Path: chuka.playstation.co.uk!news
From: James Shaughnessy <james@manc.u-net.com>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Rotating about an arbitrary axis?
Date: Fri, 18 Sep 1998 17:30:05 +0100
Organization: PlayStation Net Yaroze (SCEE)
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OK I know this is a standard and accepted problem but I would
really appreciate a quick pointer regarding object rotation:
As you may or may not be aware of my latest project is a 3D 9-ball
pool game.  I currently have all the balls on the table rolling
around (through each other :)) at constant speed bouncing "i=r" (*)
off imaginary cushions.
What I need is to know what matrix transformation I need to apply to
a ball so it will rotate in the direction it is moving:  eg.

struct POOLBALL {
  long vx, vy, vz;
  3DOBJECT *object;
} Ball;

Ball.vx = 10;
Ball.vy = 0;	// Y = vertical plane
Ball.vz = 10;

If I just rotate the object normally like this..

//                              X    Y    Z   axis rotation
RotateObject(&Ball->object, Ball.vz, 0, Ball.vx);

..clearly I run into the 'order of rotation' problem and this method
is of no use.


So, what is the matrix I need to rotate about an arbitrary axis?


muchos gracias,
Jim

PS (*) "i=r" non-physics fans refers to the "angle of incidence =
  the angle of reflection" -- a WAAY oversimplified model for pool
  balls, but enough 'till I get the buggers rolling the right way..!

PPS Sorry if this was a rediculously long-winded way to ask a very
simple question but it shows how I am currently trying to do it.
-- 
-----------------------------------------
James Shaughnessy    james@manc.u-net.com
http://www.netyaroze-europe.com/~shaughnj
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