*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/rendering/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 743 matching lines @@
     if (!boundsComputed) {
         // FIXME: If this layer's overlap bounds include its children, we don't need to add its
         // children's bounds to the overlap map.
         layerBounds = enclosingIntRect(overlapMap.geometryMap().absoluteRect(layer->overlapBounds()));
         // Empty rects never intersect, but we need them to for the purposes of overlap testing.
         if (layerBounds.isEmpty())
             layerBounds.setSize(IntSize(1, 1));
         boundsComputed = true;
     }
 
-    IntRect clipRect = pixelSnappedIntRect(layer->clipper().backgroundClipRect(ClipRectsContext(rootRenderLayer(), 0, AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.
+    IntRect clipRect = pixelSnappedIntRect(layer->clipper().backgroundClipRect(ClipRectsContext(rootRenderLayer(), AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.
     clipRect.intersect(layerBounds);
     overlapMap.add(layer, clipRect);
 }
 
 void RenderLayerCompositor::addToOverlapMapRecursive(OverlapMap& overlapMap, RenderLayer* layer, RenderLayer* ancestorLayer)
 {
     if (!canBeComposited(layer) || overlapMap.contains(layer))
         return;
 
     // A null ancestorLayer is an indication that 'layer' has already been pushed.
@@ skipping 891 matching lines @@
     // If squashing is disabled, then layers that would have been squashed should just be separately composited.
     bool needsOwnBackingForDisabledSquashing = !layerSquashingEnabled() && requiresSquashing(layer->compositingReasons());
 
     return requiresCompositing(layer->compositingReasons()) || needsOwnBackingForDisabledSquashing || (inCompositingMode() && layer->isRootLayer());
 }
 
 bool RenderLayerCompositor::canBeComposited(const RenderLayer* layer) const
 {
     // FIXME: We disable accelerated compositing for elements in a RenderFlowThread as it doesn't work properly.
     // See http://webkit.org/b/84900 to re-enable it.
-    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer() && layer->renderer()->flowThreadState() == RenderObject::NotInsideFlowThread;
+    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer();
 }
 
 CompositingReasons RenderLayerCompositor::directReasonsForCompositing(const RenderLayer* layer) const
 {
     RenderObject* renderer = layer->renderer();
     CompositingReasons directReasons = CompositingReasonNone;
 
     if (requiresCompositingForTransform(renderer))
         directReasons |= CompositingReason3DTransform;
 
@@ skipping 59 matching lines @@
         if (next == compositingAncestor) {
             computeClipRoot = curr;
             break;
         }
         curr = next;
     }
 
     if (!computeClipRoot || computeClipRoot == layer)
         return false;
 
-    return layer->clipper().backgroundClipRect(ClipRectsContext(computeClipRoot, 0, TemporaryClipRects)).rect() != PaintInfo::infiniteRect(); // FIXME: Incorrect for CSS regions.
+    return layer->clipper().backgroundClipRect(ClipRectsContext(computeClipRoot, TemporaryClipRects)).rect() != PaintInfo::infiniteRect();
 }
 
 // Return true if the given layer is a stacking context and has compositing child
 // layers that it needs to clip. In this case we insert a clipping GraphicsLayer
 // into the hierarchy between this layer and its children in the z-order hierarchy.
 bool RenderLayerCompositor::clipsCompositingDescendants(const RenderLayer* layer) const
 {
     return layer->hasCompositingDescendant() && layer->renderer()->hasClipOrOverflowClip();
 }
 
@@ skipping 889 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "Frame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore