Routines
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EE30: Check Entities Near Trap Door
Used by the routine at Open_TrapDoor.
Scan complex entity state starting at StateData_Boney. Returns with the carry flag set when the trap door should open (an entity of type 32 is present and nearby entities have been adjusted). Called by Open_TrapDoor.
Output
F Success marker set if the trap door should open
Check_EntitiesNearTrapDoor EE30 LD IX,$8EE9 Point IX at Boney's complex entity state (StateData_Boney).
EE34 LD DE,$000E Load DE with 000E.
EE37 LD HL,$72B3 Point HL at the game event flags (GameEventFlags).
Scan complex entities for ones standing in the trap door X band of rooms 02–04.
CheckNearTrapDoor_Scan EE3A LD A,(IX+$00) Fetch the current entity's type for the type test.
EE3D CP $32 Is A equal to 32? If so, jump to CheckNearTrapDoor_FoundSceneryBlock.
EE3F JP Z,CheckNearTrapDoor_FoundSceneryBlock
EE42 OR A Is A zero? If so, jump to CheckNearTrapDoor_NextEntity.
EE43 JR Z,CheckNearTrapDoor_NextEntity
EE45 CP $21 Is A less than 21? If not, jump to CheckNearTrapDoor_NextEntity.
EE47 JR NC,CheckNearTrapDoor_NextEntity
EE49 LD A,(IX+$04) Load A with the current entity's room index.
EE4C CP $05 Is A equal to 05? If so, jump to CheckNearTrapDoor_NextEntity.
EE4E JR Z,CheckNearTrapDoor_NextEntity
EE50 CP $02 Is A less than 02? If so, jump to CheckNearTrapDoor_NextEntity.
EE52 JR C,CheckNearTrapDoor_NextEntity
EE54 BIT 7,(IX+$01) Is bit 07 of the current entity's flags byte 1 set? If so, jump to CheckNearTrapDoor_NextEntity.
EE58 JR NZ,CheckNearTrapDoor_NextEntity
EE5A LD A,(IX+$08) Load A with the current entity's x-extent.
EE5D CP $6C Is A less than 6C? If so, jump to CheckNearTrapDoor_NextEntity.
EE5F JR C,CheckNearTrapDoor_NextEntity
EE61 LD A,(IX+$07) Load A with the current entity's x-coordinate.
EE64 CP $74 Is A less than 74? If not, jump to CheckNearTrapDoor_NextEntity.
EE66 JR NC,CheckNearTrapDoor_NextEntity
EE68 CP $72 Is A less than 72? If so, jump to CheckNearTrapDoor_CheckEntityType.
EE6A JR C,CheckNearTrapDoor_CheckEntityType
EE6C JR NZ,CheckNearTrapDoor_SetBit7 Jump to CheckNearTrapDoor_SetBit7 to continue if the comparison did not match.
EE6E SET 6,(IX+$03) Set bit 06 of the current entity's flags byte 3.
EE72 JR CheckNearTrapDoor_MarkEntity Jump to CheckNearTrapDoor_MarkEntity to handle the trap door.
Flag this near-trap entity with bit 07 (right-of-band side).
CheckNearTrapDoor_SetBit7 EE74 SET 7,(IX+$03) Set bit 07 of the current entity's flags byte 3.
EE78 JR CheckNearTrapDoor_MarkEntity Jump to CheckNearTrapDoor_MarkEntity to handle the trap door.
For X in the inner band: poke Bad Tempered Thing state for Berk, else just mark the entity.
CheckNearTrapDoor_CheckEntityType EE7A LD A,(IX+$00) Fetch the current entity's type for the type test.
EE7D CP $14 Is A less than 14? If not, jump to CheckNearTrapDoor_ClearPass.
EE7F JR NC,CheckNearTrapDoor_ClearPass
EE81 CP $01 Is A equal to 01? If not, jump to CheckNearTrapDoor_MarkEntity.
EE83 JR NZ,CheckNearTrapDoor_MarkEntity
EE85 LD A,$07 Load A with 07.
EE87 LD ($72C7),A Set the Bad Tempered Thing state (BadTemperedThingState).
Set bit 00 on the near-trap entity, then advance.
CheckNearTrapDoor_MarkEntity EE8A SET 0,(IX+$02) Set bit 00 of the current entity's flags byte 2.
Advance to the next complex entity in the near-trap scan.
CheckNearTrapDoor_NextEntity EE8E ADD IX,DE IX+=DE.
EE90 JR CheckNearTrapDoor_Scan Jump to CheckNearTrapDoor_Scan to handle the trap door.
Restart from StateData_Boney to clear near-trap marks when no type-32 was found.
CheckNearTrapDoor_ClearPass EE92 LD IX,$8EE9 Point IX at Boney's complex entity state (StateData_Boney).
Clear pass: wipe bit 00/06/07 marks until type 32, then refuse the open.
CheckNearTrapDoor_ClearScan EE96 LD A,(IX+$00) Fetch the current entity's type for the type test.
