Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!bbn!bbn.com!cosell
From: cosell@bbn.com (Bernie Cosell)
Newsgroups: comp.graphics
Subject: How do you do simple animation on a bitmap display?
Message-ID: <36049@bbn.COM>
Date: 15 Feb 89 18:49:57 GMT
Sender: news@bbn.COM
Reply-To: cosell@BBN.COM (Bernie Cosell)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 30

I confess that I'm a creature left over from the days of the point-plotting
scopes.  One of the neat things about doing animation on those scopes was
that it mostly came for free (by contrast: doing a STABLE single frame was a
pain, 'cause you had to keep regenerating the display!).  Can anyone give me
any tricks or tips for doing simple animation in the modern world of
bitmapped displays?  I've checked Foley&VanDam and Newman&Sproull and they
seem only to mention screen-flipping.  Is there nothing simpler?   

For example, I was writing a little program to explore the properties of
compound pendulums.  That seemed simple enough, but then I realized: on a
point-plotting scope it would all work more-or-less like magic.  I'd just
plot the position of the bob and the fading phosphors would give me enough of
a "tail" so that I could see the pattern of where it was and where it had
come from.  In fact, the impression of depth you could get essentially for
free was pretty spectacular.  The best I was able to come up with for THIS
guy (although I don't have it working yet) is to use my system's color table.
What I'll do is have a "current color" and I'll go and pump points into the
bitmap with THAT color until a little timer goes off.  THEN: I bump the
"current color". *and* diddle the color mapping table so that "current" is
now the brightest color, "current-1" (the previous current color) is just a
bit more faded, and so on around the palette.  Seems like a kludge, but it
might work!

Am I missing some set of simple tricks?  Are there any reference books that
talk about doing this sort of thing?  Thanks!

   __
  /  )                              Bernie Cosell
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