7.a.cpp

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

const char *title = "Cohen-Sutherland";

const GLfloat xmax = 5, ymax = 5, xmin = -5, ymin = -5;

void init()
{
    glClearColor(0.0, 0.0, 0.0, 0.0);                 
    glClearDepth(1.0f);                                
    glEnable(GL_DEPTH_TEST);                           
    glDepthFunc(GL_LEQUAL);                            
    glShadeModel(GL_SMOOTH);                           
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-10, 10, -10, 10);
    glMatrixMode(GL_MODELVIEW);
}

typedef int BinaryCode;

const int INSIDE = 0; // 0000
const int LEFT = 1;   // 0001
const int RIGHT = 2;  // 0010
const int BOTTOM = 4; // 0100
const int TOP = 8;    // 1000

BinaryCode ComputeOutCode(GLfloat x, GLfloat y)
{
    BinaryCode code;

    code = INSIDE;      // initialised as being inside of [[clip window]]

    if (x < xmin)       // to the left of clip window
        code |= LEFT;
    else if (x > xmax)  // to the right of clip window
        code |= RIGHT;
    if (y < ymin)       // below the clip window
        code |= BOTTOM;
    else if (y > ymax)  // above the clip window
        code |= TOP;

    return code;
}

void cohen_sutherland(GLfloat x0, GLfloat y0, GLfloat x1, GLfloat y1,
                      GLfloat &x2, GLfloat &y2, GLfloat &x3, GLfloat &y3)
{
    BinaryCode outcode0 = ComputeOutCode(x0, y0);
    BinaryCode outcode1 = ComputeOutCode(x1, y1);
    bool accept = false;

    while (true)
    {
        if (!(outcode0 | outcode1))
        {
            accept = true;
            break;
        }
        else if (outcode0 & outcode1)
        {
            break;
        }
        else
        {
            GLfloat x, y;

            BinaryCode outcodeOut = outcode0 ? outcode0 : outcode1;

            if (outcodeOut & TOP)
            {
                x = x0 + (x1 - x0) * (ymax - y0) / (y1 - y0);
                y = ymax;
            }
            else if (outcodeOut & BOTTOM)
            {
                x = x0 + (x1 - x0) * (ymin - y0) / (y1 - y0);
                y = ymin;
            }
            else if (outcodeOut & RIGHT)
            {
                y = y0 + (y1 - y0) * (xmax - x0) / (x1 - x0);
                x = xmax;
            }
            else if (outcodeOut & LEFT)
            {
                y = y0 + (y1 - y0) * (xmin - x0) / (x1 - x0);
                x = xmin;
            }

            if (outcodeOut == outcode0)
            {
                x0 = x;
                y0 = y;
                outcode0 = ComputeOutCode(x0, y0);
            }
            else
            {
                x1 = x;
                y1 = y;
                outcode1 = ComputeOutCode(x1, y1);
            }
        }
    }
    if (accept)
    {
        std::cout << "Found\n";
        x2 = x0;
        y2 = y0;
        x3 = x1;
        y3 = y1;
    }
}

void display()
{
    GLfloat x0 = -7, y0 = 6, x1 = 8, y1 = 3, x2, y2, x3, y3;
    cohen_sutherland(x0, y0, x1, y1, x2, y2, x3, y3);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glColor3f(1.0, 1.0, 1.0);
    glBegin(GL_LINE_LOOP);
    glVertex2i(xmin, ymin);
    glVertex2i(xmin, ymax);
    glVertex2i(xmax, ymax);
    glVertex2i(xmax, ymin);
    glEnd();

    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_LINES);
    glVertex2f(x0, y0);
    glVertex2f(x1, y1);
    glEnd();

    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_LINES);
    glVertex2f(x0, y0);
    glVertex2f(x2, y2);
    glEnd();

    glColor3f(1.0, 0.0, 0.0);
    glBegin(GL_LINES);
    glVertex2f(x2, y2);
    glVertex2f(x3, y3);
    glEnd();

    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_LINES);
    glVertex2f(x1, y1);
    glVertex2f(x3, y3);
    glEnd();

    glFlush();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);                                    
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(700, 700);
    glutInitWindowPosition(7000, 70);
    glutCreateWindow(title);
    glutDisplayFunc(display);
    init();
    glutMainLoop();
    return 0;
}