Liang Barsky

#include<stdio.h>
#include<GL/glut.h>

double xmin=50,ymin=50,xmax=100,ymax=100;
double xvmin=200,yvmin=200,xvmax=300,yvmax=300;

int Cliptest(double p,double q,double *t1,double *t2)
{
   double t=q/p;
   if(p<0.0)
     {
        if(t>*t1)*t1=t;
        if(t>*t2)return(false)
     }
     
   else if(p>0.0)
     {
        if(t<*t2)*t2=t;
        if(t<*t1)return(false);
     }
     
   else if(p==0.0)
     {
        if(q<0.0)return(false)
     }
     return(true);
}

void LiangBarskyLineAndClipDraw(double x0,doubley0,double x1,double y1)
{
   double dx=x1-x0,dy=y1-y0,te=0.0,t1=1.0;
   if(cliptest(-dx,x0-xmin,&te,&tl))
   if(cliptest(dx,xmax-x0,&te,&tl))
   if(cliptest(-dy,y0-ymin,&te,&tl))
   if(cliptest(dy,ymax-y0,&te,&tl))
     {
        if(t1<1.0)
          {
             x1=x0+t1*dx;
             y1=y0+t1*dy;
          }
          
        if(te>0.0)
          {
             x0=x0+te*dx;
             y0=y0+te*dy;
          }
          
        double sx=(xvmax-xvmin)/(xmax-xmin);
        double sy=(yvmax-yvmin)/(ymax-ymin);
        double vx0=xvmin+(x0-xmin)*sx;
        double vy0=yvmin+(y0-ymin)*sy;
        double vx1=xvmin+(x1-xmin)*sx;
        double vy1=yvmin+(y1-ymin)*sy;
        
        glColor3f(1.0,0.0,0.0);
        glBegin(GL_LINE_LOOP);
          glVertex2f(xvmin,yvmin);
          glVertex2f(xvmax,yvmin);
          glVertex2f(xvmax,yvmax);
          glVertex2f(xvmin,yvmax);
        glEnd();
        
        glColor3f(0.0,0.0,1.0);
        glBegin(GL_LINES);
          glVertex2D(vx0,vy0);
          glVertex2D(vx1,vy1);
         glEnd();
     }
}

void display()
{
   double x0=60, y0=20, x1=80, y1=120;
   glClear(GL_COLOR_BUFFER_BIT);
   glColor3f(1.0,0.0,0.0);
   glBegin(GL_LINES);
     glVertex2d(x0,y0);
     glVertex2d(x1,y1);
   glEnd();
   
   glColor3f(0.0,0.0,1.0);
   glBegin(GL_LINE_LOOP);
     glVertex2f(xmin,ymin);
     glVertex2f(xmax,ymin);
     glVertex2f(xmax,ymax);
     glVertex2f(xmin,ymax);
   glEnd();
   LiangBarskyLineClipAndDraw(x0,y0,x1,y1);
   glFlush();
}

void myinit()
{
   glClearColor(1.0,1.0,1.0,1.0);
   glColor3f(1.0,0.0,0.0);
   glPointSize(1.0);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluOrtho2D(0.0,499.0,0.0,499.0);
}

void main()
{
   glutInit(&argc,argv);
   glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
   glutInitWindowSize(500,500);
   glutInitWindowPosition(0,0);
   glutCreateWindow(Liang Barsky Line And Clipping Algorithm);
   glutDisplayFunc(display);
   myinit();
   glutMainLoop();
}