+/** @param allow_horiz true to allow horizontal autoscroll, otherwise false.
+ * @param allow_vert true to allow vertical autoscroll, otherwise false.
+ * @param moving_left true if we are moving left, so we only want to autoscroll on the left of the canvas,
+ * otherwise false, so we only want to autoscroll on the right of the canvas.
+ * @param moving_up true if we are moving up, so we only want to autoscroll at the top of the canvas,
+ * otherwise false, so we only want to autoscroll at the bottom of the canvas.
+ */