nes/plat.s

.segment "HEADER"

INES_MAPPER = 0
INES_MIRROR = 1
INES_SRAM   = 0

.byte 'N', 'E', 'S', $1A
.byte $02
.byte $01
.byte INES_MIRROR
.byte (INES_MAPPER & %11110000)
.byte $0, $0, $0, $0, $0, $0, $0, $0


.segment "TILES"
.incbin "background.chr"
.incbin "sprite.chr"
.segment "VECTORS"
.word nmi
.word reset
.word irq


.segment "CODE"
reset:
    sei
    lda #0
    sta $2000
    lda #0
    sta $2001
    sta $4015
    sta $4010
    lda #40
    sta $4017
    cld
    ldx #$FF
    txs

    bit $2002
    :
        bit $2002
        bpl :-

    lda #0
    ldx #0
    :
        sta $0000, X
        sta $0100, X
        sta $0200, X
        sta $0300, X
        sta $0400, X
        sta $0500, X
        sta $0600, X
        sta $0700, X
        inx
        bne :-

    lda #255
    ldx #0
    :
        sta oam, X
        inx
        inx
        inx
        inx
        bne :-

    :
        bit $2002
        bpl :-

    lda #%10101000 ; NMI enable, 8x16 sprites, ignored due to 8x16 mode
    sta $2000
    jmp main


.segment "ZEROPAGE"
nmi_lock:       .res 1
nmi_count:      .res 1
nmi_ready:      .res 1
nmt_update_len: .res 1
nmt_column:     .res 1
nmt_update_frame: .res 1
scroll_x:       .res 1
scroll_y:       .res 1
scroll_nmt:     .res 1
scroll_page:    .res 1
temp:           .res 1

PPUCTRL_default = %10101000

.segment "BSS"
nmt_update:     .res 256
palette:        .res 32

.segment "OAM"
oam:            .res 256

.segment "CODE"
nmi:
    pha
    txa
    pha
    tya
    pha

    lda nmi_lock
    beq :+
        jmp @nmi_end

    :
    lda #1
    sta nmi_lock

    lda nmi_ready
    bne :+
        jmp @ppu_update_end

    :
    cmp #2
    bne :+
        lda #%00000000
        sta $2001
        ldx #0
        stx nmi_ready
        jmp @ppu_update_end

    :
    ldx #0
    stx $2003
    lda #>oam
    sta $4014

    lda #%10101000 ; NMI enable, 8x16 sprites, ignored due to 8x16 mode
    sta $2000
    lda $2002
    lda #$3F
    sta $2006
    stx $2006
    ldx #0
    :
        lda palette, X
        sta $2007
        inx
        cpx #32
        bcc :-

    ldx #0
    cpx nmt_update_len
    bcs @scroll

    lda PPUCTRL_default
    ;ora #%00000100
    sta $2000

    ldy #0
    ldx #0
    @nmt_update_loop:
        lda nmt_update_frame
        cmp #0
        bne :+
            lda nmt_update+0, X
            sta $2006
            lda nmt_update+1, X
            sta $2006

            lda nmt_update+2, X
            sta $2007
            lda nmt_update+3, X
            sta $2007

            jmp :++
        :
            lda nmt_update+0, X
            sta $2006
            lda nmt_update+1, X
            clc
            adc #32
            sta $2006

            lda nmt_update+4, X
            sta $2007
            lda nmt_update+5, X
            sta $2007
        :


        inx
        inx
        inx
        inx
        inx
        inx

        iny
        cpy nmt_update_len
        bcc @nmt_update_loop

    lda PPUCTRL_default
    sta $2000

    inc nmt_update_frame
    lda nmt_update_frame
    cmp #2
    bne :+
        lda #0
        sta nmt_update_frame
        sta nmt_update_len
    :
@scroll:
    lda scroll_nmt
    and #%00000011
    ora #%10101000
    sta $2000
    lda scroll_x
    sta $2005
    lda scroll_y
    sta $2005

    lda #%00011110
    sta $2001

    ldx #0
    stx nmi_ready
@ppu_update_end:
    lda #0
    sta nmi_lock
@nmi_end:
    pla
    tay
    pla
    tax
    pla
    rti


.segment "CODE"
irq:
    rti


.segment "CODE"
ppu_update:
    lda #1
    sta nmi_ready
    :
        lda nmi_ready
        bne :-

    rts

ppu_skip:
    lda nmi_count
    :
        cmp nmi_count
        beq :-

    rts

ppu_off:
    lda #2
    sta nmi_ready
    :
        lda nmi_ready
        bne :-

    rts


PAD_A      = $01
PAD_B      = $02
PAD_SELECT = $04
PAD_START  = $08
PAD_U      = $10
PAD_D      = $20
PAD_L      = $40
PAD_R      = $80

