Routines
Prev: CC38 Up: Map Next: CCB2
CC9D: Test Overlap In X
Used by the routines at TestObjectIntersections, TestObjectCanBePickedUp, 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 CC9D LD A,(IX+$04) Fetch the width of the first object.
CCA0 ADD A,(IY+$04) Add the width of the second object.
CCA3 LD D,A Copy the total to D.
Take the X coordinate of the second object off the X coordinate of the first object plus the new speed.
CCA4 LD A,(IX+$01) Fetch the x position of the first object.
CCA7 ADD A,C Add C.
CCA8 SUB (IY+$01) Subtract the x position of the second object.
CCAB JP P,TestOverlapInX_TakeWidths Jump to TestOverlapInX_TakeWidths if it is not negative.
CCAE NEG Negate A.
TestOverlapInX_TakeWidths CCB0 SUB D Take the total widths off it, which sets the carry flag if the objects overlap.
CCB1 RET Return.
View the equivalent code in;
Prev: CC38 Up: Map Next: CCB2