i915g: fix incorrect gl_FragCoord value

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 this commit:
afa035031ff9e0c07a2297d864e46c76f7bfff58

The old behavior used the output at index zero, while the new behavior
uses actual zeroes. In the case of gl_FragCoord the output at index
zero happened to be the correct one, so the behavior appeared correct
although the code already had a bug.

Fixed by checking for I915_SEMANTIC_POS when setting up texCoords. If
the generic_mapping is I915_SEMANTIC_POS, look for the
TGSI_SEMANTIC_POSITION instead of a TGSI_SEMANTIC_GENERIC output.

https://bugs.freedesktop.org/show_bug.cgi?id=97477

Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Tested-by: Stéphane Marchesin <marcheu@chromium.org>

diff --git a/src/gallium/drivers/i915/i915_state_derived.c b/src/gallium/drivers/i915/i915_state_derived.c
index 177b85459855eaddd0ab8f9518e73e8a44fe1ce6..dbfbc84c9ebcf9e2b9a65439e756621299f3ab4d 100644 (file)
--- a/src/gallium/drivers/i915/i915_state_derived.c
+++ b/src/gallium/drivers/i915/i915_state_derived.c
@@ -145,7 +145,12 @@ static void calculate_vertex_layout(struct i915_context *i915)
       uint hwtc;
       if (texCoords[i]) {
          hwtc = TEXCOORDFMT_4D;
-         src = draw_find_shader_output(i915->draw, TGSI_SEMANTIC_GENERIC, fs->generic_mapping[i]);
+         if (fs->generic_mapping[i] == I915_SEMANTIC_POS) {
+            src = draw_find_shader_output(i915->draw, TGSI_SEMANTIC_POSITION, 0);
+         }
+         else {
+            src = draw_find_shader_output(i915->draw, TGSI_SEMANTIC_GENERIC, fs->generic_mapping[i]);
+         }
          draw_emit_vertex_attr(&vinfo, EMIT_4F, src);
       }
       else {