Visible objects count function

How do I write a world function which returns a count of the number of objects which are visible within the world?

That's going to be very difficult, especially if you have a lot of objects. I'm assuming you mean objects the camera can see - the total number of objects in a world can't be changed during run time.

Maybe the attached - very simple - will help get you started. Note that for even one object and a very simple test (in front of or not) - setting up the test condition is far from obvious.