Initial import attempt, just to play with. Many things disabled/removed

ui/cc/cc/CCOcclusionTracker.h

Index: ui/cc/cc/CCOcclusionTracker.h
diff --git a/ui/cc/cc/CCOcclusionTracker.h b/ui/cc/cc/CCOcclusionTracker.h
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+/*
+ * Copyright (C) 2012 Google 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
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef CCOcclusionTracker_h
+#define CCOcclusionTracker_h
+
+#include "FloatQuad.h"
+#include "Region.h"
+#include "cc/CCLayerIterator.h"
+
+namespace WebCore {
+class CCOverdrawMetrics;
+class CCLayerImpl;
+class CCRenderSurface;
+class LayerChromium;
+class RenderSurfaceChromium;
+
+// 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 RenderSurface, then occlusion on that RenderSurface 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 CCOcclusionTrackerBase {
+    WTF_MAKE_NONCOPYABLE(CCOcclusionTrackerBase);
+public:
+    CCOcclusionTrackerBase(IntRect scissorRectInScreenSpace, bool recordMetricsForFrame);
+
+    // Called at the beginning of each step in the CCLayerIterator's front-to-back traversal.
+    void enterLayer(const CCLayerIteratorPosition<LayerType>&);
+    // Called at the end of each step in the CCLayerIterator's front-to-back traversal.
+    void leaveLayer(const CCLayerIteratorPosition<LayerType>&);
+
+    // Returns true if the given rect in content space for the layer is fully occluded in either screen space or the layer's target surface.
+    bool occluded(const LayerType*, const IntRect& contentRect) const;
+    // Gives an unoccluded sub-rect of |contentRect| in the content space of the layer. Used when considering occlusion for a layer that paints/draws something.
+    IntRect unoccludedContentRect(const LayerType*, const IntRect& contentRect) const;
+
+    // Gives an unoccluded sub-rect of |contentRect| in the content space of the surface. Used when considering occlusion for a contributing surface
+    // that is rendering into another target surface.
+    IntRect unoccludedContributingSurfaceContentRect(const RenderSurfaceType*, bool forReplica, const IntRect& contentRect) const;
+
+    // Report operations for recording overdraw metrics.
+    CCOverdrawMetrics& overdrawMetrics() const { return *m_overdrawMetrics.get(); }
+
+    // Gives the region of the screen that is not occluded by something opaque.
+    Region computeVisibleRegionInScreen() const { return subtract(Region(m_scissorRectInScreenSpace), m_stack.last().occlusionInScreen); }
+
+    void setMinimumTrackingSize(const IntSize& size) { m_minimumTrackingSize = size; }
+
+    static IntSize preferredMinimumTrackingSize() { return IntSize(160, 160); }
+
+    // The following is used for visualization purposes.
+    void setOccludingScreenSpaceRectsContainer(Vector<IntRect>* rects) { m_occludingScreenSpaceRects = rects; }
+
+protected:
+    struct StackObject {
+        StackObject() : surface(0) { }
+        StackObject(const RenderSurfaceType* surface) : surface(surface) { }
+        const RenderSurfaceType* surface;
+        Region occlusionInScreen;
+        Region occlusionInTarget;
+    };
+
+    // The stack holds occluded regions for subtrees in the RenderSurface-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.
+    Vector<StackObject, 1> m_stack;
+
+    // Allow tests to override this.
+    virtual IntRect layerScissorRectInTargetSurface(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 enterTargetRenderSurface(const RenderSurfaceType* 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 finishedTargetRenderSurface(const LayerType*, const RenderSurfaceType* 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 leaveToTargetRenderSurface(const RenderSurfaceType* newTarget);
+
+    // Add the layer's occlusion to the tracked state.
+    void markOccludedBehindLayer(const LayerType*);
+
+    IntRect m_scissorRectInScreenSpace;
+    OwnPtr<CCOverdrawMetrics> m_overdrawMetrics;
+    IntSize m_minimumTrackingSize;
+
+    // This is used for visualizing the occlusion tracking process.
+    Vector<IntRect>* m_occludingScreenSpaceRects;
+};
+
+typedef CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium> CCOcclusionTracker;
+typedef CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface> CCOcclusionTrackerImpl;
+
+}
+#endif // CCOcclusionTracker_h