On Oct 11, 2010, at 3:35 PM, James Robinson wrote: > On Mon, Oct 11, 2010 at 3:15 PM, Chris Marrin <cmar...@apple.com> wrote: > > For accelerated 2D rendering we created a class called DrawingBuffer. This > encapsulates the accelerated drawing surface (usually in the GPU) and the > compositing layer used to display that surface on the page. The drawing > surface (which is called a Framebuffer Object or FBO) is allocated by > GraphicsContext3D, so DrawingBuffer needs a reference to that. Currently this > is a weak reference. DrawingBuffer has a ::create() method and you pass the > GraphicsContext3D to that method. > > If you destroy the GraphicsContext3D, DrawingBuffer has a stale pointer. If > you were to try to destroy the DrawingBuffer it would attempt to use that > pointer (to destroy its FBO) and crash or worse. Currently we have an > implicit policy that you should never destroy a GraphicsContext3D before its > DrawingBuffers are all destroyed. That works fine in the current use case, > CanvasRenderingContext2D. And we can follow that same policy when in the > future when we use DrawingBuffer in WebGLRenderingContext. > > My concern is that this sort of implicit policy can lead to errors in the > future when other potential clients of these classes use them. So I posted > https://bugs.webkit.org/show_bug.cgi?id=47501. In that patch I move the > creation of DrawingBuffer to the GraphicsContext3D and keep back pointers to > all the DrawingBuffers allocated so they can be cleaned up when > GraphicsContext3D is destroyed. In talking to James R. he's concerned this > adds unnecessary complexity and would rather stick with the implicit policy. > > So is this something I should be concerned about, or is an implicit policy > sufficient in this case? > > Before somebody suggests it, I think Chris and I are in agreement that > neither GraphicsContext3D nor DrawingBuffer should be RefCounted. They both > have clear single-ownership semantics.
True, although Simon and I just chatted and he pointed out that Refcounting both classes would solve this problem. The fact that GraphicsContext3D wouldn't need a back pointer to DrawingBuffer means we wouldn't have any circular references. I don't think the overhead of refcounting is an issue here, so maybe that would be a simpler solution? ----- ~Chris cmar...@apple.com _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
