[Piglit] GL_LIGHTING test

[Brian Paul]

On 08/11/2010 10:01 AM, Michal Suchanek wrote:
> Hello
>
> I experience issues with some 3D applications rendering odd (too
> bright) on a r600.
>
> Going through mesa demos I noticed that GL_LIGHTING produces different
> result on r600 than other cards making the bright area larger.
>
> I wrote a test that checks for this difference.
>
> For me it fails on r600, r600g and llvmpipe and succeeds on swrast. It
> should also succeed on r300 or i915 which render the demo much like
> swrast but I did not actually run the test on them.
>
> The test can be found at
> http://repo.or.cz/w/piglit/hramrach.git/shortlog/refs/heads/wip
>
> I would like to get a test for this issue into piglit so that it's
> easy to check.
>
> If the test is inadequate please specify how it should be improved.

I took a quick look and it appears that gallium/softpipe/llvmpipe are 
correct but swrast is wrong.  NVIDIA's driver agrees with gallium too.

I think the issue is the light source is positioned behind the object 
so there should be no diffuse contribution to the final color.  I 
don't know why swrast (tnl, actually) is producing non-zero diffuse 
lighting in this case.

-Brian