On 12/14/2011 02:54 PM, Paul Berry wrote: > A common use case for transform feedback is to perform one draw > operation that writes transform feedback output to a buffer, followed > by a second draw operation that consumes that buffer as vertex input. > Since vertex input is consumed at an earlier pipeline stage than > writing transform feedback output, we need to flush the pipeline to > ensure that the transform feedback output is completely written before > the data is consumed. > > In an ideal world, we would do some dependency tracking, so that we > would only flush the pipeline if the next draw call was about to > consume data generated by a previous draw call in the same batch. > However, since we don't have that sort of dependency tracking > infrastructure right now, we just unconditionally flush the buffer > every time glEndTransformFeedback() is called. This will cause a > performance hit compared to the ideal case (since we will sometimes > flush the pipeline unnecessarily), but fortunately the performance hit > will be confined to circumstances where transform feedback is in use. > --- > > Ken pointed out to me on IRC that in my last attempt at this patch, I > neglected to back out bogus the extra argument I added to > brwInitDriverFunctions(). This fixes that. I now believe the only > differences between my proposal and Ken's are: > > - I'm not doing "if (intel->gen < 6) return;" because I believe that > we will need to do this flush on every platform that supports > transform feedback, not just Gen6. > > - I'm calling the function that does the flush > "brw_end_transform_feedback" instead of > "gen6_end_transform_feedback", because it's no longer a > gen6-specific function. > > Hopefully I haven't made any other gaffes this time.
Reviewed-by: Kenneth Graunke <kenn...@whitecape.org> _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
