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From: jteh@mulga.oz (J.T. Teh)
Newsgroups: comp.sys.mac
Subject: Rotation Algorithm needed
Message-ID: <2180@mulga.oz>
Date: Thu, 27-Aug-87 22:46:10 EDT
Article-I.D.: mulga.2180
Posted: Thu Aug 27 22:46:10 1987
Date-Received: Sat, 29-Aug-87 17:23:05 EDT
Organization: Comp Sci, Melbourne Uni, Australia
Lines: 26
Keywords: Rotation, Mac

I need a rotation algorithm that will allow me to rotate the contents of
a bounding rectangle at a given angle. Currently, I am using the standard
algorithm of rotating the point around the origin with
	[ cosX -sinX ][ x ]
	[ sinX  cosX ][ y ]
but this causes the resultant image to have "holes" in it if I am rotating
a filled image (with black). Each set pixel in the bounding rectangle is
rotated in this fashion and is very tedious as each row of pixels has to 
be scanned. I know that this is a very slow method but I am currently stuck
with it for want of a better method.

The free rotation method used in SuperPaint does not have this problem and
I would like to know how those guys did it.

I am using the rotation as part of an Honours Project application in visual
recognition and would appreciate it greatly if somebody could mail me a
better algorithm. If there is anyone else who would be interested in such
an algorithm, I will post the suggested algorithms on the news.

Thanks in advance.

J.T. Teh
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