Through the Trap Door: Routines

Address	Description
34438	Display main menu and handle main game loop
34675	Pause
34695	Copy state data for all resettable complex entities into table of initial-state data for complex entities
34751	Reset all game data in preparation for new game
34864	Copy start addresses of current level's data blocks and clean up old data
34916	If fire pressed, or character-swap-pending flag set, then swap characters
35577	Change direction Berk is facing depending upon relative position of Drutt
35689	Update state of Berk and store current position in script data
35735	Update state of Berk depending upon currently selected character, control input and currently active power
36008	Make Berk eat the entity he is holding, if edible, and exit calling routine
36036	Update state of Berk (forward pressed)
36116	If Berk is not horizontally aligned with entity at IY then move Berk closer and exit calling routine
36296	Make Berk drop the entity he is holding and load IY with its complex state data address
36367	If Berk is neither facing into the screen nor walking then exit calling routine and have Berk turn into screen
36385	Script routine: (59) Have Berk interact appropriately with a door behind him
36390	Script routine: (58) Have Berk interact appropriately with a door in front of him
36471	Script routine: (56) Give Berk power corresponding to entity eaten
36542	Update state of Berk (floating power active)
36610	Script routine: (57) Cycle attributes (full-screen), clear display buffers and paint red areas outside current room
36616	Cycle attributes (full-screen), clear display buffers and paint red areas outside current room
36638	Advance to next level and if back to level 1 then exit calling routine and make Berk start falling
36753	Set Berk's horizontal position to match level 1's entry door
36778	Initialise script data positions for flying skeleton creature and bat (level 1)
36791	Update states of all level 1 entities
36887	Execute script data for Boni's kidnap and handle Trap Door opening and closing
36921	Open Trap Door if Berk is near the left side of the Trap Door room
36947	Advance HL to next script instruction and start executing
36950	Script routine: (36) Remove Boni from level 1
36957	Script routine: (37) Remove flying skeleton creature from level 1, and terminate script processing
36966	Close the Trap Door if Berk is not in room 1 and Drutt is in room 4 (level 1)
36984	Script routine: (38) Close the Trap Door
36990	Script routine: (39) Open the Trap Door
36996	Close the Trap Door
37004	Open the Trap Door
37062	Update state of bat (level 1) and store current position in script data
37085	Update state of bat (level 1)
37586	Update the states of the spiders (level 1) and store current positions in script data
37639	Update the state of a spider (level 1)
37718	Script routine: (41) Move spider up one character and, if home, reset its timer and make it wait
37753	Script routine: (42) Decrease remaining time until spider next descends and if zero, start descent
37778	Script routine: (40) Move spider down one character, and if at bottom, advance it to bounce / climb up mode
38009	Update states of all level 2 entities
38054	Update state of Bubo (level 2) and store current position in script data
38074	Update state of Bubo
38165	Script routine: (61) Fire Bubo's projectile
38219	Update state of Bubo's projectile
38377	Start level 2 key falling if Bubo's projectile is in place below it
38468	Reset current positions in ape-beasts' script data to initial values
38480	Update states of ape-beasts (level 2) and store current positions in script data
38540	Update state of an ape-beast
38554	Script routine: (60) Check position of ape-beast and turn if appropriate
38592	Update states of stalactites (level 2)
38756	Move entity at IX down one character
39137	Update states of all level 3 entities
39151	Update state of hatch (level 3)
39278	Update state of clawed foot (level 3)
39601	Update states of coloured creatures
39699	Count coloured creatures in slots and return if all are home
39760	Present reward for getting coloured creatures home
39776	Update state of large yellow creature (level 3)
39934	Set large yellow creature's mode to "returning home", and set Berk-has-been-killed flag
39944	Set graphic layout data address for entity at IY to BC
39951	Move entity at IY down two characters
39961	Move entity at IY up two characters
39971	Move entity IY such that its left edge is up to two characters closer to entity IX's
39998	Set large yellow creature's mode to "returning home", move one step closer to home and return
40008	Move entity at IY one step closer to home position
41211	Update states of all level 4 entities
41354	Reset skeleton to initial state
41381	Update state of skeleton (level 4) and store current position in script data
41424	Update state of skeleton (dying)
