendants to composite them.
+      if (layer->layoutObject().styleRef().hasTransform() &&
+          layer->layoutObject().styleRef().transform().hasSkew()) {
+        for (auto& childLayer :
+             childRecursionData.layersNeedingPostProcessing()) {
+          childLayer->setCompositingReasons(
+              CompositingReasonSkewWithCompositedSkewedAncestor);
+        }
+      }
+      childRecursionData.layersNeedingPostProcessing().clear();
+    }
+
+    // Current non-leaf layer and it descendants have been updated.
+    if (layer->firstChild()) {
+      currentRecursionData.layersNeedingPostProcessing().clear();
+    }
+
     // Turn overlap testing off for later layers if it's already off, or if we
     // have an animating transform.  Note that if the layer clips its
     // descendants, there's no reason to propagate the child animation to the
     // parent layers. That's because we know for sure the animation is contained
     // inside the clipping rectangle, which is already added to the overlap map.
     bool isCompositedClippingLayer =
         canBeComposited &&
         (reasonsToComposite & CompositingReasonClipsCompositingDescendants);
     bool isCompositedWithInlineTransform =
         reasonsToComposite & CompositingReasonInlineTransform;
     if ((!childRecursionData.m_testingOverlap && !isCompositedClippingLayer) ||
         layer->layoutObject().style()->hasCurrentTransformAnimation() ||
         isCompositedWithInlineTransform)
       currentRecursionData.m_testingOverlap = false;
 
     if (childRecursionData.m_compositingAncestor == layer)
       overlapMap.finishCurrentOverlapTestingContext();
 
     descendantHas3DTransform |=
         anyDescendantHas3DTransform || layer->has3DTransform();
   }
 
   // At this point we have finished collecting all reasons to composite this
   // layer.
   layer->setCompositingReasons(reasonsToComposite);
 }
 
 }  // namespace blink