i965: don't intepolate clip distances on pre-GEN6.

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.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

diff --git a/src/mesa/drivers/dri/i965/brw_clip_util.c b/src/mesa/drivers/dri/i965/brw_clip_util.c
index a12dab6b3509ab17a18a8a9bc670090d072348ee..15abe1668482aea2044f7b8ebeac2dd489023a7f 100644 (file)
--- 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: