pixelsort.lua

require "gd"

local base = gd.createFromJpeg("base.jpg")
local sizex, sizey = base:sizeXY()
local frame = gd.create(sizex, sizey)
local out = gd.createTrueColor(sizex, sizey)

function lum(c)
    local r = base:red(c)
    local g = base:green(c)
    local b = base:blue(c)
    return (r+g+b)/3
end

frame:gifAnimBegin("out.gif", false, 0)
for frm = 1, 32 do
    for x = 1, sizex do
        local startsort = 1
        local sortc = base:getPixel(x, 1)
        local sortw = lum(sortc)
        local sortlist = {{c = sortc, w = sortw}}
        for y = 2, sizey do
            local color = base:getPixel(x, y)
            local w = lum(color)
            if math.abs(w-sortw) > 8*(frm-1) then
--stop building a "similar colors" line: sort it, draw it then start a new one
                table.sort(sortlist, function(a, b) return a.w < b.w end)
                for ly = 1, #sortlist do
                    out:setPixel(x, startsort+ly-1, sortlist[ly].c) --sortlist[#sortlist-ly+1].c)
--the #sortlist-ly+1 index allows easily switching between the order in which sorted lines are redrawn
                end
                startsort = y
                sortw = w
                sortlist = {{c = color, w = w}}
            else
                table.insert(sortlist, {c = color, w = w})
            end
        end
    end
    frame = out:createPaletteFromTrueColor(true, 60)
    frame:gifAnimAdd("out.gif", true, 0, 0, 8, gd.DISPOSAL_NONE)
    print("frame:", frm)
end
gd.gifAnimEnd("out.gif")