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