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

[Jordan Justen]

On Thu, May 23, 2013 at 3:46 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> 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.

I was wondering what the GL spec had to say about this situation. For
example, what should happen if the index is 0x100, and bytes are used.
Should it effectively disable prim-restart? Should it use 0xff, or
0x00? Unfortunately, I didn't find anything concrete.

Reviewed-by: Jordan Justen <jordan.l.justen at intel.com>

> 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
>
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