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Wed Jul 13 12:12:12 PDT 2011

3. How does the clamping control affect the blending equation?

       RESOLVED:  For fixed-point color buffers, the inputs and the
       result of the blending equation are clamped.  For floating-point
       color buffers, no clamping occurs.

So you want to clamp the colour only before blending but NOT after ?

I suggest you just deactivate automatic clamping and perform it at the
end of the shader instead.
Unless you also need the input of the blend equation to be clamped ...
> My problem now is that I can't find any OpenGL extension that controls
> such a behavior, and also Direct 3D doesn't seems to have such a flag.
> So what I got now is a hardware feature that makes perfectly sense for
> video decoding, but doesn't seems to have an equivalent in the 3D world.
> The situation is very similarly to the "interlaced" textures feature, it
> doesn't makes sense for a 3D app to use such a feature, so mesa doesn't
> have an interface for it, but it would be really (REALLY) useful if you
> want to decode video streams.
> So any ideas guys? Should I just add an additional flag to the blender
> and hope that the other hardware vendors do it in the same way? Or do I
> need to find a workaround to do this without this feature?
> Or maybe anybody know a OpenGL extension that's currently not
> implemented and does exactly what BLEND_CLAMP does?
> Regards,
> Christian. 
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> mesa-dev at

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