Re: Overhead for rendering multiple windows
Angus Dorbie (dorbie++at++sgi.com)
Wed, 29 Jul 1998 07:07:30 -0700
Steve Baker wrote:
>
> On Wed, 29 Jul 1998, Angus Dorbie wrote:
>
> > Colin Bridgewater wrote:
> > >
> > > Hi Folks
> > >
> > > Regarding the overhead involved in rendering multiple windows from one
> > > graphics pipe, the Performer Progammers' Guide states:
> > >
> > > > The use of multiple windows on a single graphics pipe can add
> > > > overhead. The sharing of the graphics context between windows
> > > > consumes almost all of this overhead.
> > >
> > > Would anyone care to be more specific as to what "almost" means ?
> >
> > Well how much does a glViewport, glFrustum, a modelview loadmatrix,
> > a couple of matrix mode changes a glScissor and potentially another
> > glClear (quite reasonably ignoring the time taken to actually
> > perform the clear) cost?
> >
> > Not very much.
>
> An important caveat is that you either need to render to those
> two windows from within a single process - or perhaps try to
> interlock the processes writing to different windows so that
> they don't all try to draw at the same time.
>
> If you have two processes writing to the same pipe AT THE SAME TIME,
> then graphics context switching in the pipe can really kill your
> performance on some (if not all) SGI platforms. When we tested this
> (admittedly on an RE2 using IrisGL/Performer 1.2), we were seeing
> a 45% slowdown due to these kinds of effects.
Yep, usually this is easily fixed, in addition the question was about
sharing a context. I had in mind a sequential single threaded rendering
to multiple windows or at least coarse scheduling. I actually assumed
the question was related draw thread performing some windowing
allowing easy use of a single context with all of it's associated
state.
Cheers,Angus.
--
"Only the mediocre are always at their best." -- Jean Giraudoux
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
=======================================================================
List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/
Submissions: info-performer++at++sgi.com
Admin. requests: info-performer-request++at++sgi.com
This archive was generated by hypermail 2.0b2
on Mon Aug 10 1998 - 17:57:45 PDT