Re: Callbacks

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Jim Helman (jimh++at++surreal)
Thu, 06 Jul 95 10:46:13 -0700

   
> What I'd like to be told (but which doesn't seem to be the case !) is that the
> pre/post-Cull-Callback() occure for each associated Node within the Cull
> Process, out of which the node is in some way registered in a list for the
> Drawing Process. Then, in the Drawing Process, each referenced node calls its
> pre-draw-callback(), then draws itself, then calls its post-draw-callback()

This is indeed the case. The invocation of the "pre/postDrawCallback"
in the pseudo code should be interpreted as:

    if (combined CULL/DRAW && !sorting)
            invoke DRAW callback now
    else
            add DRAW callback to the pfDispList for later invocation

> (the 2 last operations being conditioned by the flag returned by the
> pre-draw-callback())

This is not the case. The return value of the DRAW callback has no
effect. Since there is no scene graph in the DRAW, PRUNE and TERM
would have little meaning. The preferred way to enable and disable
rendering of portions of the scene graph is to use a pfSwitch or to
set the DRAW traversal mask on pfNodes.

rgds,

-jim helman

jimh++at++surreal.asd.sgi.com
415/390-1151

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