Shadow geometry, fecedness

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Angus Dorbie (angus++at++division.demon.co.uk)
Thu, 26 Jan 1995 10:57:21 +0000

In the shadow technique I described in my previous email I said you should draw
the shadow extrusion backface with an increment and then the frontface with a
decrement. This depends on the orientation of the faces but is wrong from an
intuitive point of view. You should actually draw the front face with an
increment and then the backface with a decrement. This means that you can apply
the shadow by subsequently drawing the front facing extrusion (at least I got
that part right).

If you want a better but more general description of the technique see:
"Computer Graphics: Principles and Practice", second edition, by
Foley, vanDam, Feiner & Hughes, section 16.4.3 'Shadow Volumes'

Regards,

-- 
 Angus Dorbie                Division Ltd,
 Software Engineer           19 Apex Court,
 Tel: (01454)615554          Woodlands,
 Fax: (01454)615532          Bristol BS12 4JT,
 angus++at++division.demon.co.uk  UK

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