cocos2d-x中CCTextureCache图片资源的异步加载

如果没有预先加载图片，则可以通过addImageAsync()函数实现异步加载，该函数通过创建一个加载线程来加载图片，并且在主线程中通过调用回调函数来读取该图片资源纹理。其主要过程如下：

1.创建线程，用于后台加载图片

2.将对于需要加载的图片放入图片资源队列中

3.callback函数设定，用于将加载完成的图片转为纹理，等待使用其调用是由CCTimer::update调用的。

4.addImageAsyncCallBack函数在处理完纹理转换，还会调用addImageAsync传入的SEL_CallFuncO selector，实现用户加载图片纹理之后的具体处理。

 

void addImageAsync(const char *path, CCObject *target, SEL_CallFuncO selector);

函数实现过程如下：

void CCTextureCache::addImageAsync(const char *path, CCObject *target, SEL_CallFuncO selector)

{

    CCAssert(path != NULL, “TextureCache: fileimage MUST not be NULL”);

 

    CCTexture2D *texture = NULL;

 

    // optimization

 

    std::string pathKey = path;

 

    pathKey = CCFileUtils::sharedFileUtils()->fullPathFromRelativePath(pathKey.c_str());

    texture = (CCTexture2D*)m_pTextures->objectForKey(pathKey.c_str());

 

    std::string fullpath = pathKey;

    if (texture != NULL)

    {

        if (target && selector)

        {

            (target->*selector)(texture);

        }

 

        return;

    }

 

    // lazy init

    if (s_pSem == NULL)

    {

#if CC_ASYNC_TEXTURE_CACHE_USE_NAMED_SEMAPHORE

        s_pSem = sem_open(CC_ASYNC_TEXTURE_CACHE_SEMAPHORE, O_CREAT, 0644, 0);

        if( s_pSem == SEM_FAILED )

        {

            CCLOG( “CCTextureCache async thread semaphore init error: %s\n”, strerror( errno ) );

            s_pSem = NULL;

            return;

        }

#else

        int semInitRet = sem_init(&s_sem, 0, 0);

        if( semInitRet < 0 )

        {

            CCLOG( “CCTextureCache async thread semaphore init error: %s\n”, strerror( errno ) );

            return;

        }

        s_pSem = &s_sem;

#endif

          //创建一个异步信息队列

        s_pAsyncStructQueue = new queue<AsyncStruct*>();

          //创建一个图片资源队列

         s_pImageQueue = new queue<ImageInfo*>();      

 

        pthread_mutex_init(&s_asyncStructQueueMutex, NULL);

        pthread_mutex_init(&s_ImageInfoMutex, NULL);

 

        //创建加载图片资源线程，用于加载图片

        pthread_create(&s_loadingThread, NULL, loadImage, NULL);

 

        need_quit = false;

    }

 

    if (0 == s_nAsyncRefCount)

    {

        //创建调度队列，用来根据已加载图片来进行纹理转换

        CCDirector::sharedDirector()->getScheduler()->scheduleSelector(schedule_selector(CCTextureCache::addImageAsyncCallBack), this, 0, false);

    }

 

    ++s_nAsyncRefCount;

 

    if (target)

    {

        target->retain();

    }

 

    // generate async struct

    AsyncStruct *data = new AsyncStruct();

    data->filename = fullpath.c_str();

    data->target = target;

    data->selector = selector;

 

    // add async struct into queue

    pthread_mutex_lock(&s_asyncStructQueueMutex);

    //将需要加载的图片放入异步信息队列

    s_pAsyncStructQueue->push(data);

    pthread_mutex_unlock(&s_asyncStructQueueMutex);

 

    sem_post(s_pSem);

}

 

创建图片资源

static void* loadImage(void* data)

{

    // create autorelease pool for iOS

    CCThread thread;

    thread.createAutoreleasePool();

 

    AsyncStruct *pAsyncStruct = NULL;

 

    while (true)

    {

        // wait for rendering thread to ask for loading if s_pAsyncStructQueue is empty

        int semWaitRet = sem_wait(s_pSem);

        if( semWaitRet < 0 )

