Path: chuka.playstation.co.uk!news From: markt@mincom.com Newsgroups: scee.yaroze.programming.3d_graphics Subject: Object rotation Date: 2 Sep 1997 1:22:59 GMT Organization: PlayStation Net Yaroze (SCEE) Lines: 39 Message-ID: <5ufppk$2gk9@chuka.playstation.co.uk> Reply-To: markt@mincom.com NNTP-Posting-Host: chuka.playstation.co.uk Originator: news@chuka.playstation.co.uk id xma014744; Tue, 2 Sep 97 11:26:45 +1000 by portal.mincom.oz.au (8.8.7/8.8.5) with ESMTP id LAA16571 for ; Mon, 1 Sep 1997 11:26:49 +1000 Sender: markt@mincom.com From: Mark Theyer Organization: Mincom Pty Ltd X-Mailer: Mozilla 3.01SGoldC-SGI (X11; I; IRIX 6.3 IP32) MIME-Version: 1.0 To: Yaroze Newsgroups Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit >>OK, next question... Is it correct in saying that rotating a >>PSX object will result in a rotation at the transformed position >>around the object's origin (0,0,0)? In other words is the transformation >>independant of the 3x3 scale, rotation info' and is applied last? >>If this is the case may I ask why? >>Does this mean I can only rotate (and scale) an object around the >>origin? > > If I get this right you can't rotate about anything except the origin. > Hierachies is the answer. Set up your rotation within a coordinate > system that is a translation. Then your rotation is about this new > origin, but this origin is a translation from the WORLD origin. > > Get that? > > Stuart There is no difference if I do a matrix translation first then a rotation or rotation first then translation. The GsOBJ object will always be translated first (in either case) and then rotated about the object (not world) origin. I assume this is the supported behaviour but it is not what I expected given other graphics API's (which use 4x4 matricies). Mark markt@mincom.com