Re: Underlays?

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Marcus Barnes (marcus++at++multigen.com)
Thu, 12 Sep 1996 08:42:44 -0700

On Sep 12, 10:49am, Andrew Shein wrote:
> Subject: Re: Underlays?
> On Sep 12, 9:42am, Sandeep S. Mulgund wrote:
> > Subject: Underlays?
> > Is it possible to set up window _underlays_ with Performer? With the help
> > of some folks on this Performer list, I set up an OpenGL overlay last
> > month. But now, I'd like to put a few static elements behind some 2-D
> > instrumentation displays. Is there a way to do this?
> >
> > Sandeep
>
> There is no support for underlay planes in performer or on the
> new graphics hardware. I miss this because my old instrument panel
> code now has to redraw the backround. I have not been able to find
> any other workaround.

Performer does draw channels assigned to pipes in the order of creation
(generally). You can create a "stack" of overlapping channels this way, with
the last one created being the last channel drawn. Have the first (full
screen) channel clear the screen but not the others. Where ever the subsequent
channels do _not_ draw the underlying channel(s) will show through. For
instance:

    pfChannel* theWorld = pfNewChan(pipe); // draws 1st, does clear
    pfChannel* underlay = pfNewChan(pipe); // draws 2nd, no clear
    pfChannel* overlay = pfNewChan(pipe); // draws 3rd, no clear

This use of overlapping channels can work well in the right circumstances and
you can benefit from pfMultiThread( PFPROC_CULL ) on MP machines.

Regards.

--
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