Pentagram: Routine at D085

D085: Steer towards the place in +15 and +16

Used by the routines at COLLECTABLE and BUCKET.

Sets the step in U to one unit towards the U in +15, and the step in V to one unit towards the V in +16. An axis already there keeps the step it had, which the callers have cleared the turn before, so the thing goes diagonally until one axis matches and then straight.

Input
IX	the object record, with the target U and V in +15 and +16

HEAD_FOR_TARGET

D085

LD A,(IX+$01)

U: one unit down, or...

D088

CP (IX+$15)

D08B

JR Z,HEAD_FOR_TARGET_1

D08D

JR C,HEAD_FOR_TARGET_0

D08F

LD (IX+$09),$FF

D093

JR HEAD_FOR_TARGET_1

HEAD_FOR_TARGET_0

D095

LD (IX+$09),$01

...one unit up

HEAD_FOR_TARGET_1

D099

LD A,(IX+$02)

V: one unit down, or...

D09C

CP (IX+$16)

D09F

RET Z

D0A0

JR C,HEAD_FOR_TARGET_2

D0A2

LD (IX+$0A),$FF

D0A6

RET

HEAD_FOR_TARGET_2

D0A7

LD (IX+$0A),$01

...one unit up

D0AB

RET