C#非矩形窗体实现方法

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Text;using System.Windows.Forms;using System.Drawing.Drawing2D;namespace WindowsApplication1{  public partial class Form3 : Form  {    Point downPoint = Point.Empty;    public Form3()    {      InitializeComponent();    }    void Set()    {      Rectangle rect = this.ClientRectangle;      using (GraphicsPath path = new GraphicsPath())      {        path.AddEllipse(rect);        this.Region = new Region(path);      }    }    private void Form3_Load(object sender, EventArgs e)    {      Set();    }    private void Form3_MouseDown(object sender, MouseEventArgs e)    {      if (e.Button != MouseButtons.Left) return;      downPoint = new Point(e.X, e.Y);    }    private void Form3_MouseMove(object sender, MouseEventArgs e)    {      if (downPoint == Point.Empty) return;      Point location = new Point(this.Left + e.X - downPoint.X, this.Top + e.Y - downPoint.Y);      this.Location = location;    }    private void Form3_MouseUp(object sender, MouseEventArgs e)    {      if (e.Button != MouseButtons.Left) return;      downPoint = Point.Empty;    }  }}