Routines
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CCC7: 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 CCC7 LD A,(IX+$03) Fetch the z position of the first object.
CCCA ADD A,H Add H.
CCCB SUB (IY+$03) Subtract the z position of the second object.
CCCE JP P,TestOverlapInZ_Second Jump to TestOverlapInZ_Second if it is not negative.
CCD1 NEG Negate A.
CCD3 LD D,(IX+$06) Fetch the height of the first object, which is the lower.
TestOverlapInZ_Compare CCD6 SUB D Take the height off it, which sets the carry flag if the objects overlap.
CCD7 RET Return.
TestOverlapInZ_Second CCD8 LD D,(IY+$06) Fetch the height of the second object, which is the lower.
CCDB JR TestOverlapInZ_Compare Jump to TestOverlapInZ_Compare.
View the equivalent code in;
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