Hydrofool: Routines

Address	Description
61A7	JP (HL) trampoline
61A8	Initialize the object free list: chain B 24-byte records starting at DE (each record's first word points to the next)
61C1	Reset object system
61E3	New-game initialization
6254	Set object position (IX+5/+6) from grid index A (cell centre: row8+4, col8+4)
6269	Set current room to A: locate its description record and build the room
62F9	Test whether the current room is this level's Plug Room
630D	Plug Room grid setup
6329	Build the door/exit bitfield at $612B from the room description's byte1
6344	Draw single-piece doors, for $612B bits 0 and 3
6377	Draw three-piece doors, for $612B bits 1 and 2
63D0	Clear shadow screen
642F	Draw the fixed wall/decoration layout selected by $6129
6470	Redraw one terrain grid cell (index in BC), used to restore terrain hidden behind an object's sprite
64BB	Draw loop shared with 6470: resolve a grid/terrain value to a sprite via the 74CE/750B tables and draw it
64F3	Redraw the whole room's terrain grid
6503	Per-frame rust/oil tick: advances the rust timer, killing the player at $52
6543	Draw one rust-gauge segment: compute its screen column from A and its sprite from table $653F, then draw via 8128
655E	Draw the rust/oil gauge: base icon plus repeated 6543 icons, scaled by the rust timer $6502
6580	Tick the rust/oil gauge
6593	Draw the message window's border/frame: corner icon plus 8-wide top and bottom edge strips, all via 8128
65DB	Draw message window: room/creature title line + rotating clue/joke message line
6622	Use an oil can (kind $6E pickup, see 8AFB): resets rust timer, decrements oil-can count, plays sound
663B	Draw the oil-can icon and its remaining count on HUD ($6198)
6653	Prepare room with color 0
6657	Get room color from room description and store to 6175
6663	Spawn the room's creature (dynamic object)
6692	Insert a record pointer (DE) into the draw queue (60EC), sorted by the record's offset+2 byte
66CE	Room build: spawn each active object then settle it to the ground (height field +0x07, via collision test 9BF0)
6728	Queue this room's dropped items for drawing
6743	Draw the room title, awarding a first-visit bonus the first time this room is entered
676D	Draw current room
67F1	Attempt to move to an adjacent room (horizontal, via a door) in the direction given by ($8DC1)
6880	Count item-table entries whose room byte matches A
6895	Draw the currently-held item's icon, and its ammo count if it's a weapon, on HUD
68C1	Consume one shot of ammo; auto-drop the weapon when empty
69AC	Draw the room's background
6AAA	Interrupt service routine: advance the frame counter, drive the AY music chip, then run per-frame game logic
6AE7	ISR continuation setup: latch the resume address and clear the frame-ready flag
6AF1	Idle loop: enable interrupts, drive the sound-effect player each pass
6AF8	Jump to new-game initialization
6AFB	Self-modified per-frame hook, called by the ISR 6AAA (currently a RET stub, patched by 6AFC)
6AFC	Patch 6AFB to RET (disabling the hook), then jump to new-game initialization
6B05	New-game initialization
6B71	Main game loop
7CEC	Print engine entry point
7CF9	Print char routine (default mode)
7D32	Print engine mode: set inverse video flag
7D3F	Print engine mode: dispatch control code $16
7D48	Print engine mode: set cursor row
7D57	Print engine mode: set cursor column
7D68	Print string routine
7DC7	Print engine: plot one character glyph into the shadow-screen font buffer, then blit it
7E4F	Flip sprite horizontally
7EA9	Scan all 6 keyboard half-rows into the row-snapshot buffer at $6184 down to $617F, used by 7EBE's input reader
7EBE	Read input: normalize the active control method into the 5-bit mask at 6186
7F8E	Reset the redraw bounding-box trackers ($6194-$6197) to empty
7F9B	Fold a screen rectangle (DE = top/left, HL = bottom/right pair) into the running redraw bounding box $6194-$6197
7FC0	Reset the sprite-draw clip window ($610A-$610D) to the full play-field
7FCD	Compute the current sprite's own screen bounding box, clamped to the play-field, and fold it into the redraw tracker
8011	Sprite draw: clip the current sprite against the screen window ($610A-$610D), adjusting its data pointer and dimensions
809D	Sprite draw: build the per-row blit queue for the shadow screen, from the clipped sprite
8107	Sprite draw: execute the blit queue built by 809D, copying 2 planes (pixels+attributes?) per queued row
8128	Draw sprite C with its mask at screen position DE (mask sprite number from the table at 6C06; A bit 7 = mirror flag)
8230	Sprite draw: masked blit (AND mask, OR sprite data) into the shadow screen -- full-width and partial-width paths
82A6	Non-aligned sprite blit: copy the nibble-merged buffer (built by 82DB) to the destination, row by row
82DB	Sprite draw: RRD nibble-shift tail for 5 planes, non-byte-aligned blit variant
82F0	Sprite draw: full-width unmasked row copy (no mask needed, direct LDIR per row)
8315	Draw a wall/decoration piece
835E	Flush the queued redraw requests at $9D3C: draw each piece via 8315, then clear the queue
