12.　　在雾中绘制一个立方体,用<C>键控制雾颜色的变化,用<N>键控制雾浓度的变化(0.0-1.0).用<E>键控制雾的开和关. 用<PageUp>和<PageDown>键控制立方体所在的深度-12. In the mist of a cube map, using key control fog <C> color changes, with keys to control fog <N> concentration change (0.0-1.0). <E> Keys used to control fog OFF. With < PageUp> and <PageDown> keys control the depth of the cube where