Routines
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CCB2: Test Overlap In Y
Used by the routines at TestObjectIntersections, TestObjectCanBePickedUp, BlockMovementInX, BlockMovementInY and BlockMovementInZ.
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 CCB2 LD A,(IX+$05) Fetch the depth of the first object.
CCB5 ADD A,(IY+$05) Add the depth of the second object.
CCB8 LD D,A Copy the total to D.
Take the Y coordinate of the second object off the Y coordinate of the first object plus the new speed.
CCB9 LD A,(IX+$02) Fetch the y position of the first object.
CCBC ADD A,L Add L.
CCBD SUB (IY+$02) Subtract the y position of the second object.
CCC0 JP P,TestOverlapInY_TakeDepths Jump to TestOverlapInY_TakeDepths if it is not negative.
CCC3 NEG Negate A.
TestOverlapInY_TakeDepths CCC5 SUB D Take the total depths off it, which sets the carry flag if the objects overlap.
CCC6 RET Return.
View the equivalent code in;
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