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

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

const int LEFT = 1;                 // code words for LEFT, RIGHT, BOTTOM &TOP.
const int RIGHT = 2;
const int BOTTOM = 4;
const int TOP = 8;

int ComputeOutCode (double x, double y)
{
    int code = 0;
    if (y > ymax)                    //above the clip window
        code |= TOP;
    else if (y < ymin)              //below the clip window
        code |= BOTTOM;
    if (x > xmax)                   //to the right of clip window
        code |= RIGHT;
    else if (x < xmin)           //to the left of clip window
        code |= LEFT;
    return code;
}

void CohenSutherland(double x0, double y0,double x1, double y1)
{
    int outcode0, outcode1, outcodeOut;
    bool accept = false, done = false;
    outcode0 = ComputeOutCode (x0, y0);     //calculate the region of 1st point
    outcode1 = ComputeOutCode (x1, y1);      //calculate the region of 2nd point

    do
    {
        if (!(outcode0 | outcode1))
        {
            accept = true;
            done = true;
        }
        else if (outcode0 & outcode1)
            done = true;
        else
        {
            double x, y;
            double m = (y1 - y0)/(x1 - x0);
            outcodeOut = outcode0? outcode0: outcode1;

            if (outcodeOut & TOP)
            {
                x = x0 + (1/m) * (ymax - y0);
                y = ymax;
            }
            else if (outcodeOut & BOTTOM)
            {
                x = x0 + (1/m) * (ymin - y0);
                y = ymin;
            }
            else if (outcodeOut & RIGHT)
            {
                y = y0 +  m * (xmax - x0);
                x = xmax;
            }
            else
            {
                y = y0 + m * (xmin - x0);
                x = xmin;
            }
            /* Intersection calculations over */

            if (outcodeOut == outcode0)
            {
                x0 = x;
                y0 = y;
                outcode0 = ComputeOutCode (x0, y0);
            }
            else
            {
                x1 = x;
                y1 = y;
                outcode1 = ComputeOutCode (x1, y1);
            }
        }
    }
    while (!done);

    if (accept)
    {
        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;

        glBegin(GL_LINE_LOOP);
            glVertex2f(xvmin, yvmin);
            glVertex2f(xvmax, yvmin);
            glVertex2f(xvmax, yvmax);
            glVertex2f(xvmin, yvmax);
        glEnd();

        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, 1, 1);//white

    glBegin(GL_LINES);
        glVertex2d (x0, y0);
        glVertex2d (x1, y1);
    glEnd();

   glBegin(GL_LINE_LOOP);
        glVertex2f(xmin, ymin);
        glVertex2f(xmax, ymin);
        glVertex2f(xmax, ymax);
        glVertex2f(xmin, ymax);
    glEnd();

    CohenSutherland(x0, y0, x1, y1);

    glFlush();
}

void myinit()
{
    glClearColor(0, 0, 0, 1);//black
    gluOrtho2D(0, 500, 0, 500);
}

int main(int argc, char **argv)
{
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(0, 0);
    glutCreateWindow("Cohen Sutherland Line Clipping Algorithm");

    myinit();

    glutDisplayFunc(display);

    glutMainLoop();
}