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Incremental Redisplay (Animation)

    Date: Thu, 6 Dec 1990 17:44 EST
    From: miller@SOL.CS.ROCHESTER.EDU (Brad Miller)

    OK, I'm finally trying to figure out how to do this, and if this is going to
    be easier with CLIM, let me know that and I'll wait :-).

    Basically here's the problem. I'm using define-program-framework. I have a
    number of objects, each of which has a graphical presentation. One of the
    slots on the objects specifies the position it should be drawn at. This
    position may change.

    1) how do I invoke an incremental redisplay within a command (to show more
    smooth movement, and more frequent updates than waiting for returning from
    the command will do.. these commands take 5 minutes or more each).

    2) The display is basically on 3 levels - a background that doesn't change,
    an intermediate level that changes slightly periodically, and a foreground
    that moves all over the place (for the curious, the former are tracks and
    buildings, the medium are switch flags and other features that move and the
    foreground are trains that run on the tracks). How can I get incremental
    redisplay to update (redraw) the background when the foreground object moves
    off of them? Somehow I may be able to get access to the bounding box of the
    object that is moving, but how is it supposed to know what objects it no
    longer is blocking?

    Right now I'm using non-incremental redisplay which "works", but it's slow,
    and flickers in a very serious way, obviously.

Incremental redisplay is not appropriate for animations.  Use
1dw:erase-displayed-presentation0 and 1dw:redraw-displayed-presentation0 to
do your redisplay manually.  Incremental redisplay is more appropriate
when it is difficult to determine exactly what changed in any given
period of time.

The answer is the same for CLIM, except that the functions are called
1clim:erase-output-record0 and 1clim:replay0.