Chromium compositor change implementing page-scale driven pinch-zoom.

cc/CCLayerTreeHostImpl.h

Index: cc/CCLayerTreeHostImpl.h
===================================================================
--- cc/CCLayerTreeHostImpl.h	(revision 157978)
+++ cc/CCLayerTreeHostImpl.h	(working copy)
@@ -44,6 +44,34 @@
     virtual void releaseContentsTexturesOnImplThread() = 0;
 };
 
+// CCPinchZoomViewport models the bounds and offset of the viewport that is used during a pinch-zoom operation.
+// It tracks the layout-space dimensions of the viewport before any applied scale, and then tracks the layout-space
+// coordinates of the viewport respecting the pinch settings.
+class CCPinchZoomViewport {
+public:
+    CCPinchZoomViewport() : m_pageScaleFactor(1) { }
+
+    void setTotalPageScaleFactor(float factor) { m_pageScaleFactor = factor; }
+
+    // Returns the bounds and offset of the scaled and translated viewport to use for pinch-zoom.
+    FloatRect bounds() const;
+    const FloatPoint& scrollDelta() const { return m_pinchViewportScrollDelta; }
+
+    const FloatSize& unpinchedBounds() const { return m_unpinchedBounds; }
+    void setUnpinchedBounds(const FloatSize& bounds) { m_unpinchedBounds = bounds; }
+
+    // Apply the scroll offset in layout space to the offset of the pinch-zoom viewport. The viewport cannot be
+    // scrolled outside of the unpinched bounds. Returns the component of the scroll that is un-applied due to
+    // this constraint.
+    FloatSize applyScroll(FloatSize&);
+
+private:
+    float m_pageScaleFactor;
+    FloatPoint m_pinchViewportScrollDelta;
+
+    FloatSize m_unpinchedBounds;
+};
+
 // CCLayerTreeHostImpl owns the CCLayerImpl tree as well as associated rendering state
 class CCLayerTreeHostImpl : public CCInputHandlerClient,
                             public CCRendererClient,
@@ -152,10 +180,11 @@
     float deviceScaleFactor() const { return m_deviceScaleFactor; }
     void setDeviceScaleFactor(float);
 
-    float pageScale() const { return m_pageScale; }
-    void setPageScaleFactorAndLimits(float pageScale, float minPageScale, float maxPageScale);
+    float pageScaleFactor() const { return m_pageScaleFactor; }
+    void setPageScaleFactorAndLimits(float pageScaleFactor, float minPageScaleFactor, float maxPageScaleFactor);
 
     PassOwnPtr<CCScrollAndScaleSet> processScrollDeltas();
+    WebKit::WebTransformationMatrix implTransform() const;
 
     void startPageScaleAnimation(const IntSize& tragetPosition, bool useAnchor, float scale, double durationSec);
 
@@ -172,6 +201,8 @@
 
     void renderingStats(CCRenderingStats&) const;
 
+    void updateRootScrollLayerImplTransform();
+
     CCFrameRateCounter* fpsCounter() const { return m_fpsCounter.get(); }
     CCDebugRectHistory* debugRectHistory() const { return m_debugRectHistory.get(); }
     CCResourceProvider* resourceProvider() const { return m_resourceProvider.get(); }
@@ -267,10 +298,10 @@
     bool m_contentsTexturesPurged;
     size_t m_memoryAllocationLimitBytes;
 
-    float m_pageScale;
+    float m_pageScaleFactor;
     float m_pageScaleDelta;
     float m_sentPageScaleDelta;
-    float m_minPageScale, m_maxPageScale;
+    float m_minPageScaleFactor, m_maxPageScaleFactor;
 
     SkColor m_backgroundColor;
     bool m_hasTransparentBackground;
@@ -291,6 +322,9 @@
     // rendering and input event hit testing.
     CCLayerList m_renderSurfaceLayerList;
 
+    bool m_applyPinchZoomInImpl;
+    CCPinchZoomViewport m_pinchZoomViewport;
+
     OwnPtr<CCFrameRateCounter> m_fpsCounter;
     OwnPtr<CCDebugRectHistory> m_debugRectHistory;
 };