This is a desert scene containing a cactus on sandy ground with a blue sky 
background. As time passes, the cactus's shadow will change. The sky will
brighten and darken also.

Controls
Use the arrow keys to change the view direction (although there isn't much
to see outside of the default view)
press 's' to toggle shadows
press 'l' to decrease minimal lighting
press 'L' to increase minimal lighting
press 'a' to speed up time
press 'z' to slow down time
press 'w' to toggle wireframe mode

The cactus is made of several cylinders and spheres with material properties
set to reflect mostly green ambient and diffuse light. Its shadow is generated
using a matrix to project it onto the xz plane. The shadow is scaled according
to the time of day. The ground is just a quad with a sand image used as a
texture map. The background is another quad using a sky image for a texture
map.
Light from the "sun" emits only diffuse light, and the only object in the scene
to reflect diffuse light is the cactus. You can see the lighting change 
according to the time of day. There's also a small amount of diffuse light from 
"stars." This helps give the cactus some definition at night.
Ambient light changes as time passes. The ambient light is used mainly to 
illuminate the ground and background, which only reflect ambient light. Late in
the day, the ambient light changes to produce more red than green and blue,
resulting in a sort of sunset effect. 


Things I wanted to include, but didn't have time for:
bump mapping for the cactus
adding more objects to the scene, like a rock and tumbleweed
blending the shadow with the ground
having stars gradually blend in with the sky at night