[Mesa-dev] [PATCH v3] i965: Fix ETC2/EAC GetCompressed* functions on Gen7 GPUs

[Eero Tamminen]

Hi,

On 04.05.2018 22:06, Eleni Maria Stea wrote:
> On Fri, 4 May 2018 18:29:55 +0300
> Eero Tamminen <eero.t.tamminen at intel.com> wrote:
> 
>> You mean returning CAVEAT_SUPPORT in params for compressed formats
>> which are transparently converted to uncompressed data?
> 
> Well, that would be the best solution I think, if it's possible to
> modify an existing query in the extension, although I am not certain
> which is the best query to modify: TEXTURE_COMPRESSED, or
> INTERNALFORMAT_SUPPORTED (or maybe both?).
> 
> There's also another solution that we already have, but we are not sure
> if it is correct:
> 
> I noticed that both mesa and nvidia drivers return GL_FALSE when the
> pname is GL_TEXTURE_COMPRESSED and the format is emulated and GL_TRUE
> for the natively supported formats.

So, in Nvidia case only the ancient GLES 1.x GL_PALETTE_* formats
are emulated.  I guess Nvidia HW was never than HSW. :-)


> (Specifically on mesa the code that
> performs the check is in src/mesa/main/formatquery.c and tests only
> for native support).
 >
> But if you take a look at this part of the extension specification:
> 
> TEXTURE_COMPRESSED: If <internalformat> is a compressed format
>        that is supported for this type of resource, TRUE is returned in
>        <params>. If the internal format is not compressed, or the type of
>        resource is not supported, FALSE is returned.
> 
> it is not very clear if we should return true or false for an
> emulated format. Maybe returning false when we provide emulation is a
> bug in both drivers, just a convenient one in this case. :-)
> 
> Is there any way to clarify what should be the correct behavior?

Khronos documentation bug tracker?

If you can test also e.g. AMD driver, that would be good background
data for the clarification ticket.


> Do you think that even if the current behavior of the
> TEXTURE_COMPRESSED query is correct, in which case it should keep
> returning GL_FALSE for the emulated formats, we should nevertheless
> modify something else, e.g. the INTERNALFORMAT_SUPPORTED query, to
> return CAVEAT_SUPPORT?

Uh, I'm not the best person to answer that.  Maybe somebody
on Portland team who has contacts to game engine developers?


>> That API's not available for GLES v2, where I think ETC is most widely
>> used, so it would be more of a solution for GLES v3.x applications
>> only. Sounds OK to me.
>>
>> Hardest part will be propagating use of this query to engines &
>> toolkits that would benefit from using it. :-)
> 
> +1 on that :)
> 
> Thanks a lot for the suggestions and the feedback,
> Eleni
> 
> PS: here is some code to clarify the current situation:
> 
> [1]: https://github.com/hikiko/test-compression is a test program to
> quickly check the compressed formats supported (see
> the function print_compressed_formats at the end of main.c)
> 
> [2]: https://pastebin.com/Qif74fFn is the output of [1] on HSW using
> the ETC patch and on nvidia where you can see that the natively
> supported compression formats return GL_TRUE in both cards whereas the
> emulated ones return GL_FALSE in both cards

Thanks for checking these!


	- Eero