gistfile1.diff

diff --git a/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.cpp b/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.cpp
index eddb612..63fc33b 100644
--- a/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.cpp
+++ b/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.cpp
@@ -83,7 +83,7 @@ CoordinatedLayerTreeHost::CoordinatedLayerTreeHost(WebPage* webPage)
     , m_isValid(true)
     , m_isPurging(false)
     , m_isFlushingLayerChanges(false)
-    , m_waitingForUIProcess(true)
+    , m_numFramesReadyForUIProcess(0)
     , m_isSuspended(false)
     , m_shouldSyncFrame(false)
     , m_didInitializeRootCompositingLayer(false)
@@ -283,9 +283,15 @@ void CoordinatedLayerTreeHost::setPageOverlayOpacity(PageOverlay*, float value)
     scheduleLayerFlush();
 }
 
+bool CoordinatedLayerTreeHost::shouldFlushLayerChanges() const
+{
+    // We allow one frame to be prerendered before the UI process ask for it.
+    return m_numFramesReadyForUIProcess < 2;
+}
+
 bool CoordinatedLayerTreeHost::flushPendingLayerChanges()
 {
-    if (m_waitingForUIProcess)
+    if (!shouldFlushLayerChanges())
         return false;
 
     TemporaryChange<bool> protector(m_isFlushingLayerChanges, true);
@@ -305,21 +311,13 @@ bool CoordinatedLayerTreeHost::flushPendingLayerChanges()
 
     deleteCompositingLayers();
 
-    if (m_shouldSyncFrame) {
-        didSync = true;
-
-        m_state.contentsSize = roundedIntSize(m_nonCompositedContentLayer->size());
-        m_state.coveredRect = toCoordinatedGraphicsLayer(m_nonCompositedContentLayer.get())->coverRect();
-        m_state.scrollPosition = m_visibleContentsRect.location();
-
-        m_webPage->send(Messages::CoordinatedLayerTreeHostProxy::CommitCoordinatedGraphicsState(m_state));
+    didSync = m_shouldSyncFrame;
 
-        m_state.layersToUpdate.clear();
-        m_state.imagesToUpdate.clear();
-
-        m_waitingForUIProcess = true;
-        m_shouldSyncFrame = false;
-    } else
+    if (m_shouldSyncFrame) {
+        ++m_numFramesReadyForUIProcess;
+        if (m_numFramesReadyForUIProcess == 1)
+            commitFrame();
+    } else if (!m_numFramesReadyForUIProcess)
         unlockAnimations();
 
     if (m_forceRepaintAsyncCallbackID) {
@@ -330,6 +328,23 @@ bool CoordinatedLayerTreeHost::flushPendingLayerChanges()
     return didSync;
 }
 
+void CoordinatedLayerTreeHost::commitFrame()
+{
+    m_state.contentsSize = roundedIntSize(m_nonCompositedContentLayer->size());
+    m_state.coveredRect = toCoordinatedGraphicsLayer(m_nonCompositedContentLayer.get())->coverRect();
+    m_state.scrollPosition = m_visibleContentsRect.location();
+
+    m_webPage->send(Messages::CoordinatedLayerTreeHostProxy::CommitCoordinatedGraphicsState(m_state));
+
+    m_state.layersToUpdate.clear();
+    m_state.imagesToUpdate.clear();
+
+    m_shouldSyncFrame = false;
+
+    for (size_t i = 0; i < m_updateAtlases.size(); ++i)
+        m_updateAtlases[i]->didCommitBuffers();
+}
+
 void CoordinatedLayerTreeHost::createCompositingLayers()
 {
     if (m_layersToCreate.isEmpty())
@@ -481,12 +496,14 @@ void CoordinatedLayerTreeHost::unlockAnimations()
 
 void CoordinatedLayerTreeHost::performScheduledLayerFlush()
 {
-    if (m_isSuspended || m_waitingForUIProcess)
+    if (m_isSuspended || !shouldFlushLayerChanges())
         return;
 
     // We lock the animations while performing layout, to avoid flickers caused by animations continuing in the UI process while
     // the web process layout wants to cancel them.
-    lockAnimations();
+    if (!m_numFramesReadyForUIProcess)
+        lockAnimations();
+
     syncDisplayState();
 
     // We can unlock the animations before flushing if there are no visible changes, for example if there are content updates
@@ -730,10 +747,17 @@ void CoordinatedLayerTreeHost::animationFrameReady()
 
 void CoordinatedLayerTreeHost::renderNextFrame()
 {
-    m_waitingForUIProcess = false;
-    scheduleLayerFlush();
     for (unsigned i = 0; i < m_updateAtlases.size(); ++i)
         m_updateAtlases[i]->didSwapBuffers();
+
+    bool hasPrerenderedFrame = m_numFramesReadyForUIProcess > 1;
+    m_numFramesReadyForUIProcess = 0;
+    if (hasPrerenderedFrame && m_shouldSyncFrame) {
+        commitFrame();
+        ++m_numFramesReadyForUIProcess;
+    }
+
+    scheduleLayerFlush();
 }
 
 void CoordinatedLayerTreeHost::purgeBackingStores()
diff --git a/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.h b/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.h
index 19d07f9..24416e3 100644
--- a/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.h
+++ b/Source/WebKit2/WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.h
@@ -144,6 +144,8 @@ private:
     void syncDisplayState();
     void lockAnimations();
     void unlockAnimations();
+    void commitFrame();
+    bool shouldFlushLayerChanges() const;
 
     void layerFlushTimerFired(WebCore::Timer<CoordinatedLayerTreeHost>*);
 
@@ -193,8 +195,9 @@ private:
     bool m_isPurging;
     bool m_isFlushingLayerChanges;
 
-    bool m_waitingForUIProcess;
+    unsigned m_numFramesReadyForUIProcess;
     bool m_isSuspended;
+
     WebCore::FloatRect m_visibleContentsRect;
 
     LayerTreeContext m_layerTreeContext;