_onMouseDown(event, originPointer) {
    /**
     * The mouse down event with position x, y on canvas
     * @event ImageEditor#mousedown
     * @param {Object} event - browser mouse event object
     * @param {Object} originPointer origin pointer
     *  @param {Number} originPointer.x x position
     *  @param {Number} originPointer.y y position
     * @example
     * imageEditor.on('mousedown', function(event, originPointer) {
     *     console.log(event);
     *     console.log(originPointer);
     *     if (imageEditor.hasFilter('colorFilter')) {
     *         imageEditor.applyFilter('colorFilter', {
     *             x: parseInt(originPointer.x, 10),
     *             y: parseInt(originPointer.y, 10)
     *         });
     *     }
     * });
     */

    this.fire(events.MOUSE_DOWN, event, originPointer);
  }
mouse down event handler
@param {Event} event - mouse down event
@param {Object} originPointer - origin pointer
 @param {Number} originPointer.x x position
 @param {Number} originPointer.y y position
@private