weird_lines.p8

pico-8 cartridge // http://www.pico-8.com
version 16
__lua__

function _init()
    cls()
end

col = 1

function xorpset(x, y, col)
    local c = pget(x, y)
    if c ~= 0 then
        pset(x, y, 0)
    else
        pset(x, y, col)
    end
end

function xorline(x0, y0, x1, y1)
    local swap = false
    local dx = abs(x1 - x0)
    local dy = abs(y1 - y0)
    if dx < dy then
        x0, y0, x1, y1 = y0, x0, y1, x1
        swap = true
    end
    local len = sqrt(dx * dx + dy * dy)
    local lenstep = len / abs(x1 - x0) / 15
    local col = 1
    local tlen = 0
    dy = (y1 - y0) / (x1 - x0)
    local ty = y0
    local step = (x1 > x0) and 1 or -1
    if step == -1 then dy = -dy end
    for tx = x0, x1, step do
        xorpset(swap and ty or tx, swap and tx or ty, col)
        ty = ty + dy
        tlen = tlen + lenstep
        if tlen > 1 then
            tlen = tlen - 1
            col = col + 1
        end
    end
end





function _update60()
    if band(x, 7) == 0 then
        col = col + 1
        if col > 15 then
            col = 1
        end

        for c = 1, 15 do
            pal(c, band(col + c, 15))
        end
    end
end

phase = 0
x = 0

function lineloop()
    if phase == 0 then
        xorline(x, 127, 127, 127 - x)
    elseif phase == 1 then
        xorline(127, 127 - x, 127 - x, 0)
    elseif phase == 2 then
        xorline(127 - x, 0, 0, x)
    elseif phase == 3 then
        xorline(0, x, x, 127)
    end

    x = x + 1
    if x == 128 then
        x = 0
        phase = phase + 1
        if phase == 4 then
            phase = 0
        end
    end
end


function _draw()
    lineloop()
    lineloop()
end

__sfx__
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010100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
010100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
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010100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
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__music__
00 08090a40