Routines
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52402: 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 52402 LD A,(IX+5) Fetch the depth of the first object.
52405 ADD A,(IY+5) Add the depth of the second object.
52408 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.
52409 LD A,(IX+2) Fetch the y position of the first object.
52412 ADD A,L Add L.
52413 SUB (IY+2) Subtract the y position of the second object.
52416 JP P,TestOverlapInY_TakeDepths Jump to TestOverlapInY_TakeDepths if it is not negative.
52419 NEG Negate A.
TestOverlapInY_TakeDepths 52421 SUB D Take the total depths off it, which sets the carry flag if the objects overlap.
52422 RET Return.
View the equivalent code in;
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