Cocos2d-x源代码解析（1）——地图模块（3）

接上一章《Cocos2d-x源代码解析（1）——地图模块（2）》

通过前面两章的分析，我们能够知道cocos将tmx的信息结构化到 CCTMXMapInfo。CCTMXTilesetInfo，CCTMXLayerInfo之中。

当中CCTMXMapInfo存储地图的信息包扩下面几块信息：

- Map orientation (hexagonal, isometric or orthogonal)
- Tile size
- Map size

- Layers (an array of TMXLayerInfo objects)
- Tilesets (an array of TMXTilesetInfo objects)
- ObjectGroups (an array of TMXObjectGroupInfo objects)

CCTMXTilesetInfo存储瓦片信息包含：

- Tileset name
- Tileset spacing
- Tileset margin
- size of the tiles
- Image used for the tiles
- Image size

CCTMXLayerInfo存储层的信息包含：

- Layer name
- Layer size
- Layer opacity at creation time (it can be modified at runtime)
- Whether the layer is visible (if it's not visible, then the CocosNode won't be created)

接下来，我们分析cocos怎样通过这些信息，生成地图的图像：

首先我们看一个重要的函数buildWithMapInfo

void CCTMXTiledMap::buildWithMapInfo(CCTMXMapInfo* mapInfo)
{
    m_tMapSize = mapInfo->getMapSize();
    m_tTileSize = mapInfo->getTileSize();
    m_nMapOrientation = mapInfo->getOrientation();

    CC_SAFE_RELEASE(m_pObjectGroups);
    m_pObjectGroups = mapInfo->getObjectGroups();
    CC_SAFE_RETAIN(m_pObjectGroups);

    CC_SAFE_RELEASE(m_pProperties);
    m_pProperties = mapInfo->getProperties();
    CC_SAFE_RETAIN(m_pProperties);

    CC_SAFE_RELEASE(m_pTileProperties);
    m_pTileProperties = mapInfo->getTileProperties();
    CC_SAFE_RETAIN(m_pTileProperties);

    int idx=0;

    CCArray* layers = mapInfo->getLayers();
    if (layers && layers->count()>0)
    {
        CCTMXLayerInfo* layerInfo = NULL;
        CCObject* pObj = NULL;
        CCARRAY_FOREACH(layers, pObj)
        {
            layerInfo = (CCTMXLayerInfo*)pObj;
            if (layerInfo && layerInfo->m_bVisible)
            {
                CCTMXLayer *child = parseLayer(layerInfo, mapInfo);
                addChild((CCNode*)child, idx, idx);

                // update content size with the max size
                const CCSize& childSize = child->getContentSize();
                CCSize currentSize = this->getContentSize();
                currentSize.width = MAX( currentSize.width, childSize.width );
                currentSize.height = MAX( currentSize.height, childSize.height );
                this->setContentSize(currentSize);

                idx++;
            }
        }
    }
}

这个函数首相将地图信息赋给map类。接下来对于每一个layer进行处理，重要的函数是parseLayer，这个函数是将layer的信息处理好而且加上sprite，并生成CTMXlayer对象。

因此我们须要分析parseLayer函数和CTMXlayer类。

首先我们看CTMXlayer的声明：

class CC_DLL CCTMXLayer : public CCSpriteBatchNode
{
    /** size of the layer in tiles */
    CC_SYNTHESIZE_PASS_BY_REF(CCSize, m_tLayerSize, LayerSize);
    /** size of the map's tile (could be different from the tile's size) */
    CC_SYNTHESIZE_PASS_BY_REF(CCSize, m_tMapTileSize, MapTileSize);
    /** pointer to the map of tiles */
    CC_SYNTHESIZE(unsigned int*, m_pTiles, Tiles);
    /** Tileset information for the layer */
    CC_PROPERTY(CCTMXTilesetInfo*, m_pTileSet, TileSet);
    /** Layer orientation, which is the same as the map orientation */
    CC_SYNTHESIZE(unsigned int, m_uLayerOrientation, LayerOrientation);
    /** properties from the layer. They can be added using Tiled */
    CC_PROPERTY(CCDictionary*, m_pProperties, Properties);
public:
    /**
     * @js ctor
     * @lua NA
     */
    CCTMXLayer();
    /**
     * @js NA
     * @lua NA
     */
    virtual ~CCTMXLayer();
  
    /** creates a CCTMXLayer with an tileset info, a layer info and a map info */
    static CCTMXLayer * create(CCTMXTilesetInfo *tilesetInfo, CCTMXLayerInfo *layerInfo, CCTMXMapInfo *mapInfo);

    /** initializes a CCTMXLayer with a tileset info, a layer info and a map info 
     * @lua NA
     */
    bool initWithTilesetInfo(CCTMXTilesetInfo *tilesetInfo, CCTMXLayerInfo *layerInfo, CCTMXMapInfo *mapInfo);

    /** dealloc the map that contains the tile position from memory.
    Unless you want to know at runtime the tiles positions, you can safely call this method.
    If you are going to call layer->tileGIDAt() then, don't release the map
    */
    void releaseMap();

