People have been curious about the new PC game Wolfenstein 3D.
We have wondered how the speed of the "real" 3D effect was accomplished.
This explanation came off the usenet from someone at SGI:

Wolfenstein 3D cheats.  It's not really drawing 3D textured polygons.
What it's doing is sort of a cross between ray tracing and bitmap
decimation.  For each column of pixels on the screen, they shoot a ray
out and find which wall it intersects with.  From the length of the ray,
they know the top and bottom coordinates of the wall in screen space,
and from the intersection point of the ray with the wall, they know
which column to use from that wall's texture.  By decimating or
duplicating pixels from that column, they resize it to be the correct
height for the screen.

	by Tom Weinstein