User Manual

Multiplicative and Additive Bias
Shadows are essentially textures applied to objects in the scene that occasionally result in
“fighting.” Z-fighting results when portions of an object that should be receiving shadows
instead render over the top of the shadow because they effectively exist in the same exact
location in 3D space.
Results of shadow map Z-fighting (top), and the
corrected shadow shown using Biasing (bottom).
Two Biasing sliders in the Shadows group of Spotlight parameters work by adding a small depth
offset to move the shadow away from the surface it is shadowing, eliminating the Z-fighting.
When too little bias is added, the objects can self shadow themselves. When too much is
added, the shadow can become separated from the surface.
The Multiplicative and Additive Bias sliders, and the Non-Transmissive
Materials checkbox, all in the Spotlight Inspector controls.
The goal is to adjust the Multiplicative Bias slider until the majority of the Z-fighting is resolved,
and then adjust the Additive Bias slider to eliminate the rest. The softer the shadow, the higher
the bias will probably have to be. You may even need to animate the bias to get a proper result
for some particularly troublesome frames.
Force All Materials Non-Transmissive
How light passes through a semi-transparent material plays an important role in determining the
appearance of the shadow an object casts. Normally, this transmittance behavior is defined in
each object’s Materials tab. However, selecting Force All Materials Non-Transmissive in the
Spotlight Inspector overrides this, causing the shadow map produced by the node to ignore
transmittance entirely.
Chapter – 76 3D Compositing Basics 1561