Routines
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C5D3: Test Overlap In Z
Used by the routines at TestObjectIntersections, TestNearObject, 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 C5D3 LD A,(IX+$03) Fetch the z position of the first object.
C5D6 ADD A,H Add H.
C5D7 SUB (IY+$03) Subtract the z position of the second object.
C5DA JP P,TestOverlapInZ_Second Jump to TestOverlapInZ_Second if the sign flag is clear.
C5DD NEG Negate A.
C5DF LD D,(IX+$06) Fetch the height of the first object.
TestOverlapInZ_Compare C5E2 SUB D Subtract D.
C5E3 RET Return.
TestOverlapInZ_Second C5E4 LD D,(IY+$06) Fetch the height of the second object.
C5E7 JR TestOverlapInZ_Compare Jump to TestOverlapInZ_Compare.
View the equivalent code in;
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