Merge 116587 - [chromium] Don't draw when canDraw() is false

Source/WebCore/platform/graphics/chromium/cc/CCThreadProxy.cpp

 /*
  * Copyright (C) 2011 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
@@ skipping 602 matching lines @@
     ASSERT(m_layerTreeHostImpl->layerRenderer());
     if (!m_layerTreeHostImpl->layerRenderer())
         return result;
 
     // FIXME: compute the frame display time more intelligently
     double monotonicTime = monotonicallyIncreasingTime();
     double wallClockTime = currentTime();
 
     m_inputHandlerOnImplThread->animate(monotonicTime);
     m_layerTreeHostImpl->animate(monotonicTime, wallClockTime);
+
+    // This method is called on a forced draw, regardless of whether we are able to produce a frame,
+    // as the calling site on main thread is blocked until its request completes, and we signal
+    // completion here. If canDraw() is false, we will indicate success=false to the caller, but we
+    // must still signal completion to avoid deadlock.
+
+    // We guard prepareToDraw() with canDraw() because it always returns a valid frame, so can only
+    // be used when such a frame is possible. Since drawLayers() depends on the result of
+    // prepareToDraw(), it is guarded on canDraw() as well.
+
     CCLayerTreeHostImpl::FrameData frame;
-    bool drawFrame = m_layerTreeHostImpl->prepareToDraw(frame) || forcedDraw;
+    bool drawFrame = m_layerTreeHostImpl->canDraw() && (m_layerTreeHostImpl->prepareToDraw(frame) || forcedDraw);
     if (drawFrame) {
         m_layerTreeHostImpl->drawLayers(frame);
         result.didDraw = true;
     }
     m_layerTreeHostImpl->didDrawAllLayers(frame);
 
     // Check for a pending compositeAndReadback.
     if (m_readbackRequestOnImplThread) {
-        ASSERT(drawFrame); // This should be a forcedDraw
-        m_layerTreeHostImpl->readback(m_readbackRequestOnImplThread->pixels, m_readbackRequestOnImplThread->rect);
-        m_readbackRequestOnImplThread->success = !m_layerTreeHostImpl->isContextLost();
+        m_readbackRequestOnImplThread->success = false;
+        if (drawFrame) {
+            m_layerTreeHostImpl->readback(m_readbackRequestOnImplThread->pixels, m_readbackRequestOnImplThread->rect);
+            m_readbackRequestOnImplThread->success = !m_layerTreeHostImpl->isContextLost();
+        }
         m_readbackRequestOnImplThread->completion.signal();
         m_readbackRequestOnImplThread = 0;
     }
 
     if (drawFrame)
         result.didSwap = m_layerTreeHostImpl->swapBuffers();
 
     // Process any finish request
     if (m_finishAllRenderingCompletionEventOnImplThread) {
-        ASSERT(drawFrame); // This should be a forcedDraw
         m_layerTreeHostImpl->finishAllRendering();
         m_finishAllRenderingCompletionEventOnImplThread->signal();
         m_finishAllRenderingCompletionEventOnImplThread = 0;
     }
 
     // Tell the main thread that the the newly-commited frame was drawn.
     if (m_nextFrameIsNewlyCommittedFrameOnImplThread) {
         m_nextFrameIsNewlyCommittedFrameOnImplThread = false;
         m_mainThreadProxy->postTask(createCCThreadTask(this, &CCThreadProxy::didCommitAndDrawFrame));
     }
 
-    ASSERT(drawFrame || (!drawFrame && !forcedDraw));
     return result;
 }
 
 void CCThreadProxy::acquireLayerTextures()
 {
     // Called when the main thread needs to modify a layer texture that is used
     // directly by the compositor.
     // This method will block until the next compositor draw if there is a
     // previously committed frame that is still undrawn. This is necessary to
     // ensure that the main thread does not monopolize access to the textures.
@@ skipping 189 matching lines @@
     m_layerTreeHost->deleteContentsTexturesOnImplThread(m_layerTreeHostImpl->contentsTextureAllocator());
     *recreateSucceeded = m_layerTreeHostImpl->initializeLayerRenderer(adoptRef(contextPtr));
     if (*recreateSucceeded) {
         *capabilities = m_layerTreeHostImpl->layerRendererCapabilities();
         m_schedulerOnImplThread->didRecreateContext();
     }
     completion->signal();
 }
 
 } // namespace WebCore