Routines
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B8B7: Test Overlap In Y
Used by the routines at BlockMovementInX, BlockMovementInY, BlockMovementInZ, TestObjectIntersections and TestObjectCanBePickedUp.
Tests whether two objects overlap along y, once the first has moved by its new speed along y. They overlap when the distance between the y positions is smaller than the two depths added together.
Input
L New speed along y 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
Compare the y distance with the depths.
TestOverlapInY B8B7 LD A,(IX+$05) Fetch the depth of the first object.
B8BA ADD A,(IY+$05) Add the depth of the second object.
B8BD LD D,A Copy the total to D.
Work out the distance between the centres, once the first has moved.
B8BE LD A,(IX+$02) Fetch the y position of the first object.
B8C1 ADD A,L Add L.
B8C2 SUB (IY+$02) Subtract the y position of the second object.
B8C5 JP P,TestOverlapInY_Compare Jump to TestOverlapInY_Compare if the distance is positive.
B8C8 NEG Negate A.
TestOverlapInY_Compare B8CA SUB D Subtract D.
B8CB RET Return.
View the equivalent code in;
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