protected internal RectangleF BaseGroupRotate(float angle, PointF center) { DataBk.State = ControlState.GroupRotate; DataBk.Offset = Calculation.GetRotateAtOffset(DataBk, center, angle); _rotateAngle = DataBk.RotateAngle + angle; Calculation.LimitAngle(ref _rotateAngle); return(CalculateOffset()); }