Routines
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B810: Check Distance
Used by the routines at HandleMoneyBag, HandleTumbleweed, HandleHorse, HandleCactus, HandlePointer and HandleBystander.
Checks whether an object is within a number of cells of the sheriff, both across and up the screen.
Input
C The distance in cells
IX The address of the object
Output
F The carry flag is set if the object is closer than that
Compare the horizontal cells.
CheckDistance B810 LD A,($A27F) Fetch the horizontal cell of the sheriff from A27F.
B813 SUB (IX+$02) Subtract the horizontal cell of the object.
B816 JP P,CheckDistance_CompareHorizontal Jump to CheckDistance_CompareHorizontal if the difference is not negative.
B819 NEG Make the difference positive.
CheckDistance_CompareHorizontal B81B CP C Compare it with the distance.
B81C RET NC Return if the object is too far away.
Compare the vertical cells.
B81D LD A,($A281) Fetch the vertical cell of the sheriff from A281.
B820 SUB (IX+$04) Subtract the vertical cell of the object.
B823 JP P,CheckDistance_CompareVertical Jump to CheckDistance_CompareVertical if the difference is not negative.
B826 NEG Make the difference positive.
CheckDistance_CompareVertical B828 CP C Compare it with the distance.
B829 RET Return.
View the equivalent code in;
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