function copyRect(from, to, x1, y1, w, h, x2, y2)
  local fp, tp = from.pixels, to.pixels
  local fw, tw = from.width, to.width
  local ww, hh = w-1, h-1
  for y=0, hh do
    local to, fo = x2+(y2+y)*tw+1, x1+(y1+y)*fw+1
    for x=0, ww do
      tp[to+x] = fp[fo+x]
    end
  end
end