Compositor hit test performance improvement

Source/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2277 matching lines @@
             currentLayer = container->enclosingLayer();
             if (currentLayer && currentLayer->renderer() != container)
                 layerOffset.move(container->offsetFromAncestorContainer(currentLayer->renderer()));
         } else {
             currentLayer = enclosingLayer();
         }
         if (!currentLayer)
             return;
     }
 
-    this->addLayerHitTestRects(layerRects, currentLayer, layerOffset);
+    this->addLayerHitTestRects(layerRects, currentLayer, layerOffset, LayoutRect());
 }
 
-void RenderObject::addLayerHitTestRects(LayerHitTestRects& layerRects, const RenderLayer* currentLayer, const LayoutPoint& layerOffset) const
+void RenderObject::addLayerHitTestRects(LayerHitTestRects& layerRects, const RenderLayer* currentLayer, const LayoutPoint& layerOffset, const LayoutRect& containerRect) const
 {
     ASSERT(currentLayer);
     ASSERT(currentLayer == this->enclosingLayer());
 
+    // Compute the rects for this renderer only and add them to the results.
+    // Note that we could avoid passing the offset and instead adjust each result, but this
+    // seems slightly simpler.
+    Vector<LayoutRect> ownRects;
+    LayoutRect newContainerRect;
+    computeSelfHitTestRects(ownRects, layerOffset);
+
+    LayerHitTestRects::iterator iter = layerRects.find(currentLayer);
+    if (iter == layerRects.end())
+        iter = layerRects.add(currentLayer, Vector<LayoutRect>()).iterator;
+    for (size_t i = 0; i < ownRects.size(); i++) {
+        if (!containerRect.contains(ownRects[i])) {
+            iter->value.append(ownRects[i]);
+            if (newContainerRect.isEmpty())
+                newContainerRect = ownRects[i];
+        }
+    }
+    if (newContainerRect.isEmpty())
+        newContainerRect = containerRect;
+
     // If it's possible for children to have rects outside our bounds, then we need to descend into
     // the children and compute them.
     // Ideally there would be other cases where we could detect that children couldn't have rects
     // outside our bounds and prune the tree walk.
     // Note that we don't use Region here because Union is O(N) - better to just keep a list of
     // partially redundant rectangles. If we find examples where this is expensive, then we could
     // rewrite Region to be more efficient. See https://bugs.webkit.org/show_bug.cgi?id=100814.
     if (!isRenderView()) {
         for (RenderObject* curr = firstChild(); curr; curr = curr->nextSibling()) {
-            curr->addLayerHitTestRects(layerRects, currentLayer,  layerOffset);
+            curr->addLayerHitTestRects(layerRects, currentLayer,  layerOffset, newContainerRect);
         }
     }
-
-    // Compute the rects for this renderer only and add them to the results.
-    // Note that we could avoid passing the offset and instead adjust each result, but this
-    // seems slightly simpler.
-    Vector<LayoutRect> ownRects;
-    computeSelfHitTestRects(ownRects, layerOffset);
-
-    LayerHitTestRects::iterator iter = layerRects.find(currentLayer);
-    if (iter == layerRects.end())
-        layerRects.add(currentLayer, ownRects);
-    else
-        iter->value.append(ownRects);
 }
 
 bool RenderObject::isRooted(RenderView** view) const
 {
     const RenderObject* o = this;
     while (o->parent())
         o = o->parent();
 
     if (!o->isRenderView())
         return false;
@@ skipping 954 matching lines @@
 {
     if (object1) {
         const WebCore::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif