Time Tunnel

01 · Every room

Every room, as the gnome walks in

Pick a room. Dark rooms stay black until the gnome carries the lit torch in; the button lights them.

Each picture comes from the game's own code, run on the site's copy of the C64's processor, the 6502, over the game's listing (its program, as the Source code tab shows it; the numbers marked $ are addresses in it, in hexadecimal). First runs the start-up's unpacking of where every object begins (obj_start_table, $0909). Then come the era's character set, the small 8 by 8 pictures the screen is built from (era_load_charset, $3456), and room_enter ($3A47). That routine draws the room's screen, gives a sprite to each object there (a picture the video chip moves over the screen by itself) and runs the era's own code for entering the room. The era's code is why some rooms differ from their screen: the gold rush's dark house and the caves of Persia and the Stone Age go black without the lit torch, and the throne room puts the staff in the king's hand. The gnome himself is left out.

Some rooms share a screen. Persia's cave is four rooms with one picture, the Stone Age's three caves are another, and three of the spaceship's corridors are a third. What tells them apart is the code: each room has its own doorways, objects and puzzle. The time machine's controls are drawn in the C64's built-in letters (its character ROM), which this site does not carry, so that room shows the emulator's picture.

Eight of these pictures were checked against the emulator, with the gnome brought into each room at the start of a game by the game's own routine for entering an era (era_enter): the mansion's hall, the gold rush's saloon street, Persia's sunset hills, the Stone Age's first cliffs, Greece's temples, a spaceship corridor, Salem's church street, and the throne room. Apart from the gnome, and the staff in the throne room, which flickers through colours every frame, every pixel matches (test_rooms.js, against the pictures in reference/).