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

cc/CCThreadProxy.cpp

Index: cc/CCThreadProxy.cpp
===================================================================
--- cc/CCThreadProxy.cpp	(revision 157978)
+++ cc/CCThreadProxy.cpp	(working copy)
@@ -467,6 +467,7 @@
     m_pendingBeginFrameRequest = adoptPtr(new BeginFrameAndCommitState());
     m_pendingBeginFrameRequest->monotonicFrameBeginTime = monotonicallyIncreasingTime();
     m_pendingBeginFrameRequest->scrollInfo = m_layerTreeHostImpl->processScrollDeltas();
+    m_pendingBeginFrameRequest->implTransform = m_layerTreeHostImpl->implTransform();

[Jeff Timanus, 2012/09/21 18:10:01]

I pass the impl-transform from the pinch state to the main thread at this point.
 This transform is then installed on the fist scrollable layer before the call
to CalculateDrawTransforms(...) in CCLayerTreeHost.

This ensures that only those tiles that are needed are prepared, as opposed to
all the tiles covering the red box.

I think my variable naming here is not the best.  I chose impl-transform,
because that's where this transformation is installed on the impl side, but I
think for the main thread, it would be clearer if this name indicated that it
was specific to the pinch zoom state, and only applied to the root scroll layer.
 Thoughts?

     m_pendingBeginFrameRequest->memoryAllocationLimitBytes = m_layerTreeHostImpl->memoryAllocationLimitBytes();
     m_layerTreeHost->getEvictedContentTexturesBackings(m_pendingBeginFrameRequest->evictedContentsTexturesBackings);
 
@@ -511,6 +512,7 @@
     // FIXME: technically, scroll deltas need to be applied for dropped commits as well.
     // Re-do the commit flow so that we don't send the scrollInfo on the BFAC message.
     m_layerTreeHost->applyScrollAndScale(*request->scrollInfo);
+    m_layerTreeHost->setImplTransform(request->implTransform);
 
     if (!m_inCompositeAndReadback && !m_layerTreeHost->visible()) {
         m_commitRequested = false;