Routines
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EE73: Is this object in front of the other?
Used by the routines at CULL_OBJECT and SORT_AND_DRAW_BEHIND.
Sets bit 0 of IY+$71 if the object at IX stands in front of the other object whose far corner and floor are in D, E and C (FAR_CORNER): if it does not lie wholly beyond the other on any axis. That is: its +6 is less than the other's far edge along +6, its top (+7) is above the other's floor, and its +8 is less than the other's far edge along +8. Greater +6 and +8 are farther from the viewer, and something wholly below another's floor is under it, so drawn behind it. Asked only of objects that overlap on the screen, one answer is enough to order them. Krumlinde's name for it is RTN_ComparePosition.
Input
IX The object
D The other's far edge along +6
E The other's floor
C The other's far edge along +8
Output
F Carry and zero are left from the last comparison made
IS_IN_FRONT EE73 LD A,D Not in front if its +6 is at or beyond the other's far edge
EE74 RES 0,(IY+WORK_DIRECTION-V)
EE78 CP (IX+OBJ_X)
EE7B RET C
EE7C RET Z
EE7D LD A,E Or its top is at or below the other's floor
EE7E CP (IX+OBJ_TOP)
EE81 RET NC
EE82 LD A,C Or its +8 is at or beyond the other's far edge
EE83 CP (IX+OBJ_Z)
EE86 RET C
EE87 RET Z
EE88 SET 0,(IY+WORK_DIRECTION-V) In front
EE8C RET
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