Re: Identifying channels

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Aaron Hightower (aaron++at++qbert.rts.dseg.ti.com)
Sun, 28 Aug 1994 20:58:58 -0500 (CDT)

> From: "Drew Hess" <dhess++at++vision.arc.nasa.gov>
> Subject: Identifying channels in callbacks
>
> I need a way of uniquely identifying the channel passed to a post/predraw
> callback in Performer 1.2. According to the man page, the return value of
> pfNewChan() is a handle to the newly created channel, so it sounds like I could
> use the handle for what I need. (What's actually returned is of type
> (pfChannel *), so should I use the pointer itself to identify the channel or
> should I dereference the pointer and use that value? The latter would work if,

Trying to poke into Performer's data structures is dangerous. The main reason
being that using such "undocumented features," if they exist, is no guarantee
that they will continue to exist in new versions. I would not suggest
dereferencing any of the Performer objects directly.

> for instance, the pointer points to an integer that's used as a table index
> into a libpr or libpf internal table.)

There are two ways of handling this that I know of. The first way is simply
to use pfUserData() on the pfChannel pointer and then make a structure
that identifies the channel in whatever way you would like.

The second way is to use pfAllocChanData() and pfPassChanData(). This is
the way to do it if you want your data to be "frame accurate" as it keeps
a copy for each of the app cull and draw. However, the data is only sent
downstream. If you need to change things in the draw process and see it
in the app, then pfUserData is your key.

Hope this helps,
  Aaron Hightower

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