planar pattern creates a horizontal stripe plus or minus one unit above and below the X-Z plane.
It is computed by: value =1.0- min(1, abs(Y)) It starts at 1.0 at the origin and decreases to a minimum
value of 0.0 as the Y values approaches a distance of 1 unit from the X-Z plane. It remains at 0.0 for all areas
beyond that distance. This pattern was originally created for use with
media but it
may be used anywhere any pattern may be used.