[Mesa-dev] [PATCH] st/mesa: fix transform feedback of unsubscripted gl_ClipDistance array

[Bryan Cain]

On 6/16/2012 5:43 PM, Marcin Slusarz wrote:
> gl_ClipDistance needs special treatment in form of lowering pass
> which transforms gl_ClipDistance representation from float[] to
> vec4[]. There are 2 implementations - at glsl linker level (enabled
> by LowerClipDistance option) and at glsl_to_tgsi level (enabled
> unconditionally for gallium drivers). Second implementation is
> incomplete - it does not take into account transform feedback (see
> commit 642e5b413e0890b2070ba78fde42db381eaf02e5 "mesa: Fix transform
> feedback of unsubscripted gl_ClipDistance array" for details).
>
> There are 2 possible fixes:
> - adding transform feedback support into glsl_to_tgsi version
> - ripping gl_ClipDistance support from glsl_to_tgsi and enabling
>    gl_ClipDistance lowering on glsl linker side
>
> This patch implements 2nd option. All it does is:
> - reverts most of the commit 59be691638200797583bce39a83f641d30d97492
>    "st/mesa: add support for gl_ClipDistance"
> - changes LowerClipDistance to true
>
> Fixes Piglit tests "EXT_transform_feedback/builtin-varyings
> gl_ClipDistance[{2,3,4,5,6,7,8}]-no-subscript" on nv50.
> ---

I can't say I know much about how transform feedback works, but is there 
a reason that the first fix would be difficult?  It seems like a waste 
to not take advantage of hardware support for clip distances because the 
current implementation isn't complete.

-Bryan