[Mesa-dev] [PATCH 9/9] i965/gs: implement EndPrimitive() functionality in the visitor.

[Ian Romanick]

On 09/09/2013 11:31 AM, Paul Berry wrote:
> On 9 September 2013 09:18, Ian Romanick <idr at freedesktop.org
> <mailto:idr at freedesktop.org>> wrote:
> 
>     On 09/09/2013 10:20 AM, Paul Berry wrote:
>     > According to GLSL, the shader may call EndPrimitive() at any point
>     > during its execution, causing the line or triangle strip currently
>     > being output to be terminated and a new strip to be begun.
>     >
>     > This is implemented in gen7 hardware by using one control data bit per
>     > vertex, to indicate whether EndPrimitive() was called after that
>     > vertex was emitted.
>     >
>     > In order to make this work without sacrificing too much efficiency, we
>     > accumulate 32 control data bits at a time in a GRF.  When we have
>     > accumulated 32 bits (or when the shader terminates), we output them to
>     > the appropriate DWORD in the control data header and reset the
>     > accumulator to 0.
>     >
>     > We have to take special care to make sure that EndPrimitive() calls
>     > that occur prior to the first vertex have no effect.
> 
>     Does this cover the general case of EndPrimitive without a preceeding
>     EmitVertex?  Something like:
> 
>          EmitVertex();
>          EndPrimitive();
>          EndPrimitive();
> 
>     And... do we have a test for that? :)
> 
> Yes, that should work fine.  What we do in EndPrimitive() is set the
> appropriate bit in the bitfield, so calling EndPrimitive() again should
> just redundantly set a bit that's already set.
> 
> I don't think we have a test for it.  I'll add that to my list.

Ah, that makes sense.

FWIW, the series is

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>