Routines
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B8CC: Test Overlap In Z
Used by the routines at BlockMovementInX, BlockMovementInY, BlockMovementInZ, TestObjectIntersections and TestObjectCanBePickedUp.
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 B8CC LD A,(IX+$03) Fetch the z position of the first object.
B8CF ADD A,H Add H.
B8D0 SUB (IY+$03) Subtract the z position of the second object.
B8D3 JP P,TestOverlapInZ_SecondLower Jump to TestOverlapInZ_SecondLower if the first object is the higher.
B8D6 NEG Negate A.
B8D8 LD D,(IX+$06) Fetch the height of the first object, which is the lower.
Compare the distance with the height of the lower object.
TestOverlapInZ_Compare B8DB SUB D Subtract the height of the lower object, which sets the carry flag if they overlap.
B8DC RET Return.
TestOverlapInZ_SecondLower B8DD LD D,(IY+$06) Fetch the height of the second object, which is the lower.
B8E0 JR TestOverlapInZ_Compare Jump to TestOverlapInZ_Compare.
View the equivalent code in;
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