Path: chuka.playstation.co.uk!news From: James Russell Newsgroups: scee.yaroze.programming.3d_graphics Subject: Re: What is a normal? Date: Fri, 14 Aug 1998 13:28:29 +0100 Organization: Sony Computer Entertainment Europe Lines: 24 Message-ID: <35D42D6C.CEC81F6D@scee.sony.co.uk> References: <35D3F965.D5D79825@nospam.easynet.co.uk> NNTP-Posting-Host: mailgate.scee.sony.co.uk Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 4.5b1 [en] (Win95; I) X-Accept-Language: en Phil Gooch wrote: > > Could someone explain to me what a normal is? > A normal is a vector (of any length, except zero) that is perpendicular ("at right angles to") a plane. They are useful for many reasons. They are most commonly used to calculate the amount of light that falls on an object (the angle that the normal subtends with the vector from the polygon to the light source is used to attenuate the colour of the polygon) and polygon visibility (if you have a standard that states that a polygon's normal is positive on the 'viewable' side, then transform the polygon, you can easily tell if you can see that side of the polygon, because the normal will be wither facing towards you (visible) or away from you (invisible)). A 'normalised' normal is a normal vector with length 1. Cheers, James -- == James_Russell@scee.sony.co.uk +44 (171) 447-1626 == Developer Support Engineer - Sony Computer Entertainment Europe Don't judge a book by its movie.