Marsport: Routine at 873A

873A: ; TODO

Used by the routines at Game_Init, _87c9 and 8BB6.
_873a	873A	CALL Data_ClearToZero	Clear the four bytes pointed to by the next address to zero.
	873D	DEFW Door_CurrentPos
	873F	DEFB $04
	8740	CALL Bg_DrawColumn
	8743	CALL $86B9
	8746	LD A,(Hero_ThroughDoor)
	8749	BIT 5,A
	874B	JR NZ,_873a_1
	874D	BIT 4,A
	874F	RET NZ
	8750	AND A
	8751	JR NZ,_873a_1
	8753	LD A,(Hero_ThroughCompass)
	8756	LD HL,(Stage_Compass)
	8759	LD E,$12
	875B	CP L
	875C	JR Z,_873a_0
	875E	LD E,$13
	8760	ADD A,$02
	8762	AND $03
	8764	CP L
	8765	JR Z,_873a_0
	8767	LD E,$10
	8769	LD A,(Hero_ThroughCompass)
	876C	SUB L
	876D	AND $03
	876F	LD (Hero_LastDir),A
	8772	CP $03
	8774	JR NZ,_873a_0
	8776	LD A,$02
	8778	LD (Hero_LastDir),A
_873a_0	877B	LD D,$00
	877D	LD (Hero_ThroughN),DE
_873a_1	8781	CALL Stage_Colour
Update compass on screen.
	8784	LD A,$01
	8786	CALL $1601
	8789	LD HL,(Stage_Compass)	Get the current compass value.
	878C	LD H,$00	Get the current compass value.
	878E	LD DE,Str_Compass	Get the address of hte first letter matching the compass.
	8791	ADD HL,DE
	8792	LD DE,Compass_PositionString
	8795	LD C,$04	Number of compass points.
	8797	LD B,$07	Length of first part of positioning string.
_873a_2	8799	LD A,(DE)	Print positioning string for point.
	879A	CALL Print_Character
	879D	INC DE
	879E	DJNZ _873a_2
	87A0	LD A,(HL)	Print compass point letter.
	87A1	CALL Print_Character
	87A4	INC HL
	87A5	LD B,$03	From then on we only need next three characters of the positioning string.
	87A7	DEC C	Next compass point.
	87A8	JR NZ,_873a_2
	87AA	LD A,(Hero_ThroughDoor)
	87AD	BIT 5,A
	87AF	RET NZ
	87B0	AND A
	87B1	JR Z,_873a_3
	87B3	CALL $AFFA
	87B6	JR _873a_4
_873a_3	87B8	LD A,(Hero_ThroughN)
	87BB	CALL $AFFD
_873a_4	87BE	JP Screen_Update
	87C1	INC B
	87C2	RLCA
	87C3	DEC BC
	87C4	LD C,$10
	87C6	LD (DE),A
	87C7	INC DE
	87C8	DEC D