OnBecameVisible is called when the object became visible by any camera.
This message is sent to all scripts attached to the renderer.
OnBecameVisible and OnBecameInvisible are useful to avoid computations that are only necessary when the object is visible.
Note that object is considered visible when it needs to be rendered in the scene. It
might not be actually visible by any camera, but still need to be rendered for shadows
for example. Also, when running in the editor, the scene view cameras will also
cause this function to be called.
See Also: OnBecameInvisible, isVisible.