[Mesa-dev] [PATCH 1/7] gallium: add CONSTBUF type to tgsi_file_type

[Timothy Arceri]

On 23/08/17 09:42, Ilia Mirkin wrote:
> On Tue, Aug 22, 2017 at 7:41 PM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
>>
>>
>> On 23/08/17 09:28, Ilia Mirkin wrote:
>>>
>>> On Tue, Aug 22, 2017 at 7:25 PM, Timothy Arceri <tarceri at itsqueeze.com>
>>> wrote:
>>>>
>>>>
>>>>
>>>> On 23/08/17 09:08, Ilia Mirkin wrote:
>>>>>
>>>>>
>>>>> On Tue, Aug 22, 2017 at 6:55 PM, Timothy Arceri <tarceri at itsqueeze.com>
>>>>> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 23/08/17 00:56, Ilia Mirkin wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Aug 22, 2017 at 10:51 AM, Roland Scheidegger
>>>>>>> <sroland at vmware.com>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> I am probably missing something here, but why do you need a new
>>>>>>>> register
>>>>>>>> file? Since you couldn't use LOAD with TGSI_FILE_CONSTANT before,
>>>>>>>> can't
>>>>>>>> you just allow LOAD with TGSI_FILE_CONSTANT and achieve the same
>>>>>>>> thing?
>>>>>>>> Or do you need to know how it's going to be accessed in advance?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> With bindless, LOAD can take a CONST I believe [which contains the
>>>>>>> value of the bindless id]. I think it's nice to keep those concepts
>>>>>>> separate... having CONST sometimes mean the value and other times mean
>>>>>>> the address is a bit weird. This way CONSTBUF[0] is the address of the
>>>>>>> 0th constbuf.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Yeah. I think we also may need another type for bindless as I'm
>>>>>> planning
>>>>>> to
>>>>>> use TGSI_FILE_CONSTANT for regular uniforms. The plan is to use LOAD
>>>>>> for
>>>>>> supporting packed uniforms rather than padding everything to vec4.
>>>>>
>>>>>
>>>>>
>>>>> Shouldn't be necessary... we can think of CONST (and TEMP and IMM) as
>>>>> "value" registers, and MEMORY/IMAGE/BUFFER/CONSTBUF as "address"
>>>>> registers. If LOAD receives a value, then it's a bindless image
>>>>> handle, otherwise it should work based on which of the address
>>>>> registers it receives.
>>>>
>>>>
>>>>
>>>> But how do you tell the difference between a bindless image handle and a
>>>> non-indirect uniform where the "value" is just the index of the uniform?
>>>
>>>
>>> Easy - if the first arg is a CONSTBUF[], it's a uniform load. If it's
>>> a value, then it's a bindless image handle. A uniform load becomes
>>>
>>> LOAD dst, CONSTBUF[1], IMM[0].x
>>>
>>> which would be identical to doing
>>>
>>> MOV dst, CONST[1][5] (if IMM[0].x == 5)
>>>
>>
>> I'm talking about using:
>>
>> CONSTBUF for UBOs
>>
>> CONSTANT for uniforms
>>
>> SOMETHINGELSE for bindless images
>>
>> As far as I can tell we need to differentiate between uniforms and ubos, and
>> there doesn't seem to be anything else to help with that.
> 
> Gallium doesn't differentiate between uniform and UBO. In practice,
> st/mesa sticks uniforms in the zero const slot.
> 

Yeah ok, looking at the code again that makes sense. Thanks for clarifying.