gaia引擎分析（二）场景管理

只是粗略的分析原理，大虾轻喷~~

Gaia引擎中没有场景管理器（scenemanager）这种东西，但是并不是没有场景管理，而是在cGameHost类中有一课场景树进行场景组织、一棵四叉树用来进行剪裁。

class cGameHost

class cGameHost : public CD3DApplication, public cSingleton<cGameHost>
{
。。。。。。
    cSceneNode        m_rootNode;//场景树根节点
    cCamera            m_defaultCamera;
    cCamera*        m_pActiveCamera;
    cQuadTree        m_quadTree;//四叉树
    cRect3d            m_worldExtents;

    tchar    m_rootPath[MAX_PATH];

bool    m_frameReady;

// Invalid Functions...
    cGameHost(const cGameHost& Src);
    cGameHost& operator=(const cGameHost& Src);
};

cSceneNode类：场景节点，可形成树状结构组织场景，形成一种空间变换的层次结构。

cSceneObject类：渲染基石，继承自cSceneNode，所有可渲染对象都继承自cSceneObject，可挂接在四叉树节点上。

class cSceneObject

class cSceneObject : public cSceneNode
{
    。。。。。。
void attachToQuadTree(cQuadTree* parentTree);//挂接到四叉树
    

    cQuadTreeNode* quadTreeNode()const;
    u32Flags zMask()const;
    cSceneObject* forwardTreeLink()const;
    cSceneObject* rearTreeLink()const;

const cRect3d& localBounds()const;
const cRect3d& worldBounds()const;

//
// temporary functions
//
    void setWorldBounds(const cRect3d& box)
    {
        m_worldBounds = box;
    }


private:

// bounding box information
    u32Flags m_objectFlags;
    cRect3d m_localBounds;
    cRect3d m_worldBounds;

// world QuadTree membership information
    cQuadTree*        m_pQuadTree;
    cQuadTreeNode*  m_pQuadTreeNode;
    u32Flags        m_quadTreeZMask;
    cSceneObject*    m_pForwardTreeLink;
    cSceneObject*    m_pRearTreeLink;

// QuadTree search result links
    cSceneObject*    m_pForwardSearchLink;
    cSceneObject*    m_pRearSearchLink;

// private functions
    void setForwardSearchLink(cSceneObject* pForwardLink);
void setRearSearchLink(cSceneObject* pForwardLink);
virtual void refreshQuadTreeMembership();

    friend cQuadTreeNode;
void setQuadTreeData(cQuadTreeNode* parentNode, u32Flags zMask);
void setForwardTreeLink(cSceneObject* link);
void setRearTreeLink(cSceneObject* link);
};

cQuadTree：四叉树，用于剪裁掉不可见的物体，提高渲染效率

class cQuadTree

class cQuadTree
{
public:

// Data Types & Constants...
    enum eConstants
    {
        k_minimumTreeDepth = 1, 
        k_maximumTreeDepth = 9, //  must be a value between 1 and 9
    };


// Public Data...

// Creators...

    cQuadTree();
    ~cQuadTree();

void create(const cRect3d& worldExtents, int depth);
void destroy();

// Operators...

// Mutators...
    cSceneObject* buildSearchResults(
const cRect3d& worldRect, 
const cFrustum* pOptionalFrustum=0); //四叉树搜索，即剪裁，可以选用视锥体和包围盒
    u32Flags addOrUpdateSceneObject(cSceneObject* newNode);

// Accessors...
    bool isReady()const;

private:

// Private Data...
    cQuadTreeNode* m_levelNodes[k_maximumTreeDepth];//四叉树节点2维数组
    cVector3 m_worldExtents;
    cVector3 m_worldScale;
    cVector3 m_worldOffset;
int m_depth;
    uint32 m_memorySize;

// Private Functions...
    void findTreeNodeInfo(const cQuadTreeRect& worldByteRect, int& level, int& levelX, int& levelY);
    cQuadTreeNode* findTreeNode(const cQuadTreeRect& worldByteRect);
    cQuadTreeNode* getNodeFromLevelXY(int level, int x, int y);
void buildByteRect(const cRect3d& worldRect, cQuadTreeRect& worldByteRect);
};

cQuadTreeNode：四叉树节点，上面可以挂接cSceneObject

class cQuadTreeNode

class cQuadTreeNode
{
public:


    cQuadTreeNode();
    ~cQuadTreeNode();

    uint32 addOrUpdateMember(cSceneObject* member, const cQuadTreeRect& rect);
void removeMember(cSceneObject* member);

void testLocalMembersForSearchResults(
        cSceneObject** pResultList, 
        cSceneObject** pResultListTail, 
        u32Flags zMask, 
float zMin, 
float zMax,
const cFrustum* pOptionalFrustum=0);

void testLocalMembersForSearchResults(
        cSceneObject** pResultList, 
        cSceneObject** pResultListTail, 
        u32Flags zMask, 
const cRect3d& trueRect,
const cFrustum* pOptionalFrustum=0);

bool empty()const;
    u32Flags zMask()const;
    u32Flags zLocalMask()const;

private:

// Private Data...
    cQuadTreeNode* m_pChildNode[4];//子节点
    cQuadTreeNode* m_pParentNode;
    cSceneObject* m_pFirstMember;//挂接的cSceneObject列表

    u32Flags m_zLocalMask;
    u32Flags m_zMask;

// Private Functions...
    void descendantMemberAdded(u32Flags zMask);
void descendantMemberRemoved();
void rebuildLocalZMask();
void rebuildZMask();


// functions available to the quad tree
    friend cQuadTree;
void setup(cQuadTreeNode* parent, cQuadTreeNode* child0, cQuadTreeNode* child1, cQuadTreeNode* child2, cQuadTreeNode* child3);//在四叉树上配置节点
};