.segment "RODATA"

default_level:
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $80,$80,$80,$80,$80,$80,$80,$80,$80,$80,$80,$80,$80,$80,$80,$80
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
;.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
;.byte $00,$00,$00,$00,$00,$00,$00,$81,$00,$81,$00,$81,$00,$81,$00,$00
;.byte $82,$83,$00,$00,$00,$00,$00,$00,$81,$00,$0C,$00,$81,$00,$00,$00
;.byte $84,$85,$00,$00,$00,$00,$00,$81,$00,$81,$00,$81,$00,$81,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$0C,$00,$0C,$00,$0C,$00,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$81,$00,$81,$00,$81,$00,$81,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$81,$00,$0C,$00,$81,$00,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$81,$00,$81,$00,$81,$00,$81,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$8C,$87
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
;.byte $0F,$8C,$87,$87,$87,$87,$87,$87,$87,$87,$87,$87,$87,$87,$87,$87
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
;.byte $0F,$0E,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00

default_level2:
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$8C,$8C,$8C,$8C,$8C,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$09,$01,$01,$01,$8C,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$8C,$8C,$8C,$01,$06,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$09,$01,$01,$01,$8C,$00,$00,$00,$00,$00,$82,$83,$00,$00,$00
.byte $00,$8C,$8C,$8C,$8C,$8C,$00,$00,$00,$00,$00,$84,$85,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$0F,$0E,$00,$82,$83
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$0F,$0E,$00,$84,$85
.byte $00,$00,$00,$00,$00,$00,$00,$00,$82,$83,$00,$0F,$0E,$00,$0F,$0E
.byte $87,$8C,$00,$00,$00,$00,$00,$00,$84,$85,$00,$0F,$0E,$00,$0F,$0E
.byte $00,$00,$00,$00,$00,$00,$00,$00,$0F,$0E,$00,$0F,$0E,$00,$0F,$0E
.byte $00,$00,$00,$00,$00,$00,$00,$00,$0F,$0E,$00,$0F,$0E,$00,$0F,$0E
.byte $87,$87,$87,$87,$87,$8C,$00,$00,$0F,$0E,$00,$0F,$0E,$00,$0F,$0E
.byte $00,$00,$00,$00,$00,$00,$00,$00,$0F,$0E,$00,$8A,$8A,$8A,$8A,$0E
.byte $00,$00,$00,$00,$00,$00,$00,$00,$0F,$0E,$00,$8B,$8B,$8B,$8B,$0E

;level:
;.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
;.byte 0,1,0,0,1,0,0,0,0,1,0,0,2,7,7,3
;.byte 0,0,0,0,0,0,0,0,0,0,0,0,6,0,0,9
;.byte 0,1,0,0,1,7,7,7,7,1,7,7,6,0,0,9
;.byte 0,0,1,1,0,0,0,0,0,1,0,0,4,8,8,5
;.byte 0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0
;.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
;.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
;.byte 0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,0
;.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
;.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
;.byte 0,0,0,0,0,0,0,0,0,0,0,10,10,10,10,10
;.byte 0,0,1,0,0,0,0,1,0,0,0,11,11,11,11,11
;.byte 0,1,2,3,4,5,6,7,8,9,0,11,11,11,11,11
;.byte 0,0,0,0,0,0,0,0,0,0,0,11,11,11,11,11

metatiles:
.byte 0,0,0,0,0
.byte $14,$15,$16,$17,%00000000 ; 1: Full block
.byte $14,$18,$1B,$00,%00000000 ; 2: up / left
.byte $18,$15,$00,$19,%00000000 ; 3: up / right
.byte $1B,$00,$16,$1A,%00000000 ; 4: down / left
.byte $00,$19,$1A,$17,%00000000 ; 5: down / right
.byte $1B,$00,$1B,$00,%00000000 ; 6: left
.byte $18,$18,$00,$00,%00000000 ; 7: up
.byte $00,$00,$1A,$1A,%00000000 ; 8: down
.byte $00,$19,$00,$19,%00000000 ; 9: right
.byte $10,$11,$12,$13,%00000010 ; A: grass top
.byte $12,$12,$12,$12,%00000010 ; B: grass bottom
.byte $14,$15,$16,$17,%00000001 ; C: Intangible full block
.byte $01,$01,$01,$01,%00000001 ; D: Intangible grey
.byte $1B,$00,$1B,$00,%00000000 ; E: Intangible left
.byte $00,$19,$00,$19,%00000000 ; F: Intangible right

