From: "Dave Eberly" <eberly@magic-software.com>
Subject: Re: point inside a tri, z value?
Date: 03 Nov 1999 00:00:00 GMT
Message-ID: <7vqksm$gum$1@nntp2.atl.mindspring.net>
References: <7vqjep$57i$1@newssvr04-int.news.prodigy.com>
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Doug <nowhere@abcd.com> wrote in message
news:7vqjep$57i$1@newssvr04-int.news.prodigy.com...
> I have a 3 vectors forming a triangle transformed to screen space.  X,Y =
> pixel positions and Z for the zbuffer.
>
> How do I calc a Z value from the triangle's Z values for any x,y point
> inside the triangle?

Let the points be (x0,y0,z0), (x1,y1,z1), (x2,y2,z2).  Given (x,y),
solve for s and t in (x,y) = (x0,y0)+s*(x1-x0,y1-y0)+t*(x2-x0,y2-y0).
The point is inside the triangle if s >= 0, t >= 0, and s+t <= 1.
Then choose z = (1-s-t)*z0+s*z1+t*z2.

--
Dave Eberly
eberly@magic-software.com
http://www.magic-software.com