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

[Paul Berry]

On 24 May 2013 12:23, Ian Romanick <idr at freedesktop.org> wrote:

> On 05/23/2013 03:46 PM, Kenneth Graunke wrote:
>
>> According to the documentation: "The Cut Index is compared to the
>> fetched (and possibly-sign-extended) vertex index, and if these values
>>
>
> Which documentation is this?  The only types that are valid for index
> buffers are unsigned, so what does "possibly-sign-extended" even mean?
>
>
This is from the Haswell bspec.  I have never understood what they mean by
"possibly-sign-extended" either.


>
>  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.
>>
>
> For GL_PRIMITIVE_RESTART_FIXED_**INDEX (ES and desktop 4.something),
> where the setting of the restart value is out of application control, this
> is absolutely correct.  The OpenGL 4.3 spec says:
>
>     "Primitive restart can also be enabled or disabled with a target
>     of PRIMITIVE_RESTART_FIXED_INDEX. In this case, the primitive
>     restart index is equal to 2^N - 1, where N is 8, 16 or 32 if the
>     type is UNSIGNED_BYTE, UNSIGNED_SHORT, or UNSIGNED_INT,
>     respectively, and the index value specified by
>     PrimitiveRestartIndex is ignored."
>
> For GL_PRIMITIVE_RESTART, I'm not so sure.  I couldn't find anything
> conclusive any of the specs.  The only thing I found was a hint in the
> NV_primitive_restart extension spec:
>
>     *   What should the default primitive restart index be?
>
>         RESOLVED: Zero.  It's tough to pick another number that is
>         meaningful for all three element data types.  In practice, apps
>         are likely to set it to 0xFFFF or 0xFFFFFFFF.
>
> You can infer from this that applications are expected to set 0xFFFF for
> GL_UNSIGNED_SHORT and 0xFFFFFFFF for GL_UNSIGNED_LONG.  Experimentation is
> the only way to know for sure. :(
>
>
>  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,
>>
>>
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