example_palette:
.byte $0F,$00,$3D,$20 ; greyscale
.byte $0F,$3D,$30,$00 ; whitescale
.byte $0F,$09,$1A,$16 ; grass
.byte $0F,$15,$26,$37 ; bg0 purple/pink
.byte $0F,$2D,$10,$3D ; reboot bottom
.byte $0F,$2D,$10,$2C ; reboot eye
.byte $0F,$01,$11,$21 ; bg2 blue
.byte $0F,$00,$10,$30 ; bg3 greyscale
; .byte $0F,$18,$28,$38 ; sp0 yellow
; .byte $0F,$14,$24,$34 ; sp1 purple
; .byte $0F,$1B,$2B,$3B ; sp2 teal
; .byte $0F,$12,$22,$32 ; sp3 marine


terrain:
;     page pos  struct
.byte $00, $00, $00

.segment "ZEROPAGE"
buttons:    .res 1

player_pos_x:   .res 1
player_nmt_x:   .res 1
player_pos_y:   .res 1
player_subpos_x:  .res 1 ; XXXXYYYY | first 4 bits X subposition, last 4 bits Y
player_subpos_y:  .res 1 ; XXXXYYYY | first 4 bits X subposition, last 4 bits Y
player_vel_x:   .res 1 ; +PPPSSSS | first bit sign, next 3 pixels, last subpixels
player_vel_y:   .res 1 ; in subpixels

player_status:  .res 1 ; 76543210 | 0: facing (0 right, 1 left)
                       ;          | 1: nametable X
                       ;          | 2: nametable Y
                       ;          | 7: talking
horizontal_speed: .res 1
camera_speed:     .res 1

cursor_x: .res 1
cursor_y: .res 1
temp_x:   .res 1
temp_y:   .res 1
temp_mul: .res 1
var_m:    .res 1
var_n:    .res 1
var_o:    .res 1
var_p:    .res 1

jump_pressed_last_frame: .res 1

frame_counter: .res 1
last_frame_jumped: .res 1
last_frame_moving: .res 1

tile_update_pos_r: .res 1

pointer:           .res 2

.segment "BSS"
level:      .res 240
level2:     .res 240

.segment "CODE"
main:
	ldx #0
	:
		lda example_palette, X
		sta palette, X
		inx
		cpx #32
		bcc :-

	jsr setup_background
	jsr ppu_update

    lda #$40
    sta cursor_x
    sta cursor_y

    lda #0
    sta frame_counter
    sta last_frame_jumped

    jsr init_objects

@loop:
    lda $2002
    lda frame_counter
    clc
    adc #1
    sta frame_counter

    jsr controller
    jsr movement
    jsr move_camera

@draw:
    jsr draw_player
	jsr ppu_update

	jmp @loop

move_camera:
    jmp @no
    lda player_pos_x
    clc
    adc #240
    cmp scroll_x
    bmi :++
        lda #1
        clc
        adc scroll_x
        cmp scroll_x
        sta scroll_x
        bcs :+
            lda scroll_nmt
            eor #%00000001
            sta scroll_nmt
        :
    :
    rts
    @no:


    jsr btn_select
    cmp #0
    beq :+
        lda #%11111111
        sta camera_speed
        jmp @end
    :

    jsr btn_start
    cmp #0
    beq :+
        lda #1
        sta camera_speed
    :
    @end:


    jsr add_scroll_x
    jsr check_column_update
    rts

draw_player:
    lda player_pos_y
    sec
    sbc #1
    sta oam + (4 * 2) + 0
    sta oam + (4 * 3) + 0
    sec
    sbc #16
    sta oam + (4 * 0) + 0
    sta oam + (4 * 1) + 0


    ; RIGHT HALF LOGIC
    ; see if we can skip drawing the player because it's off screen
    lda player_pos_x
    sec
    sbc scroll_x
    cmp player_pos_x ; if underflow, nametable bits must be different to continue
    beq @skip_bcs_right
    bcs :+
        @skip_bcs_right:
        lda player_nmt_x
        eor scroll_nmt
        bne @hide_player_right
        jmp :++
    :
        ; if nothing, nametable bits must be same to continue
        lda player_nmt_x
        eor scroll_nmt
        beq @hide_player_right
    :
    jmp @end_hide_player_right

