Real-Time Rendering, Third Edition, 3rd Edition

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352 9. Global Illumination

Too much bias causes a problem called “Peter Panning,” in which the

object appears to be slightly above the underlying surface. One method

that helps ameliorate this effect is to make sure the light frustum’s near

plane is as far away from the light as possible, and that the far plane is as

close as possible. Doing so increases the effective precision of the Z-buffer.

Another method of avoiding self-shadowing problems is to render only

the backfaces to the shadow map. Called second-depth shadow map-

ping [1321], this scheme works well for many situations; by default, most

surfaces have no chance of shadowing themselves. Or, more precisely, the

surfaces that now self-shadow are those that face away from the light, so