程序代码：

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

namespace WindowsFormsApplication1
{
    public class StraightLine : Control
    {
        private Enums.StraightLineTypes lineType;
        private bool antiAlias;
        private int thickness;
        protected Pen pen;
        public StraightLine()
        {
            lineType = Enums.StraightLineTypes.水平;
            thickness = 1;
            antiAlias = true;
            this.Paint += StraightLine_Paint;
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing && pen != null)
            {
                pen.Dispose();
            }
            base.Dispose(disposing);
        }
        [Category("连线属性"), DefaultValue(typeof(Enums.StraightLineTypes), "StraightLineTypes.Horizontal")]
        public Enums.StraightLineTypes LineType
        {
            get
            {
                return lineType;
            }
            set
            {
                lineType = value;
                Invalidate();
            }
        }

        [Category("连线属性"), DefaultValue(1)]
        public int Thickness
        {
            get
            {
                return thickness;
            }
            set
            {
                thickness = value;
                Invalidate();
            }
        }
        [Category("连线属性"), DefaultValue(true)]
        public bool AntiAlias
        {
            get
            {
                return antiAlias;
            }
            set
            {
                antiAlias = value;
                Invalidate();
            }
        }
        /// <summary>
        /// 重写画线部分GDI实现
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void StraightLine_Paint(object sender, PaintEventArgs e)
        {
            pen = new Pen(ForeColor, Thickness);

            if (AntiAlias)
            {
                e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
            }

            switch (lineType)
            {
                case Enums.StraightLineTypes.水平:
                    DrawCenteredHorizontalLine(e.Graphics);
                    break;
                case Enums.StraightLineTypes.垂直:
                    DrawCenteredVerticalLine(e.Graphics);
                    break;
                case Enums.StraightLineTypes.斜线:
                    DrawCenteredDiagonalAscendingLine(e.Graphics);
                    break;
                case Enums.StraightLineTypes.反斜线:
                    DrawCenteredDiagonalDescendingLine(e.Graphics);
                    break;
                default: break;
            }
        }

        #region 画线函数

        private void DrawCenteredHorizontalLine(Graphics g)
        {
            g.DrawLine(pen, 0, Height / 2, Width, Height / 2);
            Graphics graphics = this.CreateGraphics();
            Point[] mypoints = { new Point(0, Height / 2 + 1), new Point(0, Height / 2 - 1), new Point(Width, Height / 2 - 1), new Point(Width, Height / 2 + 1) };
            RegionControl(mypoints);
        }

        private void DrawCenteredVerticalLine(Graphics g)
        {
            g.DrawLine(pen, Width / 2, 0, Width / 2, Height);
            Point[] mypoints = { new Point(Width / 2 - 1, 0), new Point(Width / 2 + 1, 0), new Point(Width / 2 + 1, Height), new Point(Width / 2 - 1, Height) };
            RegionControl(mypoints);
        }

        private void DrawCenteredDiagonalAscendingLine(Graphics g)
        {
            g.DrawLine(pen, 0, Height, Width, 0);
            Point[] mypoints = { new Point(1, Height), new Point(0, Height - 1), new Point(Width - 1, 0), new Point(Width, 1) };
            RegionControl(mypoints);
        }

        private void DrawCenteredDiagonalDescendingLine(Graphics g)
        {
            g.DrawLine(pen, 0, 0, Width, Height);
            Point[] mypoints = { new Point(0, 1), new Point(1, 0), new Point(Width, Height - 1), new Point(Width - 1, Height) };
            RegionControl(mypoints);
        }

        /// <summary>
        /// 按照点集合生成异形窗体
        /// </summary>
        /// <param name="points"></param>
        private void RegionControl(Point[] points)
        {
            GraphicsPath mygraphicsPath = new GraphicsPath();
            mygraphicsPath.AddPolygon(points);
            Region myregion = new Region(mygraphicsPath);
            this.Region = myregion;
        }
        #endregion
    }
    public class Enums
    {
        public enum StraightLineTypes
        {
            //Auto, 
            水平,
            垂直,
            反斜线,
            斜线,
        }
    }
}