cocos2dx 音频模块分析(4): 音效部分

我们上面几篇分析了cocos2dx音频模块的音乐部分，从这篇开始，
我们分析下音效部分：
1、
//预加载音效文件：pszFilePath 音效文件名
void SimpleAudioEngine::preloadEffect(const char* pszFilePath)
{
    //获取音效文件的全路径，如果是apk包里的路径，则不包含assets/
    std::string fullPath = getFullPathWithoutAssetsPrefix(pszFilePath);
    preloadEffectJNI(fullPath.c_str());
}

--->>>// 这里通过jni调用java端的方法
void preloadEffectJNI(const char *path)
    {
        // void preloadEffect(String)

        JniMethodInfo methodInfo;

        if (! getStaticMethodInfo(methodInfo, "preloadEffect", "(Ljava/lang/String;)V"))
        {
            return ;
        }

        jstring stringArg = methodInfo.env->NewStringUTF(path);
        methodInfo.env->CallStaticVoidMethod(methodInfo.classID, methodInfo.methodID, stringArg);
        methodInfo.env->DeleteLocalRef(stringArg);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);
    }
----->>>//Cocos2dxHelper类中的方法：
public static void preloadEffect(final String path) {
                //Cocos2dxSound类是专门处理音效的类
		Cocos2dxHelper.sCocos2dSound.preloadEffect(path);
	}
--->>>//Cocos2dxSound类的方法：
public int preloadEffect(final String pPath) {
                //private final HashMap<String, Integer> mPathSoundIDMap = new HashMap<String, Integer>();
		//这个是音效路径对应音效ID的map
		Integer soundID = this.mPathSoundIDMap.get(pPath);

		if (soundID == null) {
		        //
			soundID = this.createSoundIDFromAsset(pPath);
			// save value just in case if file is really loaded
			// 如果createSoundIDFromAsset函数调用成功，则添加到mPathSoundIDMap中。
			if (soundID != Cocos2dxSound.INVALID_SOUND_ID) {
				this.mPathSoundIDMap.put(pPath, soundID);
			}
		}

		return soundID;
	}

----->>>>根据我们传入的音效文件路径，加载音效
	public int createSoundIDFromAsset(final String pPath) {
		int soundID = Cocos2dxSound.INVALID_SOUND_ID;

		try {
		        //根据传入的路径不同，做不同处理，一个是绝对路径一个是包里的路径，加载音效文件
			//The SoundPool class manages and plays audio resources for applications.
			//private SoundPool mSoundPool;音效缓存池
			if (pPath.startsWith("/")) {
				soundID = this.mSoundPool.load(pPath, 0);
			} else {
				soundID = this.mSoundPool.load(this.mContext.getAssets().openFd(pPath), 0);
			}
		} catch (final Exception e) {
			soundID = Cocos2dxSound.INVALID_SOUND_ID;
			Log.e(Cocos2dxSound.TAG, "error: " + e.getMessage(), e);
		}

		// mSoundPool.load returns 0 if something goes wrong, for example a file does not exist
		if (soundID == 0) {
			soundID = Cocos2dxSound.INVALID_SOUND_ID;
		}

		return soundID;
	}

2、
播放音效文件。
pszFilePath：音效文件名；bLoop 是否循环播放
unsigned int SimpleAudioEngine::playEffect(const char* pszFilePath, bool bLoop)
{
    std::string fullPath = getFullPathWithoutAssetsPrefix(pszFilePath);
    return playEffectJNI(fullPath.c_str(), bLoop);
}
----->>>playEffectJNI：
   unsigned int playEffectJNI(const char* path, bool bLoop)
    {
        // int playEffect(String)

