Routines
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899C: Handler: Flight Path
Used by the routine at GameInitialise.
This routine uses Bresenham's line algorithm to plot a point between the source and destination co-ordinates to show Trashman travelling from one location to another.
Handler_FlightPath 899C LD B,$01 B=01.
899E LD HL,$EFFF Set bit 0 of *EFFF.
89A1 SET 0,(HL)
89A3 CALL $8055 Call 8055.
89A6 LD A,($EFFC) A=*EFFC.
89A9 AND %00001111 Keep only bits 0-3.
89AB CP $08 Jump to Handler_FlightPath if A is not equal to 08.
89AD JR NZ,Handler_FlightPath
89AF LD BC,($7801) BC=*Flightpath_X_MovementVector.
89B3 LD DE,($7803) DE=*Flightpath_Y_MovementVector.
89B7 LD HL,($7805) HL=*CurrentLocationCoordinates.
89BA LD A,C Compare C and B to determine the movement direction. Jump to FlightPath_NegativeDirection if C is lower than B.
89BB CP B
89BC JR C,FlightPath_NegativeDirection
Handle movement in positive X direction.
89BE SUB B C-=B.
89BF LD C,A
Move in Y direction.
89C0 LD A,E L+=E.
89C1 ADD A,L
89C2 LD L,A
89C3 LD A,($780A) Load *Flightpath_Maximum_Y_Coordinate into B.
89C6 LD B,A
Compare with remaining X movement.
89C7 CP C Jump to FlightPath_CheckArrived if *Flightpath_Maximum_Y_Coordinate is lower than C.
89C8 JR C,FlightPath_CheckArrived
89CA SUB C Adjust Y co-ordinate.
89CB LD B,A
89CC LD A,($7809) Load *Flightpath_Minimum_Y_Coordinate into C.
89CF LD C,A
89D0 LD A,($7804) Adjust X co-ordinate.
89D3 ADD A,H
89D4 LD H,A
89D5 JR FlightPath_CheckArrived Jump to FlightPath_CheckArrived.
Handle movement in negative X direction.
FlightPath_NegativeDirection 89D7 LD A,B B-=C (remaining X movement).
89D8 SUB C
89D9 LD B,A
89DA LD A,D Move in Y direction.
89DB ADD A,H
89DC LD H,A
89DD LD A,($7809) Load *Flightpath_Minimum_Y_Coordinate into C.
89E0 LD C,A
89E1 CP B Jump to FlightPath_CheckArrived if C is lower than B.
89E2 JR C,FlightPath_CheckArrived
89E4 SUB B Adjust Y co-ordinate.
89E5 LD C,A
89E6 LD A,($780A) Load *Flightpath_Maximum_Y_Coordinate into B.
89E9 LD B,A
89EA LD A,($7803) Adjust X co-ordinate.
89ED ADD A,L
89EE LD L,A
89EF JR FlightPath_CheckArrived Jump to FlightPath_CheckArrived.
Update position and check if destination reached.
FlightPath_CheckArrived 89F1 LD ($7805),HL Write new X/ Y co-ordinates to *CurrentLocationCoordinates.
89F4 LD ($7801),BC Write updated movement vector to *Flightpath_X_MovementVector.
89F8 AND A Compare current position with destination.
89F9 LD DE,($7807)
89FD SBC HL,DE
89FF JR NZ,Handler_FlightPath Jump to Handler_FlightPath until destination is reached.
8A01 LD HL,$EFFB Reset bit 1 ("Flightpath Complete") of *GameState_2.
8A04 RES 1,(HL)
8A06 RET Return.
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