Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!gem.mps.ohio-state.edu!ginosko!uunet!iscuva!jimc
From: jimc@iscuva.ISCS.COM (Jim Cathey)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Rotating Bit Images.
Keywords: Bitmaps
Message-ID: <2610@iscuva.ISCS.COM>
Date: 28 Aug 89 17:54:08 GMT
References: <1495@unocss.UUCP> <3736@ncsuvx.ncsu.edu> <34285@apple.Apple.COM> <113@vsserv.scri.fsu.edu>
Organization: ISC Systems Corporation, Spokane WA
Lines: 23

In article <113@vsserv.scri.fsu.edu> pepke@loligo.UUCP (Eric Pepke) writes:
>There is an algorithm for rotating bitmaps in November 1985 Mac Tutor, but
>although it is clever, it is not particularly efficient.  The claim is made
>that the algorithm can rotate an image n pixels on a side in log n steps.
>This is true, but the problem is that each step requires enough CopyBits
>operations to move every pixel on the image.

Do not forget that the original description of this algorithm was for
the Smalltalk-80 environment.  Xerox's Alto, Dorado, and Star computers
had the Copybits operator as a CPU instruction (BITBLT -- I think all
three machines had it), and it was very fast.  For that environment it
was an excellent choice (there it was both clever and efficient).  

On the Mac I guess it's merely clever.  That's not quite enough.

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