getVirtualCamera( camera ) {

		let virtualCamera = this.virtualCameras.get( camera );

		if ( virtualCamera === undefined ) {

			virtualCamera = camera.clone();

			this.virtualCameras.set( camera, virtualCamera );

		}

		return virtualCamera;

	}
Returns a virtual camera for the given camera. The virtual camera is used to
render the scene from the reflector's view so correct reflections can be produced.

@param {Camera} camera - The scene's camera.
@return {Camera} The corresponding virtual camera.