[Mesa-dev] [PATCH 1/3] u_format: implement fetch_rgba_uint and fetch_rgba_sint for integer formats

[Marek Olšák]

On Mon, Jan 2, 2012 at 5:56 PM, Dave Airlie <airlied at gmail.com> wrote:
> On Mon, Jan 2, 2012 at 4:40 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> On Mon, Jan 2, 2012 at 3:31 PM, Dave Airlie <airlied at gmail.com> wrote:
>>> On Mon, Jan 2, 2012 at 1:07 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>>> Fetching int as float and vice versa is not allowed.
>>>> Fetching unsigned int as signed int and vice versa is not allowed either.
>>>
>>> The first is true, the second isn't, otherwise I'd have implemented
>>> this that way.
>>>
>>>> Doing conversions like that isn't allowed in OpenGL.
>>>
>>> I don't have chapter/verse but EXT_texture_integer doesn't seem to
>>> disallow this.
>>
>> EXT_texture_integer doesn't, but that extension doesn't define the new
>> GLSL samplers, it only requires EXT_gpu_shader4.
>>
>> See this part from EXT_gpu_shader4 (modifications to section 8.7 of
>> the GLSL spec):
>>
>> Table 8.xxx lists the supported combinations of sampler types and
>> texture internal formats.
>>
>>      texture
>>      internal      default (float) integer     unsigned integer
>>      format        sampler         sampler     sampler
>>      float         vec4            n/a          n/a
>>      normalized    vec4            n/a          n/a
>>      signed int    n/a             ivec4        n/a
>>      unsigned int  n/a             n/a          uvec4
>>
>> That is, no conversions are allowed. The pack/unpack stuff is
>> different, because it doesn't involve shaders. I have no opinion on
>> whether we should be that strict in u_format or not. Being strict may
>> later prevent making programming mistakes though.
>
> Did you mean samplers instead of shaders in that sentence? if so I
> probably agree that its fine then.

I am not sure right now what the restrictions on vertex attribs are,
so yes, I meant samplers.

Marek

>
> Also I'd agree with starting simple and only enabling the conversions
> if something comes up later, so with that,
>
> Reviewed-by: Dave Airlie <airlied at redhat.com>
>
> Dave.