Comment 3 for bug 604687

I think I misunderstood your problem. Projecting on the graph plane seem to be the correct solution I guess. In 3D it may not work correctly though. Moving the camera you can in fact have your camera front vector basically perpendicular to the z-axis. In this case the intersection between your rays and the plane may suffer from precision issue. What about projecting to the plane perpendicular to the camera and containing the graph center (the point at the center of the bounding box containing the graph)?