OSG:幼儿园篇 第一章 节点类

一.简介

二.osg::Node 节点类

#include <osg/Node>

typedef std::vector<Node*> NodePath;
typedef std::vector<NodePath> NodePathList;
typedef std::vector<Matrix> MatrixList;

class OSG_EXPORT Node : public Object{

public:
  
  Node();
  Node(const Node&, const CopyOp& copyop = CopyOp::SHALLOW_COPY);

  virtual Object* cloneType() const {return new Node();}

  virtual Object* clone(const CopyOp& copyop) const {return new Node(*this, copyop);}

  virtual bool isSamKindAs(const Object* obj) const {return dynamic_cast<const Node*>(obj) != NULL;}

  virtual const char* libraryName() const {return "osg";}

  virtual const char* className() const {return "Node";}

  virtual Node* asNode() {return this;}

  virtual const Node* asNode() const {return this;}

  virtual Drawable* asDrawable() {return 0;}

  virtual const Drawable* asDrawable() const {return 0;}

  virtual Geometry* asGeometry() {return 0;}

  virtual const Geometry* asGeometry() const {return 0;}

  virtual Group* asGroup() {return 0;}

  virtual const Group* asGroup() const {return 0;}

  virtual Transform* asTransform() {return 0;}

  virtual const Transform* asTransform() const {return 0;}

  virtual Camera* asCamera() {return 0;}

  virtual const Camera* asCamera() const {return 0;}

  virtual Switch* asSwitch() {return 0;}

  virtual cosnt Switch* asSwitch() const {return 0;}

  virtual Geode* asGeode() {return 0;}

  virtual const Geode* asGeode() const {return 0;}

  virtual osgTerrain::Terrain* asTerrain() {return 0;}

  virtual void accept(NodeVisitor& nv);
  
  virtual void ascend(NodeVisitor& nv);

  virtual void traverse(NodeVisitor& /*nv*/){}

  typedef std::vector<Group*> ParentList;

  inline const ParentList& getParents() const {return _parents;}

  inline ParentList getParents() {return _parents;}

  inline Group* getParent(unsigned int i) {return _parents[i];}

  inline const Group* getParent(unsigned int i) const {return _parents[i];}

  inline unsigned int getNumParents() const {return static_cast<unsigned int> (_parents.size());}

  NodePathList getParentalNodePaths(osg::Node* haltTraversalAtNode = 0) const;

  Matrixlist getWorldMatrices(const osg::Node* haltTraversalAtNode = 0) const;

  void setUpdateCallback(Callback* nc);

  inline Callback* getUpdateCallback() {return _updateCallback.get();}

  inline const Callback* getUpdateCallback() const {return _updateCallback.get();}

  inline void addUpdateCallback(Callback* nc){
    if(nc != NULL){
      if(_updateCallback.valid())
        _updateCallback->addNestedCallback(nc);
      ele
        setUpdateCallback(nc);
    }
  }

  inline void removeUpdateCallback(Callback* nc){
    if(nc != NULL && _updateCallback.valid()){
      if(_updateCallback == nc)
      {
        ref_ptr<osg::Callback> new_nested_callback = nc->getNestedCallback();
        nc->setNestedCallback(0);
        setUpdateCallback(new_nested_callback.get());
      }
      else
        _updateCallback->remvoeNestedCallback(nc);
    }
  }
 
  inline unsigned int getNumChildrenRequiringUpdateTraversal() const {return _numChildrenRequiringUpdateTraversal;}

  void setEvent

   typedef std::vector<Group*> ParentList;

  // 返回父节点的列表
  const ParentList& getParents() const;

  // 返回指定索引处父节点的指针 
  Group* getParent(unsigned int I);

  // 返回父节点的数目
  unsigned int getNumParents() const;  
};

三.osg::Group 组节点类

osg::Group 组节点类可以向下继承有多个 osg::Group 子节点 ，也可以有多个 osg::Geode 子节点

#include <osg/Group>

class OSG_EXPORT Group : public Node{

public:

  Group();
  Group(const Group&, const CopyOp& copyop = CopyOp::SHALLOW_COPY)

  META_Node(osg, Group);

  virtual Group* asGroup()
  virtual const Group* asGroup() consst
 
  virtual void traverse(NodeVisitor& nv)
  
  // 添加一个子节点
  bool addChild(Node* child);

  //向指定索引位置插入一个子节点
  virtual bool insertChild(unsigned int index, Node* child)

  // 删除一个子节点
  virtual bool removeChild(Node* child);

  //从指定索引位置开始删除指定数目子节点
  inline bool removeChild(unsigned int pos, unsigned int numChildrenToRemove = 1)

  virtual bool removeChildren(unsigned int pos, unsigned int numChildrenToRemove)

