i915g: gl_FragCoord is always (0.0, max_y)
Submitted by Nicholas Bishop
Assigned to Default DRI bug account
Created attachment 126029 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 afa03503 (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");
Patch 126029, "Patch: Handle I915_SEMANTIC_POS when setting texCoords for gl_FragCoord":