#macro FaceCamera (Object, CL)
	#local Min = min_extent (Object);
	#local Max = max_extent (Object);
	#local OL = Min + (Max-Min)/2;
	
	#declare CamL = CameraLocation;			// wherever you're putting it
	#declare CamD = vnormalize (OL-CamL);		// direction of camera view
		// One can alternately look at this as -Caml, translated to the object's
		// location by adding OL.  -CamL+OL = (OL-CamL)
	#declare CamR = vnormalize (vcross(y,CamD));	// to the right
		// The vector cross product gives a vector that is perpendicular to the two
		// given vectors.  If we're at the vertex (camera location) and we cross the 
		// direction of view and the y-axis, we get a vector pointing out to the right
		// CamD and y are likely not perpendicular, so the resulting vcross is some
		// size != 1, so we normalize the size.
	#declare CamU = vnormalize (vcross(CamD,CamR));	// camera up
		// So now we have a view direction and a right vector, which are perpendicular
		// So we do another vector cross product, and get the new "up" vector
		// Which completes our new "frame of reference".
		// The tangent, normal, and binormal unit vectors, often called T, N, and B,
		// or collectively the Frenet–Serret frame (TNB frame or TNB basis)

		// So now when we take the old x, y, and z basis vectors or normal POV-space
		// and move them to align with the new TNB vectors, your object whose
		// orientation was based upon x, y, and z is now based upon the new
		// T, N, and B vectors.  
		// Since default camera points at z, and default orientation of most objects
		// is in the xy plane, the object is now in the same relative orientation
		// to the camera in the new TNB frame, and so always faces the camera.
	#declare Object_Transform =
	transform {
		matrix <
		CamR.x, CamR.y, CamR.z,
		CamU.x, CamU.y, CamU.z,
		CamD.x, CamD.y, CamD.z,
		    0,      0,      0
		>
	}
	
	object {
		Object
		transform {Object_Transform}
	}
#end // end macro FaceCamera