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From: mark@calvin..westford.ccur.com (Mark Thompson)
Newsgroups: comp.sys.amiga
Subject: Re: Imagine's CSG Spheres
Message-ID: <61601@masscomp.ccur.com>
Date: 7 Jan 91 20:45:08 GMT
References: <2062@beguine.UUCP> <5500044@hpfcdc.HP.COM>
Sender: news@masscomp.ccur.com
Reply-To: mark@calvin.westford.ccur.com (Mark Thompson)
Organization: Concurrent Computer Corp. Westford MA.
Lines: 26

In article <5500044@hpfcdc.HP.COM> koren@hpfcdc.HP.COM (Steve Koren) writes:
>There is a common technique called "Gereaud shading" (yeah, I know I
>badly mangled the spelling :-) ).  It involves representing curved
>surfaces as a set of polygons, and making the curved surface look
>smooth by interpolating the normal vectors between centers of the
>polygons.  

turn nit-picking mode ON.......
What you are trying to describe is Phong shading, not Gouraud. In
Phong shading, the averaged normal vectors at each polygon vertex
are bilinearly interpolated across the polygons surface in scanline
order at each pixel. Lighting calculations are then performed on that
pixel based on the interpolated normal vector, the view vector, and
the lighting vector(s). In Gouraud shading, the lighting calculations
are only performed at the polygon vertices and then these values are
interpolated rather than the normal vectors. It is far less computationally
intensive but does not handle specular highlights as well as Phong.
Most software based renderers today use a Phong shader where as hardware
implementations usually do Gouraud shading.
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