function FilledWithPixels()
  while true do
   ::begin::
    UDF1.repaint()
    for x=1,UDF1.Canvas.Width do
        for y=1,UDF1.Canvas.Height do
            local min = math.random(1, 0xFFFF)
            local max = math.random(0xFFFF, 0x00FFFFFF)
            UDF1.Canvas.SetPixel(x,y, math.random (min, max))
            if(needReUpdate) then
             needReUpdate = false
             goto begin
            end
        end
    end
    t.suspend()
  end
end

t = createNativeThreadSuspended(FilledWithPixels)
t.name = 'New thread 1'
needReUpdate = true

UDF1 = createForm()
UDF1.Width = 400
UDF1.Height = 200
btn = createButton(UDF1)
btn.OnClick = function (sender)
  needReUpdate = true
  t.resume()
end