get("#356") -- num2hex

w, h = img.width, img.height

barw = 15 -- scrollbar width

mx = math.floor(barw/2) -- in the middle

stepx, stepy = mx, 4

function topOK(x, y1, enabled)

  for y=y1-1, math.max(y1-stepy-16, 0), -1 do

    for xx = math.max(0, x-mx), math.min(w-1, x+mx) do

      local p = img.getInt(xx, y)

      if p == (enabled and 0x000000 or 0x777777) then return true end

    end

  end

  return false

end

for x = w-mx, mx, -stepx do

  last, slider, background1, background2, top = nil

  for y = 0, h-1, stepy do

    pix = img.getInt(x, y)

    if last ~= pix then

      if slider == nil and (last == 0xEAEAEA and y > starty+stepy) then

        print("possible slider: "..starty.."-"..(y-stepy))

        if top ~= nil or topOK(x, starty, false) then

          print("slider")

          if top == nil then top = starty end

          slider = x..", "..starty..", "..(x+1)..", "..(y-stepy)

          bottom = y

        end

      elseif last == 0xD3D3D3 and y > starty+stepy then

        print("possible background found: "..starty.."-"..(y-stepy))

        if top ~= nil or topOK(x, starty, true) then

          print("background")

          if top == nil then top = starty end

          bg = x..", "..starty..", "..(x+1)..", "..(y-stepy)

          if slider then

            background2 = bg

          else

            background1 = bg

          end

          bottom = y

        end

      end

      last, starty = pix, y

    end

    --print("y", y, num2hex(pix))

    if background2 then goto raus end

  end

  ::raus::

  if slider then

    upArrow = x..", "..(top-stepy-2)..", "..(x+1)..", "..(top-stepy-1)

    downArrow = x..", "..bottom..", "..(x+1)..", "..(bottom+1)

    parts = {}

    table.insert(parts, "Up arrow="..upArrow)

    if background1 then

      table.insert(parts, "Background1="..background1)

    end

    table.insert(parts, "Slider="..slider)

    if background2 then

      table.insert(parts, "Background2="..background2)

    end

    table.insert(parts, "Down arrow="..downArrow)

    return "Vertical scrollbar found: "..table.concat(parts, "|")

  end

end