Create panel > Lights > Create light. > Shadow Parameters rollout > Shadow Map chosen > Shadow Map Params rollout
The Shadow Map Parameters rollout is displayed when you have chosen shadow mapping as the shadow-generation technique for a light. You select this in the Shadow Parameters rollout. This rollout contains additional controls that are specific to mapped shadows.
Interface
Bias: Map Bias moves the shadow toward or away from the shadow-casting object (or objects).
Left: Bias set to 0.1
Right: Bias set to 2.0
If the Bias value is too low, shadows can "leak" through places they shouldn't, produce moirΘ patterns or making out-of-place dark areas on meshes. If Bias is too high, shadows can "detach" from an object. If the Bias value is too extreme in either direction, shadows might not be rendered at all.
This value depends on whether Absolute Map Bias is on or off:
When Absolute is off (the default), Bias is calculated based on the scene extents, and then normalized to one. This provides similar default shadow results, regardless of scene size. User adjustments to Bias are typically low decimal values near 1.0 (for example, 1.2).
When Absolute is on, Bias is a value in gmax units. User adjustments to Bias depend on the size of the scene, and can range from values close to zero to values in the hundreds (see the Tip at the end of this topic).
Size: Sets the size (in pixels squared) of the shadow map that's computed for the light.
Left: Size set to 128
Right: Size set to 2000
Sample Range: The sample range determines how much area within the shadow is averaged. This affects how soft the edge of the shadow is. Range=0.01 to 50.0.
Left: Sample range set to 1
Right: Sample range set to 10
Absolute Map Bias: When on, the bias for the shadow map is not normalized, but is instead based on a fixed scale expressed in gmax units. This value does not change during an animation. You must choose the value, based on the size of the scene extents.
When off, the bias is computed relative to the rest of the scene, and then normalized to 1.0. This provides a common starting bias value in scenes of any size. If the scene extents change, this internal normalization can vary from frame to frame. Default=off.
Tip: Leaving Absolute Map Bias off gives good results in most situations, because the bias is internally balanced to match the scene size. In animations, however, if moving objects cause a large change in the scene extents (or if objects are unhidden, and so on), the normalized bias value might become inappropriate, causing shadows to flicker or disappear. If this happens, turn on Absolute Map Bias. You will have to set the Bias control to a value appropriate for the scene. As a rule of thumb, try a Bias value that is the distance between the light and the target object, divided by 100.