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

[Timothy Arceri]

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.