8

Shadow Map Parameters Rollout 1209
Left: Default shadows
Right: Increasing the Bias value separates the shadow from
the object.
If the Bias value is too low, shadows can "leak"
through places they shouldn’t, produce moire
patterns or making out-of-place dark areas on
meshes.IfBiasistoohigh,shadowscan"detach"
from an object. If the Bias va lue is too extreme in
either direction, shadows mi ght not b e rendered
at all.
This va lue depends on whether Absolute Map Bias
is on or off:
• When Absolute is off (the default), Bias is
calculated based on t he scene extents, and
then norm alized to one. Th is 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) .
• WhenAbsoluteison,Biasisavaluein3dsMax
units. User adjustments to Bias depend on the
size of the scene, and can range from values
closetozerotovaluesinthehundreds(seethe
Tip at the end of this topic).
Left: Too small a Bias value causes shadow “leaks.”
Right: Increasing the Bias value fixes the problem.
Size—Sets the size (in pixels squared) of the
shadow map that’s computed for the light.
The shadow map size specifies the amount of subdivisions
for the map. The greater the value, the more detailed the
map will be.
Left: Size set to 32.
Right: Size set to 256.
Sample Range—The sample range (page 3–1098)
determineshowmuchareawithintheshadowis
averaged. This affects how soft the edge of the
shadow is. Range=0.01 to 50.0.
Increasing the Sam ple Range blends the shadow edges and
creates a smooth effect, hiding the granularity of the map.
Absolute Map Bias—When on, the bias for the
shadow map is not normalized, but is instead
basedonafixedscaleexpressedin3dsMaxunits.