41498	Kill Berk if he collides with skeleton
41550	Script routine: (63) Have skeleton advance or retreat based upon positions of Berk and yellow skull
41617	Script routine: (64) Set random (1 to 10) number of iterations in following loop script instruction
41633	Update state of ghost
41767	Update state of cannon and projectile
41961	Update state of cannon's projectile
42064	Update states of drips (level 4)
42251	Set a drip's (level 4) stage to A
42266	Update state of flying skeleton creature (level 4)
42381	Update state of snake (level 4)
42486	Open snake's mouth and set Berk-has-been-killed flag if snake and Berk have collided
42505	Move entity at IX right one character
42512	Set graphic layout data address for entity at IX to BC
45899	Populate primary display buffer with layout data for current character's current room
45965	Populate primary display buffer with graphic layout data for entity whose simple / complex state data is at address in IX
45999	Advance graphic layout data pointer by two bytes, and process data
46218	Jump to appropriate graphic layout routine
46284	Graphic layout routine: (237) Set new pending sound
46295	Graphic layout routine: (242) Set current attribute
46306	Graphic layout routine: (244) Set current graphic set index
46317	Graphic layout routine: (236) Set graphic index in next instruction to value randomly selected from list
46347	Graphic layout routine: (245) Decrease timer value, and if zero, reset and write random graphic index from list into next instruction
46363	Graphic layout routine: (246) Decrease timer value, and if zero, reset and write random attribute from list into next instruction
46385	Reset timer to initial value then load E with random value from sequence (in graphic layout data)
46418	Graphic layout routine: (255) Load HL with stored coordinates and return from drawing
46427	Graphic layout routine: (250) Adjust x- and y-coordinates for drawing without storing
46442	Graphic layout routine: (254) Adjust x- and y-coordinates for drawing and set as new base coordinates
46460	Graphic layout routine: (251) Process graphic layout data at following address and return when complete
46481	Graphic layout routine: (248) Jump to graphic layout data address
46495	Graphic layout routine: (249) Jump to time-weighted, randomly selected graphic layout data address in list
46559	Graphic layout routine: (243) Increment index, n, and jump to n-th address in following list
46577	Graphic layout routine: (247) Jump to randomly selected graphic layout data address from list
46594	Graphic layout routine: (253) Jump to graphic layout data address selected from list, based upon width of Berk's carried entity
46611	Graphic layout routine: (238) Start loop (1 / 2)
46628	Graphic layout routine: (239) End loop (1 / 2)
46647	Graphic layout routine: (240) Start loop (2 / 2)
46664	Graphic layout routine: (241) End loop (2 / 2)
46830	Display and handle main menu
46946	Draw joystick "J" (main menu) in colour depending upon joystick mode
46968	If "K" pressed then redefine controls
47043	Set carry flag if Kempston interface not present, or Kempston joystick moved / fire pressed
47060	Set zero flag if key whose index is in A matches a direction, or the Berk / Drutt key
47071	Set attribute and location and print double-height character in E
47084	Print keyboard controls on main menu
47140	Print "THROUGH the TRAPDOOR" string
47185	Print "SORRY BERK, BUT YOUR TIME IS UP" string
47213	Print "HOME SWEET HOME" string
47241	Reset show-score flag and draw timer figures bar
47302	If show-score flag reset then draw pair of timer figure eyes (closed) at attribute file address IX and advance IX by two bytes
47315	If show-score flag reset then draw pair of timer figure eyes (open, random frame) at attribute file address IX and advance IX by two bytes
47323	Draw a timer figure's eye (random frame) at attribute file address in IX and advance IX by one byte
47355	If show-score flag is reset then return to calling routine, else return to routine that called calling routine
47363	Update eyes of a randomly selected timer figure, increase timer tick counter and process timer figure blinking
47431	Select a remaining timer figure at random and update its eyes to a random (open-eyed) frame
47468	Increase timer tick counter and reduce remaining time if counter > 767
47499	Update scores and display
47628	Print score / total / high score string in current character's colours
47682	Print a double-height text character
47709	Print half of a double-height text character
47741	Convert number in HL to string at IY
47772	Convert a digit of numeric data to its string equivalent
47788	Read keyboard and load pressed key character into A
47893	Check for control key press and store
47930	If joystick mode is on, then read joystick input
47942	Wait for current key to be released and another to be pressed, storing in A
