code: function(dx, dy) {
          var previousIndex = this.getCurrentPointIndex() - 1;
          var p0 = this.line.geometry.components[previousIndex];
          if (p0 && !isNaN(p0.x) && !isNaN(p0.y)) {
              this.insertXY(p0.x + dx, p0.y + dy);
          }
      }
docs: Method: insertDeltaXY
  Insert a point given offsets from the previously inserted point.
  
  Parameters:
  dx - {Number} The x-coordinate offset of the point.
  dy - {Number} The y-coordinate offset of the point.