LIGHTS NEGATIVE SHADOWS
* Subject: ------=> Sorry NO Subject!
* Date: Wednesday, 05 October 1994 17:38:04 [55]
* From: Massimiliano Marras (mc1606@mclink.it)
Another nice use for negative values is the simulation of shadows in scanline
mode. Enter Detail Editor, add a ground and a primitive sphere, move the ground
along Z axis -160 units. Leave the sphere unchanged but transform it's axis
(only) so that has this alignment: X -45,Y 0,Z -90 and the Y axis (only) size is
280 (so that it intersects the ground). Make the sphere a parallel rays, round
shape, controlled falloff light source and enter a _negative_ value in the
intensity requester that is roughly 75% of the other lightsource's intensity. In
this case use -196,-196,-196. Quickrender with a 90 degree horizontal angle and
a 45 degree vertical angle. Here you are: istant scanline shadows. Of course you
can add softedge lite textures, arrange more negative light sources in order to
simulate more complex shapes or even create "shadow volumes" that obscure the
object travelling in their area. As long as you use controlled falloff and scale
properly the Y axis this trick will not slow the rendering down (controlled
lights do not affect objects outside their reach) and will save days of render
time compared to raytracing. A good reference about negative lightsources is in
Graphics Gems III: "Darklights" by Andrew S. Glassner. Well, i guess Wizard will
claim copyright over that book too...
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