Routines
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60976: 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 50 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 60976 LD IX,36585 Point IX at Boney's complex entity state (StateData_Boney).
60980 LD DE,14 Load DE with 0014.
60983 LD HL,29363 Point HL at the game event flags (GameEventFlags).
Scan complex entities for ones standing in the trap door X band of rooms 2–4.
CheckNearTrapDoor_Scan 60986 LD A,(IX+0) Fetch the current entity's type for the type test.
60989 CP 50 Is A equal to 50? If so, jump to CheckNearTrapDoor_FoundSceneryBlock.
60991 JP Z,CheckNearTrapDoor_FoundSceneryBlock
60994 OR A Is A zero? If so, jump to CheckNearTrapDoor_NextEntity.
60995 JR Z,CheckNearTrapDoor_NextEntity
60997 CP 33 Is A less than 33? If not, jump to CheckNearTrapDoor_NextEntity.
60999 JR NC,CheckNearTrapDoor_NextEntity
61001 LD A,(IX+4) Load A with the current entity's room index.
61004 CP 5 Is A equal to 5? If so, jump to CheckNearTrapDoor_NextEntity.
61006 JR Z,CheckNearTrapDoor_NextEntity
61008 CP 2 Is A less than 2? If so, jump to CheckNearTrapDoor_NextEntity.
61010 JR C,CheckNearTrapDoor_NextEntity
61012 BIT 7,(IX+1) Is bit 7 of the current entity's flags byte 1 set? If so, jump to CheckNearTrapDoor_NextEntity.
61016 JR NZ,CheckNearTrapDoor_NextEntity
61018 LD A,(IX+8) Load A with the current entity's x-extent.
61021 CP 108 Is A less than 108? If so, jump to CheckNearTrapDoor_NextEntity.
61023 JR C,CheckNearTrapDoor_NextEntity
61025 LD A,(IX+7) Load A with the current entity's x-coordinate.
61028 CP 116 Is A less than 116? If not, jump to CheckNearTrapDoor_NextEntity.
61030 JR NC,CheckNearTrapDoor_NextEntity
61032 CP 114 Is A less than 114? If so, jump to CheckNearTrapDoor_CheckEntityType.
61034 JR C,CheckNearTrapDoor_CheckEntityType
61036 JR NZ,CheckNearTrapDoor_SetBit7 Jump to CheckNearTrapDoor_SetBit7 to continue if the comparison did not match.
61038 SET 6,(IX+3) Set bit 6 of the current entity's flags byte 3.
61042 JR CheckNearTrapDoor_MarkEntity Jump to CheckNearTrapDoor_MarkEntity to handle the trap door.
Flag this near-trap entity with bit 7 (right-of-band side).
CheckNearTrapDoor_SetBit7 61044 SET 7,(IX+3) Set bit 7 of the current entity's flags byte 3.
61048 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 61050 LD A,(IX+0) Fetch the current entity's type for the type test.
61053 CP 20 Is A less than 20? If not, jump to CheckNearTrapDoor_ClearPass.
61055 JR NC,CheckNearTrapDoor_ClearPass
61057 CP 1 Is A equal to 1? If not, jump to CheckNearTrapDoor_MarkEntity.
61059 JR NZ,CheckNearTrapDoor_MarkEntity
61061 LD A,7 Load A with 7.
61063 LD (29383),A Set the Bad Tempered Thing state (BadTemperedThingState).
Set bit 0 on the near-trap entity, then advance.
CheckNearTrapDoor_MarkEntity 61066 SET 0,(IX+2) Set bit 0 of the current entity's flags byte 2.
Advance to the next complex entity in the near-trap scan.
CheckNearTrapDoor_NextEntity 61070 ADD IX,DE IX+=DE.
61072 JR CheckNearTrapDoor_Scan Jump to CheckNearTrapDoor_Scan to handle the trap door.
Restart from StateData_Boney to clear near-trap marks when no type-50 was found.
CheckNearTrapDoor_ClearPass 61074 LD IX,36585 Point IX at Boney's complex entity state (StateData_Boney).
Clear pass: wipe bit 0/6/7 marks until type 50, then refuse the open.
CheckNearTrapDoor_ClearScan 61078 LD A,(IX+0) Fetch the current entity's type for the type test.
