void drawAxes(double size){

    float mat_ambient_r[] = {1, 0.3, 0.3, 1};
    float mat_ambient_g[] = {0.3, 1, 0.3, 1};
    float mat_ambient_b[] = {0.3, 0.3, 1, 1};
    float no_mat[] = {0, 0, 0, 1};

    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, no_mat);
    glMaterialfv(GL_FRONT, GL_SPECULAR,            no_mat);
    glMaterialfv(GL_FRONT, GL_SHININESS,           no_mat);

    // X - Red
    glPushMatrix();
        glMaterialfv(GL_FRONT, GL_EMISSION, mat_ambient_r);
        glColor3fv(mat_ambient_r);
        glScalef(size, size * 0.01, size * 0.01);
        glTranslatef(0.5, 0, 0);
        glutSolidCube(1.0);
    glPopMatrix();

    // Y - Green
    glPushMatrix();
        glMaterialfv(GL_FRONT, GL_EMISSION, mat_ambient_g);
        glColor3fv(mat_ambient_g);
        glScalef(size * 0.01, size, size * 0.01);
        glTranslatef(0, 0.5, 0);
        glutSolidCube(1.0);
    glPopMatrix();

    // Z - Blue
    glPushMatrix();
        glMaterialfv(GL_FRONT, GL_EMISSION, mat_ambient_b);
        glColor3fv(mat_ambient_b);
        glScalef(size * 0.01, size * 0.01, size);
        glTranslatef(0, 0, 0.5);
        glutSolidCube(1.0);
    glPopMatrix();
  }