    @hide_player_right:
    lda player_status
    and #%00000001
    cmp #0
    bne :+
        lda #250
        sta oam + (4 * 1) + 0
        sta oam + (4 * 3) + 0
        jmp :++
    :
        lda #250
        sta oam + (4 * 0) + 0
        sta oam + (4 * 2) + 0
    :

    @end_hide_player_right:

    ; LEFT HALF LOGIC
    ; store what nametable the player's left half is on in var_n
    ; store what position the player's left half is at in var_p
    lda player_pos_x
    sec
    sbc #8
    sta var_p
    bcs :+
        lda player_nmt_x
        eor #%00000001
        sta var_n
        jmp :++
    :
        lda player_nmt_x
        sta var_n
    :

    lda var_p
    sec
    sbc scroll_x
    cmp var_p ; if underflow, nametable bits must be different to continue
    beq @skip_bcs_left
    bcs :+
        @skip_bcs_left:
        lda var_n
        eor scroll_nmt
        bne @hide_player_left
        jmp :++
    :
        ; if nothing, nametable bits must be same to continue
        lda var_n
        eor scroll_nmt
        beq @hide_player_left
    :
    jmp @end_hide_player_left

    @hide_player_left:
    lda player_status
    and #%00000001
    cmp #0
    bne :+
        lda #250
        sta oam + (4 * 0) + 0
        sta oam + (4 * 2) + 0
        jmp :++
    :
        lda #250
        sta oam + (4 * 1) + 0
        sta oam + (4 * 3) + 0
    :

    @end_hide_player_left:

    lda player_status
    and #%00000001
    cmp #0
    bne :+
        lda player_pos_x
        sec
        sbc scroll_x
        sta oam + (4 * 1) + 3
        sta oam + (4 * 3) + 3
        sec
        sbc #8
        sta oam + (4 * 0) + 3
        sta oam + (4 * 2) + 3
        jmp :++
    :
        lda player_pos_x
        sec
        sbc scroll_x
        sta oam + (4 * 0) + 3
        sta oam + (4 * 2) + 3
        sec
        sbc #8
        sta oam + (4 * 1) + 3
        sta oam + (4 * 3) + 3
    :

    lda player_status
    and #%10000000
    cmp #0
    bne :+
        lda #$45
        jmp :++
    :
        lda #$49
    :
    sta oam + (4 * 0) + 1
    clc
    adc #2
    sta oam + (4 * 1) + 1
    lda #$65
    sta oam + (4 * 2) + 1
    lda #$67
    sta oam + (4 * 3) + 1

    
    lda player_status
    and #%00000001
    cmp #0
    beq :+
        lda #%01000000
        jmp :++
    :
        lda #%00000000
    :

    ora #%00000001
    sta oam + (4 * 0) + 2
    ora #%00000001
    sta oam + (4 * 1) + 2
    and #%11111100
    sta oam + (4 * 2) + 2
    and #%11111100
    sta oam + (4 * 3) + 2

    rts

init_objects:
    lda #96
    sta player_pos_x ; Set X position
    lda #128
    sta player_pos_y ; Set Y position

    lda #0
    sta player_vel_x
    sta player_vel_y
    sta player_status
    sta scroll_nmt
    sta player_nmt_x

    lda #%00101000
    sta horizontal_speed

    lda #0
    sta camera_speed
    sta tile_update_pos_r

    rts

draw:
@end:
	rts

movement:
    ; Talking
    ldx #0
    jsr btn_b
    cmp #0
    beq :+
        lda player_status
        ora #%10000000
        sta player_status
        jmp :++
    :
        lda player_status
        and #%01111111
        sta player_status
    :

    ; Horizontal velocity
    ldx #0
    jsr btn_right
    cmp #0
    beq :+
        ldx #1
        lda horizontal_speed
        sta player_vel_x

        lda player_status
        and #%11111110
        sta player_status

        lda frame_counter
        sta last_frame_moving
    :

    jsr btn_left
    cmp #0
    beq :+
        ldx #1
        lda horizontal_speed
        eor #%11111111
        clc
        adc #1
        sta player_vel_x

        lda player_status
        ora #%00000001
        sta player_status

        lda frame_counter
        sta last_frame_moving
    :

    cpx #1 ; skip decay if right or left pressed
    beq @end
        lda frame_counter
        clc
        sbc last_frame_moving
        and #3
        cmp #0
        bne @end

        lda player_vel_x
        and #%01111111
        cmp #0
        beq @end ; If player_vel_x = 0, skip decay

        lda player_vel_x
        and #%10000000
        ; If player_vel_x positive, decrement
        bne :++
            lda player_vel_x
            sec
            sbc #16
            sta player_vel_x
            cmp #0
            bpl :+
                ; negative, clamp to 0
                lda #0
                sta player_vel_x
            :
            jmp @end
        :
        ; Else if player_vel_x < 0, increment
        lda player_vel_x
        clc
        adc #16
        sta player_vel_x
        cmp #0
        beq :+
        bmi :+
            ; positive, clamp to 0
            lda #0
            sta player_vel_x
        :
    @end:



