Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!gatech!ncsuvx!ecemwl!jnh
From: jnh@ecemwl.ncsu.edu (Joseph N. Hall)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Rotating Bit Images.
Keywords: Bitmaps
Message-ID: <3736@ncsuvx.ncsu.edu>
Date: 23 Aug 89 15:11:15 GMT
References: <1495@unocss.UUCP>
Sender: news@ncsuvx.ncsu.edu
Reply-To: jnh@ecemwl.UUCP (Joseph N. Hall)
Organization: North Carolina State University
Lines: 18

In article <1495@unocss.UUCP> ft035@unocss.UUCP (ft035) writes:
>I am trying to rotate some bit images and was wondering if anyone
>has any routines already written to do this.  This would be preferable to
>writing 4 different images (all rotations) of the same object.  Since some
>of these images are large I'd rather not.

There is an elegant algorithm for 90-degree rotations that is fast and
efficient.  The simplest version requires that your source pattern be both
square and a power of two bits along each side.  You can read about it
in "Smalltalk-80: The Language," by Adele Goldberg et al.  It's fairly
well known, too, so there may be someone on the net who has an adequate
implementation of it on the Mac.  (It's used for all of the 90-degree
rotations in the early Mac programs.)

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