Path: utzoo!attcan!uunet!bu.edu!purdue!haven!mimsy!midway!daisy!francis
From: francis@daisy.uchicago.edu (Francis Stracke)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Rotating PICTs or BitMaps by arbitrary angle
Message-ID: <1990Nov5.165037.25327@midway.uchicago.edu>
Date: 5 Nov 90 16:50:37 GMT
References: <1990Nov3.122649.12277@cs.uoregon.edu>
Sender: news@midway.uchicago.edu (News Administrator)
Organization: Mathematics Department, University of Chicago
Lines: 24

In article <1990Nov3.122649.12277@cs.uoregon.edu> mkelly@cs.uoregon.edu (Michael A. Kelly) writes:
>Hello peoples.  Has anyone figured out a fast way to rotate a PICT or
>BitMap by an arbitrary angle?  I can figure out how to do it slowly, but
>I need to rotate a small (e.g. 40x40) PICT (or BitMap) at least one revolution
>per second.

Fastest way to rotate a PICT will probably (depending on how complex)
be to read the actual coordinates it stores & rotate those.
Remember to rotate around the center of the picture, in its own
local coords (i.e., within the rectangle specified in the header).
Formula for rotating ( (x,y) is the old loc., (x0,y0) is the
center, (h,k) is the new loc, th is the angle ):

	h=x0+(x-x0)*cos(th)-(y-y0)*sin(th)
	k=y0+(x-x0)*sin(th)+(y-y0)*cos(th)

(you get this from the sin/cos addition formulae)

I tell you three times: fastest way is to do it beforehand &
store the results!
| Francis Stracke		| My opinions are my own.  I don't steal them.|
| Department of Mathematics	|=============================================|
| University of Chicago		| Non sequiturs make me eat lampshades	      |
| francis@zaphod.uchicago.edu	|   				       	      |