cocos2dx 音频模块分析(3):背景音乐部分

我在(2)已经分析了背景音乐文件的预加载preloadBackgroundMusic和播放playBackgroundMusic两个函数，
这里接着分析，还是基于android平台：
1、
//暂停函数，用于音乐的暂停
void SimpleAudioEngine::pauseBackgroundMusic()
{
    //在SimpleAudioEngineJni.cpp源文件中定义
    pauseBackgroundMusicJNI();
}
//--pauseBackgroundMusicJNI--->>>
void pauseBackgroundMusicJNI()
    {
        // void pauseBackgroundMusic()
        
        JniMethodInfo methodInfo;
        
        if (! getStaticMethodInfo(methodInfo,"pauseBackgroundMusic","()V"))
        {
            return;
        }
        //通过jni调用java端的函数，调用的是Cocos2dxHelper类中的
	/*
	public static void pauseBackgroundMusic() {
		Cocos2dxHelper.sCocos2dMusic.pauseBackgroundMusic();
	}
	*/
        methodInfo.env->CallStaticVoidMethod(methodInfo.classID,methodInfo.methodID);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
    }

    最终调用的是Cocos2dxMusic类中的
    public void pauseBackgroundMusic() {
                //mBackgroundMediaPlayer在(2)中有分析过，创建的MediaPlayer实例
		if (this.mBackgroundMediaPlayer != null && this.mBackgroundMediaPlayer.isPlaying()) {
			this.mBackgroundMediaPlayer.pause();
			this.mPaused = true;  //是否暂停标志
		}
	}

2、
恢复播放
void SimpleAudioEngine::resumeBackgroundMusic()
{
    resumeBackgroundMusicJNI();
}
其实和上面暂停的调用过程是一样的，就不分析了，直接进入java端看最终调用的函数,public void resumeBackgroundMusic() {
                //这里只有处于暂停状态时即mPaused变量为true时，才会接着
		//上次播放的位置开始播放
		if (this.mBackgroundMediaPlayer != null && this.mPaused) {
			this.mBackgroundMediaPlayer.start();
			this.mPaused = false; //把暂停标志位设置false
		}
	}

3、
从头开始播放音乐文件
void rewindBackgroundMusicJNI()
    {
        // void rewindBackgroundMusic()
        
        JniMethodInfo methodInfo;
        
        if (! getStaticMethodInfo(methodInfo,"rewindBackgroundMusic","()V"))
        {
            return;
        }
        
        methodInfo.env->CallStaticVoidMethod(methodInfo.classID,methodInfo.methodID);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
    }
    --->>//java端函数
    //这个函数最终也是会调用playBackgroundMusic函数，但是和playBackgroundMusic有一点不同，
    //playBackgroundMusic需要传入音乐文件名，可以播放和上一次一样的音乐也可以和是上一次不一样的
    //音乐，但是rewindBackgroundMusic函数只有在mBackgroundMediaPlayer不为null时才执行，
    //也就是必须播放过音乐，且播放的是上次播放的音乐，只不过这次是从头开始播放
    public void rewindBackgroundMusic() {
		if (this.mBackgroundMediaPlayer != null) {
			playBackgroundMusic(mCurrentPath,mIsLoop);
		}
	}

4、停止播放音乐文件
void stopBackgroundMusicJNI()
    {
        // void stopBackgroundMusic()
        
        JniMethodInfo methodInfo;
        
        if (! getStaticMethodInfo(methodInfo,"stopBackgroundMusic",methodInfo.methodID);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
    }

    --->>>//java端函数：
    public void stopBackgroundMusic() {
		if (this.mBackgroundMediaPlayer != null) {
			mBackgroundMediaPlayer.release();
			//不太明白这里为什么有从新创建了MediaPlayer实例
			//可能是一些特殊情况下会出现问题？
        	mBackgroundMediaPlayer = createMediaplayer(mCurrentPath);

			// should set the state,if not,the following sequence will be error
			// play -> pause -> stop -> resume
			//为什么设置mPaused标志，直接看上面的英文注释
			this.mPaused = false;
		}
	}
5、
返回是否处于播放状态
 bool isBackgroundMusicPlayingJNI()
    {
        // boolean rewindBackgroundMusic()
        
        JniMethodInfo methodInfo;
        jboolean ret = false;
        
        if (! getStaticMethodInfo(methodInfo,"isBackgroundMusicPlaying","()Z"))
        {
            return ret;
        }
        
        ret = methodInfo.env->CallStaticBooleanMethod(methodInfo.classID,methodInfo.methodID);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
        
        return ret;
    }
    --->>>//java端函数，没什么东西
    	public boolean isBackgroundMusicPlaying() {
		boolean ret = false;

		if (this.mBackgroundMediaPlayer == null) {
			ret = false;
		} else {
			ret = this.mBackgroundMediaPlayer.isPlaying();
		}

		return ret;
	}
6、获取播放声音音量值
    float getBackgroundMusicVolumeJNI()
    {
        // float getBackgroundMusicVolume()
        
        JniMethodInfo methodInfo;
        jfloat ret = -1.0;
        
        if (! getStaticMethodInfo(methodInfo,"getBackgroundMusicVolume","()F"))
        {
            return ret;
        }
        
        ret = methodInfo.env->CallStaticFloatMethod(methodInfo.classID,methodInfo.methodID);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
        
        return ret;
    }
------->>>//java
    	public float getBackgroundVolume() {
		if (this.mBackgroundMediaPlayer != null) {
			return (this.mLeftVolume + this.mRightVolume) / 2;
		} else {
			return 0.0f;
		}
	}

 7、设置声音音量值
    void setBackgroundMusicVolumeJNI(float volume)
    {
        // void setBackgroundMusicVolume()
        
        JniMethodInfo methodInfo;
        
        if (! getStaticMethodInfo(methodInfo,"setBackgroundMusicVolume","(F)V"))
        {
            return ;
        }
        
        methodInfo.env->CallStaticVoidMethod(methodInfo.classID,methodInfo.methodID,volume);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
    }
   ---->>>java
   public void setBackgroundVolume(float pVolume) {
		if (pVolume < 0.0f) {
			pVolume = 0.0f;
		}

		if (pVolume > 1.0f) {
			pVolume = 1.0f;
		}

		this.mLeftVolume = this.mRightVolume = pVolume;
		if (this.mBackgroundMediaPlayer != null) {
			this.mBackgroundMediaPlayer.setVolume(this.mLeftVolume,this.mRightVolume);
		}
	}

8、
end函数，这个一般在退出游戏是调用，关掉所有的音乐和音效。
 void endJNI()
    {
        // void end()
        
        JniMethodInfo methodInfo;
        
        if (! getStaticMethodInfo(methodInfo,"end","()V"))
        {
            return ;
        }
        
        methodInfo.env->CallStaticVoidMethod(methodInfo.classID,methodInfo.methodID);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
    }
    --->>>//java端函数
    public static void end() {
		Cocos2dxHelper.sCocos2dMusic.end(); //背景音乐文件的处理
		Cocos2dxHelper.sCocos2dSound.end();
	}

    ---->>>>/////背景音乐文件的处理
	public void end() {
		if (this.mBackgroundMediaPlayer != null) {
			this.mBackgroundMediaPlayer.release();
		}
                //把所有的变量恢复初始值
		/*
		private void initData() {
		this.mLeftVolume = 0.5f;
		this.mRightVolume = 0.5f;
		this.mBackgroundMediaPlayer = null;
		this.mPaused = false;
		this.mCurrentPath = null;
		}
		
		*/
		this.initData();
	}