Surround

You will probably recognize Surround as soon as you RUN it. It is a version of a fairly standard routine in which you are required to surround your adversary before he can surround you. Both players are in continuous motion and are not allowed to cross their tracks or those of their opponent, or to hit the boundary or the score display.

What will surprise you is the way in which the T/S1000/ZX81 can recognize two keys when pressed simultaneously. That is not possible using INKEY$ and is achieved by utilizing address 16421. This contains a number which changes as groups of keys are pressed. Lines 185 to 260 translate the number into a series of possible moves.

Black uses keys 1-5 to move up, Z-V to move down, Q-T for right and A-G for left. Grey uses the keys 6-0 for up, Y-P for right, B-M for down, and H-ENTER for left. After a crash the other player scores one; the winner is the first to reach 15, The routine enabling two players to participate can obviously be used in many graphics games. (T/S1000/ZX81 16K)