Cache the absolute bounding box rect on RenderLayer.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 108 matching lines @@
     , m_hasVisibleContent(false)
     , m_visibleDescendantStatusDirty(false)
     , m_hasVisibleDescendant(false)
     , m_hasVisibleNonLayerContent(false)
     , m_isPaginated(false)
     , m_3DTransformedDescendantStatusDirty(true)
     , m_has3DTransformedDescendant(false)
     , m_containsDirtyOverlayScrollbars(false)
     , m_canSkipRepaintRectsUpdateOnScroll(renderer->isTableCell())
     , m_hasFilterInfo(false)
+    , m_needsToRecomputeBounds(true)
     , m_renderer(renderer)
     , m_parent(0)
     , m_previous(0)
     , m_next(0)
     , m_first(0)
     , m_last(0)
     , m_staticInlinePosition(0)
     , m_staticBlockPosition(0)
     , m_enclosingPaginationLayer(0)
     , m_3dRenderingContextRoot(0)
@@ skipping 1065 matching lines @@
 {
     const RenderLayer* curr = (includeSelf == IncludeSelf) ? this : parent();
     for (; curr; curr = curr->parent()) {
         if (curr->requiresFullLayerImageForFilters())
             return const_cast<RenderLayer*>(curr);
     }
 
     return 0;
 }
 
+void RenderLayer::clearNeedsToRecomputeBounds()
+{
+    m_needsToRecomputeBounds = false;
+}
+
+void RenderLayer::setAbsoluteBoundingBox(const IntRect& rect)
+{
+    m_absoluteBoundingBox = rect;
+    clearNeedsToRecomputeBounds();
+}
+
 void RenderLayer::setCompositingReasons(CompositingReasons reasons, CompositingReasons mask)
 {
     ASSERT(reasons == (reasons & mask));
     if ((m_compositingProperties.compositingReasons & mask) == (reasons & mask))
         return;
     m_compositingProperties.compositingReasons = (reasons & mask) | (m_compositingProperties.compositingReasons & ~mask);
     m_clipper.setCompositingClipRectsDirty();
 }
 
 bool RenderLayer::hasAncestorWithFilterOutsets() const
@@ skipping 2187 matching lines @@
     LayoutPoint delta;
     if (offsetFromRoot)
         delta = *offsetFromRoot;
     else
         convertToLayerCoords(ancestorLayer, delta);
 
     result.moveBy(delta);
     return result;
 }
 
-IntRect RenderLayer::absoluteBoundingBox() const
-{
-    return pixelSnappedIntRect(boundingBox(root()));
-}
-
 LayoutRect RenderLayer::calculateLayerBounds(const RenderLayer* ancestorLayer, const LayoutPoint* offsetFromRoot, CalculateLayerBoundsFlags flags) const
 {
     if (!isSelfPaintingLayer())
         return LayoutRect();
 
     // FIXME: This could be improved to do a check like hasVisibleNonCompositingDescendantLayers() (bug 92580).
     if ((flags & ExcludeHiddenDescendants) && this != ancestorLayer && !hasVisibleContent() && !hasVisibleDescendant())
         return LayoutRect();
 
     RenderLayerModelObject* renderer = this->renderer();
@@ skipping 514 matching lines @@
             didPaintWithFilters = true;
         updateFilters(oldStyle, renderer()->style());
     }
 
     compositor()->updateStyleDeterminedCompositingReasons(this);
 
     // FIXME: Remove incremental compositing updates after fixing the chicken/egg issues
     // https://code.google.com/p/chromium/issues/detail?id=343756
     DisableCompositingQueryAsserts disabler;
 
+    // FIXME: We could avoid doing this ancestor walk by keeping a childNeedsToRecomputeBounds bit
+    // and using that along with needsToRecomputeBounds to set this bit in a later layer tree walk
+    // e.g. during assignLayersToBackings or computeCompositingRequirements.
     if (RenderLayer* compositingLayer = enclosingCompositingLayer())
         compositingLayer->compositedLayerMapping()->setNeedsGeometryUpdate();
+    // FIXME: We only need to set this if something changed that can change our absolute bounding rect.
+    m_needsToRecomputeBounds = true;
 
     const RenderStyle* newStyle = renderer()->style();
 
     compositor()->updateLayerCompositingState(this, RenderLayerCompositor::UseChickenEggHacks);
     // FIXME: this compositing logic should be pushed into the compositing code, not here.
     if (needsCompositingLayersRebuiltForClip(oldStyle, newStyle)
         || needsCompositingLayersRebuiltForOverflow(oldStyle, newStyle)
         || needsCompositingLayersRebuiltForFilters(oldStyle, newStyle, didPaintWithFilters)
         || needsCompositingLayersRebuiltForBlending(oldStyle, newStyle)) {
         compositor()->setCompositingLayersNeedRebuild();
@@ skipping 182 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif