[Mesa-dev] [PATCH] i915g: fix incorrect gl_FragCoord value

[Nicholas Bishop]

From: Nicholas Bishop <nicholasbishop at gmail.com>

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
---
 src/gallium/drivers/i915/i915_state_derived.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/i915/i915_state_derived.c b/src/gallium/drivers/i915/i915_state_derived.c
index 177b854..dbfbc84 100644
--- 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 {
-- 
2.7.4