[PATCH xserver] glx: Allow arbitrary context attributes for direct contexts

[Eric Anholt]

Adam Jackson <ajax at redhat.com> writes:

> On Fri, 2017-07-28 at 09:56 -0700, Eric Anholt wrote:
>> Adam Jackson <ajax at redhat.com> writes:
>> 
>> > For direct contexts, most context attributes don't require any
>> > particular awareness on the part of the server. Examples include
>> > GLX_ARB_create_context_no_error and GLX_ARB_context_flush_control, where
>> > all of the behavior change lives in the renderer; since that's on the
>> > client side for a direct context, there's no reason for the X server to
>> > validate the attribute.
>> > 
>> > The context attributes will still be validated on the client side, and
>> > we still validate attributes for indirect contexts since the server
>> > implementation might need to handle them. For example, the indirect
>> > code might internally use ARB_context_flush_control for all contexts, in
>> > which case it would need to manually emit glFlush when the client
>> > switches between two indirect contexts that didn't request the no-flush
>> > attribute.
>> > 
>> > Signed-off-by: Adam Jackson <ajax at redhat.com>
>> 
>> Does the client side even need to send the client-side attributes for
>> direct contexts?
>
> It would probably be legal for it to not? The ARB_create_context spec,
> discussing why direct/indirect is a parameter not an attribute, says
> "... different paths to the server may be taken for creating direct
> contexts, and parsing the attribute list in the client should not be
> required". One could read that to mean that creating the server-side of
> a direct context needn't be exactly like creating an indirect context,
> that you could send only those attributes the server needs to be aware
> of (although doing this would mean parsing the attribute list in the
> client, which the issue is otherwise trying to avoid...)
>
> However, none of the GLX extensions that define new context attributes
> seem to define whether that attrib is client or server state, and
> Mesa's glXCreateContextAttribsARB does not edit the attribute list
> before sending it to the server. It seems simpler to me for the server
> ignore unknown attribs for direct contexts than for Mesa to grow a list
> of attributes to censor, because e.g. ARB_create_context_no_error would
> then be exactly as easy to wire up for direct GLX as for EGL.

My thinking was: if we do it client side, then new Mesa works even with
old X.  That said, the fix here is trivial, so let's do it anyway.

Reviewed-by: Eric Anholt <eric at anholt.net>
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