android6.0源码分析之Camera API2.0下的Capture流程分析

时间：2022-06-10 09:24:04

前面对Camera2的初始化以及预览的相关流程进行了详细分析，本文将会对Camera2的capture(拍照)流程进行分析。

Camera2相关文章的目录如下：
android6.0源码分析之Camera API2.0简介
android6.0源码分析之Camera2 HAL分析
android6.0源码分析之Camera API2.0下的初始化流程分析
android6.0源码分析之Camera API2.0下的Preview(预览)流程分析
android6.0源码分析之Camera API2.0下的Capture流程分析
android6.0源码分析之Camera API2.0下的video流程分析
Camera API2.0的应用

前面分析preview的时候，当预览成功后，会使能ShutterButton，即可以进行拍照，定位到ShutterButton的监听事件为onShutterButtonClick方法：

//CaptureModule.java
@Override
public void onShutterButtonClick() {
//Camera未打开
if (mCamera == null) {
return;
    }

int countDownDuration = mSettingsManager.getInteger(SettingsManager
        .SCOPE_GLOBAL,Keys.KEY_COUNTDOWN_DURATION);
if (countDownDuration > 0) {
// 开始倒计时
        mAppController.getCameraAppUI().transitionToCancel();
        mAppController.getCameraAppUI().hideModeOptions();
        mUI.setCountdownFinishedListener(this);
        mUI.startCountdown(countDownDuration);
// Will take picture later via listener callback.
    } else {
//即刻拍照
        takePictureNow();
    }
}

首先，读取Camera的配置，判断配置是否需要延时拍照，此处分析不需延时的情况，即调用takePictureNow方法：

//CaptureModule.java
private void takePictureNow() {
if (mCamera == null) {
        Log.i(TAG, "Not taking picture since Camera is closed.");
return;
    }
//创建Capture会话并开启会话
    CaptureSession session = createAndStartCaptureSession();
//获取Camera的方向
int orientation = mAppController.getOrientationManager()
        .getDeviceOrientation().getDegrees();
//初始化图片参数
    PhotoCaptureParameters params = new PhotoCaptureParameters(
            session.getTitle(), orientation, session.getLocation(),
            mContext.getExternalCacheDir(), this, mPictureSaverCallback,
            mHeadingSensor.getCurrentHeading(), mZoomValue, 0);
//装配Session
    decorateSessionAtCaptureTime(session);
//拍照
    mCamera.takePicture(params, session);
}

它首先调用createAndStartCaptureSession来创建一个CaptureSession并且启动会话,这里并且会进行初始参数的设置，譬如设置CaptureModule(此处实参为this)为图片处理的回调(后面再分析)：

//CaptureModule.java
private CaptureSession createAndStartCaptureSession() {
//获取会话时间
long sessionTime = getSessionTime();
//当前位置
    Location location = mLocationManager.getCurrentLocation();
//设置picture name
    String title = CameraUtil.instance().createJpegName(sessionTime);
//创建会话
    CaptureSession session = getServices().getCaptureSessionManager()
           .createNewSession(title, sessionTime, location);
//开启会话
    session.startEmpty(new CaptureStats(mHdrPlusEnabled),new Size(
        (int) mPreviewArea.width(), (int) mPreviewArea.height()));
return session;
}

首先，获取会话的相关参数，包括会话时间，拍照的照片名字以及位置信息等，然后调用Session管理来创建CaptureSession，最后将此CaptureSession启动。到这里，会话就创建并启动了，所以接着分析上面的拍照流程，它会调用OneCameraImpl的takePicture方法来进行拍照：

//OneCameraImpl.java
@Override
public void takePicture(final PhotoCaptureParameters params, final CaptureSession session) {
    ...
// 除非拍照已经返回，否则就广播一个未准备好状态的广播，即等待本次拍照结束
    broadcastReadyState(false);
//创建一个线程
    mTakePictureRunnable = new Runnable() {
        @Override
public void run() {
//拍照
            takePictureNow(params, session);
        }
    };
//设置回调，此回调后面将分析，它其实就是CaptureModule,它实现了PictureCallback
    mLastPictureCallback = params.callback;
    mTakePictureStartMillis = SystemClock.uptimeMillis();

