anchor: love.touchmoved
  Callback function triggered when a touch press moves inside the touch screen.
  love.touchmoved( id, x, y, dx, dy, pressure )
  id light userdata The identifier for the touch press.
  x number The x-axis position of the touch inside the window, in pixels.
  y number The y-axis position of the touch inside the window, in pixels.
  dx number The x-axis movement of the touch inside the window, in pixels.
  dy number The y-axis movement of the touch inside the window, in pixels.
  pressure number The amount of pressure being applied. Most touch screens aren't pressure sensitive, in which case the pressure will be 1.