hammerjs/plugins/hammer.fakemultitouch.js

A javascript library for multi-touch gestures

(function(Hammer) {
  'use strict';

  /**
   * enable multitouch on the desktop by pressing the shiftkey
   * the other touch goes in the opposite direction so the center keeps at its place
   * it's recommended to enable Hammer.debug.showTouches for this one
   *
   * @usage
   * just call `Hammer.plugins.fakeMultitouch()` and you're done.
   */
  Hammer.plugins.fakeMultitouch = function() {
    // no need to fake it if it already is possible!
    var maxTouchPoints = navigator.maxTouchPoints || navigator.msMaxTouchPoints;
    if(Hammer.HAS_TOUCHEVENTS || (Hammer.HAS_POINTEREVENTS && maxTouchPoints > 1)) {
      return;
    }


    // keeps the start position to keep it centered
    var start_pos = false;

    /**
     * overwrites Hammer.event.getTouchList.
     * @method getTouchList
     * @param {Event} ev
     * @param {String} eventType
     * @return {Array} Touches
     */
    Hammer.event.getTouchList = function(ev, eventType) {
      var touches = [];
      var changedTouches = [];

      // reset on start of a new touch
      if(eventType == Hammer.EVENT_START) {
        start_pos = false;
      }

      // when the shift key is pressed, multitouch is possible on desktop
      // why shift? because ctrl and alt are taken by osx and linux
      if(ev.shiftKey) {
        // on touchstart we store the position of the mouse for multitouch
        if(!start_pos) {
          start_pos = {
            pageX: ev.pageX,
            pageY: ev.pageY,
            clientX: ev.clientX,
            clientY: ev.clientY
          };

          // new touch came up
          touches.trigger = Hammer.EVENT_TOUCH;
        }

        var distance_x = start_pos.pageX - ev.pageX;
        var distance_y = start_pos.pageY - ev.pageY;

        // fake second touch in the opposite direction
        touches.push({
            identifier: 1,
            pageX     : start_pos.pageX - distance_x - 50,
            pageY     : start_pos.pageY - distance_y + 50,
            clientX   : start_pos.clientX - distance_x - 50,
            clientY   : start_pos.clientY - distance_y + 50,
            target    : ev.target
          },{
            identifier: 2,
            pageX     : start_pos.pageX + distance_x + 50,
            pageY     : start_pos.pageY + distance_y - 50,
            clientX   : start_pos.clientX + distance_x + 50,
            clientY   : start_pos.clientY + distance_y - 50,
            target    : ev.target
          });

        changedTouches = touches;
      }
      // normal single touch
      else {
        touches.push({
            identifier: 1,
            pageX     : ev.pageX,
            pageY     : ev.pageY,
            clientX   : ev.clientX,
            clientY   : ev.clientY,
            target    : ev.target
          });

        // we came from multitouch, trigger a release event
        // and use the changed touches from the multitouch
        if(start_pos) {
          touches.trigger = Hammer.EVENT_RELEASE;
        }
        // use the touches as changedTouches, because we are in a move
        else {
          changedTouches = touches;
        }
        start_pos = false;
      }

      ev.touches = touches;
      ev.changedTouches = changedTouches;
      return touches;
    };
  };

})(window.Hammer);