8445	Per-frame sound-effect player: step the currently-playing effect's tone commands
848E	Request sound effect A (queued at $61A2, gated by the $61A0/$61A1 flags)
84AE	Dynamic object allocator
84ED	Load a sprite's A5DC record into the "current sprite" scratch variables at 618D, ready for 8128 to draw it
8501	Print string at HL until terminator byte $5E or $2B
850E	Print an inline string embedded right after the caller's CALL instruction
8513	Print a message-window string
8523	Print a BCD number
854C	Print one digit (JP target self-modified by 8523)
854F	Print BCD byte A as two digits, high digit blanked to a space if zero
8596	System/interrupt setup before the main menu
85A1	Main menu screen: title, entry list A-D, controls menu; loops until a selection starts the game
86CC	Draw the end-game stats screen
885A	Redraw the score display on HUD (last 4 BCD digits of 611B via 8523)
8879	Add a 5-digit BCD value at 8874 to the score (611B)
888E	Add a bonus (HL, 5-digit BCD) to the score, then redraw the score display
8894	Subtract a BCD value from the score
88B9	Read the next value from a small circular queue, head pointer at IY+0/1, wrap pointer at IY+2/3, advancing the head
88D7	Add a bonus to the score, value from a circular queue via 88B9
88DD	Subtract a BCD value from the score, value from a circular queue via 88B9
88E3	Search the buffer at $7C83 for byte A (CPIR, length from $7C88)
8968	PLAYER per-frame behaviour handler
8A87	Attempt to move to an adjacent room (vertical, via whirlpool/bubble)
8ABB	Apply the object's facing direction to its position (IX+5/+6), returning the OLD position in BC
8AD9	Take one walk step
8AFB	Fire/pick-up button handler: attack with the held weapon, or pick up/drop an item
8C35	Weapon hit-response text: print "BLOCKED" via 8513, then return
8CDF	Player dive-depth step
8D11	Alternate PLAYER behaviour handler (swapped into $8DB9 by 9564; see 8968 and 8DB6)
8D8D	Attack: fire the held weapon (reached from 8AFB when a weapon is held)
8E3F	Special grid-value spawn routine (value $68) -- rearing snake
8E6E	Creature spawn: compute initial height
8EA7	Special grid-value spawn routine (values $66/$6A) -- bubble source ($6A full-strength, $66 weak; see 9602)
8EF2	Special grid-value spawn routine (value $67) -- plant/coral
8F1E	Special grid-value spawn routine (value $69) -- whirlpool
8F4C	Special grid-value spawn routine (value $6B) -- plug
8F82	Spawn room-membership-gated decoration pairs
9021	Per-frame animation-table stepper
9085	Object type stub: dispatch into 90A8's creature AI setup
90A8	Creature idle/wander AI
91A6	Creature pause/transform step
9208	Object type stub: dispatch into 9232's shared setup
9232	Object type stub: dispatch into 90A8's creature AI setup
923E	Save continuation
925C	Creature waypoint movement
9341	Room-creature per-frame behaviour handler
9401	Creature hit/defeat sequence, called from 9341 when the "just hit" flag (bit 2 of +0x0D) is set
9471	Behaviour handler of the fixed object record at $8E0F (object identity not yet known)
949E	Behaviour handler of the fixed object record at $8E27 (object identity not yet known)
94CA	Object lifetime tick
94EE	Per-frame behaviour handler for value-$67 objects -- plant/coral
94F4	Plug Room win-condition trigger
952D	Per-frame behaviour handler for value-$69 objects -- whirlpool
957C	Per-frame behaviour handler for value-$66/$6A objects -- bubble source
9602	Per-frame behaviour handler for the individual rising-bubble particle spawned by 957C
9684	Per-frame behaviour handler for value-$68 objects -- rearing snake
9745	Mark and redraw the static terrain cells behind an object's sprite, so moving objects don't leave trails
97BA	Draw an object's sprite
97FC	Change current room to A = new room number
9808	Per-frame main loop entry
983C	Per-frame dynamic object dispatcher (walks the active object list from the head at 610E)
9900	Draw all queued objects: walk the record-pointer list at $60EC (count at $60EB), drawing each via 97BA
9923	Spawn the weapon projectile object (thrown from the player's position, facing $8DC1), handler 9963
9963	Weapon projectile per-frame handler: move (double step) and detect a hit on collision
99A1	Direction-indexed sprite-animation stepper
99D1	NEG / not NEG
99D5	Sprite-animation stepper: read next entry from a per-object sprite-number table, advancing a phase counter
9A49	Snap the object's position (IX+5/+6) to its grid-cell centre, then finalize via 9A60
9A60	Dynamic object finalizer
9AAB	Search the (key,data) pair table at $74CE for key A; returns Z with HL pointing at the matched pair's data byte
9ABC	Terrain collision test for one screen point (B,C): convert to a grid cell and check its content
9AFD	Terrain sub-cell shape resolver
9B5A	Collision/overlap scan
9BD4	Depth-tie resolver
9BF0	Collision test
9C35	End-of-frame screen flip
FB90	Menu tune + key-wait driver
FBB4	Melody-index table reader/advancer, used by FBD7
FBC1	Melody-index to period lookup, used by FBD7
FBCF	Continuation of FBB4
FBD7	Play one note / check key selection
FC34	Tone generator loop (continued)
FC46	Plain delay loop (no sound)