C# 实现线段的编码裁剪算法（vs2010）

 using System;

 using System.Collections.Generic;

 using System.ComponentModel;

 using System.Data;

 using System.Drawing;

 using System.Linq;

 using System.Text;

 using System.Windows.Forms;

 namespace cutLine

 {

     unsafe public partial class Form1 : Form

     {

         const int left = ;

         const int right = ;

         const int bottom = ;

         const int top = ;

         Point window1, window2;     //保存裁剪区矩形

         Point line1, line2;         //保存线段的两个端点坐标

         int start, x , y;           //标志点击次数，取值范围0,1,2

         Graphics g;                 //GDI 对象

         public Form1()

         {

             InitializeComponent();

             g = CreateGraphics();

             window1 = new Point(, );//裁剪区左下角

             window2 = new Point(, ); //裁剪区右上角

             start = ;

         }

         private void Form1_MouseClick(object sender, MouseEventArgs e)

         {

             int x = e.X, y = e.Y;    //记录鼠标点击位置：

             Pen p = new Pen(Brushes.Black, );

             switch (start)

             {

                 case :

                     {

                         g.Clear(Color.Silver);

                         Background();

                         start = ;

                         line1 = new Point(e.X, e.Y);

                         g.DrawRectangle(Pens.Black, x - , y - , , ); //画一个小方块，显示点击位置

                         break;

                     }

                 case :

                     {

                         start = ;

                         line2 = new Point(e.X, e.Y);

                         g.DrawRectangle(Pens.Black, x - , y - , , ); //画一个小方块，显示点击位置

                         g.DrawLine(p, line1, line2);

                         //DrawString_1();

                         cutLine(line1, line2, window1.X, window2.X, window1.Y, window2.Y);

                         break;

                     }

             }

         }

         private void Background()

         {

             if (start == )

                 g.DrawRectangle(Pens.Black, window1.X, window1.Y,window2.X - window1.X, window2.Y - window1.Y);

             DrawString();

         }

         private void DrawString()

         {

             String str;

             str = "                              黑色矩形为裁剪窗口\n                              点鼠标输入线段的两个点,自动执行裁剪\n                              红色为线段裁剪后的部分";     //临时字体对象              //画刷枚举     //位置

             g.DrawString(str, new Font("宋体", , FontStyle.Regular), Brushes.Black, , );

         }

         private void DrawString_1(int code1, int code2)

         {

             String str;

             g.FillRectangle (Brushes.White, , , , );

             str = "\n编码: "   Convert.ToString(code1, ).PadLeft(, ’’’’)   "  "   Convert.ToString(code2, ).PadLeft(, ’’’’);

             g.DrawString(str, new Font("宋体", , FontStyle.Regular), Brushes.Black, , );

         }

         private void Form1_Load(object sender, EventArgs e)

         {  

         }

         private void Form1_Paint(object sender, PaintEventArgs e)

         {

             Background();

         }

        private void Encode(int x, int y,int *code,int xl, int xr, int yb, int yt)

         {

             int c = ;

             if (x < xl)

                 c = c | left;

             else if (x > xr)

                 c = c | right;

             if (y < yb)

                 c = c | bottom;

             else if (y > yt)

                 c = c | top;

             (*code) = c;

         }

         public void cutLine(Point p1, Point p2, int xl, int xr, int yb, int yt)

         {

             Pen p = new Pen(Brushes.Red, );

             int x1, x2, y1, y2,code1, code2, code;

             x1 = p1.X; x2 = p2.X; y1 = p1.Y; y2 = p2.Y;

             Encode(x1,y1, &code1, xl,xr,yb,yt);

             Encode(x2,y2, &code2, xl,xr,yb,yt);

             DrawString_1(code1, code2);

             while (code1 !=  || code2 != )

             {

                 if ((code1 & code2) != ) return;

                 code = code1;

                 if (code1 == )

                     code = code2;

                 if ((left & code) != )//线段与左边界相交

                 {

                     x = xl;

                     y = y1   (y2 - y1) * (xl - x1) / (x2 - x1);

                 }

                 else if ((right & code) != )//线段与右边界相交

                 {

                     x = xr;

                     y = y1   (y2 - y1) * (xr - x1) / (x2 - x1);

                 }

                 else if ((bottom & code) != )//线段与下边界相交

                 {

                     y = yb;

                     x = x1   (x2 - x1) * (yb - y1) / (y2 - y1);

                 }

                 else if ((top & code) != )//线段与上边界相交

                 {

                     y = yt;

                     x = x1   (x2 - x1) * (yt - y1) / (y2 - y1);

                 }

                 if (code == code1)

                 {

                     x1 = x;

                     y1 = y;

                     Encode(x, y, &code1, xl, xr, yb, yt);

                 }

                 else

                 {

                     x2 = x;

                     y2 = y;

                     Encode(x, y, &code2, xl, xr, yb, yt);

                 }

             }

             p1.X = x1; p1.Y = y1;

             p2.X = x2; p2.Y = y2;

             g.DrawLine(p, p1, p2);

         }

     }

 }