; ===========================================================================
; Scrolling BG from the The Pirates of Dark Water.
; Ripped by TheBlad768.
; ===========================================================================

; RAM Address
long_221E:					= RAM+$00		; 4 bytes
long_2222:					= RAM+$04		; 4 bytes
long_2226:					= RAM+$08		; 4 bytes
long_222A:					= RAM+$0C		; 4 bytes
long_222E:					= RAM+$10		; 4 bytes
long_2232:					= RAM+$14		; 4 bytes

; =============== S U B R O U T I N E =======================================

Scrolling_BG_Init:
		bsr.w	Random_Number
		andi.l	#$1FF,d0
		btst	#4,d0
		beq.s	+
		neg.l	d0
		subi.l	#$100,d0
+		addi.l	#$80,d0
		move.l	d0,(long_221E).w
		bsr.w	Random_Number
		andi.l	#$1FF,d0
		btst	#4,d0
		beq.s	+
		neg.l	d0
		subi.l	#$100,d0
+		addi.l	#$80,d0
		move.l	d0,(long_222A).w
		bsr.w	Random_Number
		andi.l	#$7FF,d0
		btst	#4,d0
		beq.s	+
		neg.l	d0
		subi.l	#$200,d0
+		addi.l	#$100,d0
		move.l	d0,(long_2222).w
		bsr.w	Random_Number
		andi.l	#$7FF,d0
		btst	#4,d0
		beq.s	+
		neg.l	d0
		subi.l	#$200,d0
+		addi.l	#$100,d0
		move.l	d0,(long_222E).w
		bsr.w	Random_Number
		andi.l	#$3F0000,d0
		subi.l	#$1F0000,d0
		move.l	d0,(long_2226).w
		bsr.w	Random_Number
		andi.l	#$3F0000,d0
		subi.l	#$1F0000,d0
		move.l	d0,(long_2232).w
		rts
; End of function Scrolling_BG_Init

; =============== S U B R O U T I N E =======================================

Scrolling_BG:
		move.l	(long_221E).w,d0
		add.l	d0,(long_2222).w
		tst.l	(long_2226).w
		bpl.s	loc_6CC56
		tst.l	(long_221E).w
		bpl.s	loc_6CCB4
		neg.l	(long_221E).w
		bra.s	loc_6CC64
; ---------------------------------------------------------------------------

loc_6CC56:
		tst.l	(long_221E).w
		bmi.s	loc_6CCB4
		neg.l	(long_221E).w

loc_6CC64:
		add.l	d0,(long_2222).w
		bsr.w	Random_Number
		andi.l	#$1FF,d0
		subi.l	#$FF,d0
		sub.l	d0,(long_221E).w
		move.l	(long_221E).w,d0
		bpl.s	loc_6CC9E
		cmpi.l	#-$800,d0
		bge.s	loc_6CCAE
		move.l	#-$800,d0
		bra.s	loc_6CCAE
; ---------------------------------------------------------------------------

loc_6CC9E:
		cmpi.l	#$800,d0
		ble.s		loc_6CCAE
		move.l	#$800,d0

loc_6CCAE:
		move.l	d0,(long_221E).w

loc_6CCB4:
		move.l	(long_222A).w,d0
		add.l	d0,(long_222E).w
		tst.l	(long_2232).w
		bpl.s	loc_6CCD8
		tst.l	(long_222A).w
		bpl.s	loc_6CD36
		neg.l	(long_222A).w
		bra.s	loc_6CCE6
; ---------------------------------------------------------------------------

loc_6CCD8:
		tst.l	(long_222A).w
		bmi.s	loc_6CD36
		neg.l	(long_222A).w

loc_6CCE6:
		add.l	d0,(long_222E).w
		bsr.w	Random_Number
		andi.l	#$1FF,d0
		subi.l	#$FF,d0
		sub.l	d0,(long_222A).w
		move.l	(long_222A).w,d0
		bpl.s	loc_6CD20
		cmpi.l	#-$800,d0
		bge.s	loc_6CD30
		move.l	#-$800,d0
		bra.s	loc_6CD30
; ---------------------------------------------------------------------------

loc_6CD20:
		cmpi.l	#$800,d0
		ble.s		loc_6CD30
		move.l	#$800,d0

loc_6CD30:
		move.l	d0,(long_222A).w

loc_6CD36:
		move.l	(long_2222).w,d0
		bpl.s	loc_6CD54
		cmpi.l	#-$30000,d0
		bge.s	loc_6CD64
		move.l	#-$30000,d0
		bra.s	loc_6CD64
; ---------------------------------------------------------------------------

loc_6CD54:
		cmpi.l	#$30000,d0
		ble.s		loc_6CD64
		move.l	#$30000,d0

loc_6CD64:
		move.l	(long_222E).w,d1
		bpl.s	loc_6CD82
		cmpi.l	#-$30000,d1
		bge.s	loc_6CD92
		move.l	#-$30000,d1
		bra.s	loc_6CD92
; ---------------------------------------------------------------------------

loc_6CD82:
		cmpi.l	#$30000,d1
		ble.s		loc_6CD92
		move.l	#$30000,d1

loc_6CD92:
		add.l	d0,(long_2226).w
		add.l	d1,(long_2232).w
		move.w	(long_2226).w,(H_scroll_buffer+2).w
		move.w	(long_2232).w,(V_scroll_value+2).w
		rts
; End of function Scrolling_BG
; ---------------------------------------------------------------------------
; Generates a pseudo-random number in d0
; ---------------------------------------------------------------------------

word_CB6:					= RAM+$18		; 2 bytes
byte_CC54:					= RAM+$1A		; 1 byte
byte_CC55:					= RAM+$1B		; 1 byte

; =============== S U B R O U T I N E =======================================

Random_Number:
		tst.w	(word_CB6).w
		beq.s	Random_Number_2
		move.w	(V_int_run_count).w,d0
		rts
; ---------------------------------------------------------------------------

Random_Number_2:
		movem.l	d1-d2/a0,-(sp)
		move.w	(V_int_run_count).w,d2
		move.w	d2,d1
		andi.w	#$FF,d2
		lsr.w	#8,d1
		move.b	(byte_CC55).w,d0
		eor.b	d0,d2
		move.b	(byte_CC54).w,d0
		eor.b	d0,d1
		moveq	#0,d0
		move.w	d1,d0
		lsl.w	#8,d0
		or.b	d2,d0
		add.l	d0,d0
		movea.l	d0,a0
		moveq	#0,d0
		move.w	(a0),d0
		sub.w	d0,d2
		sub.w	d0,d1
		ror.b	#1,d2
		rol.b	#1,d1
		add.b	d1,(byte_CC55).w
		add.b	d2,(byte_CC54).w
		eor.b	d2,d0
		lsl.w	#8,d1
		eor.b	d1,d0
		movem.l	(sp)+,d1-d2/a0
		rts
; End of function Random_Number