cc: Make occlusion tracker always work in target space.

cc/occlusion_tracker.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OCCLUSION_TRACKER_H_
 #define CC_OCCLUSION_TRACKER_H_
 
 #include "base/basictypes.h"
 #include "cc/cc_export.h"
 #include "cc/layer_iterator.h"
 #include "cc/region.h"
 #include "ui/gfx/rect.h"
 
 namespace cc {
 class OverdrawMetrics;
 class LayerImpl;
 class RenderSurfaceImpl;
 class Layer;
 class RenderSurface;
 
 // This class is used to track occlusion of layers while traversing them in a front-to-back order. As each layer is visited, one of the
 // methods in this class is called to notify it about the current target surface.
 // Then, occlusion in the content space of the current layer may be queried, via methods such as occluded() and unoccludedContentRect().
 // If the current layer owns a RenderSurfaceImpl, then occlusion on that RenderSurfaceImpl may also be queried via surfaceOccluded() and surfaceUnoccludedContentRect().
 // Finally, once finished with the layer, occlusion behind the layer should be marked by calling markOccludedBehindLayer().
 template<typename LayerType, typename RenderSurfaceType>
 class CC_EXPORT OcclusionTrackerBase {
 public:
-    OcclusionTrackerBase(gfx::Rect rootTargetRect, bool recordMetricsForFrame);
+    OcclusionTrackerBase(gfx::Rect screenSpaceClipRect, bool recordMetricsForFrame);
     ~OcclusionTrackerBase();
 
     // Called at the beginning of each step in the LayerIterator's front-to-back traversal.
     void enterLayer(const LayerIteratorPosition<LayerType>&);
     // Called at the end of each step in the LayerIterator's front-to-back traversal.
     void leaveLayer(const LayerIteratorPosition<LayerType>&);
 
     // Returns true if the given rect in content space for a layer is fully occluded in either screen space or the layer's target surface.  |renderTarget| is the contributing layer's render target, and |drawTransform|, |transformsToTargetKnown| and |clippedRectInTarget| are relative to that.
     bool occluded(const LayerType* renderTarget, const gfx::Rect& contentRect, const gfx::Transform& drawTransform, bool implDrawTransformIsUnknown, const gfx::Rect& clippedRectInTarget, bool* hasOcclusionFromOutsideTargetSurface = 0) const;
     // Gives an unoccluded sub-rect of |contentRect| in the content space of a layer. Used when considering occlusion for a layer that paints/draws something. |renderTarget| is the contributing layer's render target, and |drawTransform|, |transformsToTargetKnown| and |clippedRectInTarget| are relative to that.
     gfx::Rect unoccludedContentRect(const LayerType* renderTarget, const gfx::Rect& contentRect, const gfx::Transform& drawTransform, bool implDrawTransformIsUnknown, const gfx::Rect& clippedRectInTarget, bool* hasOcclusionFromOutsideTargetSurface = 0) const;
 
     // Gives an unoccluded sub-rect of |contentRect| in the content space of the renderTarget owned by the layer.
     // Used when considering occlusion for a contributing surface that is rendering into another target.
     gfx::Rect unoccludedContributingSurfaceContentRect(const LayerType*, bool forReplica, const gfx::Rect& contentRect, bool* hasOcclusionFromOutsideTargetSurface = 0) const;
 
     // Report operations for recording overdraw metrics.
     OverdrawMetrics& overdrawMetrics() const { return *m_overdrawMetrics.get(); }
 
     // Gives the region of the screen that is not occluded by something opaque.
-    Region computeVisibleRegionInScreen() const { return SubtractRegions(m_rootTargetRect, m_stack.back().occlusionInScreen); }
+    Region computeVisibleRegionInScreen() const {
+        DCHECK(!m_stack.back().target->parent());
+        return SubtractRegions(m_screenSpaceClipRect, m_stack.back().occlusionFromInsideTarget);
+    }
 
     void setMinimumTrackingSize(const gfx::Size& size) { m_minimumTrackingSize = size; }
 
     // The following is used for visualization purposes. 
     void setOccludingScreenSpaceRectsContainer(std::vector<gfx::Rect>* rects) { m_occludingScreenSpaceRects = rects; }
     void setNonOccludingScreenSpaceRectsContainer(std::vector<gfx::Rect>* rects) { m_nonOccludingScreenSpaceRects = rects; }
 
 protected:
     struct StackObject {
         StackObject() : target(0) { }
         StackObject(const LayerType* target) : target(target) { }
         const LayerType* target;
-        Region occlusionInScreen;
-        Region occlusionInTarget;
+        Region occlusionFromOutsideTarget;
+        Region occlusionFromInsideTarget;
     };
 
     // The stack holds occluded regions for subtrees in the RenderSurfaceImpl-Layer tree, so that when we leave a subtree we may
     // apply a mask to it, but not to the parts outside the subtree.
     // - The first time we see a new subtree under a target, we add that target to the top of the stack. This can happen as a layer representing itself, or as a target surface.
     // - When we visit a target surface, we apply its mask to its subtree, which is at the top of the stack.
     // - When we visit a layer representing itself, we add its occlusion to the current subtree, which is at the top of the stack.
     // - When we visit a layer representing a contributing surface, the current target will never be the top of the stack since we just came from the contributing surface.
     // We merge the occlusion at the top of the stack with the new current subtree. This new target is pushed onto the stack if not already there.
     std::vector<StackObject> m_stack;
 
     // Allow tests to override this.
     virtual gfx::Rect layerClipRectInTarget(const LayerType*) const;
 
 private:
     // Called when visiting a layer representing itself. If the target was not already current, then this indicates we have entered a new surface subtree.
     void enterRenderTarget(const LayerType* newTarget);
 
     // Called when visiting a layer representing a target surface. This indicates we have visited all the layers within the surface, and we may
     // perform any surface-wide operations.
     void finishedRenderTarget(const LayerType* finishedTarget);
 
     // Called when visiting a layer representing a contributing surface. This indicates that we are leaving our current surface, and
     // entering the new one. We then perform any operations required for merging results from the child subtree into its parent.
     void leaveToRenderTarget(const LayerType* newTarget);
 
     // Add the layer's occlusion to the tracked state.
     void markOccludedBehindLayer(const LayerType*);
 
-    gfx::Rect m_rootTargetRect;
+    gfx::Rect m_screenSpaceClipRect;
     scoped_ptr<OverdrawMetrics> m_overdrawMetrics;
     gfx::Size m_minimumTrackingSize;
 
     // This is used for visualizing the occlusion tracking process.
     std::vector<gfx::Rect>* m_occludingScreenSpaceRects;
     std::vector<gfx::Rect>* m_nonOccludingScreenSpaceRects;
 
     DISALLOW_COPY_AND_ASSIGN(OcclusionTrackerBase);
 };
 
 typedef OcclusionTrackerBase<Layer, RenderSurface> OcclusionTracker;
 typedef OcclusionTrackerBase<LayerImpl, RenderSurfaceImpl> OcclusionTrackerImpl;
 #if !defined(COMPILER_MSVC)
 extern template class OcclusionTrackerBase<Layer, RenderSurface>;
 extern template class OcclusionTrackerBase<LayerImpl, RenderSurfaceImpl>;
 #endif
 
 }  // namespace cc
 
 #endif  // CC_OCCLUSION_TRACKER_H_