cslc.c

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

const int INSIDE = 0;
const int LEFT = 1;
const int RIGHT = 2;
const int BOTTOM = 4;
const int TOP = 8;
double xmin = 50, ymin = 50, xmax = 100, ymax = 100;

void drawRectangle(float x0, float y0, float x1, float y1) {
    glColor3f(1.0, 0.0, 0.0);
    glBegin(GL_LINE_LOOP);
    glVertex2f(x0, y0);
    glVertex2f(x1, y0);
    glVertex2f(x1, y1);
    glVertex2f(x0, y1);
    glEnd();
}
void drawLine(float x0, float y0, float x1, float y1) {
    glColor3f(0, 1, 0.0);
    glBegin(GL_LINES);
    glVertex2f(x0, y0);
    glVertex2f(x1, y1);
    glEnd();
}
void init() {
    glClearColor(0, 0, 0, 0);
    glClear(GL_COLOR_BUFFER_BIT);
    gluOrtho2D(0, 500, 0, 500);
    glFlush();
}
int Computecode(double x, double y) {
    int code = INSIDE;
    if (x < xmin)
        code |= LEFT;
    else if (x > xmax)
        code |= RIGHT;
    else if (y < ymin)
        code |= BOTTOM;
    else if (y > ymax)
        code |= TOP;
    return code;
}

void CohenSutherlandline(double x0, double a, double x1, double b) {
    bool accept = false;
    int outcode0 = Computecode(x0, a);
    int outcode1 = Computecode(x1, b);

    double x, y;

    while (true) {
        if (!(outcode0 | outcode1)) {
            accept = true;
            break;
        } else if (outcode0 & outcode1) {
            break;
        } else {
            int outcodeout = outcode0 ? outcode0 : outcode1;
            if (outcodeout & TOP) {
                x = x0 + (x1 - x0) * (ymax - a) / (b - a);
                y = ymax;
            } else if (outcodeout & BOTTOM) {
                x = x0 + (x1 - x0) * (ymin - a) / (b - a);
                y = ymin;
            } else if (outcodeout & RIGHT) {
                y = a + (b - a) * (xmax - x0) / (x1 - x0);
                x = xmax;
            } else if (outcodeout & LEFT) {
                y = a + (b - a) * (xmin - x0) / (x1 - x0);
                x = xmin;
            }
            if (outcodeout == outcode0) {
                x0 = x;
                a = y;
                outcode0 = Computecode(x0, a);
            } else {
                x1 = x;
                b = y;
                outcode1 = Computecode(x1, b);
            }
        }
    }
    if (accept) {
        drawRectangle(100 + xmin, 100 + ymin, 100 + xmax, 100 + ymax);
        drawLine(100 + x0, 100 + a, 100 + x1, 100 + b);
    }
}

void display() {
    double x0 = 60, a = 20, x1 = 80, b = 120;
    drawRectangle(xmin, ymin, xmax, ymax);
    drawLine(x0, a, x1, b);
    CohenSutherlandline(x0, a, x1, b);
    glFlush();
}

int main(int argc, char ** argv) {
    glutInit( & argc, argv);
    glutCreateWindow("Cohen Sutherland line clipping window");
    init();
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}