function ShadowPass(context) {
  this.camera = new ShadowMapCamera();
  this.passState = new PassState(context);
  this.framebuffer = undefined;
  this.textureOffsets = undefined;
  this.commandList = [];
  this.cullingVolume = undefined;
}
Global maximum shadow distance used to prevent far off receivers from extending
the shadow far plane. This helps set a tighter near/far when viewing objects from space.

@private