Routines
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B8A2: Test Overlap In X
Used by the routines at BlockMovementInX, BlockMovementInY, BlockMovementInZ, TestObjectIntersections and TestObjectCanBePickedUp.
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 B8A2 LD A,(IX+$04) Fetch the width of the first object.
B8A5 ADD A,(IY+$04) Add the width of the second object.
B8A8 LD D,A Copy the total to D.
Work out the distance between the centres, once the first has moved.
B8A9 LD A,(IX+$01) Fetch the x position of the first object.
B8AC ADD A,C Add C.
B8AD SUB (IY+$01) Subtract the x position of the second object.
B8B0 JP P,TestOverlapInX_Compare Jump to TestOverlapInX_Compare if the distance is positive.
B8B3 NEG Negate A.
TestOverlapInX_Compare B8B5 SUB D Subtract D.
B8B6 RET Return.
View the equivalent code in;
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