width=100
height=50
--print("pixels:", pixels)
repaint=not notFirstTime
notFirstTime=true
pixels=nil -- optimization (no redraw effort if image not changed)

if inputEvents then
  for _, e in ipairs(inputEvents) do
    --print(e[1])
    if e[1] == 'mousePressed' then
      mouse = true
      repaint = true
    elseif e[1] == 'mouseReleased' then
      mouse = false
      repaint = true
    end
  end
end

if repaint then
  pixels = {}
  if mouse then
    for i=1, width*height do pixels[i] = -1 end
  end
end

animateAgainIn = 100

It works! :)

Now with optimization to avoid idle redraws.