GDI+绘制半圆按钮

新建一个用户控件：

public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);

            //设置控件区域
            GraphicsPath path = new GraphicsPath();
            path.AddPie(0, 0, this.Width, this.Height, 180, 180);
            this.Region = new Region(path);

            //获取画笔
            using (Graphics g = this.CreateGraphics())
            {
                g.FillPie(Brushes.Pink, new Rectangle(0, 0, this.Width, this.Height), 180, 180);//绘制半圆

                g.DrawString(Text, new Font("微软雅黑", 12, FontStyle.Regular), Brushes.Black, TextPosition);//绘制显示文本
            }
        }

        /// <summary>
        /// 公开属性，修改文本显示位置
        /// </summary>
        public PointF TextPosition
        {
            get;
            set;
        }
    }

窗体调用代码：

 this.userControl11.Text = "Hello World.";
 this.userControl11.TextPosition = new PointF(this.userControl11.Width / 4, this.userControl11.Height / 4);

效果图：

类似的原理，可以定义任意形状的按钮。