Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!usc!elroy.jpl.nasa.gov!ames!ptolemy!eos!shelby!med!hanauma!rick
From: rick@hanauma.stanford.edu (Richard Ottolini)
Newsgroups: comp.graphics
Subject: Re: 3D Hiding and Data Help Needed!!
Message-ID: <1679@med.Stanford.EDU>
Date: 4 Jul 90 06:00:23 GMT
References: <1990Jul3.232543.119@csuf3b.CSUFresno.EDU>
Sender: news@med (USENET News System)
Organization: Stanford University, Department of Geophysics
Lines: 10

In article <1990Jul3.232543.119@csuf3b.CSUFresno.EDU> davidw@csuf3b.UUCP (David Warness) writes:
>I have just finished writing a program that once given end points, it will 
>draw lines in 3D space.  Here's my real problem.  I don't know of a fast way 
>to determine when walls are hidden or not.  

A cheap, but fallible method is called "backface culling".
If the points have been triangulated, compute the normal of the triangles
(vector cross product of two lines connecting the three points),
then erase all faces with negative normals.  This assumes the object is
essentially convex, which is likely in many situations.