像素转毫米 宽度

/// <summary>
        /// 像素转毫米  宽度
        /// </summary>
        /// <param name="length"></param>
        /// <param name="frmHandle">当前窗口/控件句柄</param>
        /// <returns></returns>
        public static float PixelsToMillimetersWidth(this float length, IntPtr frmHandle)
        {
            Graphics g = Graphics.FromHwnd(frmHandle);
            return length * (25.4f / g.DpiX);
        }