C# 画线 Draw a Line

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using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Forms;namespace BCSVClient{  /// <summary>    /// 窗口定义    /// </summary>    public partial class LineTest : Form    {        public LineTest()        {            drawPanel.BackColor = Color.White;            drawPanel.Cursor = Cursors.Cross;            drawPanel.Dock = DockStyle.Fill;            drawPanel.MouseDown += new MouseEventHandler(drawPanel_MouseDown);            drawPanel.MouseUp += new MouseEventHandler(drawPanel_MouseUp);            drawPanel.MouseMove += new MouseEventHandler(drawPanel_MouseMove);            drawPanel.Paint += new PaintEventHandler(drawPanel_Paint);            Controls.Add(drawPanel);        }        /// <summary>        /// 线条对象        /// </summary>        class Line        {            /// <summary>            /// 建立线条对象，并设置起点            /// </summary>            /// <param name="startPoint">此线条的起点</param>            public Line(Point startPoint)            {                StartPoint = startPoint;                EndPoint = startPoint;            }            public Point StartPoint = Point.Empty;            public Point EndPoint = Point.Empty;        }        public class DrawPanel : Control        {            public DrawPanel()            {                this.DoubleBuffered = true;                this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.ResizeRedraw, true);            }        }        /// <summary>        /// 用于保存绘出线条的集合        /// </summary>        private List<Line> lines = new List<Line>();        /// <summary>        /// 用于保存当前正在绘制的线条        /// </summary>        private Line drawingLine = null;        /// <summary>        /// 用于显示绘图的面板组件        /// </summary>        private DrawPanel drawPanel = new DrawPanel();        /// <summary>        /// 在绘图区释放鼠标，结束当前线条绘制        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        void drawPanel_MouseUp(object sender, MouseEventArgs e)        {            if (drawingLine == null) return;            drawingLine.EndPoint = e.Location;            drawingLine = null;        }        /// <summary>        /// 在绘图区按下鼠标，开始绘制新线条        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        void drawPanel_MouseDown(object sender, MouseEventArgs e)        {            drawingLine = new Line(e.Location);            lines.Add(drawingLine);        }        /// <summary>        /// 在绘图区移动鼠标时，如果正在绘制新线条，就更新绘制面板        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        void drawPanel_MouseMove(object sender, MouseEventArgs e)        {            if (drawingLine != null)            {                drawingLine.EndPoint = e.Location;                drawPanel.Invalidate();            }        }        /// <summary>        /// 绘制效果到面板        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        void drawPanel_Paint(object sender, PaintEventArgs e)        {            Bitmap bp = new Bitmap(drawPanel.Width, drawPanel.Height); // 用于缓冲输出的位图对象            Graphics g = Graphics.FromImage(bp);            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias; // 消锯齿（可选项）            Pen p = new Pen(Color.Black);            foreach (Line line in lines)            {                if (line == drawingLine)                {                    // 当前绘制的线条是正在鼠标定位的线条                    p.Color = Color.Blue;                }                else                {                    p.Color = Color.Black;                }                g.DrawLine(p, line.StartPoint, line.EndPoint);            }            // 将缓冲位图绘制到输出            e.Graphics.DrawImage(bp, Point.Empty);        }    }}
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