  // 用新的子节点替换一个子节点
  virtual bool replaceChild(Node* origChild, Node* newChild)

  // 返回子节点的数目
  virtual unsigned int getNumChildren() const

  virtual bool setChild(unsigned int i, Node* node)

  //获取一个指定位置的子节点
  inline Node* getChild(unsigned int i)
  inline const Node* getChild(unsigned int i) const

  // 如果指定节点是一个子节点，返回true
  inline bool containsNode(const Node* node) const

  //获取一个子节点索引位置
  inline unsigned int getChildIndex(const Node* node) const

  virtual void setThreadSafeRefUnref(bool threadSafe)

  virtual void resizeGLObjectBuffers(unsigned int maxSize)

  virtual void releaseGLObjects(osg::State* = 0) const
  virtual BoundingSphere computeBound() const

protected:

  virtual ~Group()

  virtual void childRemoved(unsigne int /*pos*/, unsigne int /*numChildrenToRemove*/)
  virtual void childInserted(unsigned int /*pos*/)

  NodeList _children; 
    

};

三.osg::Geode 叶节点类

 osg::Geode 叶节点类用于保存几何信息以便渲染

osg::Geode 叶节点无法向下继承子节点，只能向上继承 osg::Group 父节点

#include <osg/Geode>

 

class OSG_EXPORT Geode : public Group
{
public:

  //构造函数
  Geode();
  Geode(const Geode&, const CopyOp& copyop = CopyOp::SHALLOW_COPY);


  virtual Geode* asGeode()
  virtual const Geode* asGeode() const

  //从叶节点追加一个可绘制体对象
  virtual bool addDrawable(Drawable* drawable);

  //从叶节点删除一个可绘制体对象
  virtual bool removeDrawable(Drawable* drawable);
  virtual bool removeDrawables(unsigned int i, unsigned int numDrawablesToRemove = 1)

  //将当前节点中包含的一个可绘制体替换为新的可绘制体
  virtual bool replaceDrawable(Drawable* origDraw, Drawable* newDraw);

  virtual bool setDrawable(unsigned int i, Drawable* drawable);

  //获取可绘制体的数目
  inline unsigned int getNumDrawables() const

  //获取一个指定位置的可绘制体
  inline Drawable* getDrawable(unsigned int i)
  inline const Drawable* getDrawable(unsigned int i) const

  inline bool constainsDrawable(const Drawable* drawable) const

  //获取一个可绘制体在叶节点的索引位置
  inline unsigned int getDrawableIndex(const Drawable* drawable) const

  void compileDrawables(RenderInfo& renderInfo)
  inline const BoundingBox& getBoundingBox() const
  virtual BoundingSphere computeBound() const;

protected:
  virtual ~Geode();
  mutable osg::BoundingBox _bbox;

};

四.osg::Geometry 绘图基元类

在osg中，通常有三种生成几何体的方法：1.用封装的OpenGL绘图基元osg::Geometry，2.是用OSG中预定义的基本几何体，3.是从文件中导入场景模型

osg::Geometry 几何体类可以通过指定顶点 颜色和法线的方式，绘制简单的线段 三角形 多边形并将绘图的结果添加到场景的叶节点Geode中

osg::Group* root = new osg::Group();            //组节点
osg::Geode* geode = new osg::Geode();           //叶节点
osg::Geometry* geometry = new osg::Geometry();  //几何图元

root->addChild(geode);
geode->addDrawable(geometry);

五.osg::LOD 细节层次节点类

 osg::LOD节点可以实现不同细节层次下物体的渲染。通过指定各个子节点的有效范围，该范围包含了最大和最小值。当子节点与观察者的距离在这个节点的有效范围之内时，LOD将显示这个节点。

基本实现方法：在不影响渲染外观的前提下，根据场景对象与观察者的距离，从多个预置方案中选择一种更为简单的方法来表达要渲染的物体，减轻系统绘制场景的负担，模型越靠近观察者时越精细。

LOD()
bool addChild(Node* child, float min, float max)    //添加一个子节点，并设置对应的观察距离

//设置指定位置的子节点对应的观察范围，或者获取某个子节点对应的观察最小值/最大值
void setRange(unsigned int childNo, float min, float max)
float getMinRange(unsigned int childNo) const
float getMaxRange(unsigned int childNo) const

const RangeList& getRangeList() const    //获取所有子节点观察范围的列表

六.osg::Switch 开关节点类

osg::Switch开关节点类可以渲染或者跳过指定的子节点。根据当前渲染的负荷有选择地渲染子图形以实现渲染性能的均衡，或者在界面和层级进行有选择地切换