[Mesa-dev] [PATCH 9.1] i965: Fix an inconsistency inb the VUE map with gl_ClipVertex on gen4/5.

[Jordan Justen]

From: Eric Anholt <eric at anholt.net>

We are intentionally not allocating a slot for gl_ClipVertex.  But by
leaving the bit set in the slots_valid, the fragment shader's computation
of where varyings are in urb entry coming out of the SF would be off by
one.  Fixes rendering in Freespace 2 SCP, and improves rendering in TF2.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=62830
Tested-by: Joaquín Ignacio Aramendía <samsagax at gmail.com>
NOTE: This is a candidate for the 9.1 branch.
Reviewed-and-tested-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Paul Berry <stereotype441 at gmail.com>
[jordan.l.justen at intel.com: backport for 9.1 branch]
Signed-off-by: Jordan Justen <jordan.l.justen at intel.com>
Cc: Kenneth Graunke <kenneth at whitecape.org>
Cc: Eric Anholt <eric at anholt.net>
Cc: Paul Berry <stereotype441 at gmail.com>
---
Ken: Can you test this on 9.1 with Ironlake+TF2?
Eric/Paul: Does this backport of 0967c362 to 9.1 seem right?

 src/mesa/drivers/dri/i965/brw_vs.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vs.c b/src/mesa/drivers/dri/i965/brw_vs.c
index 0810471..705309c 100644
--- a/src/mesa/drivers/dri/i965/brw_vs.c
+++ b/src/mesa/drivers/dri/i965/brw_vs.c
@@ -65,6 +65,12 @@ brw_compute_vue_map(struct brw_context *brw, struct brw_vs_compile *c)
    GLbitfield64 outputs_written = c->prog_data.outputs_written;
    int i;
 
+   /* Prior to Gen6, don't assign a slot for VARYING_SLOT_CLIP_VERTEX, since
+    * it is unsupported.
+    */
+   if (intel->gen < 6)
+      outputs_written &= ~VERT_RESULT_CLIP_VERTEX;
+
    vue_map->num_slots = 0;
    for (i = 0; i < BRW_VERT_RESULT_MAX; ++i) {
       vue_map->vert_result_to_slot[i] = -1;
@@ -143,15 +149,12 @@ brw_compute_vue_map(struct brw_context *brw, struct brw_vs_compile *c)
     * assign them contiguously.  Don't reassign outputs that already have a
     * slot.
     *
-    * Also, prior to Gen6, don't assign a slot for VERT_RESULT_CLIP_VERTEX,
-    * since it is unsupported.  In Gen6 and above, VERT_RESULT_CLIP_VERTEX may
-    * be needed for transform feedback; since we don't want to have to
-    * recompute the VUE map (and everything that depends on it) when transform
-    * feedback is enabled or disabled, just go ahead and assign a slot for it.
+    * We generally don't need to assign a slot for VARYING_SLOT_CLIP_VERTEX,
+    * since it's encoded as the clip distances by emit_clip_distances().
+    * However, it may be output by transform feedback, and we'd rather not
+    * recompute state when TF changes, so we just always include it.
     */
    for (int i = 0; i < VERT_RESULT_MAX; ++i) {
-      if (intel->gen < 6 && i == VERT_RESULT_CLIP_VERTEX)
-         continue;
       if ((outputs_written & BITFIELD64_BIT(i)) &&
           vue_map->vert_result_to_slot[i] == -1) {
          assign_vue_slot(vue_map, i);
-- 
1.7.10.4