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

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

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：

待续