Routines
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54806: Handler: Sea Creature Movement
Used by the routines at GoldfishGame_UpdatePlayer and Handler_SeaCreatures.
Applies horizontal and vertical movement deltas. Clone used in the main game is at ApplyMovementDeltas.
Input
IX Creature data
Output
B Updated vertical position
C Updated horizontal position
D Updated vertical offset
E Updated horizontal offset
Fetch the current position and apply horizontal movement.
Handler_SeaCreatureMovement 54806 LD C,(IX+0) C=horizontal co-ordinate.
54809 LD B,(IX+1) B=vertical co-ordinate.
54812 LD E,(IX+2) E=horizontal offset.
54815 LD D,(IX+3) D=vertical offset.
54818 LD A,(IX+4) A=horizontal movement.
54821 ADD A,E Add it to the horizontal offset.
54822 CP 128 Jump to Handler_SeaCreatureMovement_StepColumnRight if the offset overflowed (moving right).
54824 JR NC,Handler_SeaCreatureMovement_StepColumnRight
54826 CP 4 Jump to Handler_SeaCreatureMovement_StoreHorizontalOffset if the offset is still in-range.
54828 JR C,Handler_SeaCreatureMovement_StoreHorizontalOffset
54830 INC C Step the horizontal co-ordinate two left, then...
54831 INC C
Handler_SeaCreatureMovement_StepColumnRight 54832 DEC C ...one right, so a crossed boundary updates the column.
54833 AND %00000011 Keep the horizontal offset in the range 0-3.
Handler_SeaCreatureMovement_StoreHorizontalOffset 54835 LD E,A E=the updated horizontal offset.
Apply vertical movement the same way.
54836 LD A,(IX+5) A=vertical movement.
54839 ADD A,D Add it to the vertical offset.
54840 CP 128 Jump to Handler_SeaCreatureMovement_StepRowDown if the offset overflowed (moving down).
54842 JR NC,Handler_SeaCreatureMovement_StepRowDown
54844 CP 4 Jump to Handler_SeaCreatureMovement_StoreVerticalOffset if the offset is still in-range.
54846 JR C,Handler_SeaCreatureMovement_StoreVerticalOffset
54848 INC B Step the vertical co-ordinate two up, then...
54849 INC B
Handler_SeaCreatureMovement_StepRowDown 54850 DEC B ...one down, so a crossed boundary updates the row.
54851 AND %00000011 Keep the vertical offset in the range 0-3.
Handler_SeaCreatureMovement_StoreVerticalOffset 54853 LD D,A D=the updated vertical offset.
54854 RET Return.
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