[Mesa-dev] [PATCH] st/mesa: add a fallback for clear_with_quad when no vs_layer

[Marek Olšák]

Hi Jose,

First of all, sorry for breaking Draw yesterday.

On Sun, Nov 16, 2014 at 2:57 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
>> Fun fact -- llvmpipe also needs this.
>
> I think this is because this functionality was developed with D3D10 in mind, and
>
> http://msdn.microsoft.com/en-gb/library/windows/desktop/bb509647.aspx
>
> states that SV_RenderTargetArrayIndex "an be written from the geometry shader and read by the pixel shader."

There's also the OpenGL extension AMD_vertex_shader_layer which is
supported by all GS-capable Mesa drivers except for nouveau and
llvmpipe I think.

>
>
> BTW, coding these helper shaders as text is not a great idea IMO:
>
> - The tgsi_parse thing was written for debugging purposes mainly.
>
> - Whenever there are TGSI interface changes, any breakage with ureg will cause compile errors, where as it will only be detected at runtime with TGSI
>
> - ureg module makes it really easy to write shaders.  It's not really much more work.

tgsi_parse is something else. Did you mean tgsi_text_translate? I
don't like using ureg for helper shaders unless I have to. Shaders
written with ureg are harder to read and the code is longer. I've been
thinking of rewriting all simple shaders to text.

Marek