winfrom-绘制十字线

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

namespace crossline
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            ResizeRedraw = true; //改变大小重绘
            DoubleBuffered = true;
            SetStyle(ControlStyles.UserPaint | ControlStyles.OptimizedDoubleBuffer | ControlStyles.AllPaintingInWmPaint, true);

            this.Paint += new PaintEventHandler(Form1_Paint);
            this.MouseClick += new MouseEventHandler(Form1_MouseClick);
            this.MouseMove += new MouseEventHandler(Form1_MouseMove);
            this.Resize += new EventHandler(this.Form1_Resize);
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Pen pen = new Pen(Color.Black);
            e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
            e.Graphics.Clear(SystemColors.Control);

            foreach (var p in dicPoint)
            {
                e.Graphics.DrawLine(pen, p[0], p[1]);
                e.Graphics.DrawLine(pen, p[2], p[3]);
            }

            var lineP = GetPoint();
            e.Graphics.DrawLine(pen, lineP[0], lineP[1]);
            e.Graphics.DrawLine(pen, lineP[2], lineP[3]);

            if (clickTag)
            {
                dicPoint.Add(lineP);
                clickTag = false; //重置标记
            }
        }

        private Point[] GetPoint()
        {
            Point[] p = new Point[4];

            var w = this.Width;
            var h = this.Height;

            p[0] = new Point(0, clickTag ? clickPoint.Y : mousePoint.Y);
            p[1] = new Point(w, clickTag ? clickPoint.Y : mousePoint.Y);
            p[2] = new Point(clickTag ? clickPoint.X : mousePoint.X, 0);
            p[3] = new Point(clickTag ? clickPoint.X : mousePoint.X, h);

            return p;
        }

        bool clickTag = false;
        Point clickPoint, mousePoint;
        readonly List dicPoint = new List();

        private void Form1_MouseClick(object sender, MouseEventArgs e)
        {
            //if (e.Button == MouseButtons.Left)
            clickTag = true;
            clickPoint = new Point(e.X, e.Y);
        }

        private void Form1_Resize(object sender, EventArgs e)
        {
            this.label1.Text = string.Format("{0},{1}", Width, Height);

            foreach (var p in dicPoint)
            {
                p[1].X = this.Width;
                p[3].Y = this.Height;
            }
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            mousePoint = e.Location;
            Invalidate();
        }

        //...

    }
}