EE99 CP $32 Is A equal to 32? If so, jump to CheckNearTrapDoor_NoOpen.
EE9B JR Z,CheckNearTrapDoor_NoOpen
EE9D BIT 0,(IX+$02) Is bit 00 of the current entity's flags byte 2 set? If not, jump to CheckNearTrapDoor_ClearNext.
EEA1 JR Z,CheckNearTrapDoor_ClearNext
EEA3 RES 0,(IX+$02) Reset bit 00 of the current entity's flags byte 2.
EEA7 RES 6,(IX+$03) Reset bit 06 of the current entity's flags byte 3.
EEAB RES 7,(IX+$03) Reset bit 07 of the current entity's flags byte 3.
EEAF CP $01 Is A equal to 01? If not, jump to CheckNearTrapDoor_ClearNext.
EEB1 JR NZ,CheckNearTrapDoor_ClearNext
EEB3 LD A,$05 Load A with sound index 05.
EEB5 LD ($72C7),A Set the Bad Tempered Thing state (BadTemperedThingState).
Advance during the clear pass.
CheckNearTrapDoor_ClearNext EEB8 ADD IX,DE IX+=DE.
EEBA JR CheckNearTrapDoor_ClearScan Jump to CheckNearTrapDoor_ClearScan to handle the trap door.
No open: clear the falling-entity latch (bit 02 of GameEventFlags) and return carry clear.
CheckNearTrapDoor_NoOpen EEBC RES 2,(HL) Clear the falling-entity latch (bit 02 of GameEventFlags).
EEBE RET Return.
Type 32 found: restart from StateData_Boney to nudge marked entities before opening.
CheckNearTrapDoor_FoundSceneryBlock EEBF LD IX,$8EE9 Point IX at Boney's complex entity state (StateData_Boney).
Adjust pass: shrink or bump entities that were marked near the trap door.
CheckNearTrapDoor_AdjustScan EEC3 LD A,(IX+$00) Fetch the current entity's type for the type test.
EEC6 CP $32 Is A equal to 32? If so, jump to CheckNearTrapDoor_ShouldOpen.
EEC8 JR Z,CheckNearTrapDoor_ShouldOpen
EECA BIT 0,(IX+$02) Is bit 00 of the current entity's flags byte 2 set? If not, jump to CheckNearTrapDoor_AdjustNext.
EECE JR Z,CheckNearTrapDoor_AdjustNext
EED0 LD A,(IX+$03) Load A with the current entity's flags byte 3.
EED3 LD C,A Keep the flags byte in C.
EED4 AND %00111111 A&=3F.
EED6 LD (IX+$03),A Set the current entity's flags byte 3.
EED9 LD A,C Copy the saved count/flag from C into A.
EEDA AND %11000000 A&=C0.
EEDC JR Z,CheckNearTrapDoor_ShrinkBounds Jump to CheckNearTrapDoor_ShrinkBounds to continue if the comparison matched.
EEDE RES 0,(IX+$02) Reset bit 00 of the current entity's flags byte 2.
EEE2 BIT 6,A Is bit 06 of A set? If not, jump to CheckNearTrapDoor_BumpCoordinates.
EEE4 JR Z,CheckNearTrapDoor_BumpCoordinates
EEE6 INC (IX+$07) Move this entity one character right.
EEE9 INC (IX+$08)
Bump a marked entity one character right away from the trap door band.
CheckNearTrapDoor_BumpCoordinates EEEC INC (IX+$07) Bump this entity one character right.
EEEF INC (IX+$08)
EEF2 JR CheckNearTrapDoor_AdjustNext Jump to CheckNearTrapDoor_AdjustNext to handle the trap door.
Randomly shrink a marked entity's Y/Y-extent by 04–07 characters.
CheckNearTrapDoor_ShrinkBounds EEF4 LD A,$04 Load A with 04.
EEF6 CALL PseudoRandom Call PseudoRandom to pick a pseudo-random value.
EEF9 ADD A,$04 A+=04.
EEFB LD C,A Keep A in C for the next calculation.
EEFC LD A,(IX+$05) Load A with the current entity's y-coordinate.
EEFF SUB C A-=C.
EF00 LD (IX+$05),A Set the current entity's y-coordinate.
EF03 LD A,(IX+$06) Load A with the current entity's y-extent.
EF06 SUB C A-=C.
EF07 LD (IX+$06),A Set the current entity's y-extent.
Advance to the next entity in the adjust pass.
CheckNearTrapDoor_AdjustNext EF0A ADD IX,DE IX+=DE.
EF0C JR CheckNearTrapDoor_AdjustScan Jump to CheckNearTrapDoor_AdjustScan to handle the trap door.
Signal that the trap door should open (set bit 02 of GameEventFlags, carry set).
CheckNearTrapDoor_ShouldOpen EF0E SET 2,(HL) Set the falling-entity latch (bit 02 of GameEventFlags).
EF10 SCF Signal success.
EF11 RET Return.
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