; set this if you're using this as a UberASM GM14 code
!gm14_uberasm = 0

; what tile to convert stuff to
!tile_to_use = $012F
; power of 2, tile is (attempted to be) placed every this many frames
!delay = $02
; whether to only replace solid tiles
; (if you turn this off, you should turn down the speed too)
!onlySolid = 1

if !gm14_uberasm
    main:
else
    org $008F5B
    autoclean JSL everyframe
    NOP #2
    freecode
    everyframe:
endif
;JSL $01ACF9
;LDA $148D
;CMP #$80 ; for testing - ~1/sec is 04
; though if we only do something on ground tiles then it may be fine as $80
;BCS .return
LDA $9D
ORA $13D4
BNE .return

LDA $14
AND.b #!delay-1
BNE .return

; only do shit while mario is moving
; (a futile attempt to make this a bit more fair)
LDA $7B
BEQ .return

REP #$20
STZ $1933

; random offset from mario X - magnitude 64-128, sign any
SEP #$20
JSL $01ACF9
LDA $148D
REP #$21 ; CLC too
BMI .neg
    AND #$003F
    ADC #$0040
BRA +
.neg
    AND #$003F
    ADC #$0040
    EOR #$FFFF ;\ negate
    INC        ;/
+
ADC $94 ; player X
BCS .return_sep ; if we overflowed, don't even try to write the tile
AND #$FFF0
STA $9A

LDA $148E ; use the high part of last RNG call
REP #$21 ; CLC too
BMI .neg_y
    AND #$007F
    ;ADC #$0040
BRA +
.neg_y
    AND #$007F
    ;ADC #$0040
    EOR #$FFFF ;\ negate
    INC        ;/
+
ADC $96 ; player Y
BCS .return_sep
AND #$FFF0
STA $98

if !onlySolid
    LDA $9A
    STA $00
    LDA $98
    STA $02
    SEP #$20
    JSL FindMap16TileNum
    XBA
    CMP #$01
    BNE .return
    REP #$20
endif
LDA.w #!tile_to_use
JSL ChangeMap16

.return_sep
SEP #$20
.return
; restore old code and return
if not(!gm14_uberasm)
    LDX $0DB3
    LDA $0F48,x
endif
RTL


;;;;;;;;;;;;;;
;; routines ;;
;;;;;;;;;;;;;;

ChangeMap16:
!Base2 = 0
!BankB = 0
!SA1 = 0
!EXLEVEL = 0
; PIXI's ChangeMap16 routine, by Akaginite
; Slightly modified by Tattletale
	PHX
	PHP
	REP #$10
	TAX
	SEP #$20
	PHB
	PHY
	PHX
	LDY $98
	STY $0E
	LDY $9A
	STY $0C
	SEP #$30
	LDA $5B
	LDX $1933|!Base2
	BEQ .layer1
	LSR A
.layer1
	STA $0A
	LSR A
	BCC .horz
	LDA $9B
	LDY $99
	STY $9B
	STA $99
.horz
if !EXLEVEL
	BCS .verticalCheck
	REP #$20
	LDA $98
	CMP $13D7|!Base2
	SEP #$20
	BRA .check
endif
.verticalCheck
	LDA $99
	CMP #$02
.check
	BCC .noEnd
	REP #$10
	PLX
	PLY
	PLB
	PLP
	PLX
	RTL
	
.noEnd
	LDA $9B
	STA $0B
	ASL A
	ADC $0B
	TAY
	REP #$20
	LDA $98
	AND.w #$FFF0
	STA $08
	AND.w #$00F0
	ASL #2			; 0000 00YY YY00 0000
	XBA			; YY00 0000 0000 00YY
	STA $06
	TXA
	SEP #$20
	ASL A
	TAX
	
	LDA $0D
	LSR A
	LDA $0F
	AND #$01		; 0000 000y
	ROL A			; 0000 00yx
	ASL #2			; 0000 yx00
	ORA #$20		; 0010 yx00
	CPX #$00
	BEQ .noAdd
	ORA #$10		; 001l yx00
.noAdd
	TSB $06			; $06 : 001l yxYY
	LDA $9A			; X LowByte
	AND #$F0		; XXXX 0000
	LSR #3			; 000X XXX0
	TSB $07			; $07 : YY0X XXX0
	LSR A
	TSB $08

	LDA $1925|!Base2
	ASL A
	REP #$31
	ADC $00BEA8|!BankB,x
	TAX
	TYA
if !SA1
    ADC.l $00,x
    TAX
    LDA $08
    ADC.l $00,x
else
    ADC $00,x
    TAX
    LDA $08
    ADC $00,x
endif
	TAX
	PLA
	ASL A
	TAY
	LSR A
	SEP #$20
if !SA1
	STA $400000,x
	XBA
	STA $410000,x
else
	STA $7E0000,x
	XBA
	STA $7F0000,x
endif
	LSR $0A
	LDA $1933|!Base2
	REP #$20
	BCS .vert
	BNE .horzL2
.horzL1
	LDA $1A			;\
	SBC #$007F		; |$08 : Layer1X - 0x80
	STA $08			;/
	LDA $1C			;  $0A : Layer1Y
	BRA +
.horzL2
	LDA $1E			;\ $08 : Layer2X
	STA $08			;/
	LDA $20			;\ $0A : Layer2Y - 0x80
	SBC #$007F		;/
	BRA +
	
.vert
	BNE .vertL2
	LDA $1A			;\ $08 : Layer1X
	STA $08			;/
	LDA $1C			;\ $0A : Layer1Y - 0x80
	SBC #$0080		;/
	BRA +
.vertL2
	LDA $1E			;\
	SBC #$0080		; |$08 : Layer2X - 0x80
	STA $08			;/
	LDA $20			;  $0A : Layer2Y
+
	STA $0A
	PHK
-	PEA.w (-)+9
	PEA $804C
	JML $00C0FB|!BankB
	PLY
	PLB
	PLP
	PLX
	RTL

; Map16 tile number finder, from imamelia's shared subroutines
!F = |$800000
FindMap16TileNum:
	PHX
	LDA $02
	AND #$F0
	STA $06
	LDA $00
	LSR #4
	ORA $06
	PHA
	LDA $5B
	AND #$01
	BNE .L0
	PLA
	LDX $01
	CLC
	ADC $00BA60!F,x
	STA $05
	LDA $00BA9C!F,x
	ADC $03
	STA $06
	BRA .L1
.L0
	PLA
	LDX $03
	CLC
	ADC $00BA80!F,x
	STA $05
	LDA $00BABC!F,x
	ADC $01
	STA $06
.L1
	LDA #$7E
	STA $07
	PLX
	LDA [$05]
	XBA
	INC $07
	LDA [$05]
	XBA
	RTL