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Routines |
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'Interactions' in Avalon are based on matching event values. For example:
Items that can be affected by other actions/items have extra data in the room item table (29551). This additional data indicates the next 'state' of the item (e.g. closed chest > open chest)
Some items are hidden until another item is used (in the aforementioned case of chests holding objects).
A successful value match between the acting item, and the item acted upon, advances the state of the object to the next one.
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| 52263 | LD A,(60303) | Event number ID to check for this item (acting on another item, e.g. a key opening its corresponding chest) | ||
| 52266 | CP 0 | |||
| 52268 | JR Z,52278 | If zero, there's nothing to check | ||
| 52270 | CP 137 | |||
| 52272 | JP Z,55944 | Special check for event/collision #137 - Maroc using CALIBURN on AVELACH. This ends the game. | ||
| 52275 | CALL 58032 | Copy room item event data into working buffer | ||
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Event/collision checking:
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| 52278 | LD A,(60302) | Event number for items acting on this item (e.g. for a chest, which is opened by a key) | ||
| 52281 | LD C,A | |||
| 52282 | CP 15 | Event 15 means an item is collectible (Maroc can pick it up) | ||
| 52284 | JP Z,52338 | If so, check if Maroc has picked up the item, either by moving over it or given it by the servant | ||
| 52287 | CALL 57293 | For all other events, run an event check for this item | ||
| 52290 | CP 1 | Has a collision/event occurred? | ||
| 52292 | JP NZ,52338 | If not, skip to the next routine | ||
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EVENT/COLLISION HAS TAKEN PLACE
For the object acted upon, advance its 'state' by one, to the next state:
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| 52295 | LD A,(60300) | Grab the byte containing the number of 'states' for the object | ||
| 52298 | LD C,A | |||
| 52299 | LD A,(60297) | Current object state number (starts at 1 for default object state) | ||
| 52302 | INC A | Increment object state by one | ||
| 52303 | CP C | |||
| 52304 | JR C,52310 | |||
| 52306 | JR Z,52310 | Object state <= max states for this item, skip the next instruction | ||
| 52308 | LD A,1 | Object state > max states for this item, so reset the object state to 1 | ||
| 52310 | LD HL,(60228) | Address pointer to start of item's data set at 29551 | ||
| 52313 | INC HL | |||
| 52314 | INC HL | |||
| 52315 | INC HL | |||
| 52316 | INC HL | Move to the 5th byte of set, containing the item's state number | ||
| 52317 | LD (HL),A | ...and store the new state number. | ||
| 52318 | CALL 56028 | Fetch object state and prepare graphics for printing | ||
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Set properties for the new object state
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| 52321 | LD A,(60301) | Get first byte of object state data | ||
| 52324 | AND 248 | Filter out bits 0-2 (values 0-7) | ||
| 52326 | LD C,A | |||
| 52327 | LD A,(60238) | Get the current item properties byte | ||
| 52330 | AND 31 | Keep bits 0-4... | ||
| 52332 | OR 5 | Set bits 0 (item is visible) and 2 (item is moving/will need erasing) | ||
| 52334 | OR C | ...append the rest of the bits from the new-state-object... | ||
| 52335 | LD (60238),A | ...and re-store. | ||
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