Bubble Bobble

01 · Controls

Two sticks, and what each move costs in frames

The game reads both joysticks every other frame, inside the raster interrupt, and never the keyboard during play except for two keys.

Move	What happens	Where
Left, right	Two pixels a step, 25 steps a second. A wall stops the step unless the player is above Y `$2D` or between two cells.	`$226B`
Up	A jump of 15 steps up the arc, 43 pixels in the running game. The player drifts sideways only when the stick leans the way the player already faces.	`$222B`
Up, in the air	With up held, the game looks for a bubble under the player and starts the jump again from it: the manual's "bounce on the bubbles".	`$217A`
Fire	A bubble, then eight passes of the main loop before the next. The bubble flies 64 pixels in eight passes, small for three, medium for three, full size from the seventh.	`$22E8`, `$7F53`
Fire, when out	A player with no lives rejoins on their own stick while a credit is left, with three lives in play and a score of zero.	`$052A`
RUN/STOP	Pauses. The game waits for the key to go up, come down and go up again, with the round timer held.	`$7E80`
Q	Quits: the sound stops, and 25 frames later the score table is back.	`$7EC1`

The player's routine runs on every other frame ($1CBD), so a step a call is 25 a second. The shoe item sets a flag that gives the player a second call on alternate runs: three steps in four frames.

Player 1 is the stick in port 2 and player 2 the stick in port 1 ($1CBD reads $DC00 and then $DC01). On the title page fire on either stick goes on to the score table, where 1 or 2 picks the number of players. The C64-Wiki says Space switches between one and two players; nothing in the code reads the Space key, and the jump height and the bubble's flight above were measured in the emulator from the round-start snapshot.