[Mesa-dev] [PATCH 5/5] st/mesa: clean up min/max_index handling in st_draw_vbo

[Nicolai Hähnle]

On 25.04.2017 11:29, Marek Olšák wrote:
> On Tue, Apr 25, 2017 at 8:41 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> On 24.04.2017 15:31, Marek Olšák wrote:
>>>
>>> On Mon, Apr 24, 2017 at 12:01 PM, Nicolai Hähnle <nhaehnle at gmail.com>
>>> wrote:
>>>>
>>>> On 23.04.2017 01:10, Marek Olšák wrote:
>>>>>
>>>>>
>>>>> From: Marek Olšák <marek.olsak at amd.com>
>>>>>
>>>>> There is no reason to check for ~0.
>>>>> Also remove the incorrect comment.
>>>>> ---
>>>>>  src/mesa/state_tracker/st_draw.c | 9 ++-------
>>>>>  1 file changed, 2 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/src/mesa/state_tracker/st_draw.c
>>>>> b/src/mesa/state_tracker/st_draw.c
>>>>> index d710284..e510d43 100644
>>>>> --- a/src/mesa/state_tracker/st_draw.c
>>>>> +++ b/src/mesa/state_tracker/st_draw.c
>>>>> @@ -200,28 +200,23 @@ st_draw_vbo(struct gl_context *ctx,
>>>>>     if (ib) {
>>>>>        /* Get index bounds for user buffers. */
>>>>>        if (!index_bounds_valid)
>>>>>           if (!all_varyings_in_vbos(arrays))
>>>>>              vbo_get_minmax_indices(ctx, prims, ib, &min_index,
>>>>> &max_index,
>>>>>                                     nr_prims);
>>>>>
>>>>>        setup_index_buffer(st, ib);
>>>>>
>>>>>        info.indexed = TRUE;
>>>>> -      if (min_index != ~0U && max_index != ~0U) {
>>>>> -         info.min_index = min_index;
>>>>> -         info.max_index = max_index;
>>>>> -      }
>>>>> +      info.min_index = min_index;
>>>>> +      info.max_index = max_index;
>>>>
>>>>
>>>>
>>>> For this and the previous patch, I think it would be cleaner to keep the
>>>> semantics of pipe_draw_info::min_index/max_index to always make sense.
>>>> This
>>>> would mean dropping the previous patch, and changing this patch to only
>>>> set
>>>> the min_index/max_index if index_bounds_valid (rather than the ~0U
>>>> check).
>>>
>>>
>>> The old code didn't check index_bounds_valid, and u_vbuf already
>>> treats max_index == ~0 as invalid range. Instead of starting to use
>>> index_bounds_valid here, I'd prefer it if we removed
>>> index_bounds_valid and only rely on max_index == ~0 from vbo.
>>
>>
>> Hmm. Legitimate and valid max_index == ~0 is definitely possible on 64-bit
>> systems. It's ridiculously unlikely in practice though, so I guess it's
>> worth considering this change in the name of eliminating a branch here.
>>
>> That said, it looks like some drivers are actually using max_index, so at
>> least it needs to be checked that this change is okay for them.
>
> It's not necessary if vbo sets min=0 max=~0, which is what
> util_draw_init_info does.

True. I think with the corresponding change in vbo, that would be okay. 
It would avoid the change in the draw module as well.

Cheers,
Nicolai

>
> Marek
>


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