GameMaker's built-in view following, run once a step after the end step events.

An enabled view that follows an object moves so that the first instance of that object (or of an object descending from it) stays at least border {x, y} pixels inside the view's edges. It moves at most speed {x, y} pixels a step on each axis, -1 for no limit, and never past the room's edges. A view that follows nothing, or whose object has no instance, stays where it is.