[Mesa-dev] [PATCH] i965: Increase BRW_MAX_UBO to 15.

[Roland Scheidegger]

That's interesting.
Some d3d10 docs list this indeed as 15+1 (and that +1 is really needed
too for the immediates, as you can have indirectly addressed immediates
which are little more than ordinary uniforms for the hw).
So does d3d11:
https://msdn.microsoft.com/en-us/library/windows/desktop/ff819065%28v=vs.85%29.aspx
"Common-shader core constant-buffer slots
D3D11_COMMONSHADER_CONSTANT_BUFFER_HW_SLOT_COUNT (15) (+1 set aside for
an immediate constant buffer in shaders)"

Albeit currently for d3d10 it indeed lists 14:
https://msdn.microsoft.com/en-us/library/windows/desktop/cc308052%28v=vs.85%29.aspx
"Common-shader core constant-buffer slots	14"

Maybe it got lowered because nvidia couldn't do more...

Roland

Am 01.12.2015 um 01:55 schrieb Ilia Mirkin:
> How sure are you about this? This would make it very annoying to
> implement on recent (kepler+) nvidia hardware... there are 16 constbuf
> positions total, of which one has to contain texture descriptor data
> (mandated by the hw), and it's common to have at least one
> driver-internal one. If you're careful it could be shared with the
> texture one, but iirc nvidia isn't too careful about it. FWIW nouveau
> currently exposes 13, while nvidia apparently does 14.
> 
> On Mon, Nov 30, 2015 at 7:49 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
>> I believe that DirectX offers 16 UBOs, with one reserved for special
>> purposes.  This means that the practical lower bound is 15, even if
>> OpenGL only mandates 12.
>>
>> Without this, Shadow of Mordor shaders fail to work because of limit
>> checking around GL_MAX_UNIFORM_BUFFER_BINDINGS.
>>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>> ---
>>  src/mesa/drivers/dri/i965/brw_context.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> Shadow of Mordor also needs tessellation, so backporting this wouldn't
>> help the game any.
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
>> index e45df46..e20082f 100644
>> --- a/src/mesa/drivers/dri/i965/brw_context.h
>> +++ b/src/mesa/drivers/dri/i965/brw_context.h
>> @@ -414,7 +414,7 @@ struct brw_ff_gs_prog_data {
>>  #define BRW_MAX_DRAW_BUFFERS 8
>>
>>  /** Max number of UBOs in a shader */
>> -#define BRW_MAX_UBO 12
>> +#define BRW_MAX_UBO 15
>>
>>  /** Max number of SSBOs in a shader */
>>  #define BRW_MAX_SSBO 12
>> --
>> 2.6.2
>>
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