function init()
    ink_color = 15
    paper_color = 0
    setchar(0,0xff,0x81,0x81,0x81,0x81,0x81,0x81,0xff)
    sprite={0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
            0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
            0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
            0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00}
            --0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x18,
            --0x81,0x81,0x81,0x81,0x81,0x81,0x81,0x81,
            --0xc0,0xc0,0xc0,0xc0,0xc0,0xc0,0xc0,0xc0,
            --0x03,0x03,0x03,0x03,0x03,0x03,0x03,0x03}
end

function update()
    -- Borra pantalla
    color(15,1)
    cls()

    -- Pinta sprite en gran a pantalla
    color(ink_color,paper_color)
    drawbigspr(sprite,1,1)

    -- Pinta el sprite en els caracters A, B, C i D
    drawspr(sprite,65)

    -- Pinta els caracters AB CD a pantalla
    print("AB",18,1) print("CD",18,2)

    -- Pinta la paleta
    for i=0,15 do
        color(0,i)
        poke(721+i,0) poke(1921+i,i<<4)
        poke(761+i,0) poke(1961+i,i<<4)
    end

    -- Pinta el borde roig a les entrades en la paleta seleccionades
    poke(1921+ink_color, peek(1921+ink_color)+4)
    poke(1961+paper_color, peek(1961+paper_color)+4)

    -- Gestió dels clicks en la paleta
    if mousebutton(1) and mousex()>=1 and mousey()>=18 and mousex()<=16 and mousey()<=19 then
        if mousey()==18 then
            ink_color = mousex()-1
        else
            paper_color = mousex()-1
        end
    end

    -- Gestió dels clicks sobre l'sprite
    handlesprmouse()

    -- Si pulsem 'C', borrar el sprite
    if btnp(KEY_C) then
        for i=1,32 do
            sprite[i]=0;
        end
    end
end

mousepressed = false
mousepos = {x=-1,y=-1}
function handlesprmouse()
    local mx,my=mousex(),mousey()
    if mx>=1 and my>=1 and mx<=16 and my<=16 then
        if mousebutton(1) then
            if (not mousepressed or (mousepos.x ~= mx or mousepos.y ~= my)) then
                mousepressed = true mousepos.x = mx mousepos.y = my
                local quadrant = flr((mx-1)/8)+flr((my-1)/8)*2
                local x=(mx-1)%8
                local y=(my-1)%8
                local val = sprite[quadrant*8+y+1]
                val = val ~ (1<<(7-x))
                sprite[quadrant*8+y+1] = val
            end
        else
            mousepressed = false
        end
    end
end

function drawbigspr(spr,x,y)
    drawbigsprchr(spr,0,x,y)
    drawbigsprchr(spr,1,x+8,y)
    drawbigsprchr(spr,2,x,y+8)
    drawbigsprchr(spr,3,x+8,y+8)
end

function drawbigsprchr(spr,chr,x,y)
    local pos = 1+chr*8
    for i=1,8 do
        local val = spr[pos]
        print("        ",x,y)
        if val&1==1 then print("\143",x+7,y) end
        if val&2==2 then print("\143",x+6,y) end
        if val&4==4 then print("\143",x+5,y) end
        if val&8==8 then print("\143",x+4,y) end
        if val&16==16 then print("\143",x+3,y) end
        if val&32==32 then print("\143",x+2,y) end
        if val&64==64 then print("\143",x+1,y) end
        if val&128==128 then print("\143",x,y) end
        y=y+1
        pos=pos+1
    end
end

function drawspr(spr,chr)
    for i=0,31 do poke(i+2560+chr*8,spr[i+1]) end
end