Routines
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52423: Test Overlap In Z
Used by the routines at TestObjectIntersections, TestObjectCanBePickedUp, BlockMovementInX, BlockMovementInY and BlockMovementInZ.
Tests whether two objects overlap along z, once the first has moved by its new speed along z. They overlap when the distance between the z positions is smaller than the height of whichever of the objects is lower.
Input
H New speed along z of the first object
IX The address of the first object
IY The address of the second object
Output
F Carry flag set if the objects overlap
Use the height of the lower object.
TestOverlapInZ 52423 LD A,(IX+3) Fetch the z position of the first object.
52426 ADD A,H Add H.
52427 SUB (IY+3) Subtract the z position of the second object.
52430 JP P,TestOverlapInZ_Second Jump to TestOverlapInZ_Second if it is not negative.
52433 NEG Negate A.
52435 LD D,(IX+6) Fetch the height of the first object, which is the lower.
TestOverlapInZ_Compare 52438 SUB D Take the height off it, which sets the carry flag if the objects overlap.
52439 RET Return.
TestOverlapInZ_Second 52440 LD D,(IY+6) Fetch the height of the second object, which is the lower.
52443 JR TestOverlapInZ_Compare Jump to TestOverlapInZ_Compare.
View the equivalent code in;
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