Index Making Pictures

Inside our outside?

It is a common need to determine which side of a plane the viewer or a character lies. As with everything else, speed is preferred to absolute accuracy. You can see some consequences in the "collision detection" section, but here are some direct examples

Our hero is climbing up a hill; but what is that bird on the ground to the left? In fact it is the other side of the hill, much larger than our hero but a distance away. It should be hidden by the hill.

This interior has a big gap in the wall, which should not be there. The picture below shows what it should look like.

The correct version.

Here there is a shadow on the ceiling. The tailed character casting the shadow is in the room above and the ceiling is opaque; so it should not be there.

Our hero approaches a door to find some hands reaching through to him. They belong to some creature the other side of the door and are not supposed to be visible.