text: var h = 200;
  var k = 450;
  var r = 100;
  
  /**
   * simple helper function to draw a circle
   * @param  {Number} h    horizontal center of the circle
   * @param  {Number} k    vertical center of the circle
   * @return {Actions[]}   list of actions for touchAction command
   */
  module.exports.circleAction = function (h, k) {
      var theta = 0;
      var r = 100;
      var prev = { action: 'press', x: h + r * Math.cos(theta), y: k + r * Math.sin(theta) };
      var actions = [];
  
      actions.push(prev);
      for (theta; theta < 2*Math.PI; theta+=2*Math.PI/36) {
          var next = { x: h + r * Math.cos(theta), y: k + r * Math.sin(theta) };
          actions.push({ action: 'moveTo', x: next.x - prev.x, y: next.y - prev.y });
          prev = next;
      }
  
      actions.push('release');
      return actions;
  }
  
  /**
   * helper function to draw an arc
   * @param  {Numver} start start point
   * @param  {Number} end   end point
   * @return {Actions[]}    list of action for touchAction command
   */
  module.exports.arcAction = function(start, end) {
      var theta = start;
      var prev = { action: 'press', x: h + r * Math.cos(theta), y: k + r * Math.sin(theta) };
      var actions = [];
      actions.push(prev);
  
      for (; theta < end; theta += 2 * Math.PI / 100) {
          var next = { x: h + r * Math.cos(theta), y: k + r * Math.sin(theta) };
          actions.push({ action: 'moveTo', x: next.x - prev.x, y: next.y - prev.y });
          prev = next;
      }
  
      actions.push('release');
      return actions;
  }
  
  /**
   * helper function to draw an curved arc
   * @param  {Numver} start start point
   * @param  {Number} end   end point
   * @return {Actions[]}    list of action for touchAction command
   */
  module.exports.innerArcAction = function(start, end) {
      var theta = start;
      var step = 4 * Math.PI / 100;
      var min_radius = 30;
  
      var prev = { action: 'press', x: h - r * Math.cos(theta), y: k + r * Math.sin(theta) };
      var actions = [];
      actions.push(prev);
  
      for (; theta < end; theta += step) {
          var rad = 7.5991 * Math.pow(theta - start - Math.PI, 2) + 25;
          var next = { x: h - rad * Math.cos(theta), y: k + rad * Math.sin(theta) };
          actions.push({ action: 'moveTo', x: next.x - prev.x, y: next.y - prev.y });
          prev = next;
      }
  
      actions.push('release');
      return actions;
  }
  