Simply rules for compositing fixed position elements

Source/core/rendering/compositing/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 355 matching lines @@
     }
 
     // Inform the inspector that the layer tree has changed.
     if (m_renderView.frame()->isMainFrame())
         InspectorInstrumentation::layerTreeDidChange(m_renderView.frame());
 }
 
 bool RenderLayerCompositor::allocateOrClearCompositedLayerMapping(RenderLayer* layer, const CompositingStateTransitionType compositedLayerUpdate)
 {
     bool compositedLayerMappingChanged = false;
-    bool nonCompositedReasonChanged = updateLayerIfViewportConstrained(layer);
 
     // FIXME: It would be nice to directly use the layer's compositing reason,
     // but allocateOrClearCompositedLayerMapping also gets called without having updated compositing
     // requirements fully.
     switch (compositedLayerUpdate) {
     case AllocateOwnCompositedLayerMapping:
         ASSERT(!layer->hasCompositedLayerMapping());
         setCompositingModeEnabled(true);
 
         // If we need to repaint, do so before allocating the compositedLayerMapping and clearing out the groupedMapping.
@@ skipping 49 matching lines @@
         RenderLayerCompositor* innerCompositor = frameContentsCompositor(toRenderPart(layer->renderer()));
         if (innerCompositor && innerCompositor->staleInCompositingMode())
             innerCompositor->updateRootLayerAttachment();
     }
 
     if (compositedLayerMappingChanged)
         layer->clipper().clearClipRectsIncludingDescendants(PaintingClipRects);
 
     // If a fixed position layer gained/lost a compositedLayerMapping or the reason not compositing it changed,
     // the scrolling coordinator needs to recalculate whether it can do fast scrolling.
-    if (compositedLayerMappingChanged || nonCompositedReasonChanged) {
+    if (compositedLayerMappingChanged) {
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->frameViewFixedObjectsDidChange(m_renderView.frameView());
     }
 
-    return compositedLayerMappingChanged || nonCompositedReasonChanged;
-}
-
-bool RenderLayerCompositor::updateLayerIfViewportConstrained(RenderLayer* layer)
-{
-    RenderLayer::ViewportConstrainedNotCompositedReason viewportConstrainedNotCompositedReason = RenderLayer::NoNotCompositedReason;
-    m_compositingReasonFinder.requiresCompositingForPositionFixed(layer->renderer(), layer, &viewportConstrainedNotCompositedReason);
-
-    if (layer->viewportConstrainedNotCompositedReason() != viewportConstrainedNotCompositedReason) {
-        ASSERT(viewportConstrainedNotCompositedReason == RenderLayer::NoNotCompositedReason || layer->renderer()->style()->position() == FixedPosition);
-        layer->setViewportConstrainedNotCompositedReason(viewportConstrainedNotCompositedReason);
-        return true;
-    }
-    return false;
+    return compositedLayerMappingChanged;
 }
 
 void RenderLayerCompositor::repaintOnCompositingChange(RenderLayer* layer)
 {
     // If the renderer is not attached yet, no need to repaint.
     if (layer->renderer() != &m_renderView && !layer->renderer()->parent())
         return;
 
     layer->repainter().repaintIncludingNonCompositingDescendants();
 }
@@ skipping 687 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink