Is there any way to tell whether an object is within the frustum of an OpenGL camera - in other words whether the object is on screen or off screen? I have a bunch of jit.gl.videoplanes in a 3D space - each videoplane plays a movie, and I want to be able to stop the movie when the object is offscreen. (I've tried writing a javascript to do this, but my math skills are, um, limited, and it's not working very well.) Figured I might be missing something, and that maybe there's a more straightforward way to do this.