[Mesa-dev] [PATCH 7/7] i965: don't intepolate clip distances on pre-GEN6.

[Paul Berry]

On pre-GEN6 chips, the VUE slots set aside for clip distance aren't
actually used, so there is no reason for the clipper to waste time
interpolating them.

When commit 62bad54727690bff5ed42a74272e7822fd36cdb6 changed the enum
value used to represent these VUE slots, that caused the clipper to
start interpolating them as an accidental side effect.  This patch
reverts to the old clipper behavior.
---
 src/mesa/drivers/dri/i965/brw_clip_util.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_clip_util.c b/src/mesa/drivers/dri/i965/brw_clip_util.c
index a12dab6..15abe16 100644
--- a/src/mesa/drivers/dri/i965/brw_clip_util.c
+++ b/src/mesa/drivers/dri/i965/brw_clip_util.c
@@ -160,8 +160,14 @@ void brw_clip_interp_vertex( struct brw_clip_compile *c,
 	    brw_MOV(p, deref_4f(dest_ptr, delta), brw_imm_f(1));
 	 else
 	    brw_MOV(p, deref_4f(dest_ptr, delta), deref_4f(v0_ptr, delta));
-      } else if (vert_result == VERT_RESULT_PSIZ) {
-	 /* PSIZ doesn't need interpolation */
+      } else if (vert_result == VERT_RESULT_PSIZ ||
+                 vert_result == VERT_RESULT_CLIP_DIST0 ||
+                 vert_result == VERT_RESULT_CLIP_DIST1) {
+	 /* PSIZ doesn't need interpolation because it isn't used by the
+          * fragment shader.  CLIP_DIST0 and CLIP_DIST1 don't need
+          * intepolation because on pre-GEN6, these are just placeholder VUE
+          * slots that don't perform any action.
+          */
       } else if (vert_result < VERT_RESULT_MAX) {
 	 /* This is a true vertex result (and not a special value for the VUE
 	  * header), so interpolate:
-- 
1.7.6.2