    ; Jump
    jsr btn_a
    cmp #0
    beq @fail_jump ; If jump not pressed, forget it
    lda jump_pressed_last_frame
    cmp #1
    beq @fail_jump ; If jump last frame, forget it

    ; Jump newly pressed this frame
    lda #249
    sta player_vel_y

    lda frame_counter
    sta last_frame_jumped

    @fail_jump:
    
    jsr btn_a
    sta jump_pressed_last_frame


    ; Gravity
    lda frame_counter
    sec
    sbc last_frame_jumped
    and #%00000001
    cmp #0
    bne :+
        lda player_vel_y
        clc
        adc #1    ; Add 2 to velocity
        sta player_vel_y
    :

    ; Apply Y velocity
    lda player_pos_y
    clc
    adc player_vel_y
    sta player_pos_y

    ; Apply X velocity
    ; Position
    lda player_vel_x
    and #%10000000
    cmp #0
    bne :+
        ; 0: right
        lda player_vel_x
        sta var_o ; store initial velocity in o
        and #%01111111
        clc
        ror
        clc
        ror
        clc
        ror
        clc
        ror
        clc
        adc player_pos_x
        sta player_pos_x ; add pixels
        bcc @end_pixel_overflow_right
            lda player_nmt_x
            eor #%00000001
            sta player_nmt_x
        @end_pixel_overflow_right:


        lda player_vel_x
        ; A contains signed subpixels

        clc
        adc player_subpos_x ; add subposition and velocity subpixels
        and #%00001111
        cmp player_subpos_x ; if A (result) is less than current subpos, overflow occurred
        sta player_subpos_x
        beq @end_add_subpos
        bcs @end_add_subpos ; so skip if subpos is smaller than result
            lda player_pos_x
            clc
            adc #1
            sta player_pos_x
            bcc @end_subpixel_overflow_right
                lda player_nmt_x
                eor #%00000001
                sta player_nmt_x
            @end_subpixel_overflow_right:
        @end_add_subpos:

        jmp :++
    :
        ; 1: left
        lda player_vel_x
        sta var_o
        sec
        ror
        sec
        ror
        sec
        ror
        sec
        ror
        ora #%10000000
        clc
        adc player_pos_x
        sta player_pos_x ; add pixels
        bcs @end_pixel_overflow_left
            lda player_nmt_x
            eor #%00000001
            sta player_nmt_x
        @end_pixel_overflow_left:
        ;                               :|
        lda player_pos_x
        clc
        adc #1
        sta player_pos_x ; add... correction?
        bcc @end_correction
            lda player_nmt_x
            eor #%00000001
            sta player_nmt_x
        @end_correction:


        lda player_vel_x
        ; A contains signed subpixels

        clc
        adc player_subpos_x ; add subposition and velocity subpixels
        and #%00001111
        cmp player_subpos_x ; if A (result) is greater than current subpos, underflow occurred
        sta player_subpos_x
        beq @end_sub_subpos
        bcc @end_sub_subpos ; so skip if subpos is bigger than result
            lda player_pos_x
            sec
            sbc #1
            sta player_pos_x
            bcs @end_subpixel_overflow_left
                lda player_nmt_x
                eor #%00000001
                sta player_nmt_x
            @end_subpixel_overflow_left:
        @end_sub_subpos:
    :






    ; load x pos, filter blocks, check up and down
    
    lda player_vel_y
    cmp #0
    bmi :+ ; branch if moving up
        jsr downward_collision_check
        jsr left_collision_check
        jsr right_collision_check
        jsr upward_collision_check
        jmp :++
    :
        jsr upward_collision_check
        jsr left_collision_check
        jsr right_collision_check
        jsr downward_collision_check
    :

    rts

    ; Keep grounded
    cmp #200
    bcc :+
        lda #0
        sta player_vel_y
        lda #200
        sta player_pos_y
    :
    ; Bonk
    lda #8
    cmp player_pos_y
    bcc :+
        lda #0
        sta player_vel_y
        lda #8
        sta player_pos_y
    :

