Created attachment 126029 [details] [review]
Patch: Handle I915_SEMANTIC_POS when setting texCoords for gl_FragCoord

On Intel Pineview M hardware, the i915 gallium driver doesn't output the
correct gl_FragCoord. It seems to always have an X coord of 0.0 and a Y coord
of the window's height in pixels, e.g. 600.0f or such.

I believe this is a regression caused in part by commit
afa035031ff9e0c07a2297d864e46c76f7bfff58
(https://lists.freedesktop.org/archives/mesa-commit/2016-January/061181.html)

The old behavior used output zero, while the new behavior uses actual zeroes.
In the case of gl_FragCoord output zero happened to be the correct one.

I've attached a patch that seems to fix the issue for me. I ran the piglit
"quick" tests and observed 17 new tests passing, and one regression. I suspect
the regression is unimportant since it involves derivatives that aren't
implemented for this driver anyway:

"fs-dfdy-accuracy" test failed ... in i915_fpc_translate.c:
case TGSI_OPCODE_DDY:
      /* XXX We just output 0 here */
      debug_printf("Punting DDX/DDX\n");