Mesa (mesa_7_4_branch): i965: Fix fog coordinate g,b, a values when glFrontFacing isn't used.

[Ian Romanick]

Module: Mesa
Branch: mesa_7_4_branch
Commit: 0e5d1f43af953ee344777ce67a2e87544f481302
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=0e5d1f43af953ee344777ce67a2e87544f481302

Author: Eric Anholt <eric at anholt.net>
Date:   Mon Mar 23 22:35:03 2009 -0700

i965: Fix fog coordinate g,b,a values when glFrontFacing isn't used.

Previously, we would sample (f,glFrontFacing,undef,undef) instead of the
(f,0,0,1) that fragment.fogcoord is supposed to return.  Due to
glFrontFacing's presence in FOGC.y, we'll still give bad results there when
glFrontFacing is used.

Bug #19122, piglit testcase fp-fog.
(cherry picked from commit 411d913ccea362dbd75411266d7abb685214ee93)

---

 src/mesa/drivers/dri/i965/brw_wm_fp.c |   50 +++++++++++++++++++++++++++++++++
 1 files changed, 50 insertions(+), 0 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_wm_fp.c b/src/mesa/drivers/dri/i965/brw_wm_fp.c
index de867d6..3b2883d 100644
--- a/src/mesa/drivers/dri/i965/brw_wm_fp.c
+++ b/src/mesa/drivers/dri/i965/brw_wm_fp.c
@@ -356,6 +356,56 @@ static void emit_interp( struct brw_wm_compile *c,
 		 src_undef());
       }
       break;
+   case FRAG_ATTRIB_FOGC:
+      /* The FOGC input is really special.  When a program uses glFogFragCoord,
+       * the results returned are supposed to be (f,0,0,1).  But for Mesa GLSL,
+       * the glFrontFacing and glPointCoord values are also stashed in FOGC.
+       * So, write the interpolated fog value to X, then either 0, 1, or the
+       * stashed values to Y, Z, W.  Note that this means that
+       * glFogFragCoord.yzw can be wrong in those cases!
+       */
+
+      /* Interpolate the fog coordinate */
+      emit_op(c,
+	      WM_PINTERP,
+	      dst_mask(dst, WRITEMASK_X),
+	      0,
+	      interp,
+	      deltas,
+	      get_pixel_w(c));
+
+      /* Move the front facing value into FOGC.y if it's needed. */
+      if (c->fp->program.UsesFrontFacing) {
+	 emit_op(c,
+		 WM_PINTERP,
+		 dst_mask(dst, WRITEMASK_Y),
+		 0,
+		 interp,
+		 deltas,
+		 get_pixel_w(c));
+      } else {
+	 emit_op(c,
+		 OPCODE_MOV,
+		 dst_mask(dst, WRITEMASK_Y),
+		 0,
+		 src_swizzle1(interp, SWIZZLE_ZERO),
+		 src_undef(),
+		 src_undef());
+      }
+
+      /* Should do the PointCoord thing here. */
+      emit_op(c,
+	      OPCODE_MOV,
+	      dst_mask(dst, WRITEMASK_ZW),
+	      0,
+	      src_swizzle(interp,
+			  SWIZZLE_ZERO,
+			  SWIZZLE_ZERO,
+			  SWIZZLE_ZERO,
+			  SWIZZLE_ONE),
+	      src_undef(),
+	      src_undef());
+      break;
    default:
       emit_op(c,
 	      WM_PINTERP,