customDepthMaterial property
Custom depth material to be used when rendering to the depth map. Can only be used in context of meshes. When shadow-casting with a DirectionalLight or SpotLight, if you are (a) modifying vertex positions in the vertex shader, (b) using a displacement map, (c) using an alpha map with alphaTest, or (d) using a transparent texture with alphaTest, you must specify a customDepthMaterial for proper shadows.
Implementation
Material? customDepthMaterial;