Routines
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50601: Test Overlap In X
Used by the routines at TestObjectIntersections, TestNearObject, BlockMovementInX, BlockMovementInY and BlockMovementInZ.
Tests whether two objects overlap along x, once the first has moved by its new speed along x. They overlap when the distance between the x positions is smaller than the two widths added together.
Input
C New speed along x 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 x distance with the widths.
TestOverlapInX 50601 LD A,(IX+4) Fetch the width of the first object.
50604 ADD A,(IY+4) Add the width of the second object.
50607 LD D,A Copy the total to D.
50608 LD A,(IX+1) Fetch the x position of the first object.
50611 ADD A,C Add C.
50612 SUB (IY+1) Subtract the x position of the second object.
50615 JP P,TestOverlapInX_Compare Jump to TestOverlapInX_Compare if the sign flag is clear.
50618 NEG Negate A.
TestOverlapInX_Compare 50620 SUB D Subtract D.
50621 RET Return.
View the equivalent code in;
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