Bresenham's Circle Algorithm

BresenhamCircle.cpp

#include <glut.h>
#include <math.h>
#include <cmath>

int width = 600, height = 600;
int xOg = 200, yOg = 200;
int xa, ya, xb, yb;

void putPixel(int x, int y) {
    glColor3f(1.0f, 1.0f, 1.0f);
    glBegin(GL_POINTS);
    glVertex2i(x, y);
    glEnd();

    glFlush();
}

void init() {
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, width, 0, height);
    glMatrixMode(GL_MODELVIEW);
}

void display() {
    glClearColor(0, 1, 0, 1);
    glClear(GL_COLOR_BUFFER_BIT);
    glFlush();
}

void plotCircle(int h, int k, int x, int y) {
    putPixel((x + h), (y + k));
    putPixel((y + h), (x + k));
    putPixel((-y + h), (x + k));
    putPixel((-x + h), (y + k));
    putPixel((-x + h), (-y + k));
    putPixel((-y + h), (-x + k));
    putPixel((y + h), (-x + k));
    putPixel((x + h), (-y + k));
}

void bresenhamCircle(int h, int k, int r)
{
    int x = 0, y = r, d = 3 - 2 * r;
    while (x <= y) {
        plotCircle(h, k, x, y);

        if (d < 0) {
            d = d + 4 * x + 6;
        }
        else {
            d = d + 4 * (x - y) + 10;
            y--;
        }
        x++;
    }
}

void mouse(int button, int state, int x, int y) {
    if (button == GLUT_LEFT_BUTTON) {
        if (state == GLUT_DOWN) {
            xa = x;
            ya = height - y;
        }

        if (state == GLUT_UP) {
            xb = x;
            yb = height - y;
            glutPostRedisplay();
            int r = (int) sqrt(pow((double)(xb - xa), 2) + pow((double)(yb - ya), 2));

            bresenhamCircle(xa, ya, r);
        }
    }

}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(width, height);
    glutCreateWindow("Polygon Creator");
    init();

    glutDisplayFunc(display);
    glutMouseFunc(mouse);

    glutMainLoop();

    return 0;
}