FASTEST - use the fastest available method for shading. May be
hardware-dependent.
NICEST - use the nicest (highest quality) available method for
shading. May be hardware-dependent.
FLAT - use the flat shading model. This shading model does not
interpolate color across the primitive.
GOURAUD - use the Gouraud (smooth) shading model. This shading
model smoothly interpolates the color at each vertex across the primitive.
The primitive is drawn with many different colors and the color at each
vertex is treated individually.
