Martianoids: Routine at A4C3

A4C3: Choose Direction

Used by the routine at MoveProgramPacket.

Finds a direction for a program packet to go in, which is the one that it is heading in if that is possible, and otherwise the one to the side, the opposite one, and the other side.

Input
A	Direction of the packet
DE	X position
HL	Y position

Output
A	The type of the cell, if the zero flag is set
C	The direction that has been chosen
F	The zero flag is set if the packet can go on

ChooseDirection

A4C3

CALL TestCellInDirection

Try the direction that the packet is heading in, and return if it can go there.

A4C6

RET Z

A4C7

LD A,C

Try the direction before it...

A4C8

DEC A

A4C9

AND $03

A4CB

CALL TestCellInDirection

...and return if the packet can go there.

A4CE

RET Z

A4CF

LD A,C

Try the opposite direction...

A4D0

XOR $02

A4D2

CALL TestCellInDirection

...and return if the packet can go there.

A4D5

RET Z

A4D6

LD A,C

Try the direction after the original one...

A4D7

INC A

A4D8

AND $03

A4DA

JR TestCellInDirection

Jump to TestCellInDirection.