Little Computer People

01 · The house

One picture, loaded whole

The house is a multicolour bitmap that arrives with the program: 8,000 bytes of pixels at $6000, 1,000 colour pairs at $5C00, and 1,000 colours for colour RAM. A file cannot load colour RAM, so the crack copies them in from $CC00 before the game starts. The game never draws the house. It redraws only the spots that change.

02 · The cast

183 images, packed three bytes at a time

Every image that moves is unpacked when it is needed from $E5C1–$FFB9. A count byte either copies that many literal rows of three bytes or repeats one row that many times. The 183 images take 6,649 bytes instead of 11,529. The small objects shrink most, some to 8 bytes; a body pose takes about 44.

The person on screen is four hardware sprites: his body, his head, and a black outline behind each. The dog is two and anything he carries is one. The main loop shares the eight sprites out once a pass, nearest figure first ($0FD2), and writes them at raster line $FA. There is no raster multiplexing.

His head comes in three sets of fifteen images, one set for each mood ($0D65): happy, content and sad.

The three moods, captured in the emulator with the mood byte $035F set to 0, 1 and 2.

03 · Talking to him

156 words, 34 rules and a score for manners

Every word he knows carries five bytes of concept bits, and words with the same bits are synonyms. As you type, the bits of each word are added to the sentence, and after every word the game tries its 34 rules in order. A rule fires when all of its bits are there. Then the sentence gets a score, and the score decides whether he does it.

At 8 or more the main loop empties the queue of waiting requests and he does this one at once; at 12 or more he turns to face you first (activity 46). Below 8 the request waits in a 16-entry queue at $E12A: from 4 to 7 the activity chooser takes it later, and below 4 it stays there until a request that scores 8 or more empties the queue. In the emulator, with his mood set to sad, "light a fire" scored 4 and was still waiting 25 seconds later, and "please light a fire" scored 8 and started at once.

All 34 rules

Struck-out words can never be found: WHAT'S because the apostrophe splits it, and the second entries of START, LIKE, APATHETIC and IS because the lookup stops at the first. A rule that needs one of them can never fire.

04 · His day

128 activities and a chooser

Everything he does is an activity: a small state machine whose phase picks a handler from a table. The table sits in the code right after the call that uses it, as a list of handler addresses minus one. The call does not come back: the routine pushes the chosen address and returns to that instead ($3F0C). There are 103 of these tables. The activity number lives in $8D9B and is dispatched through a table of 128 at $8DC9.

When an activity ends, the chooser ($E13F) decides what comes next, in this order: a request from a CTRL key, a typed request, food and water, bed, the activities fixed to the time of day, the morning and evening lists, and then a random pick from lists that depend on the time of day, the weekday and his routine setting.

The house clock

Every 256 frames a counter steps down from 9, and at 0 the house clock ticks ($09EB): 2,304 frames. Twelve ticks make an hour, so a day in the house is 12 × 24 × 2,304 frames. Timed in the emulator, one tick is 45,287,427 cycles, exactly 2,304 PAL frames or 45.97 seconds, which makes his day 3 hours 41 minutes long. The time you type at the start sets only the wall clock in the study.

Food, water and illness

Hunger and thirst each rise from 0 to 3 on their own timers, every 20 ticks and every 15. A need that rises from 2 makes him ill: his skin turns green (sprite multicolour $D026 = 5). The illness gets a level worse every twelve ticks and ends once both needs are below 3 ($392F). He looks after his needs before anything else, so with food and water in the house he eats, drinks and recovers. With the cupboard and the tank empty, in the emulator the illness rose one level each house hour, and at level 3 he went to bed.

Ill, in bed on the middle floor: the green is his skin colour.

Answering the phone, which also rings by itself every 32 to 63 ticks.

05 · The keys

Eight CTRL keys

The game reads the keyboard matrix itself, from the main loop, not the interrupt ($05C7): a key has to stay down until a pass of the loop comes round. CTRL with a letter gives its control code, and $2B54 turns each code into a delivery, a ring or a request.

06 · Letters

Two letters, chosen by the cupboard and the tank

Ask him to write and he goes to the typewriter in the attic and types a letter into the band above the roof. There are two bodies. The thank-you comes only while there is both food in the cupboard and water in the tank ($55C4); otherwise he writes the complaint. Both are signed "Your Friend".

"Thank you for keeping me well stocked with food and water."

"Please notice that my supplies are running low. I can't stay happy and healthy without your support."

The letter is put together at $7F40, which is the record player's work area. The complaint is 158 characters long and writes over the copy of the SID registers the player keeps at $7FCD. It does no harm, because he switches the record off before he starts to type.

07 · The music

Four piano pieces, and a record played upside down

Two sound drivers share the SID. One plays the records on the attic stereo, clocked by a CIA timer. The other plays the piano and all the effects, ticked by the raster interrupt. Both drivers' note tables are exact for an NTSC machine, so on PAL everything plays about two-thirds of a semitone flat.

The piano pieces are Mozart's Sonata in C, K. 545, Beethoven's Für Elise, the fugue in C minor from the first book of Bach's Well-Tempered Clavier, and a fourth piece that has not been identified. Activity 78 picks one at random, and while he plays, the game builds his image from three part images chosen by which keys the driver is holding down ($1585).

Record tune 2 is tune 0 upside down

The squawks

Whenever his mouth opens wide, the mouth routine ($24C8) asks for sound $15. Each call starts with a random syllable of noise through one of four band-pass filters and goes on with a random phrase of gliding notes. During one phone call in the emulator that happened 24 times.

08 · Secrets, quirks and bugs

Things the manual never told you

09 · Where it lives

From the jump table to the vectors