[Mesa-dev] [PATCH 08/10] i965: Handle rasterizer discard in the clipper rather than SOL on Gen7.

[Eric Anholt]

Kenneth Graunke <kenneth at whitecape.org> writes:

> In order to implement the GL_PRIMITIVES_GENERATED query in a sane
> fashion on our hardware, we can't discard primitives until the clipper.
> The patch after next explains the rationale.
>
> By setting the clipper to REJECT_ALL mode, all primitives get thrown away,
> so rendering is still appropriately disabled.
>
> This may negatively impact performance in the rasterizer discard case,
> but it's unclear how much and this hasn't been observed to be a
> bottleneck in any application we've looked at.  The clipper is the very
> next stage in the pipeline, so I don't think it will be terrible.

I'm tempted to drop a perf_debug() in this and the next patch to remind
us, if some important app starts doing discard, that we could use the
previous rasterizer discard support outside of a GL_PRIMITIVES_GENERATED
query.
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