shadowAmbientStrength property
How much the cast shadow also darkens the image-based-lighting ambient,
from 0.0 to 1.0.
Physically the analytic light is additive over the IBL ambient, so a
shadow only removes the direct sun and leaves the ambient (sky) fully
lighting the shadowed area. That is correct when the IBL excludes the
sun, but a sky-baked environment already contains the sun's energy, so
the ambient alone reads as fully lit. This control multiplies the ambient
by mix(1.0, shadow, shadowAmbientStrength), so 0.0 leaves the ambient
untouched (the physical default) and 1.0 lets the shadow darken the
ambient as much as the direct light. A non-physical artistic control for
sky-lit scenes that want shadows to read as shadows.
Implementation
double shadowAmbientStrength;