关于nehe教程的一个问题，请大虾帮助解惑

templar721

我是一个opengl的初学者，看到了nehe教程的第九课，其中有这样一段代码
for (loop=0; loop<num; loop++)                                                // Loop Through All The Stars
        {
                glLoadIdentity();                                                                // Reset The View Before We Draw Each Star
                glTranslatef(0.0f,0.0f,zoom);                                        // Zoom Into The Screen (Using The Value In 'zoom')
                glRotatef(tilt,1.0f,0.0f,0.0f);                                        // Tilt The View (Using The Value In 'tilt')
                glRotatef(star[loop].angle,0.0f,1.0f,0.0f);                // Rotate To The Current Stars Angle
                glTranslatef(star[loop].dist,0.0f,0.0f);                // Move Forward On The X Plane
                glRotatef(-star[loop].angle,0.0f,1.0f,0.0f);        // Cancel The Current Stars Angle
                glRotatef(-tilt,1.0f,0.0f,0.0f);                                // Cancel The Screen Tilt
               
                if (twinkle)
。。。。。。。。

glRotatef(tilt,1.0f,0.0f,0.0f);glRotatef(star[loop].angle,0.0f,1.0f,0.0f);这两句话意思是场景先绕x轴旋转90度，然后在y轴上旋转星星的角度，然后是把星星绕y轴来旋转。那为什么不能
直接绕z轴旋转呢。。。我试验了一下
for (loop=0; loop<num; loop++)                                                // Loop Through All The Stars
        {
                glLoadIdentity();                                                                // Reset The View Before We Draw Each Star
                glTranslatef(0.0f,0.0f,zoom);                                        // Zoom Into The Screen (Using The Value In 'zoom')
                glRotatef(star[loop].angle,0.0f,0.0f,1.0f);                // Rotate To The Current Stars Angle
                glTranslatef(star[loop].dist,0.0f,0.0f);                // Move Forward On The X Plane               
                if (twinkle)
.............
这样的话,执行程序的情况和上面代码是一样的,但是教程上面为什么采用了第一种方法呢??是不是有什么玄机呢?请各位大虾帮忙解惑.......谢谢了

templar721

明白了,
那些代码主要是为了保证场景转动中星星永远面朝观察者....