[Mesa-dev] [PATCH 4/5] glsl: Optionally lower TCS gl_PatchVerticesIn to a uniform.

[Alejandro Piñeiro]

On 09/06/16 05:44, Kenneth Graunke wrote:
> On Wednesday, June 8, 2016 7:45:43 PM PDT Alejandro Piñeiro wrote:
>> On 02/06/16 23:09, Kenneth Graunke wrote:
>>> i965 has no special hardware for this, so the best way to implement
>>> this is to pass it in via a uniform.
>> Is this comment accurate? On the next patch you implement the i965 bits,
>> and you only do the lowering on gen8+, mentioning that you would like to
>> do the same on gen7. So for gen7 it is implemented, but an uniform is
>> not used. Or am I missing something?
> i965 hardware doesn't provide gl_PatchVerticesIn in the TCS thread
> payload, as one might expect.  Currently, we implement it as a
> compile-time constant, and recompile the shader whenever it changes
> (on all generations).
>
> Another way to implement it is to pass it in as a uniform.  This is
> arguably better because it doesn't require recompiling the shader
> whenever you change the number of vertices in your input patch.
>
> The next patch makes it use a uniform and stop recompiling on Gen8+.
>
> However, on Gen7, we also have to loop over all the input vertices
> and emit a URB write message (input release) for every pair.  Because
> we know this at compile time, it's easy to emit the right number of
> URB write messages.  So I left it as is for now (still recompiling).
>
> I could instead rework that to use an actual DO..WHILE loop in the
> shader itself, and then a uniform would work.

Ok, thanks for the further explanation. I was extrapolating "the best
way to implement this" to "the only way  to implement this".

BR

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