47955	Wait for key-press, store pressed key code in A and play main menu sound
48096	Advance HL to next script instruction and execute
48133	Script routine: (04) If current character and target entity are in the same room then set pending sound
48142	Script routine: (62) Move entity at IX into room to the left, if appropriate
48148	Script routine: (16) Have Berk hold an entity, and position it appropriately between his hands
48154	Script routine: (17) Have Berk put down an entity in front of him, if appropriate
48158	Script routine: (18) Have Berk put down an entity behind him, if appropriate
48212	Script routine: (10) Reset walking-left and walking-right flags
48216	Script routine: (12) Reset walking-left flag and set walking-right flag
48220	Script routine: (11) Set walking-left flag and reset walking-right flag
48234	Script routine: (07) Reset Berk's facing-into-screen, facing-left and facing-right flags
48238	Script routine: (06) Set Berk's facing-into-screen flag, and reset his facing-left and facing-right flags
48242	Script routine: (13) Set Berk's facing-left flag, and reset his facing-into-screen and facing-right flags
48246	Script routine: (14) Set Berk's facing-right flag, and reset his facing-into-screen and facing-left flags
48260	Script routine: (09) Reset must-process-current-script-data flag for entity at IX
48267	Script routine: (08) Set must-process-current-script-data flag for entity at IX
48274	Script routine: (15) Jump to new address if Berk is carrying something
48285	Script routine: (01) Load HL (script data pointer) with new address
48295	Script routine: (23) Start loop (1 / 3)
48307	Script routine: (24) End loop (1 / 3)
48324	Script routine: (25) Start loop (2 / 3)
48336	Script routine: (26) End loop (2 / 3)
48353	Script routine: (27) Start loop (3 / 3)
48365	Script routine: (28) End loop (3 / 3)
48382	Load A with script instruction parameter then advance HL to next instruction
48388	Decrease remaining time for current power and if zero, exit calling routine and run script data for removal of power
48417	Remove Berk's current power and reset sweet / mushroom / edible eyes / sausage to its original position
48487	Script routine: (32) Update Berk's position and state (flying) depending upon control input
48567	Script routine: (35) Move entity at IX (and any carried entities) down one character
48593	Move entity right one character, and into new room if appropriate
48641	Move entity left one character, and into new room if appropriate
48686	Script routine: (22) Move carried entity behind Berk as he faces into screen
48692	Script routine: (21) Move carried entity in front of Berk as he faces out of screen
48698	Script routine: (19) Move carried entity to Berk's left as he faces left
48704	Script routine: (20) Move carried entity to Berk's right as he faces right
48710	Move carried entity in front of Berk as he faces out of screen
48715	Move carried entity behind Berk as he faces into screen
48727	Move carried entity to Berk's right as he faces right
48738	Move carried entity to Berk's left as he faces left
48760	Load A, D and E with positional data for a carried entity or return
48850	Have Berk hold an entity, and position it appropriately between his hands
48920	Script routine: (29) Make Berk start falling, and drop his carried entity if appropriate
48934	Script routine: (30) Check Berk's fall velocity, and react to landing
49010	Script routine: (33) Advance Berk's jump and select next phase if current phase complete
51732	Reset Drutt to initial state
51739	Update states of Drutt and worm and store current positions in script data
51765	Update state of Drutt
51779	Script routine: (43) Select next action for Drutt depending upon control input
51904	Randomly select script data for rightward hop of size three or four, and execute
51924	Randomly select script data for leftward hop of size three or four, and execute
51944	Start Drutt jumping
51954	Point HL at script data for Drutt swapping depth levels and execute
51960	Move Drutt closer to the worm and eat it if close enough
52029	Script routine: (44) Move entity up one character
52038	Script routine: (45) Move entity down one character
52047	Script routine: (46) Move Drutt, or entity he is pushing left one character and start pushed entity falling if appropriate
52053	Move Drutt, or entity he is pushing left one character and start pushed entity falling if appropriate
52098	Advance position of entity pushed left by Drutt
52142	Script routine: (47) Move Drutt, or entity he is pushing right one character and start pushed entity falling if appropriate
52148	Move Drutt, or entity he is pushing right one character and start pushed entity falling if appropriate
52193	Advance position of entity pushed right by Drutt
52243	Script routine: (50) Advance Drutt's jump and select next phase if current phase complete
