[Mesa-dev] Mesa (master): draw: fix flat shading and screen-space linear interpolation in clipper

[Olivier Galibert]

On Mon, Jul 02, 2012 at 06:44:37AM -0700, Jose Fonseca wrote:
> But I think that this fix is too ad-hoc, and I suspect it may
> introduce other regressions.
> 
> If I understood the problem correctly, the issue here is that some
> drivers want system values in floats, others want in
> integers. Right?

It's slightly more perverted than that.  GLSL 1.20 says "if a value is
an integer, it will be forced into a float but don't expect more than
16 bits precision", while 1.30 has native integers.  Next to that,
some extensions (and gl versions) introduce integer system values but
require native integer support to have them implemented.  The glsl
parser handles that correctly by adding the needed type conversions
when accessing these values from a 1.20 shader.

But then in mesa someone decided to extend the extensions and
implement things like draw_instanced without native integer support.
st_glsl_to_tgsi behaves very differently when native integers aren't
there, forcing evey type to float and ignoring the integer->float type
conversions.  What tells you that is that the requested type (dtype)
is float while the system value itself is integer.

In fact, I suspect the conversion code is ill-advised.  It was picked
up from the previous code, but actually it should only check that the
types are identical or that float is requested for an int, and bitch
otherwise.  Still, it would be interesting to know if that patch works
for i915g, even if we make things more cranky afterwards.

  OG.