    rts

setup_background:
    ldx #0
    :
        lda default_level, X
        sta level, X

        inx
        cpx #240
        bne :-

    ldx #0
    :
        lda default_level2, X
        sta level2, X

        inx
        cpx #240
        bne :-

    ldx #0
    :
        lda default_level, X
        sta level, X

        inx
        cpx #240
        bne :-

    ldx #0
    :
        lda default_level2, X
        sta level2, X

        inx
        cpx #240
        bne :-

	lda $2002 ; reset latch
	lda #$20
	sta $2006
	lda #$00
	sta $2006
	; empty nametable
	lda #0
	ldy #30 ; 30 rows
	:
		ldx #32 ; 32 columns
		:
			sta $2007
			dex
			bne :-
		dey
		bne :--

; ------------- Nametable 1: level
    lda $2002
    lda #$20
    sta $2006
    lda #$00
    sta $2006
	ldy #0
	@row_start_nmt1:
        ldx #0
        :
            txa
            pha

            ; index is (Y * 16) + X
            stx temp_x
            lda #16
            jsr mul_y
            clc
            adc temp_x
            tax

            lda level, X
            and #%01111111
            ldx #5
            jsr mul_x
            tax
            
            lda metatiles+0, X
            sta $2007
            lda metatiles+1, X
            sta $2007

            pla
            tax
            inx
            cpx #16
            bne :-

        ; again
        ldx #0
        :
            txa
            pha

            ; index is (Y * 16) + X
            stx temp_x
            lda #16
            jsr mul_y
            clc
            adc temp_x
            tax

            lda level, X
            and #%01111111
            ldx #5
            jsr mul_x
            tax

            lda metatiles+2, X
            sta $2007
            lda metatiles+3, X
            sta $2007

            pla
            tax
            inx
            cpx #16
            bne :-
		iny
        cpy #15
		bne @row_start_nmt1

	; clear attributes
    ;lda #0
	;ldx #64 ; 64 bytes
	;:
    ;    lda #%11100100
;
	;	sta $2007
	;	dex
	;	bne :-

    lda #0
    sta $50

    ldy #0
    :
        tya
        pha

        ldx #0
        :
            tya
            pha
            txa
            pha

            tya
            asl
            asl
            asl
            asl
            asl
            sta temp_y

            txa
            asl

            clc
            adc temp_y

            tax

            lda level, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            sta temp_x

            lda level+1, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            asl
            asl
            adc temp_x
            sta temp_x

            lda level+16, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            asl
            asl
            asl
            asl
            adc temp_x
            sta temp_x

            lda level+17, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            asl
            asl
            asl
            asl
            asl
            asl
            adc temp_x
            sta $2007

            ldx $50
            inx
            stx $50

            sta $60, X

            pla
            tax
            pla
            tay
            inx
            cpx #8
            beq @left_jump
                jmp :-
            @left_jump:

        pla
        tay
        iny
        cpy #8
        beq :+
            jmp :--
        :
; ---------------- End nametable 1: Level
; ---------------- Begin nametable 2: Level 2
    lda $2002
    lda #$24
    sta $2006
    lda #$00
    sta $2006
	ldy #0
	@row_start_nmt2:
        ldx #0
        :
            txa
            pha

            ; index is (Y * 16) + X
            stx temp_x
            lda #16
            jsr mul_y
            clc
            adc temp_x
            tax

            lda level2, X
            and #%01111111
            ldx #5
            jsr mul_x
            tax
            
            lda metatiles+0, X
            sta $2007
            lda metatiles+1, X
            sta $2007

            pla
            tax
            inx
            cpx #16
            bne :-

        ; again
        ldx #0
        :
            txa
            pha

            ; index is (Y * 16) + X
            stx temp_x
            lda #16
            jsr mul_y
            clc
            adc temp_x
            tax

            lda level2, X
            and #%01111111
            ldx #5
            jsr mul_x
            tax

            lda metatiles+2, X
            sta $2007
            lda metatiles+3, X
            sta $2007

            pla
            tax
            inx
            cpx #16
            bne :-
		iny
        cpy #15
		bne @row_start_nmt2