52309	Script routine: (51) Swap Drutt's current depth level if possible
52315	Swap Drutt's current depth level if possible
52837	Update state of worm and store current position in script data
52860	Update state of worm
52870	Script routine: (53) Move worm left if possible, otherwise choose new direction
52889	Script routine: (54) Move worm right if possible, otherwise choose new direction
52908	Execute script data for worm choosing next direction
52914	Script routine: (55) Choose new direction and start crawling (worm)
52967	Script routine: (52) Increase worm's age and decrease time until direction change, or react to Drutt's presence
53057	Increase worm's age and set its depth to zero if it has expired
53083	Attempt to spawn a new worm
53194	Load A with value indicating which direction room A lies relative to room in state data at IX
53309	Add entry to pathfinding data table for room B in direction A
53317	Set zero flag if room B has an entry in pathfinding data table, otherwise reset
53333	Load A with direction index in pathfinding data table entry at address in IX, restore registers and return
53577	Cycle attributes (long, full-screen) and clear display buffers
53581	Cycle attributes (short, full-screen) and clear display buffers
53649	Fill top 22 rows of attribute file with attribute value in A
53667	Set Berk-has-been-killed flag
53723	If Berk has been killed then reset his position and state, flash screen and decrease time / lives
53782	Set each value in primary display buffer within play area to zero
53814	Advance DE by 2 × A bytes and load word at this location into DE
53825	Copy room dimension data entry for current character / entity's current room to temporary store location
53887	Paint red areas outside accessible areas of current character's current room
53968	Print red cell to current attribute file position (outside play area) and mark as unused in display buffers
53987	Reset complex state data for first entity of class A to that stored in initial-state table
54019	Point IY at first entry in current level's complex state data that has class A
54034	Draw contents of primary display buffer to display
54144	Draw a graphic character block to display
54222	Load A with a pseudo-random number between 0 and the higher of 2 and A (input)
54283	Move entity at IX into new room (left or right) if it is at the edge of its current room
54313	Move entity at IX into room to the right, if appropriate
54348	Move entity at IX into room to the left, if appropriate
54383	Move entity at IX into room to right of its current room and update position of carried entity if moving entity is Berk
54398	Set entity's position to be left-hand side of new room to right
54419	Move entity at IX into room to left of its current room and update position of carried entity if moving entity is Berk
54434	Set entity's position to be right-hand side of new room to left
54456	Paint red areas outside current character's room if IX points to current character's complex state data
54480	Set room of entity at IX to B, store room size data for new room and load E with entity's width minus one
54505	Load B with index of room to right of an entity's current room
54539	Load B with index of room to left of an entity's current room
54569	Check entity at IX for collision with another (impassable / pushable) entity immediately to the right
54666	Check entity at IX for collision with another (impassable / pushable) entity immediately to the left
54764	Check entity at IX for collision with another entity at next depth level out of screen whose interaction-(11,6) flag is set
54768	Check entity at IX for collision with another entity at same depth whose interaction-(11,6) flag is set
54878	Check entity at IX for collision with another entity (only those defined before, and in reverse order) at same depth level whose interaction-(11,7) flag is set
54890	Check entity at IX for collision with another entity (in reverse order) at next depth level into screen whose interaction-(11,7) flag is set
55023	Handle Drutt's jump, and load E with jump state index as appropriate
55041	Handle Berk's jump, and load E with jump state index as appropriate
55187	Set character-swap-pending flag
55196	Handle vertical component of character's jump, and load E with jump state index as appropriate
55421	Increase current velocity of character's jump if less than 7
55433	Change entity's room up one if appropriate
55516	Set can-fall flag and set initial velocity factor of 2 for entity defined at address in IX
55525	Move all falling entities down by distances appropriate to their current velocity factors
55616	Change entity's room down one if appropriate
59601	If current character is in same room as target entity at IX then set pending sound to A
59722	Set sound of index A as pending if appropriate, then play and clear pending sound