Routines
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49593: Get Distance To Monster
Used by the routine at FindNearestMonster.
Works out the distance from the object at IX to a monster, which is the sum of the differences in their columns and rows.
Input
IX Object
IY Monster
Output
A The distance, or 255 if the monster is dead
Return 255 if the monster is dead.
GetDistanceToMonster 49593 LD A,(IY+0) Check whether the monster is alive, and jump to GetDistanceToMonster_Alive if it is.
49596 AND A
49597 JR NZ,GetDistanceToMonster_Alive
49599 LD A,255 The monster has been killed, so return a distance of 255, which is too far away to matter.
49601 RET Return.
Add the absolute differences in columns and rows.
GetDistanceToMonster_Alive 49602 LD A,(IX+2) Work out how many columns the object is from the monster.
49605 SUB (IY+2)
49608 JP P,GetDistanceToMonster_Rows Jump to GetDistanceToMonster_Rows if the difference is not negative.
49611 NEG Otherwise turn the distance round, so that it is positive.
GetDistanceToMonster_Rows 49613 LD C,A Keep the distance in columns.
49614 LD A,(IX+4) Work out how many rows the object is from the monster.
49617 SUB (IY+4)
49620 JP P,GetDistanceToMonster_Add Jump to GetDistanceToMonster_Add if the difference is not negative.
49623 NEG Otherwise turn the distance round, so that it is positive.
GetDistanceToMonster_Add 49625 ADD A,C Add the two distances together to get the distance from the monster.
49626 RET Return.
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