fabric.js/src/canvas.gestures.js

(function() {

  var degreesToRadians = fabric.util.degreesToRadians,
      radiansToDegrees = fabric.util.radiansToDegrees;

  fabric.util.object.extend(fabric.Canvas.prototype, {

    /**
     * Method that defines actions when an Event.js gesture is detected on an object. Currently only supports
     * 2 finger gestures.
     *
     * @method __onTransformGesture
     * @param e Event object by Event.js
     * @param self Event proxy object by Event.js
     */
    __onTransformGesture: function(e, self) {

      if (this.isDrawingMode || e.touches.length !== 2 || 'gesture' !== self.gesture) {
        return;
      }

      var target = this.findTarget(e);
      if ('undefined' !== typeof target) {
        this.onBeforeScaleRotate(target);
        this._rotateObjectByAngle(self.rotation);
        this._scaleObjectBy(self.scale);
      }

      this.fire('touch:gesture', {target: target, e: e, self: self});
    },

    /**
     * Scales an object by a factor
     * @param s {Number} The scale factor to apply to the current scale level
     * @param by {String} Either 'x' or 'y' - specifies dimension constraint by which to scale an object.
     *                    When not provided, an object is scaled by both dimensions equally
     */
    _scaleObjectBy: function(s, by) {
      var t = this._currentTransform,
        target = t.target;

      var lockScalingX = target.get('lockScalingX'),
        lockScalingY = target.get('lockScalingY');

      if (lockScalingX && lockScalingY)
        return;

      target._scaling = true;

      if (!by) {
        if (!lockScalingX) {
          target.set('scaleX', t.scaleX * s);
        }
        if (!lockScalingY) {
          target.set('scaleY', t.scaleY * s);
        }
      }
      else if (by === 'x' && !target.get('lockUniScaling')) {
        lockScalingX || target.set('scaleX', t.scaleX * s);
      }
      else if (by === 'y' && !target.get('lockUniScaling')) {
        lockScalingY || target.set('scaleY', t.scaleY * s);
      }
    },

    /**
     * Rotates object by an angle
     * @param curAngle {Number} the angle of rotation in degrees
     */
    _rotateObjectByAngle: function(curAngle) {
      var t = this._currentTransform;

      if (t.target.get('lockRotation'))
        return;

      t.target.angle = radiansToDegrees(degreesToRadians(curAngle) + t.theta);
    }
  });
})();