	; clear attributes
    ;lda #0
	;ldx #64 ; 64 bytes
	;:
    ;    lda #%11100100
;
	;	sta $2007
	;	dex
	;	bne :-

    lda #0
    sta $50

    ldy #0
    :
        tya
        pha

        ldx #0
        :
            tya
            pha
            txa
            pha

            tya
            asl
            asl
            asl
            asl
            asl
            sta temp_y

            txa
            asl

            clc
            adc temp_y

            tax

            lda level2, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            sta temp_x

            lda level2+1, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            asl
            asl
            adc temp_x
            sta temp_x

            lda level2+16, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            asl
            asl
            asl
            asl
            adc temp_x
            sta temp_x

            lda level2+17, X
            and #%01111111
            tay
            lda #5
            jsr mul_y
            tay
            lda metatiles+4, Y
            and #%00000011
            asl
            asl
            asl
            asl
            asl
            asl
            adc temp_x
            sta $2007

            ldx $50
            inx
            stx $50

            sta $60, X

            pla
            tax
            pla
            tay
            inx
            cpx #8
            beq @right_jump
                jmp :-
            @right_jump:

        pla
        tay
        iny
        cpy #8
        beq :+
            jmp :--
        :

    rts

add_scroll_x:
    lda camera_speed
    bmi @left
        clc
        adc scroll_x
        cmp scroll_x
        sta scroll_x
        bcs :+
            lda scroll_nmt
            eor #%00000001
            sta scroll_nmt
            ldx scroll_page
            inx
            sta scroll_page
        :
        rts
    @left:
        clc
        adc scroll_x
        cmp scroll_x
        sta scroll_x
        bcc :+
            lda scroll_nmt
            eor #%00000001
            sta scroll_nmt
            ldx scroll_page
            dex
            sta scroll_page
        :
        rts
    
check_column_update:
    clc
    lda scroll_nmt
    beq :+
        sec
    :

    lda scroll_x
    ror
    lsr
    lsr
    lsr

    cmp tile_update_pos_r
    bne :+
        jsr update_nmt_column
        lda tile_update_pos_r
        clc
        adc #1
        and #%00011111
        sta tile_update_pos_r

    :

    rts

update_nmt_column:
    ; X represents the row of the current tile being updated
    ldx #0
    @row_loop:
        lda tile_update_pos_r
        clc
        ; Add offset in tiles from left edge of screen
        adc #8
        sta var_n

        ; Nametable base
        lda #$20
        sta var_o

        lda #<level
        sta pointer
        lda #>level
        sta pointer+1


        lda var_n
        and #%00010000
        cmp #0
        beq:+
            lda pointer
            clc
            adc #240
            sta pointer

            lda pointer+1
            adc #0
            sta pointer+1

            lda #$24
            sta var_o
        :

            lda var_n
        and #%00001111
        sta var_p


        lda #16
        jsr mul_x
        clc
        adc var_p
        tay
        ; Specifies what tile gets written to the column
        lda #%10110001
        sty var_m
        :
            lsr
            dec var_m
            bne :-
        
        and #%00000001
        sta (pointer), Y

        and #%01111111
        ldy #5
        jsr mul_y
        tay


        ; Preserve X
        txa
        pha

        lda #6
        jsr mul_x
        tax

        lda metatiles+0, Y
        sta nmt_update+2, X
        lda metatiles+1, Y
        sta nmt_update+3, X
        lda metatiles+2, Y
        sta nmt_update+4, X
        lda metatiles+3, Y
        sta nmt_update+5, X


        ; Recover X (to Y)
        pla
        tay

        lsr
        lsr
        ; Add nametable base
        clc
        adc var_o
        sta nmt_update+0, X

        lda #64
        jsr mul_y
        clc
        adc var_p
        clc
        adc var_p
        sta nmt_update+1, X



        tya
        tax

        inx
        cpx #15
        beq :+
            jmp @row_loop
        :


    lda #15
    sta nmt_update_len

    rts

mul_x:
    cmp #0
    beq @zero
    cpx #0
    beq @zero

    sta temp_mul

    txa
    pha
    lda #0
    :
        clc
        adc temp_mul
        dex
        bne :-
    sta temp_mul
    pla
    tax
    lda temp_mul
    rts

    @zero:
    lda #0
    rts

mul_y:
    cmp #0
    beq @zero
    cpy #0
    beq @zero

    sta temp_mul

    tya
    pha
    lda #0
    :
        clc
        adc temp_mul
        dey
        bne :-
    sta temp_mul
    pla
    tay
    lda temp_mul
    rts

