Microsoft now owns the patent covering split-screen seamless drop-in and drop-out co-op.
When you join, the patent adds, you are assigned as a squad member and the "screen is split to present a viewing panel" for you. And when you leave, the AI takes the reins and the screen is "un-split" to become whole again.
The patent refers to a "squad-based shooter" and is adorned with sketches that appear to be from Xbox game Brute Force.
Microsoft has yet to comment.