----- Original Message -----
From: Michael I Gold <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, September 16, 1999 1:37 PM
Subject: Re: [oglbase-discuss] OK, back to Re: 2nd draft:
GL_EXT_get_proc_address spec
> At 01:46 PM 9/16/99 -0600, you wrote:
> >
> >What I've been trying to say with this approach does have bearing on the
ABI
> >spec though. I think it's a bad idea to return context-specific function
> >pointers from the proposed gl*GetProcAddress function. The only valid
> >objection I've heard to returning a context-independant pointer is that
it
> >would adversely affect performance. So my venture into the architecture
> >realm was to show that such an architecture could be high performance,
> >therefore, performance degradation was not a valid argument for a poor
> >design decision (i.e. returning context-specific pointers).
>
> I don't see a way around the double-indirection, however. Consider
> per-vertex calls such as MultiTexCoord2fvARB(), you're adding another
> branch indirect per vertex. I do believe this will be measurable and
> therefore to be avoided.
Am I missing something, or doesn't the idea of using context neutral wrapper
procs solve this? Imagine getProc returns (for an unknown extension) one of
a number of "wrapper" procs (where <number> ranges from 0 to MAX)
wrapper_<number>(args)
context->extra[<number>].proc(args)
and when faced with an unknown (to libGL) extension available in the driver,
have getProc return the address of the next available wrapper function and
fill in the entry in an "extra extensions" structure (the context specific
proc, and any other information need to manage that proc (EXT id for
example). Then the driver can manage the extra proc similarly to if it
where in the regular dispatch table, right?
Again this is a architectural discussion motivated by the desiring to NOT go
down the road of context (or even display) specific function procs from
getProc. If a problem can be solved in implementation, we can avoid causing
one in the specification.
John Zulauf
Santa Barbara, CA