    @zero:
    lda #0
    rts

controller:
    lda #1
    sta $4016
    sta buttons
    lda #0
    sta $4016
    :
        lda $4016
        lsr
        rol buttons
        bcc :-

    rts

btn_right:
    lda buttons
    and #%00000001
    rts

btn_left:
    lda buttons
    and #%00000010
    lsr
    rts

btn_down:
    lda buttons
    and #%00000100
    lsr
    lsr
    rts

btn_up:
    lda buttons
    and #%00001000
    lsr
    lsr
    lsr
    rts

btn_start:
    lda buttons
    and #%00010000
    lsr
    lsr
    lsr
    lsr
    rts

btn_select:
    lda buttons
    and #%00100000
    lsr
    lsr
    lsr
    lsr
    lsr
    rts

btn_b:
    lda buttons
    and #%01000000
    lsr
    lsr
    lsr
    lsr
    lsr
    lsr
    rts

btn_a:
    lda buttons
    and #%10000000
    lsr
    lsr
    lsr
    lsr
    lsr
    lsr
    lsr
    rts

downward_collision_check:
    lda #0
    sta var_n
    @begin_check:
    lda player_pos_x
    ldx var_n
    cpx #0
    bne :+
        sec
        sbc #5
        jmp :++
    :
        clc
        adc #4
    :
    ; divide by 16
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    sta temp_x

    lda player_pos_y
    ; divide by 16
    clc
    adc #8
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    tay

    lda #16
    jsr mul_y
    adc temp_x
    tax
    lda player_nmt_x
    cmp #0
    beq :+
        lda level2, X
        jmp :++
    :
        lda level, X
    :
    and #%10000000
    cmp #0
    beq :+
        tya
        asl
        asl
        asl
        asl
        sec
        sbc #8
        cmp player_pos_y
        bcs :+
        sta player_pos_y
        lda #0
        sta player_vel_y
    :

    ldx var_n
    inx
    stx var_n
    cpx #1
    beq @begin_check

    rts

upward_collision_check:
    lda #0
    sta var_n
    @begin_check:
    lda player_pos_x
    ldx var_n
    cpx #0
    bne :+
        sec
        sbc #5
        jmp :++
    :
        clc
        adc #4
    :
    ; divide by 16
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    sta temp_x

    lda player_pos_y
    ; divide by 16
    sec
    sbc #8
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    tay

    lda #16
    jsr mul_y
    adc temp_x
    tax
    lda player_nmt_x
    cmp #0
    beq :+
        lda level2, X
        jmp :++
    :
        lda level, X
    :
    and #%10000000
    cmp #0
    beq :+
        iny
        tya
        asl
        asl
        asl
        asl
        clc
        adc #8
        cmp player_pos_y
        bcc :+
        sta player_pos_y
        lda #0
        sta player_vel_y
    :

    ldx var_n
    inx
    stx var_n
    cpx #1
    beq @begin_check

    rts

right_collision_check:
    lda #0
    sta var_n
    @begin_check:
    lda player_pos_x
    ; divide by 16
    clc
    adc #8
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    sta temp_x

    lda player_pos_y
    ldx var_n
    cpx #0
    bne :+
        sec
        sbc #7
        jmp :++
    :
        clc
        adc #6
    :
    ; divide by 16
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    tay

    lda #16
    jsr mul_y
    adc temp_x
    tax
    lda player_nmt_x
    cmp #0
    beq :+
        lda level2, X
        jmp :++
    :
        lda level, X
    :
    and #%10000000
    cmp #0
    beq :+
        lda temp_x
        asl
        asl
        asl
        asl
        sec
        sbc #8
        cmp player_pos_x
        bcs :+
        sta player_pos_x
        lda #0
        sta player_vel_x
    :

    ldx var_n
    inx
    stx var_n
    cpx #1
    beq @begin_check

    rts

left_collision_check:
    lda #0
    sta var_n
    @begin_check:
    lda player_pos_x
    ; divide by 16
    sec
    sbc #8
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    sta temp_x

    lda player_pos_y
    ldx var_n
    cpx #0
    bne :+
        sec
        sbc #7
        jmp :++
    :
        clc
        adc #6
    :
    ; divide by 16
    clc
    ror
    clc
    ror
    clc
    ror
    clc
    ror
    tay

    lda #16
    jsr mul_y
    adc temp_x
    tax
    lda player_nmt_x
    cmp #0
    beq :+
        lda level2, X
        jmp :++
    :
        lda level, X
    :
    and #%10000000
    cmp #0
    beq :+
        lda temp_x
        clc
        adc #1
        asl
        asl
        asl
        asl
        clc
        adc #8
        cmp player_pos_x
        bcc :+
        sta player_pos_x
        lda #0
        sta player_vel_x
    :

    ldx var_n
    inx
    stx var_n
    cpx #1
    beq @begin_check

    rts