自绘GroupBox控件

下面显示的是效果图：

然后是代码，其中有一些解释：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Drawing2D;

namespace scyGroupBox
{
    public partial class scyGroupBox : GroupBox
    {

        private GraphicsPath gpRegion = null;
        private bool _mouseHover = false;
        private bool _mouseDown = false;
        private int textHeight = 0;  //文本高度

        public scyGroupBox()
        {
            InitializeComponent();
            BackColor = Color.YellowGreen;
            gpRegion = CreateRadiusRect(this.ClientRectangle, radius);
            if (gpRegion != null)
            {
                this.Region = new Region(gpRegion);
            }
            this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.DoubleBuffer | ControlStyles.UserPaint, true);
        }

        #region 圆角大小 Property
        private int radius = 3;
        public int Radius
        {
            get
            {
                return radius;
            }
            set
            {
                if (value < 0)
                {
                    return;
                }
                else
                {
                    radius = value;
                }
            }
        }
        #endregion

        #region 边线颜色
        private Color borderColor = Color.DarkGreen;
        public Color BorderColor
        {
            get { return borderColor; }
            set { borderColor = value; }
        }
        #endregion

        #region 上部渐变颜色
        private Color uShineColor = Color.FromArgb(140, Color.White);
        public Color UShineColor
        {
            get { return uShineColor; }
            set { uShineColor = value; }
        }
        #endregion

        /// <summary>
        /// 描绘具有圆角的button原型路径
        /// </summary>
        protected virtual GraphicsPath CreateRadiusRect(Rectangle rectangle, int radius)
        {
            GraphicsPath path = new GraphicsPath();

            int l = rectangle.Left;  //左边
            int t = rectangle.Top; //上边
            int w = rectangle.Width; //宽度
            int h = rectangle.Height;// 高度
            int d = radius / 2; //除以2，得到半径

            path.AddArc(l,t,d,d,180,90);  //左上角
            path.AddLine(l + radius, t, l + w - radius, t);//上边线

            path.AddArc(l + w - d, t, d, d, 270, 90);//右上角
            path.AddLine(l + w, t + radius, l + w, t + h - radius); //右边线

            path.AddArc(l + w - d, t + h - d, d, d, 0, 90);//右下角
            path.AddLine(l + w - radius, t + h, l + radius, t + h); //下边线

            path.AddArc(l, t + h - d, d, d, 90, 90); //左下角
            path.AddLine(l, t + h - radius, l, t + radius); //左边线

            path.CloseFigure();
            return path;
        }

        protected override void OnSizeChanged(EventArgs e)
        {
            gpRegion = CreateRadiusRect(this.ClientRectangle, radius);
            if (gpRegion != null)
            {
                this.Region = new Region(gpRegion);
            }
            base.OnSizeChanged(e);
        }

        //按照button路径进行border绘制
        protected virtual void DrawBorder(Graphics g, Pen pen)
        {
            if (gpRegion != null)
            {
                g.SmoothingMode = SmoothingMode.HighQuality;  
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.DrawPath(pen, CreateRadiusRect(new Rectangle(this.ClientRectangle.Left, this.ClientRectangle.Top, this.ClientRectangle.Width - 1, this.ClientRectangle.Height - 1), radius));
                g.SmoothingMode = SmoothingMode.Default;
                g.InterpolationMode = InterpolationMode.Default;
            }
            pen.Dispose();
            pen = null;
        }

        //绘制上部渐变色
        protected virtual void DrawUpperShine(Graphics g)
        {
            Color c1 = Color.FromArgb(200,uShineColor);
            Color c2 = Color.FromArgb(100,Color.White);
            Rectangle rc = new Rectangle(this.ClientRectangle.Left, this.ClientRectangle.Top, Width - 1, Height / 2);
            if (_mouseDown)
            {
                rc = new Rectangle(this.ClientRectangle.Left, this.ClientRectangle.Top, Width - 1, (Height - 10) / 2);
            }
            using (LinearGradientBrush lbrush = new LinearGradientBrush(rc, c1, c2, LinearGradientMode.Vertical))
            {
                g.FillRectangle(lbrush,rc);
            }
        }

        //设置字体的大小，宽高，位置信息
        protected virtual void DrawText(Graphics g)
        {
            if (!String.IsNullOrEmpty(this.Text.Trim()))
            {
                int x = 0;
                int y = 0;
                int w = 0;
                int h = 0;

                Size size = g.MeasureString(Text, Font).ToSize();
                w = size.Width > Width ? Width : size.Width;
                h = size.Height > Height ? Height : size.Height;

                Pen pen = new Pen(ForeColor);

                g.DrawString(Text, Font, pen.Brush, new RectangleF((float)x + 10, (float)y + 3, (float)w + 3, (float)h));
                pen.Dispose();
                pen = null;
                textHeight = w;
            }
        }

        //绘制内部的方块
        protected virtual void DrawInner(Graphics g, Rectangle rectangle, Pen p)
        {
            int l = rectangle.Left; //左边
            int t = rectangle.Top;//上边
            int w = rectangle.Width;//宽度
            int h = rectangle.Height;//高度

            g.DrawLine(p, l + 10, t + 20, l + w - 10, t + 20);//上边线
            g.DrawLine(p, l + w - 10, t + 20, l + w - 10, t + h - 10);  //右边线
            g.DrawLine(p, l + w - 10, t + h - 10, l + 10, t + h - 10);  //下边线
            g.DrawLine(p, l + 10, t + h - 10, l + 10, t + 20); //左边线

            Rectangle r = new Rectangle(l + 10, t + 20, w - 18, h - 28);


            g.FillRectangle(new SolidBrush(Color.Wheat), r);
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            Pen pen = new Pen(borderColor);
            Brush brush = new SolidBrush(BackColor);
            e.Graphics.FillPath(brush, gpRegion);
            DrawText(e.Graphics);
            DrawBorder(e.Graphics,pen);
            DrawInner(e.Graphics,this.ClientRectangle,new Pen(Color.Red));
            DrawUpperShine(e.Graphics);
        }

    }
}

后续做详细的解释。