[Piglit] [PATCH 0/6] Cleanup and prepare for pre OpenGL 3.0 drivers

Thu Mar 31 16:26:12 UTC 2016

On 31 March 2016 at 12:21, Jose Fonseca <jfonseca at vmware.com> wrote:
> On 31/03/16 00:44, Emil Velikov wrote:
>>
>> On 30 March 2016 at 21:54, Jose Fonseca <jfonseca at vmware.com> wrote:
>>>
>>> On 30/03/16 11:14, Emil Velikov wrote:
>>>>
>>>>
>>>> On 29 March 2016 at 23:53, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>>>
>>>>>
>>>>> Isn't this backwards? Shouldn't waffle just work without the
>>>>> ARB_create_context or whatever ext and just create a context and see
>>>>> what version it is?
>>>>>
>>>> It isn't, imho.
>>>>
>>>> Waffle follows the GL winsys semantics, as such it should not do more
>>>> (create a context, make it current, etc) unless explicitly asked. It
>>>> translates the winsys/platform specifics, not the GL crazy. Although I
>>>> can see how one would want both to be hidden/handled in waffle.
>>>>
>>>> That's my take on it, at least. If people familiar with waffle think
>>>> I've misunderstood things, please shout.
>>>>
>>>> -Emil
>>>
>>>
>>>
>>> FWIW, I agree with Ilia.  Ideally Waffle should abstract away these sort
>>> of
>>> behavioral differences.
>>>
>>> On Mac, there isn't even WGL/GLX_ARB_create_context equivalent.
>>>
>> Indeed that's correct. I'm afraid I don't get how that's applicable here
>> :-(
>>
>>> Furthermore, not setting WAFFLE_CONTEXT_DEBUG for 2.x context is IMO a
>>> functionality regression here. Many implementations support debug for 2.x
>>> contexts, and it can be quite useful for diagnosing issues.
>>>
>> Can you please elaborate - are you talking about a 3.0+ capable
>> driver, where the user requests a debug context and version 2.x via
>> ARB_create_context ? It does sound a bit strange, but sure.
>
>
> Yes, if somebody wants to debug a 2.x OpenGL application, there's no other
> way to do it.
>
> apitrace does this for the record.  By default it will enable debug context
> on every context.  Even if it was a 1.x context.
>
> There's nothing strange about it.
>
"Strange" being - one is actually working out how to request a debug
context and at the same time they're not using any of the 'performance
enhancing' GL 3.0+ goodies.

> Note https://www.opengl.org/registry/specs/KHR/debug.txt says the minimum
> required is OpenGL 1.1.  Not 3.0.  Allowing debugging 1.x 2.x was a design
> goal from the start.
>
>>
>>>
>>> So when a app requests a context <= 3.0
>>
>> Am I loosing my mind here or the comparison is the wrong way around ?
>> It should be requested_context >= 3.0, right ?
>
>
> No, I wrote what I meant...
>
> I don't think anynody is arguing what needs to be done for context > 3.0 --
> the host should support WGL/GLX_ARB_create_context anyway and we should use
> it.
>
>
> My focus here is how to handle requests for 1.x/2.x context.  You propose
> always use GLXCreateContext, I say that's throwing away the baby with the
> water.
>
Arr there seems to be a misscomunication here - the this is exactly
what I was thinking/talking about (a few lines below).

>
>>
>>> : if the OpenGL implementation
>>> supports WGL/GLX_ARB_create_context waffle should use it.  If not, it
>>> should
>>> request a ordinary context, and check the version matches the requested.
>>>
>
>> Waffle can use ARB_create_context for 3.0+/debug/fwd compat context,
>> although it cannot do the make_current and alike for on behalf of the
>> user. It doesn't need to either - piglit already checks the version
>> :-)
>>
>> Does this sound like a good middle ground ?
>
>
> I don't really understand what you're proposing.  I suspect we're talking
> about different things.
>
>
> Let me see if I can explain this differently.  Here is what I'd expect from
> Waffle as app developer:
>
> - If my app requests a 2.1 context and WGL/GLX_ARB_create_context is not
> supported, Waffle should still create a context using
> wglCreateContext/glxCreateContext.  (The point of using wrappers like Waffle
> is hide away that complexity, otherwise one's better off talking the GLX/WGL
> directly.)
>
> - If an app requests a 2.1 debug context, Waffle should just honour it if
> WGL/GLX_ARB_create_context.
>
Minor clarification:

 - If an app requests a 2.1 debug context, Waffle should just honour it if
WGL/GLX_ARB_create_context or error otherwise.

Right ?

This is precisely what I was saying earlier... so I believe I
understood you the first time ;-)
Just in case in an alternative form:

(somewhere in waffle)

if (requested_version > 3.0 ||
    requested_debug ||
    requested_fwd_compat)
   use_arb_create_context
else
   use_legacy_create_context

>
> This is BTW, what other similar wrappers do:
>
> - https://github.com/raedwulf/glfw/blob/master/src/glx_context.c#L401
>
> - https://github.com/apitrace/apitrace/blob/master/retrace/glws_glx.cpp#L345
>
Afaics there is a small (but significant) difference between waffle
and the above two. If you want a debug context and there's no way to
create one waffle will give you an error, as opposed to silently
ignoring you and creating a non-debug one ;-)

> In fact, looking at waffle src/waffle/glx/glx_context.c , it already
> fallbacks to glXCreateNewContext when it's not supported.
>
>
> So I don't understand why is Patch 6/6 necessary at all.
>
Because seemingly things don't work. As mentioned previously we can
tweak waffle and drop the patch. Does that mean that the first 5 are
ok ?

Thanks
Emil