public partial class FrmLogin : Form, ILoginView
    {
        private ILog _log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
        public FrmLogin()
        {
            InitializeComponent();
            Load += FrmLogin_Load;
            SetFormRoundRectRgn(this, 5);    //设置圆角
        }

        private void FrmLogin_Load(object sender, EventArgs e)
        {
            this.BackColor = ColorTranslator.FromHtml("#FF5DB3AB"); //171, 179, 93
            BackgroundImage = ImageHelper.GetImage("Login\\login_bg.png");
        }}
/// <summary>
        /// 设置窗体的圆角矩形
        /// </summary>
        /// <param name="form">需要设置的窗体</param>
        /// <param name="rgnRadius">圆角矩形的半径</param>
        public static void SetFormRoundRectRgn(Form form, int rgnRadius)
        {
            int hRgn = 0;
            hRgn = Win32.CreateRoundRectRgn(0, 0, form.Width + 1, form.Height + 1, rgnRadius, rgnRadius);
            Win32.SetWindowRgn(form.Handle, hRgn, true);
            Win32.DeleteObject(hRgn);
        }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;

namespace UClass.View.Login
{
    public class Win32
    {
        #region Window Const

        public const int WM_ERASEBKGND = 0x0014;
        public const int WM_LBUTTONDOWN = 0x0201;
        public const int WM_LBUTTONUP = 0x0202;
        public const int WM_LBUTTONDBLCLK = 0x0203;
        public const int WM_WINDOWPOSCHANGING = 0x46;
        public const int WM_PAINT = 0xF;
        public const int WM_CREATE = 0x0001;
        public const int WM_ACTIVATE = 0x0006;
        public const int WM_NCCREATE = 0x0081;
        public const int WM_NCCALCSIZE = 0x0083;
        public const int WM_NCPAINT = 0x0085;
        public const int WM_NCACTIVATE = 0x0086;
        public const int WM_NCLBUTTONDOWN = 0x00A1;
        public const int WM_NCLBUTTONUP = 0x00A2;
        public const int WM_NCLBUTTONDBLCLK = 0x00A3;
        public const int WM_NCMOUSEMOVE = 0x00A0;

        public const int WM_NCHITTEST = 0x0084;

        public const int HTLEFT = 10;
        public const int HTRIGHT = 11;
        public const int HTTOP = 12;
        public const int HTTOPLEFT = 13;
        public const int HTTOPRIGHT = 14;
        public const int HTBOTTOM = 15;
        public const int HTBOTTOMLEFT = 0x10;
        public const int HTBOTTOMRIGHT = 17;
        public const int HTCAPTION = 2;
        public const int HTCLIENT = 1;

        public const int WM_FALSE = 0;
        public const int WM_TRUE = 1;



        #endregion

        #region Public extern methods

        [DllImport("gdi32.dll")]
        public static extern int CreateRoundRectRgn(int x1, int y1, int x2, int y2, int x3, int y3);

        [DllImport("user32.dll")]
        public static extern int SetWindowRgn(IntPtr hwnd, int hRgn, Boolean bRedraw);

        [DllImport("gdi32.dll", EntryPoint = "DeleteObject", CharSet = CharSet.Ansi)]
        public static extern int DeleteObject(int hObject);

        [DllImport("user32.dll")]
        public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

        [DllImport("user32.dll")]
        public static extern bool ReleaseCapture();

        #endregion
    }
}