;This patches causes the screen to orientate so that the player is always in the center.

!FreeramLinePosH =	$60	;[2 bytes] X position of the line the player will be when moving the screen horizontally.
!FreeramDir =		$62	;[1 byte], bits to determine scrolling direction.

;!FreeramDir is a bitwise that indicate the direction of scrolling the screen, format: UDLRudlr. Uppercase
;is screen lock direction, if set, won't scroll in that direction. Lowercase is the current scroll direction
;by the player. Also, the lowercase bits are still set, even if that particular direction is locked.

;Note that this is not finished!
;issues:
;
;-scrolling left doesn't load layer 1 correctly
;-background layer 2 scrolling doesn't work
;

;currently working:

;future features:
;-A shovel knight-styled scrolling screen after hitting the edge of an area.
;
;
org $00F71A
autoclean JML ScreenScroll

freecode

ScreenScroll:

	REP #$20

	LDA #$0078		;\debug.
	STA !FreeramLinePosH	;/

	LDA $94			;\Let $00~$01 holds the x-coordinates of the player
	SEC			;|within the borders of the screen in next frame.
	SBC $1A			;|
	STA $00			;/

	SEP #$20
	LDA $0100
	CMP #$12		;level load 12
	REP #$20
	BNE skip

	LDA $00
	SEC
	SBC !FreeramLinePosH
	JSL AdjustScreenH
	SEP #$20
	JMP done

skip:
	LDA $00
	CMP !FreeramLinePosH	;
	SEP #$20
	BNE +
	;BEQ NoScroll		;>If mario is exactly on the line, Don't move.
	JML NoScroll
+
	BPL ScrollRight		;>If mario is right of the line

;ScrollLeft:
	LDA !FreeramDir		;\Set going left direction bit to indicate the player
	ORA.b #%00000010	;|is trying to scroll the screen.
	STA !FreeramDir		;/
	STZ $55
	STZ $56

	LDA !FreeramDir		;\If left direction locked, then don't scroll.
	AND.b #%00100000	;|
	BNE NoScrollLeft	;/

	REP #$20
	LDA !FreeramLinePosH	;\If mario is less than 8 pixels left from
	SEC			;|the line, then snap the screen to the player instantly.
	SBC $00			;|
	CMP #$0008		;|
	BCC SnapScreenPosLft	;/

	LDA $1462		;\Otherwise, if the player is too far to the left, then
	SEC			;|gradually move the screen left
	SBC #$0008		;|
	JSL AdjustScreenH		;/
	SEP #$20
NoScrollLeft:
	BRA done

SnapScreenPosLft:
	LDA !FreeramLinePosH
	SEC
	SBC $00
	STA $02 

	LDA $1462
	SEC
	SBC $02
	JSL AdjustScreenH
	SEP #$20
	BRA done

ScrollRight:
	LDA !FreeramDir		;\Set going left direction bit to indicate the player
	ORA.b #%00000010	;|is trying to scroll the screen.
	STA !FreeramDir		;/
	LDA #$02
	STA $55
	STA $56

	LDA !FreeramDir		;\If right direction locked, then don't scroll
	AND.b #%00010000	;|
	BNE NoScrollRight	;/

	REP #$20
	LDA $00			;\If mario is less than 8 pixels right from
	SEC			;|the line, then snap the screen to the player instantly.
	SBC !FreeramLinePosH	;|
	CMP #$0008		;|
	BCC SnapScreenPosRgt	;/

	LDA $1462		;\Otherwise, if the player is too far to the right, then
	CLC			;|gradually move the screen right
	ADC #$0008		;|
	JSL AdjustScreenH		;/
	SEP #$20
NoScrollRight:
	BRA done

SnapScreenPosRgt:
	LDA $00
	SEC
	SBC !FreeramLinePosH
	STA $02 

	LDA $1462
	CLC
	ADC $02
	JSL AdjustScreenH
	SEP #$20
	BRA done

NoScroll:
	LDA !FreeramDir		;\Clear left and right bits.
	AND.b #%11111100	;|
	STA !FreeramDir		;/
done:
	JML $00F7A2
	PLB
	RTL


AdjustScreenH:
	STA $04			;>save for later
	;STA $1462
	BMI PastLeftEdge	;>If screen x pos < 0, then set it to zero
;	LDA $5E			;\If screen x pos > last screen, then set it to position as
;	AND #$FF00		;|last screen.
;	CMP $1462		;|
;	BMI PastRightEdge	;/
	LDA $04
	STA $1462
	RTL

PastLeftEdge:
	STZ $1462
	RTL
PastRightEdge:
	STA $1462
	RTL