OPENGL—编码裁剪（Cohen-Sutherland）法裁剪图

红太狼 2022-06-15 11:29 233阅读 0赞

//编码裁剪（Cohen-Sutherland）法裁剪图
    #include"stdafx.h"
    #include<Gl/glut.h>
    #include <process.h>
    
    class wcPt2D {
    public:
        float x, y;
    };
    
    const int winLeftBitCode = 0x1;
    const int winRightBitCode = 0x2;
    const int winBottomBitCode = 0x4;
    const int winTopBitCode = 0x8;
    
    GLubyte encode(wcPt2D pt, wcPt2D winMin, wcPt2D winMax) {    //进行编码
        GLubyte code = 0x00;
        if (pt.x < winMin.x)        //D0=1,否则为0
    		code = code | winLeftBitCode;
        if (pt.x > winMax.x)        //D1=1,否则为0
    		code = code | winRightBitCode;
        if (pt.y < winMin.y)        //D2=1,否则为0
    		code = code | winBottomBitCode;
        if (pt.y > winMax.y)        //D3=1,否则为0
    		code = code | winTopBitCode;
        return (code);
    }
    
    inline int inside(int code) {               //在内部，inside=1
        return int(!code);
    }
    
    inline int reject(int code1, int code2) {   //code1&code2不等于0，“简弃”，reject=true
        return int(code1 & code2);
    }
    
    inline int accept(int code1, int code2) {   //code1|code2等于0，“简取”，accept=true
        return int(!(code1 | code2));
    }
    
    void swapPts(wcPt2D *p1, wcPt2D *p2) {      //交换坐标值
        wcPt2D tmp;
        tmp = *p1;
        *p1 = *p2;
        *p2 = tmp;
    }
    
    void swapCodes(GLubyte *c1, GLubyte *c2) {   //交换编码
        GLubyte tmp;
        tmp = *c1;
        *c1 = *c2;
        *c2 = tmp;
    }
    
    void lineClip(wcPt2D winMin, wcPt2D winMax, wcPt2D p1, wcPt2D p2)    //裁剪
    {
        GLubyte code1, code2;
        int done = false, plotLine = false;
        float m;
        while (!done)                       //保证用新的P1P2重新进行计算
    	{
            code1 = encode(p1, winMin, winMax);   //对p1、p2进行编码，分别为code1、code2
            code2 = encode(p2, winMin, winMax);
            if (accept(code1, code2))		//对直线P1P2“简取”之
    		{
                done = true;
                plotLine = true;
            } 
    		else if (reject(code1, code2)) //对直线P1P2“简弃”之
    		{
                done = true;
            } 
    		else                           //否则
    		{
                if (inside(code1))         //若P1在窗口内，则交换P1和P2的坐标值和编码
    			{
                    swapPts(&p1, &p2);
                    swapCodes(&code1, &code2);
                }
    
    			//判断P1在窗口外哪一侧，然后求出两者的交点，并用交点的值替代P1的坐标值，以达到去掉P1S线段的目的
                if (p2.x != p1.x) 
    				m = (p2.y - p1.y) / (p2.x - p1.x);
                if (code1 & winLeftBitCode) 
    			{
                    p1.y += (winMin.x - p1.x) * m;
                    p1.x = winMin.x;
                }
    			else if (code1 & winRightBitCode) 
    			{
                    p1.y += (winMax.x - p1.x) * m;
                    p1.x = winMax.x;
                } 
    			else if (code1 & winBottomBitCode) 
    			{
                    if (p2.x != p1.x)
                        p1.x += (winMin.y - p1.y) / m;
                    p1.y = winMin.y;
                } 
    			else if (code1 & winTopBitCode) 
    			{
                    if (p2.x != p1.x)
                        p1.x = (winMax.y - p1.y) / m;
                    p1.y = winMax.y;
                }
            }
        }
    	//重新绘制当前的直线段P1P2
        if (plotLine)
            glBegin(GL_LINES);
        glColor3f(1, 0, 0);
        glVertex2f(p1.x, p1.y);
        glVertex2f(p2.x, p2.y);
        glEnd();
    }
    
    void drawpolygon(double cd[]) 
    {
        glBegin(GL_LINE_LOOP);    //绘制直线
        glLineWidth(10);
        for (int i = 0; i < 8; i = i + 2) {
            glVertex2f(cd[i], cd[i + 1]);
        }
        glEnd();
    }
    
    void drawline(double cd[]) 
    {
        glBegin(GL_LINES);      //绘制点
        glLineWidth(10);
        for (int i = 0; i < 8; i = i + 2) {
            glVertex2f(cd[i], cd[i + 1]);
        }
        glEnd();
    }
    
    void myKeyBoard(unsigned char key, int x, int y) //处理按键信息
    {   
        wcPt2D winMin = {200, 200};
        wcPt2D winMax = {400, 400};
        wcPt2D p1 = {100, 0};
        wcPt2D p2 = {500, 500};
    
        if (key == 13)   //按下Enter键
            lineClip(winMin, winMax, p1, p2);
    
        glFlush();
        if (key == 27)   //按下ESC键
            exit(0);
    }
    
    void display(void) 
    {
        double re[8] = {200, 200, 400, 200, 400, 400, 200, 400};   //按照比例输出
        double line[4] = {100,0 , 500, 500};
     
        glClear(GL_COLOR_BUFFER_BIT);
    	glViewport(0, 0, 600, 600);
        glColor3f(0, 0, 0);
    	//绘制
        drawpolygon(re);
        drawline(line);
     
        glFlush();
    }
    
    int main(int argc, char **argv) 
    {
    	//初始化
        glutInit(&argc, argv);
        glutInitDisplayMode(GLUT_SINGLE | GLUT_RED);
        glutInitWindowSize(600, 600);
        glutInitWindowPosition(100, 100);
        glutCreateWindow("Cohen-Sutherland算法");
        glClearColor(1, 1, 1, 0.0);
        glMatrixMode(GL_PROJECTION);
        gluOrtho2D(0.0, 600.0, 0.0, 600.0);
    
        glutKeyboardFunc(myKeyBoard);   //键盘输入控制
        glutDisplayFunc(display);
    
        glutMainLoop();
        return 0;
    
    }

运行结果：

![Center][]

[Center]: /images/20220615/2c7dab959f82463a87dbcfb5fa08a365.png