discourse/vendor/assets/javascripts/jquery.detect_swipe.js

/**
 * jquery.detectSwipe v2.1.1
 * jQuery Plugin to obtain touch gestures from iPhone, iPod Touch, iPad and Android
 * http://github.com/marcandre/detect_swipe
 * Based on touchwipe by Andreas Waltl, netCU Internetagentur (http://www.netcu.de)
 */
(function($) {

  $.detectSwipe = {
    version: '2.1.1',
    enabled: 'ontouchstart' in document.documentElement,
    preventDefault: true,
    threshold: 20
  };

  var startX,
    startY,
    isMoving = false;

  function onTouchEnd() {
    this.removeEventListener('touchmove', onTouchMove);
    this.removeEventListener('touchend', onTouchEnd);
    isMoving = false;
  }

  function onTouchMove(e) {
    if ($.detectSwipe.preventDefault) { e.preventDefault(); }
    if(isMoving) {
      var x = e.touches[0].pageX;
      var y = e.touches[0].pageY;
      var dx = startX - x;
      var dy = startY - y;
      var dir;
      if(Math.abs(dx) >= $.detectSwipe.threshold) {
        dir = dx > 0 ? 'left' : 'right'
      }
      else if(Math.abs(dy) >= $.detectSwipe.threshold) {
        dir = dy > 0 ? 'down' : 'up'
      }
      if(dir) {
        onTouchEnd.call(this);
        $(this).trigger('swipe', dir).trigger('swipe' + dir);
      }
    }
  }

  function onTouchStart(e) {
    if (e.touches.length === 1) {
      startX = e.touches[0].pageX;
      startY = e.touches[0].pageY;
      isMoving = true;
      this.addEventListener('touchmove', onTouchMove, false);
      this.addEventListener('touchend', onTouchEnd, false);
    }
  }

  function setup() {
    this.addEventListener && this.addEventListener('touchstart', onTouchStart, false);
  }

  function teardown() {
    this.removeEventListener('touchstart', onTouchStart);
  }

  $.event.special.swipe = { setup: setup, teardown: teardown };

  $.each(['left', 'up', 'down', 'right'], function () {
    $.event.special['swipe' + this] = { setup: function() {
      $(this).on('swipe', $.noop);
    } };
  });
})(jQuery);