Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!cwjcc!gatech!psuvax1!psuvm.bitnet!dn5
From: DN5@PSUVM.BITNET
Newsgroups: comp.sys.mac.programmer
Subject: Re: help needed dragging a non-rectangular PICT
Message-ID: <64148DN5@PSUVM>
Date: 7 Dec 88 14:28:15 GMT
References: <6095@mva.cs.liv.ac.uk>
Organization: Penn State University - Center for Academic Computing
Lines: 16

Hi,

   To drag something across another pattern I use two off-screen bitmaps.
One is the background (I copy the background into this once, and then use
it as a constant), and the other is the work bitmap.  I copy the background
into the work bitmap, then put the irregular region where it should be on
this bitmap, then I CopyBits the work bitmap to the screen.

   This technique worked fast enough for me to rotate a simple polygon on
a MacPlus in real-time (as a student dragged it around) or as animation
(smooth, in 3 degree increments, which was the best comprimise of smoothness
and speed).  You will have to experiment to see how you want this to look,
but I suggest testing it on the slowest machine you have (something that
looks fast enought on a Mac II can look like a dog on a Plus).

                                      Jay, etc...