[Mesa-dev] [PATCH 2/6] gallium: implement clamping controls (ARB_color_buffer_float)

[Marek Olšák]

On Mon, Mar 21, 2011 at 4:50 PM, Brian Paul <brianp at vmware.com> wrote:

> On 03/21/2011 09:10 AM, Keith Whitwell wrote:
>
>> On Mon, 2011-03-21 at 02:12 +0100, Marek Olšák wrote:
>>
>>> diff --git a/src/gallium/include/pipe/p_state.h
>>> b/src/gallium/include/pipe/p_state.h
>>> index cf6c5b5..f6ad456 100644
>>> --- a/src/gallium/include/pipe/p_state.h
>>> +++ b/src/gallium/include/pipe/p_state.h
>>> @@ -81,6 +81,8 @@ struct pipe_rasterizer_state
>>>  {
>>>     unsigned flatshade:1;
>>>     unsigned light_twoside:1;
>>> +   unsigned clamp_vertex_color:1;
>>> +   unsigned clamp_fragment_color:1;
>>>     unsigned front_ccw:1;
>>>     unsigned cull_face:2;      /**<  PIPE_FACE_x */
>>>     unsigned fill_front:2;     /**<  PIPE_POLYGON_MODE_x */
>>>
>>
>> Don't know if this affects the overall packing of the struct.  Have you
>> been able to check?
>>
>> Otherwise the interface changes look good to me.
>>
>
>
> How do most GPUs handle this clamping?  Is it done with extra shader code
> or is it a discrete operation?  If most hardware does it with shader code,
> maybe we should just do it that way too in Gallium and avoid the new cap
> bits, etc.
>

There is a bit in the CB_COLOR[0-7]_INFO register on R600 which controls
color clamping before blending. I am not sure whether it can be used for
ARB_color_buffer_float or whether it's strictly dependent on the colorbuffer
format.

Christopher, do you happen to know whether NV50/NVC0 has a hardware state
for it too?



> OpenGL 3.0 deprecates the per-vertex and per-fragment clamp controls so
> people will have to do it in their shaders eventually.
>
>
> Re: your comment in rasterizer.rst:
>
>
> XXX: this happens _before_ the geometry shader and thus might not belong
> here.
>
> So is there some question about where the per-vertex clamp is to be done?
>  It seems to me that it should be done after the geometry shader.
>

You're right. I will remove that comment.

Marek
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