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From: jcs@crash.cts.com (John Schultz)
Newsgroups: comp.graphics
Subject: Re: Oh, yeah? well Phong this!
Message-ID: <3447@crash.cts.com>
Date: 9 Jul 90 18:16:10 GMT
References: <7834@ccncsu.ColoState.EDU>
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Organization: Crash TimeSharing, El Cajon, CA
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  Gouraud Shading: For each vertex of the polygon, average all of the
polygon's normal vectors that share the vertex. Now each vertex of the 
model has the average of the normal vectors at each vertex. To scan convert
a polygon, compute the intensity at each vertex using the dot product
(cosine method) of the vector and a normalized vector from the light
source. Linearly interpolate between vertices, horizontally and vertically,
then average those two. The end result is the intensity for a pixel.

  Phong Shading: Works as above, except *normal* vectors are interpolated
between vertices (not shade intensities). This is much more expensive
computationally, but produces better looking results.

  Silicon Graphics workstations have Gouraud shading built into the 
hardware. For real time graphics, Gouraud is most appropriate, where
Phong is better for static images (if you have time to wait for rendering).

  This was a readers digest condensed description.

  For more information see "Principles of Interactive Computer Graphics" by
Newman and Sproull, McGraw Hill.


  John