[Mesa-dev] gl_FragCoord / FBOs vs mesa/st

[Marek Olšák]

Hi,

the attached patch fixes this gl_FragCoord madness. It uses a fragment
shader constant to do the transformation and the constant is set
transparently with other STATE_* constants in Mesa core. The changes are
quite small. Please review.

Best regards
Marek

On Mon, Nov 15, 2010 at 10:28 AM, Keith Whitwell <keithw at vmware.com> wrote:

> On Sun, 2010-11-14 at 20:18 -0800, Dave Airlie wrote:
> > Eric just checked in a test into piglit that tests that the
> > gl_FragCoord works the right way up for FBOs,
> >
> > Now all the gallium drivers fail this currently and fixing it creates
> > an ugly linkage between the currently bound buffer and the fragment
> > shader, since if you swap from an FBO to rendering to the front
> > buffer, you need recompile the fragment shader to emit a proper wpos
> > manipulation. Just wondering if anyone sees a nicer way to do this,
> > than caching frag shaders with some sort of key in the state tracker,
> > (which is pretty much what 965 has done.).
>
> I guess the other possibility would be to have a couple of constants in
> the constant buffer which get factored into the fragcood calculation in
> such a way as to effect a flip based on their value, eg:
>
>   fc' = fc * const[0].x + const[0].y
>
> where const[0] is either
> -> {1, 0} for non-flipped
> -> {-1, fb_height} for flipped
>
> Keith
>
>
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