射击游戏实例。派生出游戏所需要得游戏实体

				#ifndef __OBJECT_H
				#define __OBJECT_H
				
				#include "tree.h"
				#include "vector.h"
				#include "camera.h"
				
				
				class CObject : public CNode
				{
				protected:
				
				     // perform basic physics on the object
				     virtual void OnAnimate(scalar_t deltaTime) 
				     {
				          position += velocity * deltaTime;
				          velocity += acceleration * deltaTime;
				     }
				
				     // draw the object given the camera position
				     virtual void OnDraw(CCamera *camera) {} 
				
				     // collide with other objects
				     virtual void OnCollision(CObject *collisionObject) {}
				
				     // perform collision and other preparations for this object
				     virtual void OnPrepare() 
				     {
				          ProcessCollisions(FindRoot());     // perform collisions starting with
				                                             // root world object
				     }
				
				public:
				     CVector position;        // object position
				     CVector velocity;        // velocity of object
				     CVector acceleration;    // acceleration
				     scalar_t size;           // size of bounding sphere (radius)
				
				     bool isDead;
				
				     CObject() { isDead = false; }
				     ~CObject() {}
				
				     virtual void Load() {}
				     virtual void Unload() {}
				
				     // draw object
				     void Draw(CCamera *camera) 
				     {
				          // push modelview matrix on stack
				          glPushMatrix();
				               OnDraw(camera);          // draw this object
				               if (HasChild())          // draw children
				                    ((CObject*)childNode)->Draw(camera);
				          glPopMatrix();
				
				          // draw siblings
				          if (HasParent() && !IsLastChild())
				               ((CObject*)nextNode)->Draw(camera);
				     }
				
				     // animate object
				     void Animate(scalar_t deltaTime) 
				     {
				          OnAnimate(deltaTime);         // animate this object
				     
				          // animate children
				          if (HasChild())
				               ((CObject*)childNode)->Animate(deltaTime);
				
				          // animate siblings
				          if (HasParent() && !IsLastChild())
				               ((CObject*)nextNode)->Animate(deltaTime);
				
				          if (isDead)
				               delete this;
				     }
				
				     // perform collision detection
				     void ProcessCollisions(CObject *obj) 
				     {
				          // if this object's bounding sphere collides with obj's sphere
				          // and obj is not this object
				          if (((obj->position - position).Length() size + size)) &&
				               (obj != ((CObject*)this)))
				          {
				               OnCollision(obj);        // perform this object's collision with obj
				
				               // test child collisions with obj
				               if (HasChild())
				                    ((CObject*)childNode)->ProcessCollisions(obj);
				
				               // test sibling collisions with obj
				               if (HasParent() && !IsLastChild())
				                    ((CObject*)nextNode)->ProcessCollisions(obj);
				          }
				
				          // if obj has children, check collisions with these children
				          if (obj->HasChild())
				               ProcessCollisions((CObject*)(obj->childNode));
				
				          // if obj has siblings, check collisions with these siblings
				          if (obj->HasParent() && !obj->IsLastChild())
				               ProcessCollisions((CObject*)(obj->nextNode));
				     }
				
				     // prepare object
				     void Prepare()
				     {
				          OnPrepare();                            // prepare this object
				
				          if (HasChild())                         // prepare children
				               ((CObject*)childNode)->Prepare();
				
				          if (HasParent() && !IsLastChild())      // prepare siblings
				               ((CObject*)nextNode)->Prepare();
				     }
				
				     // find root object of cyclic linked list tree
				     CObject *FindRoot()
				     {
				          // if this object has a parent node, return the root of the parent node
				          if (parentNode)
				               return ((CObject*)parentNode)->FindRoot();
				
				          return this;
				     }
				};
				
				
				#endif