[Mesa-dev] [PATCH] i965: Mask the cut index based on the index buffer type in 3DSTATE_VF.

[Kenneth Graunke]

According to the documentation: "The Cut Index is compared to the
fetched (and possibly-sign-extended) vertex index, and if these values
are equal, the current primitive topology is terminated.  Note that,
for index buffers <32bpp, it is possible to set the Cut Index to a
(large) value that will never match a sign-extended vertex index."

This suggests that we should not set the value to 0xFFFFFFFF for
unsigned byte or short index buffers, but rather 0xFF or 0xFFFF.

Fixes sporadic failures in the ES 3 instanced_arrays_primitive_restart
conformance test when run in combination with other tests.  No Piglit
regressions.

Cc: Ian Romanick <idr at freedesktop.org
Cc: Paul Berry <stereotype441 at gmail.com>
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_primitive_restart.c | 27 ++++++++++++++++-------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_primitive_restart.c b/src/mesa/drivers/dri/i965/brw_primitive_restart.c
index f824915..cf4a1ea 100644
--- a/src/mesa/drivers/dri/i965/brw_primitive_restart.c
+++ b/src/mesa/drivers/dri/i965/brw_primitive_restart.c
@@ -183,19 +183,30 @@ haswell_upload_cut_index(struct brw_context *brw)
    if (!intel->is_haswell)
       return;
 
-   const unsigned cut_index_setting =
-      ctx->Array._PrimitiveRestart ? HSW_CUT_INDEX_ENABLE : 0;
-
-   BEGIN_BATCH(2);
-   OUT_BATCH(_3DSTATE_VF << 16 | cut_index_setting | (2 - 2));
-   OUT_BATCH(ctx->Array._RestartIndex);
-   ADVANCE_BATCH();
+   if (ctx->Array._PrimitiveRestart) {
+      int cut_index = ctx->Array._RestartIndex;
+
+      if (brw->ib.type == GL_UNSIGNED_BYTE)
+         cut_index &= 0xff;
+      else if (brw->ib.type == GL_UNSIGNED_SHORT)
+         cut_index &= 0xffff;
+
+      BEGIN_BATCH(2);
+      OUT_BATCH(_3DSTATE_VF << 16 | HSW_CUT_INDEX_ENABLE | (2 - 2));
+      OUT_BATCH(cut_index);
+      ADVANCE_BATCH();
+   } else {
+      BEGIN_BATCH(2);
+      OUT_BATCH(_3DSTATE_VF << 16 | (2 - 2));
+      OUT_BATCH(0);
+      ADVANCE_BATCH();
+   }
 }
 
 const struct brw_tracked_state haswell_cut_index = {
    .dirty = {
       .mesa  = _NEW_TRANSFORM,
-      .brw   = 0,
+      .brw   = BRW_NEW_INDEX_BUFFER,
       .cache = 0,
    },
    .emit = haswell_upload_cut_index,
-- 
1.8.2.2