Re: mapping pfChannel to hardware channel

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Angus Dorbie (dorbie++at++sgi.com)
Wed, 22 Sep 1999 14:06:40 -0700

Robert Wolfe wrote:
>
> Hi everyone,
>
> Out of curiosity I am trying to understand the
> relationship between software channels and
> hardware channels on, say, an Onyx2IR2 with
> 2 hardware channels per pipe.
>
> Let's say I use ircombine to produce 2 output
> channels side by side as for stereo.
> What is happening when I create 2 pfChannels
> with different viewports and viewpoints in order
> to produce an image for each eye?
> Is it just the splitting of the viewport which
> ultimately determines which software channel
> is mapped to which hardware channel ?
> Or is there something to do with pfVideoChannels
> going on here whereby for each new channel created
> a new pfVideoChannel is created for which the
> default hardware channel index is one greater
> than for the last pfVideoChannel (and hence channel)
> created ?
>
> Can someone please straighten me out here ?

Yes they are completely disconnected entities, and the alignment of the
window & viewport to match the video position in the .cmb is what does
the trick. The exception to prove the rule being when you try to use DVR
and must use the video channel object to match the viewport resize to
the video magnification all frame synchronous ofcourse. That's probably
more advanced than you need to get initially, but it's not that tricky.

Some stereo is special in that some applications use quad buffered
stereo so the viewports actually overlap in the framebuffer and one
video channel outputs both buffers sequentially but it sounds like you
have multiple video channels for stereo so you don't need to worry about
this.

Cheers,Angus.

-- 
"One of the best-known folk theorems of software engineering is that
60% to 75% of conventional software projects are either never
completed or rejected by their intended users. If that range is
anywhere near true (and I've never met a manager of any experience
who disputes it) then more projects than not are being aimed at goals
which are either (a) not realistically attainable, or (b) just plain
wrong."
                 Eric S. Raymond - The Cathedral and The Bazaar


For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/

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