        JniMethodInfo methodInfo;
        int ret = 0;

        if (! getStaticMethodInfo(methodInfo, "playEffect", "(Ljava/lang/String;Z)I"))
        {
            return ret;
        }

        jstring stringArg = methodInfo.env->NewStringUTF(path);
        ret = methodInfo.env->CallStaticIntMethod(methodInfo.classID, methodInfo.methodID, stringArg, bLoop);
        methodInfo.env->DeleteLocalRef(stringArg);
        methodInfo.env->DeleteLocalRef(methodInfo.classID);

        return (unsigned int)ret;
    }
------>>>>playEffect：
public int playEffect(final String pPath, final boolean pLoop) {
                //从mPathSoundIDMap中，根据音效path得到音效ID
		Integer soundID = this.mPathSoundIDMap.get(pPath);
		int streamID = Cocos2dxSound.INVALID_STREAM_ID;

		if (soundID != null) {
			// play sound
			// 如果音效ID存在，则表明我们已经预先加载过这个音效文件，则调用mSoundPool.play直接播放
			/*
			private int doPlayEffect(final String pPath, final int soundId, final boolean pLoop) {
				// play sound
				// Play a sound from a sound ID.
				// return non-zero streamID if successful, zero if failed如果成功会返回一个streamID
				int streamID = this.mSoundPool.play(soundId, this.mLeftVolume, this.mRightVolume, Cocos2dxSound.SOUND_PRIORITY, pLoop ? -1 : 0, Cocos2dxSound.SOUND_RATE);

				// record stream id
				// 记录上面调用mSoundPool.play返回的streamID，至于为什么需要这样，看下面源码的说明：
				// sound path and stream ids map
				// a file may be played many times at the same time
				// so there is an array map to a file path
				// private final HashMap<String, ArrayList<Integer>> mPathStreamIDsMap = new HashMap<String, ArrayList<Integer>>();
				ArrayList<Integer> streamIDs = this.mPathStreamIDsMap.get(pPath);
				if (streamIDs == null) {
					streamIDs = new ArrayList<Integer>();
					this.mPathStreamIDsMap.put(pPath, streamIDs);
				}
				streamIDs.add(streamID);

				return streamID;
			}
			*/
			streamID = this.doPlayEffect(pPath, soundID.intValue(), pLoop);
		} else {
			// the effect is not prepared，如果音效没有预先加载，则需要先加载
			soundID = this.preloadEffect(pPath); //加载音效文件
			if (soundID == Cocos2dxSound.INVALID_SOUND_ID) {
				// can not preload effect
				return Cocos2dxSound.INVALID_SOUND_ID;
			}

			// only allow one playEffect at a time, or the semaphore will not work correctly
			synchronized(this.mSoundPool) {
				// add this effect into mEffecToPlayWhenLoadedArray, and it will be played when loaded completely
				// 这个应该和mSoundPool加载音效文件有关，我也不是很明白
				/*
				不过在初始化时设置了一个：this.mSoundPool.setOnLoadCompleteListener(new OnLoadCompletedListener());
				//加载完成回调函数，应该和这个有关，这里我们就不关心了。 只需要知道如果我们提前加载音效文件
				//也可以直接调用play函数，在调用play函数时会调用加载函数，并放入加载队列中，加载完成后进行播放。
				//这样做会有一些延时，所以我们还是最好先加载，然后在播放。这个延时只在第一次播放时有，以后就不会了，
				//不过最好还是先加载。
				*/
				/*
					@Override
					//加载完成回调函数。
					public void onLoadComplete(SoundPool soundPool, int sampleId, int status) {
						if (status == 0)
						{
							// only play effect that are in mEffecToPlayWhenLoadedArray
							for ( SoundInfoForLoadedCompleted info : mEffecToPlayWhenLoadedArray) {
								if (sampleId == info.soundID) {
									// set the stream id which will be returned by playEffect()
									// 加载完成后调用doPlayEffect进行播放，并从mEffecToPlayWhenLoadedArray加载列表中
									// 移除。
									mStreamIdSyn = doPlayEffect(info.path, info.soundID, info.isLoop);

									// remove it from array, because we will break here
									// so it is safe to do
									mEffecToPlayWhenLoadedArray.remove(info);

									break;
								}
							}
						} else {
							mStreamIdSyn = Cocos2dxSound.INVALID_SOUND_ID;
						}

						mSemaphore.release();
					}
				}
				*/
				mEffecToPlayWhenLoadedArray.add(new SoundInfoForLoadedCompleted(pPath, soundID.intValue(), pLoop));

				try {
					// wait OnloadedCompleteListener to set streamID
					this.mSemaphore.acquire();

					streamID = this.mStreamIdSyn;
				} catch(Exception e) {
					return Cocos2dxSound.INVALID_SOUND_ID;
				}
			}
		}

		return streamID;
	}