- Find the vector from the camera origin to the object’s center.
- Determine the horizontal and vertical angles of that vector from the camera’s forward vector.
- Compare those angles to the horizontal and vertical FOV of the camera. If the angles to the object are greater than half the FOV, the center of the object is off the screen.
If you want to make sure the object is fully on screen, do the comparisons described above for the points on bounding box of the object instead of the center.