Simplify application of perspective origin.

Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.h

 /*
  * 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 91 matching lines @@
 
     bool hasMaskLayer() const { return m_maskLayer; }
     GraphicsLayer* maskLayer() const { return m_maskLayer.get(); }
 
     bool hasChildClippingMaskLayer() const { return m_childClippingMaskLayer; }
     GraphicsLayer* childClippingMaskLayer() const { return m_childClippingMaskLayer.get(); }
 
     GraphicsLayer* parentForSublayers() const;
     GraphicsLayer* childForSuperlayers() const;
 
+    bool hasChildTransformLayer() const { return m_childTransformLayer; }
     GraphicsLayer* childTransformLayer() const { return m_childTransformLayer.get(); }
 
     GraphicsLayer* squashingContainmentLayer() const { return m_squashingContainmentLayer.get(); }
     GraphicsLayer* squashingLayer() const { return m_squashingLayer.get(); }
-    // Contains the bottommost layer in the hierarchy that can contain the children transform.
-    GraphicsLayer* layerForChildrenTransform() const;
 
     void setSquashingContentsNeedDisplay();
     void setContentsNeedDisplay();
     // r is in the coordinate space of the layer's render object
     void setContentsNeedDisplayInRect(const LayoutRect&, PaintInvalidationReason);
 
     void invalidateDisplayItemClient(const DisplayItemClientWrapper&);
 
     // Notification from the renderer that its content changed.
     void contentChanged(ContentChangeType);
@@ skipping 165 matching lines @@
 
     // Return true if |m_owningLayer|'s compositing ancestor is not a descendant (inclusive) of the
     // clipping container for |m_owningLayer|.
     bool owningLayerClippedByLayerNotAboveCompositedAncestor();
 
     DeprecatedPaintLayer& m_owningLayer;
 
     // The hierarchy of layers that is maintained by the CompositedDeprecatedPaintLayerMapping looks like this:
     //
     //  + m_ancestorClippingLayer [OPTIONAL]
-    //     + m_graphicsLayer
-    //        + m_childContainmentLayer [OPTIONAL] <-OR-> m_scrollingLayer [OPTIONAL] <-OR-> m_childTransformLayer
-    //        |                                            + m_scrollingContentsLayer [Present iff m_scrollingLayer is present]
-    //        |                                               + m_scrollingBlockSelectionLayer [Present iff m_scrollingLayer is present]
-    //        |
-    //        + m_overflowControlsClippingLayer [OPTIONAL] // *The overflow controls may need to be repositioned in the
-    //          + m_overflowControlsHostLayer              //  graphics layer tree by the RLC to ensure that they stack
-    //            + m_layerForVerticalScrollbar            //  above scrolling content.
-    //            + m_layerForHorizontalScrollbar
-    //            + m_layerForScrollCorner
+    //    + m_graphicsLayer
+    //      + m_childTransformLayer [OPTIONAL]
+    //      | + m_childContainmentLayer [OPTIONAL] <-OR-> m_scrollingLayer [OPTIONAL]
+    //      |                                             + m_scrollingContentsLayer [Present iff m_scrollingLayer is present]
+    //      |                                               + m_scrollingBlockSelectionLayer [Present iff m_scrollingLayer is present]
+    //      + m_overflowControlsClippingLayer [OPTIONAL] // *The overflow controls may need to be repositioned in the
+    //        + m_overflowControlsHostLayer [OPTIONAL]   //  graphics layer tree by the RLC to ensure that they stack
+    //          + m_layerForVerticalScrollbar [OPTIONAL] //  above scrolling content.
+    //          + m_layerForHorizontalScrollbar [OPTIONAL]
+    //          + m_layerForScrollCorner [OPTIONAL]

[Ian Vollick, 2015/04/01 18:00:09]

Thank you for updating this comment.

[jbroman, 2015/04/02 15:34:15]

No problem. :)

     //
     // We need an ancestor clipping layer if our clipping ancestor is not our ancestor in the
     // clipping tree. Here's what that might look like.
     //
     // Let A = the clipping ancestor,
     //     B = the clip descendant, and
     //     SC = the stacking context that is the ancestor of A and B in the stacking tree.
     //
     // SC
     //  + A = m_graphicsLayer
     //  |  + m_childContainmentLayer
     //  |     + ...
     //  ...
     //  |
     //  + B = m_ancestorClippingLayer [+]
     //     + m_graphicsLayer
     //        + ...
     //
     // In this case B is clipped by another layer that doesn't happen to be its ancestor: A.
     // So we create an ancestor clipping layer for B, [+], which ensures that B is clipped
     // as if it had been A's descendant.
     OwnPtr<GraphicsLayer> m_ancestorClippingLayer; // Only used if we are clipped by an ancestor which is not a stacking context.
     OwnPtr<GraphicsLayer> m_graphicsLayer;
     OwnPtr<GraphicsLayer> m_childContainmentLayer; // Only used if we have clipping on a stacking context with compositing children.
-    OwnPtr<GraphicsLayer> m_childTransformLayer; // Only used if we have perspective and no m_childContainmentLayer.
+    OwnPtr<GraphicsLayer> m_childTransformLayer; // Only used if we have perspective.
     OwnPtr<GraphicsLayer> m_scrollingLayer; // Only used if the layer is using composited scrolling.
     OwnPtr<GraphicsLayer> m_scrollingContentsLayer; // Only used if the layer is using composited scrolling.
     OwnPtr<GraphicsLayer> m_scrollingBlockSelectionLayer; // Only used if the layer is using composited scrolling, but has no scrolling contents apart from block selection gaps.
 
     // This layer is also added to the hierarchy by the RLB, but in a different way than
     // the layers above. It's added to m_graphicsLayer as its mask layer (naturally) if
     // we have a mask, and isn't part of the typical hierarchy (it has no children).
     OwnPtr<GraphicsLayer> m_maskLayer; // Only used if we have a mask.
     OwnPtr<GraphicsLayer> m_childClippingMaskLayer; // Only used if we have to clip child layers or accelerated contents with border radius or clip-path.
 
@@ skipping 67 matching lines @@
     unsigned m_pendingUpdateScope : 2;
     unsigned m_isMainFrameLayoutViewLayer : 1;
 
     unsigned m_backgroundLayerPaintsFixedRootBackground : 1;
     unsigned m_scrollingContentsAreEmpty : 1;
 };
 
 } // namespace blink
 
 #endif // CompositedDeprecatedPaintLayerMapping_h