glVertex2f(cx, cy);

 float range_of_sector=0.5;
  int ii;
    for(ii = 0; ii < num_segments; ii++)
    {
      float theta = 2.0f * 3.1415926f * range_of_sector * (float)(ii) / (float)(num_segments);/
        float x = r * cosf(theta);//calculate the x component
        float y = r * sinf(theta);//calculate the y component

        glVertex2f(x + cx, y + cy);//output vertex

    }