Routines
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42474: Compare Positions
Used by the routines at CheckEnemyOverlap and CheckShotHit.
Compares the position of an entity with the position of another one, in both directions.
Input
IY Entity to compare with
DE X position
HL Y position
B Maximum difference in the Y direction
C Maximum difference in the X direction
Output
F The carry flag is set if both differences are small enough
ComparePositions 42474 PUSH HL Save the Y position...
42475 PUSH DE ...and the X position.
42476 LD E,(IY+3) Fetch the Y position of the other entity.
42479 LD D,(IY+4)
42482 AND A Subtract it from the Y position, and jump if the result is positive.
42483 SBC HL,DE
42485 JR NC,ComparePositions_TestY
42487 EX DE,HL Otherwise negate it.
42488 AND A
42489 LD HL,0
42492 SBC HL,DE
ComparePositions_TestY 42494 LD A,H Jump if the difference is more than the size of the world.
42495 AND 63
42497 JR NZ,ComparePositions_Done
42499 LD A,L Jump if the difference is not less than the maximum.
42500 CP B
42501 JR NC,ComparePositions_Done
42503 POP HL Restore the X position into HL and save it again.
42504 PUSH HL
42505 LD E,(IY+1) Fetch the X position of the other entity.
42508 LD D,(IY+2)
42511 AND A Subtract it from the X position, and jump if the result is positive.
42512 SBC HL,DE
42514 JR NC,ComparePositions_TestX
42516 EX DE,HL Otherwise negate it.
42517 AND A
42518 LD HL,0
42521 SBC HL,DE
ComparePositions_TestX 42523 LD A,H Jump if the difference is more than the size of the world.
42524 AND 63
42526 JR NZ,ComparePositions_Done
42528 LD A,L Compare the difference with the maximum, which sets the carry flag if it is less.
42529 CP C
ComparePositions_Done 42530 POP DE Restore the X position...
42531 POP HL ...and the Y position.
42532 RET Return.
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