# updates the canvas
update_canvas = (width, height) ->
  canvas.width = width
  canvas.height = height

# a range mapper which maps 's' to 'to' based on 'from'
map_range = (from, to, s) ->
  to[0] + (s-from[0]) * (to[1] - to[0]) / (from[1] - from[0])