    /** returns the tile (CCSprite) at a given a tile coordinate.
    The returned CCSprite will be already added to the CCTMXLayer. Don't add it again.
    The CCSprite can be treated like any other CCSprite: rotated, scaled, translated, opacity, color, etc.
    You can remove either by calling:
    - layer->removeChild(sprite, cleanup);
    - or layer->removeTileAt(ccp(x,y));
    @js getTileGIDAt
    */
    CCSprite* tileAt(const CCPoint& tileCoordinate);

    /** returns the tile gid at a given tile coordinate.
    if it returns 0, it means that the tile is empty.
    This method requires the the tile map has not been previously released (eg. don't call layer->releaseMap())
    @js tileGIDAt
    */
    unsigned int  tileGIDAt(const CCPoint& tileCoordinate);

    /** returns the tile gid at a given tile coordinate. It also returns the tile flags.
     This method requires the the tile map has not been previously released (eg. don't call [layer releaseMap])
     @js tileGIDAt
     @lua NA
     */
    unsigned int tileGIDAt(const CCPoint& tileCoordinate, ccTMXTileFlags* flags);

    /** sets the tile gid (gid = tile global id) at a given tile coordinate.
    The Tile GID can be obtained by using the method "tileGIDAt" or by using the TMX editor -> Tileset Mgr +1.
    If a tile is already placed at that position, then it will be removed.
    */
    void setTileGID(unsigned int gid, const CCPoint& tileCoordinate);

    /** sets the tile gid (gid = tile global id) at a given tile coordinate.
     The Tile GID can be obtained by using the method "tileGIDAt" or by using the TMX editor -> Tileset Mgr +1.
     If a tile is already placed at that position, then it will be removed.
     
     Use withFlags if the tile flags need to be changed as well
     */

    void setTileGID(unsigned int gid, const CCPoint& tileCoordinate, ccTMXTileFlags flags);

    /** removes a tile at given tile coordinate */
    void removeTileAt(const CCPoint& tileCoordinate);

    /** returns the position in points of a given tile coordinate 
     * @js getPositionAt
     */
    CCPoint positionAt(const CCPoint& tileCoordinate);

    /** return the value for the specific property name 
     *  @js getProperty
     */
    CCString *propertyNamed(const char *propertyName);

    /** Creates the tiles */
    void setupTiles();

    /** CCTMXLayer doesn't support adding a CCSprite manually.
     *  @warning addchild(z, tag); is not supported on CCTMXLayer. Instead of setTileGID.
     *  @lua NA
     */
    virtual void addChild(CCNode * child, int zOrder, int tag);
    /** super method
     *  @lua NA
     */
    void removeChild(CCNode* child, bool cleanup);

    inline const char* getLayerName(){ return m_sLayerName.c_str(); }
    inline void setLayerName(const char *layerName){ m_sLayerName = layerName; }
private:
    CCPoint positionForIsoAt(const CCPoint& pos);
    CCPoint positionForOrthoAt(const CCPoint& pos);
    CCPoint positionForHexAt(const CCPoint& pos);

    CCPoint calculateLayerOffset(const CCPoint& offset);

    /* optimization methods */
    CCSprite* appendTileForGID(unsigned int gid, const CCPoint& pos);
    CCSprite* insertTileForGID(unsigned int gid, const CCPoint& pos);
    CCSprite* updateTileForGID(unsigned int gid, const CCPoint& pos);

    /* The layer recognizes some special properties, like cc_vertez */
    void parseInternalProperties();
    void setupTileSprite(CCSprite* sprite, CCPoint pos, unsigned int gid);
    CCSprite* reusedTileWithRect(CCRect rect);
    int vertexZForPos(const CCPoint& pos);

    // index
    unsigned int atlasIndexForExistantZ(unsigned int z);
    unsigned int atlasIndexForNewZ(int z);
protected:
    //! name of the layer
    std::string m_sLayerName;
    //! TMX Layer supports opacity
    unsigned char        m_cOpacity;

    unsigned int        m_uMinGID;
    unsigned int        m_uMaxGID;

    //! Only used when vertexZ is used
    int                    m_nVertexZvalue;
    bool                m_bUseAutomaticVertexZ;

    //! used for optimization
    CCSprite            *m_pReusedTile;
    ccCArray            *m_pAtlasIndexArray;
    
    // used for retina display
    float               m_fContentScaleFactor;            
};

尽管有一大堆的属性和函数，可是归根结底他是一个CCSpriteBatchNode对象，因为地图中非常多图片是同样的。CCSpriteBatchNode就是cocos2d-x为了减少渲染批次而建立的一个专门管理精灵的类。

然后是函数parseLayer

CCTMXLayer * CCTMXTiledMap::parseLayer(CCTMXLayerInfo *layerInfo, CCTMXMapInfo *mapInfo)
{
    CCTMXTilesetInfo *tileset = tilesetForLayer(layerInfo, mapInfo);
    CCTMXLayer *layer = CCTMXLayer::create(tileset, layerInfo, mapInfo);

    // tell the layerinfo to release the ownership of the tiles map.
    layerInfo->m_bOwnTiles = false;
    layer->setupTiles();

    return layer;
}

这个函数又分为3步

第一步tilesetForLayer是拿到随意一块属于这个layer的tile。

第二步是依据layerInfo创建一个真正的层信息。

第三步是将tiled增加到这个层中去。