OPENGL—参数裁剪（Liang-Barsky算法）

秒速五厘米 2022-06-14 03:41 220阅读 0赞

#include"stdafx.h"  
    #include<Gl/glut.h>     
    #include <cmath>  
    #include <iostream>
    using namespace std;
      
    void drawpolygon(double cd[])   
    {  
        glBegin(GL_LINE_LOOP);   
        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);     
        glLineWidth(10);  
        for (int i = 0; i < 8; i = i + 2) {  
            glVertex2f(cd[i], cd[i + 1]);  
        }  
        glEnd();  
    }  
    
    
     void putpixel(int x, int y)  
    {  
        glColor3f(1.0, 0.0, 0.0);        
        glPointSize(3.0f);  
        glBegin(GL_POINTS);  
        glVertex2f(x, y);  
        glEnd();  
        glFlush();  
    }  
    
      void DDALine(int x0,int y0,int x1,int y1)  
    {  
        int dx,dy,epsl,k;  
        float x,y,xIncre,yIncre;  
        dx=x1-x0;  
        dy=y1-y0;  
        x=x0;  
        y=y0;  
        if(abs(dx)>abs(dy))  
            epsl=abs(dx);  
        else  
            epsl=abs(dy);  
        xIncre=(float)dx/(float)epsl;  
        yIncre=(float)dy/(float)epsl;  
        for(k=0;k<=epsl;k++)  
        {  
            putpixel(int(x+0.5),(int)(y+0.5));  
            x+=xIncre;  
            y+=yIncre;  
        }  
    }  
    
    
    
    int LBLineClipTest(float p,float q,float &umax,float &umin)
    {
    	float r=0.0;  
      
    	if(p<0.0)
    	{
    		r=q/p;
    		if(r>umin)   	
    			return 0; 
    		else if(r>umax)	
    				umax = r;
    	}
    
    	else if(p>0.0) 
    	{
         	r=q/p;
        	
    		if(r<umax)      
    			return 0; 
         	else if(r<umin)      	
    				umin = r;
    	}
    	
    	else if(q<0.0)    
    			return 0; 
    	return 1;
    }
    
    void LBLineClip(float xwl,float xwr,float ywb,float ywt,float x1,float y1,float x2,float y2)
    {	
    	float umax,umin,deltax,deltay,i1,j1;
    	deltax=x2-x1;
    	deltay=y2-y1;
    	umax=0.0;
    	umin=1.0;
    
    	if(LBLineClipTest(-deltax,x1-xwl,umax,umin))
    	{
    		if(LBLineClipTest(deltax,xwr-x1,umax,umin)) 
    		{		
    			if(LBLineClipTest(-deltay,y1-ywb,umax,umin))
    			{
    				if(LBLineClipTest(deltay,ywt-y1,umax,umin))  
    				{
    					i1=int(x1+umax*deltax+0.5);
    					j1=int(y1+umax*deltay+0.5);
    					x2=int(x1+umin*deltax+0.5);
    					y2=int(y1+umin*deltay+0.5);
    					cout<<i1<<" "<<j1<<" "<<x2<<" "<<y2<<endl;
    				}
    				DDALine(i1,j1,x2,y2);
    			}
    		}
    	}
    }
    
    
    void display()  
     {  
    	double re[8] = {200, 200, 400, 200, 400, 400, 200, 400};     
        double line[4] = {100,0, 500, 500};  
       
        glClear(GL_COLOR_BUFFER_BIT);  
        glViewport(0, 0, 600, 600);  
        glColor3f(0, 0, 0);  
        
        drawpolygon(re);  
        drawline(line);  
              
        LBLineClip(200, 400, 200, 400, 500, 500,100, 0);     
    	glFlush();  
     }
    
    
    int _tmain(int argc,  char **argv)
    {
       	 glutInit(&argc, argv);  
         glutInitDisplayMode(GLUT_SINGLE | GLUT_RED);  
         glutInitWindowSize(600, 600);  
         glutInitWindowPosition(100, 100);    
         glutCreateWindow("参数裁剪");    
    	 glClearColor(1, 1, 1, 0.0);  
    	 glMatrixMode(GL_PROJECTION);  
         gluOrtho2D(0.0, 600.0, 0.0, 600.0);  
         glutDisplayFunc(display);           
         glutMainLoop();   
    
    	 return 0;
    }

运行结果：

![Center][]

[Center]: /images/20220614/723f976cfec444f78b5799cb092d51fe.png