2. LiangBarsky.cpp

2. LiangBarsky

#include<stdio.h>
#include<GL/glut.h>
double xmin=50,xmax=100,ymax=100,ymin=50;   //window boundary
double xvmin=200,yvmin=200,xvmax=300,yvmax=300;     //viewport boundary
#define true 1
#define false 0
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;   //line portion is outside
    }
    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;   //line portion is outside
    return true;
}

void liang(double x0,double y0,double x1,double y1)
{
    double dx=x1-x0,dy=y1-y0,tc=0.0,t1=1.0;
    if(cliptest(-dx,x0-xmin,&tc,&t1))   //inside test wrt left edge
        if(cliptest(dx,xmax-x0,&tc,&t1))    //inside test wrt Right edge
            if(cliptest(-dy,y0-ymin,&tc,&t1))   //inside test wrt Bottom edge
                if(cliptest(dy,ymax-y0,&tc,&t1))    //inside test wrt Top edge
                {
                    if(t1<1.0)
                    {
                        x1=x0+t1*dx;
                        y1=y0+t1*dy;
                    }
                    if(tc>0.0)
                    {
                        x0=x0+tc*dx;
                        y0=y0+tc*dy;
                    }
            //sx and sy is used to scale the line. it zooms the the clipping window 
                    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;
                    //draw red coloured viewport
                    glColor3f(1.0,0.0,0.0);
                    glBegin(GL_LINE_LOOP);      //draw a box to show clipped line.
                        glVertex2f(xvmin,yvmin);
                        glVertex2f(xvmax,yvmin);
                        glVertex2f(xvmax,yvmax);
                        glVertex2f(xvmin,yvmax);
                    glEnd();
                    glColor3f(0.0,0.0,1.0);
                    glBegin(GL_LINES);          //draw line after clipping
                        glVertex2d(vx0,vy0);
                        glVertex2d(vx1,vy1);
                    glEnd();
                }
}

void display()
{
    double x0=60,y0=20,x1=80,y1=120;        //line coordinates
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0,0.0,0.0);
    glBegin(GL_LINES);          //draw a line that needs to be clipped 
        glVertex2d(x0,y0);
        glVertex2d(x1,y1);
    glEnd();
    glColor3f(0.0,0.0,1.0);
    glBegin(GL_LINE_LOOP);      //draw a box
        glVertex2f(xmin,ymin);
        glVertex2f(xmax,ymin);
        glVertex2f(xmax,ymax);
        glVertex2f(xmin,ymax);
    glEnd();
    liang(x0,y0,x1,y1);         //function liang() is called by passing line endpoints
    glFlush();
}
//initialses point sizes and colors
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);
}

int main(int argc,char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowSize(500,500);
    glutInitWindowPosition(0,0);
    glutCreateWindow("Liang Barksy Line Clipping algorithm");
    glutDisplayFunc(display);
    myinit();
    glutMainLoop();
    return 0;
}