The size of the m_clipLayer created by RenderLayerCompositor doesn't get updated when the layoutWidth of the associated frameView changes. This can happen if for example the content of the page changes and the scrollbar is removed. It's fairly easy to reproduce the problem in Chromium by visiting: http://www.youtube.com/watch?v=PEZiZ9G-gNs and switching the video over to full screen mode (note that in this case the video doesn't expand to cover the entire screen, it just stretches to use the entire window size). You'll notice that the video doesn't render in the area that used to be occupied by the scroll bar. What happens here is that in non-fullscreen mode the page has a scrollbar whereas in fullscreen mode it doesn't. Switching between the two modes effectively changes the layoutWidth of the FrameView. If you change the window size the problem goes away. (Safari on mac doesn't exhibit the issue in this particular case as it handles scrolling differently and the RenderLayerCompositor doesn't create a clip or scroll layer) The problem appears to be that when RenderLayerCompositor::rebuildCompositingLayerTree() is called, even though the size of m_rootPlayerformLayer is set correctly, the clip layer size doesn't get updated. The most natural place to update the clip layer size appears to be in RenderLayerCompositor::updateRootLayerPosition.
Created attachment 83577 [details] Patch
Comment on attachment 83577 [details] Patch Is it possible to make a layout test with pixel results that test this?
(In reply to comment #2) > (From update of attachment 83577 [details]) > Is it possible to make a layout test with pixel results that test this? A layout test would be useful here. Ideally I'd like to find a way to programmatically change the frame's layout width that doesn't involve scrollbars. This would make the test useful for safari mac as well. Any ideas?
Committed r79699: <http://trac.webkit.org/changeset/79699>