require'vcs'
mappers['2K']()

#pragma alias and dna

local i = 0x80
local ramk=i i=i+51
local spritestack=i i=i+31
local stackbackup=i i=i+1
local time=i i=i+2
local seed=i i=i+2
local spritepos=i i=i+1
local tmp=i

-- load the 6 sprites and the shared color palette
local img = assert(l65.image("dotbin.png"))
@@col samepage byte(linecol{image=img, y0=30, y1=0, yinc=-1}, 0, 0) end
local sp = sprite{image=img, y0=185, y1=0, yinc=-1}
for i=1,6 do
    section{"spr"..i, align=256} byte(sp[i])
end

-- sprite anim frames offset in spr*
@@frame samepage dc.b 0,31,62,93,124,155 end
-- sprite anim palette offset
@@paloff samepage dc.b 0,0,0,2,0,0 end

-- division by 3 table: result in 6 LSB, remainder in 2 MSB
do
    local t = {}
    for x=0,113 do t[#t+1] = x//3 & 0x3f | x%3 << 6 end
    @@div3 samepage byte(t) end
end

-- y: sprite pos
-- return result of division in x
@@slide
    lda#_start>>8 pha
    lax div3,y and#0x3f clc adc#_start&0xff pha
    samepage
        sta WSYNC
@_start
        rts
        for i=1,35 do dc.b 0xc9 end
        dc.b 0xc5 nop
    end 
    rts

-- y: sprite pos
@@setpos
    jsr slide sleep(6) sta RESP0 sta RESP1
    txa lsr lsr and#0x30 sta HMP0 adc#0x10 sta HMP1 sta WSYNC sta HMOVE
    rts

-- y: frame index
@@setframe -- modify ram kernel with new palette offset and sprite frame pointers
    lda#col&0xff sta tmp lda paloff,y clc adc tmp sta ramk+3
    lda frame,y
    local off = { 10, 15, 20, 29, 32 }
    for _,o in ipairs(off) do sta ramk,o end
    tsx stx tmp ldx#spritestack+30 txs
    sta tmp+2 clc adc#31 sta tmp+1 ldy tmp+2 @_push lda spr4,y pha iny cpy tmp+1 bne _push
    ldx tmp txs
    rts

@@spritek
    ldy tmp lda col,y sta COLUP1 sta COLUP0
    ldx spr1,y stx GRP0 lda spr2,y sta GRP1 lda spr3,y sta GRP0
    sleep(8) -- use this time to set COLUPF :)
    ldx spr5,y lda spr6,y tay pla
    sta GRP1 stx GRP0 sty GRP1 stx GRP0
    dec tmp bpl spritek
    jmp spritek_done

local kernel = function()
    ldy#50 @_delay sta WSYNC dey bpl _delay

    tsx stx stackbackup
    lda#30 sta tmp ldy spritepos
    samepage
        jsr slide sleep(24)
        ldx#(spritestack&0xff)-1 txs
        jmp ramk
    end
@spritek_done
    lda#0 sta GRP0 sta GRP1 sta GRP0
    ldx stackbackup txs
end

@@rand
    beq _xor asl beq _nor bmi _nor
    @_xor eor#0x5f
    @_nor rts

@@glitch_cmphi dc.b 0xFF,0x03,0x02,0x02,0x02,0x01,0x00,0x00,0x00,0x00
@@glitch_cmplo dc.b 0xFF,0x10,0xA0,0x60,0x30,0x20,0xE0,0xC0,0x90,0x60
@@glitch dc.b 4,3,2,1,0,1,2,3,4
@@sproff_cmphi dc.b 0xFF,0x03,0x03,0x02,0x01,0x00,0x00
@@sproff_cmplo dc.b 0xFF,0x40,0x10,0x80,0x20,0xA0,0x60
@@sproff dc.b 7,3,1,0,1,3,7
@@sproff_add dc.b 6,8,10,11,10,8,6

local on_vblank = function()
    inc time bne _noover inc time+1 @_noover

    -- frame change
    lda time dna#3 bne _keep lda seed jsr rand sta seed @_keep
    ldy#8 @_glitch
        lda time+1 cmp glitch_cmphi,y bcc _glitchdone bne _glitchnext
        lda time cmp glitch_cmplo,y bcc _glitchdone
        @_glitchnext dey bne _glitch
    @_glitchdone
    lda glitch,y tay lda seed cpy#1 bcc _wait @_lower lsr dey bne _lower @_wait cmp#6 bcc _noreset lda#5 @_noreset
    tay jsr setframe

    -- position change
    lda time; and#7 bne _skipmove -- alias opcode 'and' to 'dna' to avoid use of ';', as on line 107
    ldy#6 @_move
        lda time+1 cmp sproff_cmphi,y bcc _stay bne _movenext
        lda time cmp sproff_cmplo,y bcc _stay
        @_movenext dey bne _move
    @_stay
    lda sproff,y sta tmp lda sproff_add,y sta tmp+1
    lda seed+1 jsr rand sta seed+1; and tmp clc adc tmp+1 adc#50 sta spritepos tay jsr setpos
    @_skipmove
end

@@main
    init()
    lda#vdel.ENABLE sta VDELP1 sta VDELP0
    lda#nusiz.THREE_COPIES_CLOSE sta NUSIZ0 sta NUSIZ1
    -- load kernel into RAM
    ldy#50 @_loadk lda spritek,y sta ramk,y dey bpl _loadk
@doframe
    overscan() vblank(on_vblank) screen(kernel) jmp doframe

;
writebin(filename..'.bin')
writesym(filename..'.sym')
print(stats)