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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Dragging playing pieces on a playing field (ANIMATION)...
Keywords: Here is a valuable solution.....
Message-ID: <27062@ucbvax.BERKELEY.EDU>
Date: 8 Dec 88 07:19:14 GMT
References: <33198@bbn.COM>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 13

I am the author of Shepard Tones, among many others. The reason this
solution flickers is:
1.) you restore the background, erasing the old position of the piece
2.) you draw the pice in its new location.
in between the two draws, there is a split second where the background is
visible, because you haven't drawn the new piece yet. to get this to be
smooth, you need to add the following:

if the old and new positions alllow any part of the old and new objects to
overlap, then do all of the above to an off-screen bitmap, then copy the
result to the screen, This gets around the transient background problem.
Note, this offscreen bitmap can be quite small: at most twice the size of
the object you are moving.