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

[Jose Fonseca]

On 15/04/16 23:35, Emil Velikov wrote:
> 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.

Right, creating fwd compat context requires XXX_ARB_create_context, but 
your patch has `|| attrs->context_forward_compatible` so it should be 
alright.


> 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
>

Jose