12--使用背景音乐

        Cocos2DX为我们提供了简单易用的音乐引擎，对于简单的使用只需要掌握libCocosDenshion库中的SimpleAudioEngine使用即可。

        libCocosDenshion将音乐分为两个大类：背景音乐和音效

• 背景音乐：通常背景音乐时间较长；
• 音效：而音效通常在特定的动作执行时播放，时间较短，更换频率高。

      下面就以背景音乐的实例为例看看怎么使用SimpleAudioEngine

      新建工程DemoMusic，去掉不必要的并加载bg.mp3文件到工程的Resources目录下：

    还是先看看SimpleAudioEngine为我们提供了那些方法：

//获取单例对象
    static SimpleAudioEngine* sharedEngine();
    //释放对象资源
    static void end();
    //预加载背景音乐
    void preloadBackgroundMusic(const char* pszFilePath);    
   //播放背景音乐，根据参数选择循环播放
    void playBackgroundMusic(const char* pszFilePath, bool bLoop);
   //停止背景音乐
    void stopBackgroundMusic(bool bReleaseData);
    //暂停
    void pauseBackgroundMusic();
   //恢复
    void resumeBackgroundMusic();
  //获取音量大小
    float getBackgroundMusicVolume();
   //设置音量大小
    void setBackgroundMusicVolume(float volume);

从方法名称就很容易的明白如何使用下面init方法修改如下：

bool HelloWorld::init()
{
    float fontSize = 16,startY = 10 , offset=15;

    //////////////////////////////
    // 1. super init first
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CocosDenshion::SimpleAudioEngine::sharedEngine()->preloadBackgroundMusic("bg.mp3");

    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();

    /////////////////////////////
    // 2. add a menu item with "X" image, which is clicked to quit the program
    //    you may modify it.

    // add a "close" icon to exit the progress. it's an autorelease object
    CCMenuItemImage *pCloseItem = CCMenuItemImage::create(
        "CloseNormal.png",
        "CloseSelected.png",
        this,
        menu_selector(HelloWorld::menuCloseCallback));

    pCloseItem->setPosition(ccp(origin.x + visibleSize.width - pCloseItem->getContentSize().width/2 ,
        origin.y + pCloseItem->getContentSize().height/2));

    CCMenuItem* pPlayBGMusic = CCMenuItemLabel::create(
        CCLabelTTF::create("Play BG Music","HiraKakuProN-W6",fontSize) ,
        this,
        menu_selector(HelloWorld::menuPlayBGMusic));
    pPlayBGMusic->setPosition(ccp(visibleSize.width/2-pPlayBGMusic->getContentSize().width/2,startY));

    CCMenuItem* pStopBGMusic = CCMenuItemLabel::create(
        CCLabelTTF::create("Stop BG Music","HiraKakuProN-W6",fontSize) ,
        this,
        menu_selector(HelloWorld::menuStopBGMusic));
    pStopBGMusic->setPosition(ccp(visibleSize.width/2-pStopBGMusic->getContentSize().width/2,startY+offset));

    CCMenuItem* pPauseBGMusic = CCMenuItemLabel::create(
        CCLabelTTF::create("Pause BG Music","HiraKakuProN-W6",fontSize) ,
        this,
        menu_selector(HelloWorld::menuPauseBGMusic));
    pPauseBGMusic->setPosition(ccp(visibleSize.width/2-pPauseBGMusic->getContentSize().width/2,startY+offset*2));
    
    CCMenuItem* pResumeBGMusic = CCMenuItemLabel::create(
        CCLabelTTF::create("Resume BG Music","HiraKakuProN-W6",fontSize) ,
        this,
        menu_selector(HelloWorld::menuResumeBGMusic));
    pResumeBGMusic->setPosition(ccp(visibleSize.width/2-pResumeBGMusic->getContentSize().width/2,startY+offset*3));
    
    CCMenuItem* pVolumeAddBGMusic = CCMenuItemLabel::create(
        CCLabelTTF::create("Volume + BG Music","HiraKakuProN-W6",fontSize) ,
        this,
        menu_selector(HelloWorld::menuVolumeAddBGMusic));
    pVolumeAddBGMusic->setPosition(ccp(visibleSize.width/2-pVolumeAddBGMusic->getContentSize().width/2,startY+offset*4));

    CCMenuItem* pVolumeSubBGMusic = CCMenuItemLabel::create(
        CCLabelTTF::create("Volume - BG Music","HiraKakuProN-W6",fontSize) ,
        this,
        menu_selector(HelloWorld::menuVolumeSubBGMusic));
    pVolumeSubBGMusic->setPosition(ccp(visibleSize.width/2-pVolumeSubBGMusic->getContentSize().width/2,startY+offset*5));

    // create menu, it's an autorelease object
    CCMenu* pMenu = CCMenu::create(pCloseItem,pPlayBGMusic,pStopBGMusic,pPauseBGMusic ,pResumeBGMusic,pVolumeAddBGMusic , pVolumeSubBGMusic , NULL);
    pMenu->setPosition(CCPointZero);
    this->addChild(pMenu, 1);

    return true;
}

几个菜单回调函数：

void HelloWorld::menuVolumeSubBGMusic(CCObject* pSender)
{
    float volume=CocosDenshion::SimpleAudioEngine::sharedEngine()->getBackgroundMusicVolume();
    CocosDenshion::SimpleAudioEngine::sharedEngine()->setBackgroundMusicVolume(volume-0.2);

    CCLOG ("volume - : %f", CocosDenshion::SimpleAudioEngine::sharedEngine()->getBackgroundMusicVolume());
}

void HelloWorld::menuVolumeAddBGMusic(CCObject* pSender)
{
    float volume=CocosDenshion::SimpleAudioEngine::sharedEngine()->getBackgroundMusicVolume();
    CocosDenshion::SimpleAudioEngine::sharedEngine()->setBackgroundMusicVolume(volume+0.2);
    CCLOG ("volume + : %f", CocosDenshion::SimpleAudioEngine::sharedEngine()->getBackgroundMusicVolume());
}

void HelloWorld::menuResumeBGMusic(CCObject* pSender)
{
    CocosDenshion::SimpleAudioEngine::sharedEngine()->resumeBackgroundMusic();
}

void HelloWorld::menuPauseBGMusic(CCObject* pSender)
{
    CocosDenshion::SimpleAudioEngine::sharedEngine()->pauseBackgroundMusic();
}

void HelloWorld::menuStopBGMusic(CCObject* pSender)
{
    CocosDenshion::SimpleAudioEngine::sharedEngine()->stopBackgroundMusic(false);
}

void HelloWorld::menuPlayBGMusic(CCObject* pSender)
{
    CocosDenshion::SimpleAudioEngine::sharedEngine()->playBackgroundMusic("bg.mp3");
}

        运行看看效果：        

   音量设置还有问题，貌似没有起到作用，待解！！