void sfera(GLfloat radius, GLfloat slices, GLfloat stacks) {
    GLfloat slcInc = 2 * M_PI / slices;
    GLfloat stkInc = M_PI / stacks;

    glPushMatrix();
    glRotatef(-90, 1, 0, 0);

    glColor3f(1, 1, 1);
    glBegin(GL_TRIANGLE_STRIP);
    int z = 0;
    for (int i = 0; i < stacks; i++, z++) {
        for (int j = 0; j < slices; j++) {
            glVertex3f(OX(radius, i * stkInc, j * slcInc), OY(radius, i * stkInc, j * slcInc), OZ(radius, i * stkInc));
            glVertex3f(OX(radius, (i + 1) * stkInc, j * slcInc), OY(radius, (i + 1) * stkInc, j * slcInc), OZ(radius, (i + 1) * stkInc));
            glVertex3f(OX(radius, i * stkInc, (j + 1) * slcInc), OY(radius, i * stkInc, (j + 1) * slcInc), OZ(radius, i * stkInc));
            glVertex3f(OX(radius, (i + 1) * stkInc, (j + 1) * slcInc), OY(radius, (i + 1) * stkInc, (j + 1) * slcInc), OZ(radius, (i + 1) * stkInc));
        }
    }
    glEnd();
    glPopMatrix();
}