[Mesa-dev] [PATCH 0/2 v2] Add support for clip distances in Gallium

[Christoph Bumiller]

On 12/13/2011 09:11 PM, Jose Fonseca wrote:
> 
> 
> ----- Original Message -----
>> This is an updated version of the patch set I sent to the list a few
>> hours
>> ago.  
> 
> 
>> There is now a TGSI property called
>> TGSI_PROPERTY_NUM_CLIP_DISTANCES
>> that drivers can use to determine how many of the 8 available clip
>> distances
>> are actually used by a shader.
> 
> Can't the info in TGSI_PROPERTY_NUM_CLIP_DISTANCES be easily derived from the shader, and queried through src/gallium/auxiliary/tgsi/tgsi_scan.h ?
> 
> 
> Could you also elaborate on why TGSI_SEMANTIC_CLIPDIST is useful for the drivers? I personally don't have nothing against it, but just like to understand why it makes a difference.
> 

Why does TGSI_SEMANTIC_*POSITION* make a difference ?

Right, because the position values are consumed by the fixed function
rasterizer. So are the clip distances.

This is not about pipe_clip_state.ucp but about what this legacy cruft
has to be turned into if GL_CLIP_PLANEi is used instead of GLSL 1.3's
gl_ClipDistance[i].

The same mentality ("What's information useful for ?") cost me
TGSI_SEMANTIC_TEXCOORD and now I have to rely on a hack to make point
coordinate replacement work on nvc0
(http://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/drivers/nvc0/nvc0_program.c#n29).

I'm sorry I'm a bit sensitive on the issue of dropping information at
the gallium threshold.

> Jose
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