//如果需要自动聚焦
if (mLastResultAFState == AutoFocusState.ACTIVE_SCAN) {
        mTakePictureWhenLensIsStopped = true;
    } else {
//拍照
        takePictureNow(params, session);
    }
}

在拍照里，首先广播一个未准备好的状态广播，然后进行拍照的回调设置，并且判断是否有自动聚焦，如果是则将mTakePictureWhenLensIsStopped 设为ture，即即刻拍照被停止了，否则则调用OneCameraImpl的takePictureNow方法来发起拍照请求：

//OneCameraImpl.java
public void takePictureNow(PhotoCaptureParameters params, CaptureSession 
        session) {
long dt = SystemClock.uptimeMillis() - mTakePictureStartMillis;
try {
// 构造JPEG图片拍照的请求
        CaptureRequest.Builder builder = mDevice.createCaptureRequest(
            CameraDevice.TEMPLATE_STILL_CAPTURE);
        builder.setTag(RequestTag.CAPTURE);
        addBaselineCaptureKeysToRequest(builder);

// Enable lens-shading correction for even better DNGs.
if (sCaptureImageFormat == ImageFormat.RAW_SENSOR) {
            builder.set(CaptureRequest.STATISTICS_LENS_SHADING_MAP_MODE,
                CaptureRequest.STATISTICS_LENS_SHADING_MAP_MODE_ON);
        } else if (sCaptureImageFormat == ImageFormat.JPEG) {
            builder.set(CaptureRequest.JPEG_QUALITY, JPEG_QUALITY);
                .getJpegRotation(params.orientation, mCharacteristics));
        }
//用于preview的控件
        builder.addTarget(mPreviewSurface);
//用于图片显示的控件
        builder.addTarget(mCaptureImageReader.getSurface());
        CaptureRequest request = builder.build();

if (DEBUG_WRITE_CAPTURE_DATA) {
            final String debugDataDir = makeDebugDir(params.debugDataFolder,
"normal_capture_debug");
            Log.i(TAG, "Writing capture data to: " + debugDataDir);
            CaptureDataSerializer.toFile("Normal Capture", request, 
new File(debugDataDir,"capture.txt"));
        }
//拍照，mCaptureCallback为回调
        mCaptureSession.capture(request, mCaptureCallback, mCameraHandler);
    } catch (CameraAccessException e) {
        Log.e(TAG, "Could not access camera for still image capture.");
        broadcastReadyState(true);
params.callback.onPictureTakingFailed();
return;
    }
    synchronized (mCaptureQueue) {
        mCaptureQueue.add(new InFlightCapture(params, session));
    }
}

与preview类似，都是通过CaptureRequest来与Camera进行通信的，通过session的capture来进行拍照，并设置拍照的回调函数为mCaptureCallback：

//CameraCaptureSessionImpl.java
@Override
public synchronized int capture(CaptureRequest request,CaptureCallback callback,Handler handler)throws CameraAccessException{
...
    handler = checkHandler(handler,callback);
return addPendingSequence(mDeviceImpl.capture(request,createCaptureCallbackProxy(
        handler,callback),mDeviceHandler));
}

代码与preview中的类似，都是将请求加入到待处理的请求集，现在看CaptureCallback回调：

//OneCameraImpl.java
private final CameraCaptureSession.CaptureCallback mCaptureCallback = new CameraCaptureSession.CaptureCallback(){
    @Override
    public void onCaptureStarted(CameraCaptureSession session,CaptureRequest request,long 
            timestamp,long frameNumber){
　　　　　//与preview类似
if(request.getTag() == RequestTag.CAPTURE&&mLastPictureCallback!=null){
            mLastPictureCallback.onQuickExpose();
        }
    }
...
    @Override
    public void onCaptureCompleted(CameraCaptureSession session,CaptureRequest request
            ,TotalCaptureResult result){
        autofocusStateChangeDispatcher(result);
if(result.get(CaptureResult.CONTROL_AF_STATE) == null){
　　　　　　　//检查自动聚焦的状态
            AutoFocusHelper.checkControlAfState(result);
        }
...
if(request.getTag() == RequestTag.CAPTURE){
            synchronized(mCaptureQueue){
if(mCaptureQueue.getFirst().setCaptureResult(result).isCaptureComplete()){
                    capture = mCaptureQueue.removeFirst();
                }
            }
if(capture != null){
　　　　　　　　　//拍照结束
                OneCameraImpl.this.onCaptureCompleted(capture);
            }
        }
        super.onCaptureCompleted(session,request,result);
    }
...
}

