C# 异型窗口，圆形窗口

【实例截图】打开后窗体如下效果，无边框，无标题

【核心代码】

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
            //窗体显示特效
            this.Opacity = 0;//设置窗体不透明度
            timer1.Start();//时间控件开始运行 
            pictureBox1.MouseEnter  = new System.EventHandler(pseEnter);

            pictureBox1.MouseLeave  = new System.EventHandler(pseLeave);
        }

        int intTime = 0;
        private void timer1_Tick(object sender, EventArgs e)
        {
            intTime  = timer1.Interval;

            if (intTime == 3000) //定义多长时间显示第三个窗口 
            {
                timer2.Start();
            }
            this.Opacity  = 0.03;//改变窗体透明度
        }

        private void timer2_Tick(object sender, EventArgs e)
        {
            this.timer1.Stop();//关闭定时器1
            this.Opacity = this.Opacity - 0.03;//改变窗体透明度
            if (this.Opacity == 0)//当窗体透明度为0时(看不到窗体了)
            {
                this.Close();//关闭窗体
            }
        }

        private void timer3_Tick(object sender, EventArgs e)
        {
            this.timer1.Stop();//关闭定时器1
            this.Opacity  = 0.03;//改变窗体透明度
        }

        private void pseEnter(object sender, EventArgs e)
        {
            timer3.Start();
        }
        private void pseLeave(object sender, EventArgs e)
        {
            timer1.Start();
        }

    }
     
 }