[Mesa-dev] [PATCH 2/2] i965 gen6: Implement rasterizer discard.

[Paul Berry]

On 16 December 2011 19:53, Kenneth Graunke <kenneth at whitecape.org> wrote:

> On 12/14/2011 11:59 AM, Paul Berry wrote:
> > This patch enables rasterizer discard functionality (a part of
> > transform feedback) in Gen6, by generating an alternate GS program
> > when rasterizer discard is active.  Instead of forwarding vertices
> > down the pipeline, the alternate GS program uses a URB Write message
> > to deallocate the URB entry that was allocated by FF sync and
> > terminate the thread.
> >
> > Note: parts of the Sandy Bridge PRM seem to imply that we could do
> > this more efficiently, by clearing the GEN6_GS_RENDERING_ENABLE bit,
> > and not allocating a URB entry at all.  However, it's not clear how we
> > are supposed to terminate the thread if we do that.  Volume 2 part 1,
> > section 4.5.4, says "GS threads must terminate by sending a URB_WRITE
> > message with the EOT and Complete bits set.", and my experiments so
> > far confirm that.
> > ---
> >
> > This patch needs to be applied on top of the series "[PATCH 0/8] i965
> > gen6: Initial implementation of transform feedback.", which is still
> > under review on the mailing list.
>
> Assuming the dirty bit gets sorted out,
> Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
>
>
Thanks, Ken.  Fortunately, this patch is independent of the dirty bit stuff
(since this patch adds a use of ctx->TransformFeedback.RasterDiscard to
brw_gs_prog, which already depends on _NEW_TRANSFORM).  So I'll push it as
soon as the remaining discussion on my main transform feedback series is
resolved.
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