commit 7dd18d02750f8f0951c16df3d006e8f0904fe9d9
Author: Eric Anholt <eric@anholt.net>
Date:   Mon Jan 28 16:17:59 2008 -0800

    [965] Emit front facing to fogc.y in for glFrontFacing in the fragment shader.

diff --git a/src/mesa/drivers/dri/i965/brw_sf_emit.c b/src/mesa/drivers/dri/i965/brw_sf_emit.c
index 080a02b..55e927a 100644
--- a/src/mesa/drivers/dri/i965/brw_sf_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_sf_emit.c
@@ -79,6 +79,44 @@ static void copy_bfc( struct brw_sf_compile *c,
    }
 }
 
+/**
+ * Sets VERT_RESULT_FOGC.Y of the vertices to the front facing flag of the
+ * primitive.
+ *
+ * This is currently executed if the fragment program uses VERT_RESULT_FOGC
+ * at all, but this could be eliminated with a scan of the FP contents.
+ */
+static void
+set_frontfacing( struct brw_sf_compile *c )
+{
+   struct brw_compile *p = &c->func;
+   GLuint frontface_conditional;
+   int i;
+
+   if (!have_attr(c, VERT_RESULT_FOGC))
+      return;
+
+   if (c->key.frontface_ccw)
+      frontface_conditional = BRW_CONDITIONAL_G;
+   else
+      frontface_conditional = BRW_CONDITIONAL_L;
+
+   /* Store the front facing result (1 or 0) in the low bit of the flag reg */
+   brw_CMP(p, vec4(brw_null_reg()), frontface_conditional, c->det,
+	   brw_imm_f(0));
+   brw_set_predicate_control(p, BRW_PREDICATE_NONE);
+
+   for (i = 0; i < 3; i++) {
+      struct brw_reg fogc = get_vert_attr(c, c->vert[i], VERT_RESULT_FOGC);
+
+      /* Move the front facing result from the flag reg low bit to the Y
+       * component of fogcoord for this vertex, where the fragment shader
+       * would look for it.
+       */
+      brw_AND(p, brw_writemask(fogc, WRITEMASK_Y), brw_flag_reg(),
+	      brw_imm_ud(1));
+   }
+}
 
 static void do_twoside_color( struct brw_sf_compile *c )
 {
@@ -355,6 +393,7 @@ void brw_emit_tri_setup( struct brw_sf_compile *c, GLboolean allocate)
 
    invert_det(c);
    copy_z_inv_w(c);
+   set_frontfacing(c);
 
    if (c->key.do_twoside_color) 
       do_twoside_color(c);