lbc.c

//LIANG BARKSY ALGORITHM
#include <GL/glut.h>

#include <stdio.h>

double xmin = 50, xmax = 100, ymin = 50, ymax = 100;
double r[4], p[4], q[4];

void init() {
    glClearColor(0, 0, 0, 1);
    glClear(GL_COLOR_BUFFER_BIT);
    gluOrtho2D(0, 500, 0, 500);
}
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(0.0, 1.0, 0.0);
    glBegin(GL_LINES);
    glVertex2f(x0, y0);
    glVertex2f(x1, y1);
    glEnd();
}
double maximum() {
    int i;
    double max = 0;
    for (i = 0; i < 4; i++) {
        if (p[i] < 0) {
            if (max < r[i]) {
                max = r[i];
            }
        }
    }
    return max;
}
double minimum() {
    int i;
    double min = 1;
    for (i = 0; i < 4; i++) {
        if (p[i] > 0) {
            if (min > r[i]) {
                min = r[i];
            }
        }
    }
    return min;
}
void liang_barsky(double x0, double y00, double x1, double y11) {
    double x = x0, y = y00;
    double t1 = 0, t2 = 1;
    double dx = x1 - x0;
    double dy = y11 - y00;
    int i;
    int reject = 0;

    p[0] = -dx;
    q[0] = x0 - xmin;

    p[1] = dx;
    q[1] = xmax - x0;

    p[2] = -dy;
    q[2] = y00 - ymin;

    p[3] = dy;
    q[3] = ymax - y00;

    for (i = 0; i < 4; i++) {
        if (p[i] == 0 && q[i] < 0) {
            reject = 1;
            break;
        } else {
            r[i] = q[i] / p[i];
        }
    }
    t1 = maximum();
    t2 = minimum();
    drawRectangle(200 + xmin, 200 + ymin, 200 + xmax, 200 + ymax);
    if (t1 > t2) {

    } else {
        if (reject == 1) {

        } else {

            x1 = x + (dx * t2);
            y11 = y + (dy * t2);

            x0 = x + (dx * t1);
            y00 = y + (dy * t1);
            drawLine(x0 + 200, y00 + 200, x1 + 200, y11 + 200);
            glFlush();

        }
    }

}
void display() {
    double x0 = 50, y00 = 110, x1 = 100, y11 = 110;

    drawRectangle( xmin, ymin, xmax, ymax);

    drawLine(x0, y00, x1, y11);

    liang_barsky(x0, y00, x1, y11);

    glFlush();
}
int main(int argc, char * argv[]) {
    glutInit( & argc, argv);
    glutInitWindowSize(750, 750);
    glutCreateWindow("liang barsky algorithm");
    init();
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}