61081 CP 50 Is A equal to 50? If so, jump to CheckNearTrapDoor_NoOpen.
61083 JR Z,CheckNearTrapDoor_NoOpen
61085 BIT 0,(IX+2) Is bit 0 of the current entity's flags byte 2 set? If not, jump to CheckNearTrapDoor_ClearNext.
61089 JR Z,CheckNearTrapDoor_ClearNext
61091 RES 0,(IX+2) Reset bit 0 of the current entity's flags byte 2.
61095 RES 6,(IX+3) Reset bit 6 of the current entity's flags byte 3.
61099 RES 7,(IX+3) Reset bit 7 of the current entity's flags byte 3.
61103 CP 1 Is A equal to 1? If not, jump to CheckNearTrapDoor_ClearNext.
61105 JR NZ,CheckNearTrapDoor_ClearNext
61107 LD A,5 Load A with sound index 5.
61109 LD (29383),A Set the Bad Tempered Thing state (BadTemperedThingState).
Advance during the clear pass.
CheckNearTrapDoor_ClearNext 61112 ADD IX,DE IX+=DE.
61114 JR CheckNearTrapDoor_ClearScan Jump to CheckNearTrapDoor_ClearScan to handle the trap door.
No open: clear the falling-entity latch (bit 2 of GameEventFlags) and return carry clear.
CheckNearTrapDoor_NoOpen 61116 RES 2,(HL) Clear the falling-entity latch (bit 2 of GameEventFlags).
61118 RET Return.
Type 50 found: restart from StateData_Boney to nudge marked entities before opening.
CheckNearTrapDoor_FoundSceneryBlock 61119 LD IX,36585 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 61123 LD A,(IX+0) Fetch the current entity's type for the type test.
61126 CP 50 Is A equal to 50? If so, jump to CheckNearTrapDoor_ShouldOpen.
61128 JR Z,CheckNearTrapDoor_ShouldOpen
61130 BIT 0,(IX+2) Is bit 0 of the current entity's flags byte 2 set? If not, jump to CheckNearTrapDoor_AdjustNext.
61134 JR Z,CheckNearTrapDoor_AdjustNext
61136 LD A,(IX+3) Load A with the current entity's flags byte 3.
61139 LD C,A Keep the flags byte in C.
61140 AND %00111111 A&=63.
61142 LD (IX+3),A Set the current entity's flags byte 3.
61145 LD A,C Copy the saved count/flag from C into A.
61146 AND %11000000 A&=192.
61148 JR Z,CheckNearTrapDoor_ShrinkBounds Jump to CheckNearTrapDoor_ShrinkBounds to continue if the comparison matched.
61150 RES 0,(IX+2) Reset bit 0 of the current entity's flags byte 2.
61154 BIT 6,A Is bit 6 of A set? If not, jump to CheckNearTrapDoor_BumpCoordinates.
61156 JR Z,CheckNearTrapDoor_BumpCoordinates
61158 INC (IX+7) Move this entity one character right.
61161 INC (IX+8)
Bump a marked entity one character right away from the trap door band.
CheckNearTrapDoor_BumpCoordinates 61164 INC (IX+7) Bump this entity one character right.
61167 INC (IX+8)
61170 JR CheckNearTrapDoor_AdjustNext Jump to CheckNearTrapDoor_AdjustNext to handle the trap door.
Randomly shrink a marked entity's Y/Y-extent by 4–7 characters.
CheckNearTrapDoor_ShrinkBounds 61172 LD A,4 Load A with 4.
61174 CALL PseudoRandom Call PseudoRandom to pick a pseudo-random value.
61177 ADD A,4 A+=4.
61179 LD C,A Keep A in C for the next calculation.
61180 LD A,(IX+5) Load A with the current entity's y-coordinate.
61183 SUB C A-=C.
61184 LD (IX+5),A Set the current entity's y-coordinate.
61187 LD A,(IX+6) Load A with the current entity's y-extent.
61190 SUB C A-=C.
61191 LD (IX+6),A Set the current entity's y-extent.
Advance to the next entity in the adjust pass.
CheckNearTrapDoor_AdjustNext 61194 ADD IX,DE IX+=DE.
61196 JR CheckNearTrapDoor_AdjustScan Jump to CheckNearTrapDoor_AdjustScan to handle the trap door.
Signal that the trap door should open (set bit 2 of GameEventFlags, carry set).
CheckNearTrapDoor_ShouldOpen 61198 SET 2,(HL) Set the falling-entity latch (bit 2 of GameEventFlags).
61200 SCF Signal success.
61201 RET Return.
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