[waffle] [PATCH 1/3] glx: don't use ARB_create_context with pre 3.0 contexts

[Emil Velikov]

On 15 April 2016 at 20:04, Chad Versace <chad.versace at intel.com> wrote:
> On 04/06/2016 02:12 AM, Jose Fonseca wrote:
>> On 05/04/16 22:45, Emil Velikov wrote:
>>> This way if the user requests GL pre 3.0 context which lacks the
>>> flags/extra bits which require ARB_create_context one can safely fall
>>> back to the normal/legacy entry point.
>>>
>>> This resolves piglits on non 3.0 capable drivers such as classic swrast,
>>> nouveau_vieux and alike.
>>>
>>> Cc: Jose Fonseca <jfonseca at vmware.com>
>>> Cc: Ilia Mirkin <imirkin at alum.mit.edu>
>>> Signed-off-by: Emil Velikov <emil.l.velikov at gmail.com>
>
>
>
>>> +static inline bool
>>> +glx_context_needs_arb_create_context(const struct wcore_config_attrs *attrs)
>>> +{
>>> +    if (attrs->context_api == WAFFLE_CONTEXT_OPENGL &&
>>> +        (wcore_config_attrs_version_ge(attrs, 30) ||
>>> +         attrs->context_forward_compatible))
>>> +        return true;
>>> +
>>> +    if (attrs->context_debug)
>>> +        return true;
>>> +
>>> +    return false;
>>> +}
>
>> Looks good to me.  Thanks.
>>
>> Reviewed-by: Jose Fonseca <jfonseca at vmware.com>
>
> I reviewed the thread on the Piglit list, and I'm in favor of this change.
>
> Jose and Emil, I believe the critical version should be 3.2, not 3.0. I don't
> understand why this patch uses 3.0 as the cutoff version.  The
> GLX_ARB_create_context spec says:
>
>     The presence of an OpenGL 3.2 or later implementation determines whether or
>     not GLX_ARB_create_context_profile is required.
>
> And the WGL spec contains the same text.
>
> In other words, it never makes sense to request a 3.2 context without
> GLX_ARB_create_context, because the availability of 3.2 mandates the
> availability of GLX_ARB_create_context_profile.

Looking at another hunk from the spec makes me wonder:

    created. Forward-compatible contexts are defined only for OpenGL
    versions 3.0 and later.

So one cannot get a fwd compat context with 3.0 or 3.1, if they don't
support OpenGL 3.2. Not sure I'm getting why they choose to make it
its way - there must be something subtle :-) Regardless, updated
patches coming in a second.

-Emil