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

[Roland Scheidegger]

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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