[Mesa-dev] [PATCH] st/mesa: don't try to clear depth and stencil together in glClear fallback

[Marek Olšák]

Indeed, it is rare. I thought this was hit more often, but apparently
not. Nevermind.

Marek

On Fri, Jul 31, 2015 at 7:44 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> Actually, since the code says it can only happen with a non-full stencil
> mask, isn't clearing depth/stencil with a non-full stencil mask
> incredibly rare?
>
> Roland
>
> Am 31.07.2015 um 18:51 schrieb Roland Scheidegger:
>> I don't think that's quite true in general.
>> For gpus which have combined ds buffers I can'see why you'd wanted to do
>> separate clears for depth and stencil in this case (i.e. doing
>> pipe->clear for depth, then draw a quad for clearing stencil).
>> At least for "simple" hw like llvmpipe which don't have special depth
>> clear, this clearly seems to be much worse (you have to go through the
>> memory twice).
>>
>> I vaguely remember something like this being proposed some time ago with
>> some discussion that not the same thing is optimal depending on the
>> hw... I don't think though there's anything at the moment where you
>> could figure out what is better.
>>
>> Roland
>>
>>
>>
>> Am 31.07.2015 um 17:15 schrieb Marek Olšák:
>>> From: Marek Olšák <marek.olsak at amd.com>
>>>
>>> A lot of GPUs allocate separate depth and stencil buffers, so clearing them
>>> together doesn't make much sense. If some GPUs don't allocate separate
>>> depth & stencil, it's still beneficial to clear the HiZ / HiS information
>>> for only one of the two.
>>> ---
>>>  src/mesa/state_tracker/st_cb_clear.c | 9 ---------
>>>  1 file changed, 9 deletions(-)
>>>
>>> diff --git a/src/mesa/state_tracker/st_cb_clear.c b/src/mesa/state_tracker/st_cb_clear.c
>>> index 137fac8..1e404a2 100644
>>> --- a/src/mesa/state_tracker/st_cb_clear.c
>>> +++ b/src/mesa/state_tracker/st_cb_clear.c
>>> @@ -515,15 +515,6 @@ st_Clear(struct gl_context *ctx, GLbitfield mask)
>>>        }
>>>     }
>>>
>>> -   /* Always clear depth and stencil together.
>>> -    * This can only happen when the stencil writemask is not a full mask.
>>> -    */
>>> -   if (quad_buffers & PIPE_CLEAR_DEPTHSTENCIL &&
>>> -       clear_buffers & PIPE_CLEAR_DEPTHSTENCIL) {
>>> -      quad_buffers |= clear_buffers & PIPE_CLEAR_DEPTHSTENCIL;
>>> -      clear_buffers &= ~PIPE_CLEAR_DEPTHSTENCIL;
>>> -   }
>>> -
>>>     /* Only use quad-based clearing for the renderbuffers which cannot
>>>      * use pipe->clear. We want to always use pipe->clear for the other
>>>      * renderbuffers, because it's likely to be faster.
>>>
>>
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>>
>