Which parts should be rendered: opaque (False) or transparent (True).
ShadowVolumesReceivers: boolean;
Should we render parts that may receive shadow volumes, or ones that don't. During rendering, simply check does it match TCastleScene.ReceiveShadowVolumes.
InShadow: boolean;
If True, means that we're using multi-pass shadowing technique (like shadow volumes), and currently doing the "shadowed" pass.