Missiles & the Ball#

The other three movable objects — two missiles and one ball — are the TIA’s single-bit shapes. They have no bitmap; each is just a solid colored rectangle whose only graphic choice is its width. That makes them cheap to position and toggle, which is exactly what you want for bullets, balls, and small markers.

The missiles#

Missile 0 and missile 1 are turned on by ENAM0 / ENAM1 and positioned with the same strobe-and-HMOVE dance as the players (RESM0/RESM1, HMM0/HMM1). The catch — and the convenience — is color: a missile has none of its own. M0 always draws in player 0’s color (COLUP0), M1 in player 1’s. A missile is, by design, this player’s projectile.

One special register ties them together: RESMP0 / RESMP1 — “reset missile to player.” While its bit is set, the missile is hidden and locked to the center of its player; clear it, and the missile is released exactly there. That’s the standard way to fire a shot from a character’s position: lock the missile to the player, then unlock it the frame the trigger is pulled, and the bullet starts dead-center on the sprite.

The ball#

The ball (ENABL to enable, RESBL/HMBL to position) works the same way, with one difference in where it borrows its color: the ball uses the playfield color, COLUPF. That’s why the ball in Pong, Combat, and Breakout matches the walls — and why the ball is so often repurposed as a piece of playfield: a center divider, a moving wall segment, a status pip. It’s a fifth colored block you can put anywhere.

Its width is set by CTRLPF (the same playfield control register) rather than NUSIZ, in the same 1/2/4/8-clock steps as a missile. VDELBL gives it the same one-line vertical delay the players have.

In Practice#

• Borrowed colors are a feature, not a limit. Because missiles inherit player colors and the ball inherits the playfield color, you rarely have to think about coloring them — and you can lean on it: a missile reads as belonging to its player, a ball reads as part of the wall.
• The ball is a free movable object. Out of bullets to fire but need one more thing that moves? The ball is a general-purpose colored rectangle — many games use it for something that has nothing to do with a “ball.”
• They collide too. Missile-to-player, ball-to-playfield, missile-to-missile — every overlap is latched in hardware, which is what turns “the bullet reached the tank” into a game event. That’s the Collisions chapter.