Routines
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62E8: Check missile collision against viewport objects
Used by the routine at check_collision.
Iterates through viewport_slots (viewport_slots) checking if the player's missile collides with any object. Each slot is 3 bytes: X, Y, and definition.
Collision detection uses type-specific bounding boxes. Most objects are 10x8 pixels, but balloons and fuel depots are taller (17-25 pixels), and ships are wider (19 pixels).
On hit, dispatches to type-specific handlers: hit_helicopter_reg (helicopter), hit_ship (ship), hit_helicopter_adv (advanced helicopter), hit_fighter (fighter), hit_balloon (balloon), hit_fuel (fuel). If no known type matches, checks check_fragment_collision for fragment collision.
During GAMEPLAY_MODE_REFUEL, object Y coordinates are adjusted for scrolling before and after collision checks.
check_missile_vs_objects 62E8 LD HL,($5F60) Load object coordinates (C=X, B=Y) from list pointer current_slot_ptr and advance by 3.
62EB LD C,(HL)
62EC INC HL
62ED LD B,(HL)
62EE INC HL
62EF INC HL
62F0 LD ($5F60),HL Store updated pointer; copy X to A for marker check.
62F3 LD A,C
62F4 CP $00 If empty slot, skip to next object.
62F6 JP Z,check_missile_vs_objects
62F9 CP $FF If end-of-set marker, jump to check_missile_vs_objects_end for fragment collision check.
62FB JP Z,check_missile_vs_objects_end
62FE LD A,($5F68) If GAMEPLAY_MODE_REFUEL, call advance_object to adjust object Y for scrolling.
6301 CP $06
6303 CALL Z,advance_object
Y-axis collision check (entity height: 9 pixels).
6306 LD DE,($5EF3) Check if entity_Y + 9 >= object_Y; if not, next object.
630A LD A,D
630B ADD A,$09
630D LD H,$00
630F LD L,A
6310 LD D,$00
6312 OR A
6313 LD E,B
6314 SBC HL,DE
6316 JP M,check_missile_vs_objects (continued).
6319 LD A,B Set up D = object_Y + 8, E = 0 (height offset).
631A ADD A,$08
631C LD D,A
631D LD E,$00
631F LD HL,($5F60) Load object type from viewport pointer.
6322 DEC HL
6323 LD A,(HL)
6324 AND $07 If balloon, call get_offset_balloon (E = 9, taller).
6326 CP $06
6328 CALL Z,get_offset_balloon
632B CP $07 If fuel depot, call get_offset_fuel (E = 17, tallest).
632D CALL Z,get_offset_fuel
6330 LD A,D Check if object_Y + 8 + offset >= entity_Y; if not, next object.
6331 ADD A,E
6332 LD DE,($5EF3)
6336 LD H,$00
6338 LD L,A
6339 LD E,D
633A LD D,$00
633C OR A
633D SBC HL,DE
633F JP M,check_missile_vs_objects (continued).
X-axis collision check (entity width: 8 pixels).
6342 LD DE,($5EF3) Check if entity_X + 8 >= object_X; if not, next object.
6346 LD A,E
6347 ADD A,$08
6349 LD E,A
634A LD H,$00
634C LD L,E
634D LD D,$00
634F LD E,C
6350 OR A
6351 SBC HL,DE
6353 JP M,check_missile_vs_objects (continued).
6356 LD A,C Set up D = object_X + 10, E = 0 (width offset).
6357 ADD A,$0A
6359 LD D,A
635A LD E,$00
635C LD HL,($5F60) Load object type from viewport pointer.
635F DEC HL
6360 LD A,(HL)
6361 AND $07 If ship, call get_offset_balloon (E = 9, wider).
6363 CP $02
6365 CALL Z,get_offset_balloon
6368 LD A,D Store object coordinates to collision_coordinates for hit handlers.
6369 ADD A,E
636A LD DE,($5EF3)
636E LD ($5F8B),BC (continued).
6372 LD H,$00 Check if object_X + 10 + offset >= entity_X; if not, next object.
6374 LD L,A
6375 OR A
6376 LD D,$00
6378 SBC HL,DE
637A JP M,check_missile_vs_objects (continued).
Collision detected - prepare for type dispatch.
637D LD A,($5F68) If GAMEPLAY_MODE_REFUEL, call retract_object to undo Y adjustment.
6380 CP $06
6382 CALL Z,retract_object
6385 LD ($5F8B),BC Store object coordinates to collision_coordinates.
6389 LD HL,($5F60) Load object type from viewport pointer.
638C DEC HL
638D LD A,(HL)
638E AND $07 If type is 0, jump to process_collision_hit to process collision.
6390 CP $00
6392 JP Z,process_collision_hit
6395 DEC HL Mark object slot as empty.
6396 DEC HL
6397 LD (HL),$00
6399 LD D,$00 Clear D for type dispatch.
639B CP $01 If helicopter, jump to hit_helicopter_reg.
639D JP Z,hit_helicopter_reg
63A0 CP $02 If ship, jump to hit_ship.
63A2 JP Z,hit_ship
63A5 CP $03 If advanced helicopter, jump to hit_helicopter_adv.
63A7 JP Z,hit_helicopter_adv
63AA CP $05 If fighter, jump to hit_fighter.
63AC JP Z,hit_fighter
63AF CP $06 If balloon, jump to hit_balloon.
63B1 JP Z,hit_balloon
63B4 CP $07 If fuel depot, jump to hit_fuel.
63B6 JP Z,hit_fuel
End of object list - check fragment collision and tank shell.
check_missile_vs_objects_end 63B9 CALL check_fragment_collision Reset current_slot_ptr/exploding_fragments_ptr to list starts.
63BC LD HL,$5F00
63BF LD ($5F60),HL
63C2 LD HL,$5F2E
63C5 LD ($5F62),HL
63C8 LD A,($5F8B) If fragment collision detected ($02), jump to reset_gameplay_mode.
63CB CP $02
63CD JP Z,reset_gameplay_mode
63D0 LD BC,($7385) Compare missile Y with tank shell Y; if equal, jump to reset_gameplay_mode.
63D4 LD DE,($8B0C)
63D8 LD A,B
63D9 CP D
63DA JP Z,reset_gameplay_mode
Entry point for collision hit processing. Cleans up stack and finalizes collision.
process_collision_hit 63DD POP DE Pop four words from stack (unwind call frames).
63DE POP DE
63DF POP DE
63E0 POP BC
63E1 LD A,D Store hit Y coordinate to state_collision_y.
63E2 LD ($5EF6),A
63E5 LD HL,$5F2E Reset exploding_fragments_ptr and current_slot_ptr to list starts.
63E8 LD ($5F62),HL
63EB LD HL,$5F00
63EE LD ($5F60),HL
63F1 LD BC,($5F8D) Load saved coordinates from state_saved_object_coords.
63F5 LD ($5EF3),BC Store to state_plane_missile_y.
63F9 JP finalize_collision Finalize collision.
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