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 = 1;

        const int right = 2;

        const int bottom = 4;

        const int top = 8;

        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(120, 120);//裁剪区左下角

            window2 = new Point(600, 420); //裁剪区右上角

            start = 0;

        }

 

        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, 1);

            switch (start)

            {

                case 0:

                    {

                        g.Clear(Color.Silver);

                        Background();

                        start = 1;

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

                        g.DrawRectangle(Pens.Black, x - 2, y - 2, 2, 2); //画一个小方块，显示点击位置

                        break;

                    }

                case 1:

                    {

                        start = 0;

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

                        g.DrawRectangle(Pens.Black, x - 2, y - 2, 2, 2); //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 == 0)

                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", 16, FontStyle.Regular), Brushes.Black, 20, 20);

        }

 

        private void DrawString_1(int code1, int code2)

        {

            String str;

            g.FillRectangle (Brushes.White, 120, 40, 190, 30);

            str = "\n编码: "   Convert.ToString(code1, 2).PadLeft(4, ’’0’’)   "  "   Convert.ToString(code2, 2).PadLeft(4, ’’0’’);

            g.DrawString(str, new Font("宋体", 16, FontStyle.Regular), Brushes.Black, 120, 20);

        }

 

        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 = 0;

            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, 2);

            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 != 0 || code2 != 0)

            {

                if ((code1 & code2) != 0) return;

                code = code1;

                if (code1 == 0)

                    code = code2;

                if ((left & code) != 0)//线段与左边界相交

                {

                    x = xl;

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

                }

                else if ((right & code) != 0)//线段与右边界相交

                {

                    x = xr;

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

                }

                else if ((bottom & code) != 0)//线段与下边界相交

                {

                    y = yb;

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

                }

                else if ((top & code) != 0)//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);

        }

    }

}