        {

            CCLOG( “CCTextureCache async thread semaphore error: %s\n”, strerror( errno ) );

            break;

        }

 

        //从异步信息队列中取出

        std::queue<AsyncStruct*> *pQueue = s_pAsyncStructQueue;

 

        pthread_mutex_lock(&s_asyncStructQueueMutex);// get async struct from queue

        if (pQueue->empty())

        {

            pthread_mutex_unlock(&s_asyncStructQueueMutex);

            if (need_quit)

                break;

            else

                continue;

        }

        else

        {

            pAsyncStruct = pQueue->front();

            pQueue->pop();

            pthread_mutex_unlock(&s_asyncStructQueueMutex);

        }

 

        const char *filename = pAsyncStruct->filename.c_str();

 

        // compute image type

        CCImage::EImageFormat imageType = computeImageFormatType(pAsyncStruct->filename);

        if (imageType == CCImage::kFmtUnKnown)

        {

            CCLOG(“unsupported format %s”,filename);

            delete pAsyncStruct;

 

            continue;

        }

 

        //创建图片资源 

        CCImage *pImage = new CCImage();

        if (! pImage->initWithImageFileThreadSafe(filename, imageType))

        {

            delete pImage;

            CCLOG(“can not load %s”, filename);

            continue;

        }

 

        // 创建图片资源信息

        ImageInfo *pImageInfo = new ImageInfo();

        pImageInfo->asyncStruct = pAsyncStruct;

        pImageInfo->image = pImage;

        pImageInfo->imageType = imageType;

 

        // 把图片资源加入图片资源队列

        pthread_mutex_lock(&s_ImageInfoMutex);

        s_pImageQueue->push(pImageInfo);

        pthread_mutex_unlock(&s_ImageInfoMutex);

    }

 

    if( s_pSem != NULL )

    {

    #if CC_ASYNC_TEXTURE_CACHE_USE_NAMED_SEMAPHORE

        sem_unlink(CC_ASYNC_TEXTURE_CACHE_SEMAPHORE);

        sem_close(s_pSem);

    #else

        sem_destroy(s_pSem);

    #endif

        s_pSem = NULL;

        delete s_pAsyncStructQueue;

        delete s_pImageQueue;

    }

 

    return 0;

}

 

创建图片纹理

void CCTextureCache::addImageAsyncCallBack(float dt)

{

    // 从图片资源队列中取出

    std::queue<ImageInfo*> *imagesQueue = s_pImageQueue;

 

    pthread_mutex_lock(&s_ImageInfoMutex);

    if (imagesQueue->empty())

    {

        pthread_mutex_unlock(&s_ImageInfoMutex);

    }

    else

    {

        ImageInfo *pImageInfo = imagesQueue->front();

        imagesQueue->pop();

        pthread_mutex_unlock(&s_ImageInfoMutex);

 

        AsyncStruct *pAsyncStruct = pImageInfo->asyncStruct;

        CCImage *pImage = pImageInfo->image;

 

        CCObject *target = pAsyncStruct->target;

        SEL_CallFuncO selector = pAsyncStruct->selector;

        const char* filename = pAsyncStruct->filename.c_str();

 

        // 创建2D纹理

        CCTexture2D *texture = new CCTexture2D();

#if 0 //TODO: (CC_TARGET_PLATFORM == CC_PLATFORM_IOS)

        texture->initWithImage(pImage, kCCResolutioniPhone);

#else

        texture->initWithImage(pImage);

#endif

 

#if CC_ENABLE_CACHE_TEXTURE_DATA

       // cache the texture file name

       VolatileTexture::addImageTexture(texture, filename, pImageInfo->imageType);

#endif

 

        // 加入缓存

        m_pTextures->setObject(texture, filename);

        texture->autorelease();

 

        if (target && selector)

        {

            (target->*selector)(texture);

            target->release();

        }

 

        pImage->release();

        delete pAsyncStruct;

        delete pImageInfo;

 

        –s_nAsyncRefCount;

        if (0 == s_nAsyncRefCount)

        {

            CCDirector::sharedDirector()->getScheduler()->unscheduleSelector(schedule_selector(CCTextureCache::addImageAsyncCallBack), this);

        }

    }

}