这是Native层在处理请求时，会调用相应的回调，如capture开始时，会回调onCaptureStarted,具体的在preview中有过分析，当拍照结束时，会回调onCaptureCompleted方法，其中会根据CaptureResult来检查自动聚焦的状态，并通过TAG判断其是Capture动作时，再来看它是否是队列中的第一个请求，如果是，则将请求移除，因为请求已经处理成功，最后再调用OneCameraImpl的onCaptureCompleted方法来进行处理：

//OneCameraImpl.java
private void onCaptureCompleted(InFlightCapture capture){
    if(isCaptureImageFormat == ImageFormat.RAW_SENSOR){
        ...
        File dngFile = new File(RAW_DIRECTORY,capture.session.getTitle()+".dng");
        writeDngBytesAndClose(capture.image,capture.totalCaptureResult,mCharacteristics,dngFile);
    }else{
        //解析result中的图片数据
        byte[] imageBytes = acquireJpegBytesAndClose(capture.image);
        //保存Jpeg图片
        saveJpegPicture(imageBytes,capture.parameters,capture.session,capture.totalCaptureResult);
    }
    broadcastReadyState(true);
    //调用回调
    capture.parameters.callback.onPictureTaken(capture.session);
}

如代码所示，首先，对result中的图片数据进行了解析，然后调用saveJpegPicture方法将解析得到的图片数据进行保存，最后再调用里面的回调(即CaptureModule，前面在初始化Parameters时说明了，它实现了PictureCallbak接口)的onPictureTaken方法，所以，接下来先分析saveJpegPicture方法：

//OneCameraImpl.java
private void saveJpegPicture(byte[] jpegData,final PhotoCaptureParameters captureParams,CaptureSession session,CaptureResult result){
    ...
    ListenableFuture<Optional<Uri>> futureUri = session.saveAndFinish(jpegData,width,
            height,rotation,exif);
    Futures.addCallback(futureUri,new FutureCallback<Optional<Uri>>(){
@Override
public void onSuccess(Optional<Uri> uriOptional){
            captureParams.callback.onPictureSaved(mOptional.orNull());
        }

@Override
public void onFailure(Throwable throwable){
            captureParams.callback.onPictureSaved(null);
        }
    });
}

它最后会回调onPictureSaved方法来对图片进行保存，所以需要分析CaptureModule的onPictureSaved方法：

//CaptureModule.java
@Override
public void onPictureSaved(Uri uri){
    mAppController.notifyNewMedia(uri);
}

mAppController的实现为CameraActivity，所以分析notifyNewMedia方法：

//CameraActivity.java
@Override
public void notifyNewMedia(Uri uri){
...
if(FilmstripItemUtils.isMimeTypeVideo(mimeType)){
　　　　//如果拍摄的是video
        sendBroadcast(new Intent(CameraUtil.ACTION_NEW_VIDEO,uri));
        newData = mVideoItemFactory.queryContentUri(uri);
...
    }else if(FilmstripItemUtils.isMimeTypeImage(mimeType)){
　　　　//如果是拍摄图片
        CameraUtil.broadcastNewPicture(mAppContext,uri);
        newData = mPhotoItemFactory.queryCotentUri(uri);
...
    }else{
return;
    }
    new AsyncTask<FilmstripItem,Void,FilmstripItem>(){
        @Override
        protected FilmstripItem doInBackground(FilmstripItem... Params){
            FilmstripItem data = params[0];
            MetadataLoader.loadMetadata(getAndroidContet(),data);
return data;
        }
...
    }
}

由代码可知，这里有两种数据的处理，一种是video，另一种是image。而我们这里分析的是capture图片数据，所以首先会根据在回调函数传入的参数Uri和PhotoItemFactory来查询到相应的拍照数据，然后再开启一个异步的Task来对此数据进行处理，即通过MetadataLoader的loadMetadata来加载数据，并返回。至此，capture的流程就基本分析结束了，下面将给出capture流程的整个过程中的时序图：
android6.0源码分析之Camera API2.0下的Capture流程分析
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