Sets the smoothing mode for the shadow map.
Mode 0 turns smoothing off and results in the fastest shadows
Mode 1 uses 4 fixed samples to smooth out the shadows
Mode 2 uses 4 random samples to avoid banding produced by mode 1
Mode 3 uses 16 fixed samples
Mode 4 uses 16 random samples and is the slowest
SetShadowSmoothing( mode )