[Mesa-dev] Samping GL_R32UI?

[Roland Scheidegger]

Am 02.02.2017 um 09:11 schrieb Andrew A.:
> Thank you for the help! It was indeed an incomplete texture issue.
> Setting the MIN/MAG filters to GL_NEAREST ended up resolving it.
> 
> I did have one other question -- why is this considered a silent
> non-error condition?
I did put quotation marks around that :-).
Incomplete textures have been like that since day one in OpenGL (or
rather, since GL got support for textures). Not considered an error, you
just get all black, even though really everybody would consider that an
error in practice...
Maybe it's because this error is only detectable at draw command time,
and there weren't really any errors which got detected (and returned as
such) with draw commands then (just invalid parameters of draw itself).
Albeit this is no longer the case now. But really I have no idea... And
yes it is annoying and sometimes makes for interesting debugging
(especially since some vendors don't actually implement it as literal as
the spec says in cases the filters don't matter and don't even warn
about it...).

Roland

> Even with KHR_debug enabled and set to use
> DEBUG_SEVERITY_NOTIFICATION, I don't seem to get any error or warning
> messages about this.
> It seems like incomplete textures would be a very handy thing to know
> about when debugging.
> 
> Thanks again,
> 
> Andrew
> 
> On Wed, Feb 1, 2017 at 5:31 PM, Roland Scheidegger <sroland at vmware.com> wrote:
>> Am 01.02.2017 um 05:32 schrieb Andrew A.:
>>> Are there any known issues with using usampler2D on a GL_R32UI texture
>>> in llvmpipe from within a VS/FS? I'm getting expected results on
>>> Nvidia drivers (proprietary), but not with mesa llvmpipe (always get
>>> zero).
>>
>> Not that I know of. There should be plenty of tests testing this.
>> My best guess is your texture is incomplete - nvidia is known to ignore
>> this for some cases but mesa would not.
>> This would affect all mesa drivers presumably, not just llvmpipe.
>> (This silent "non-error condition" is quite nasty and non-obvious in
>> some cases - for instance if you use texelFetch which ignores all
>> ordinary texture parameters such as wrap modes or filtering, however
>> according to OpenGL rules the texture would still be incomplete
>> depending on min/mag filter - and I know nvidia would ignore this
>> particular case.)
>>
>> Roland
>>