camera2 (api2)打开预览过程（二）

下面就开始获取CameraService的句柄，调用CameraService中的connectDevice函数。

private CameraDeviceopenCameraDeviceUserAsync(String cameraId,           CameraDevice.StateCallback callback, Handler handler, final int uid)           throws CameraAccessException@ CameraManager.java {//首先是获取CameraService的句柄         ICameraServicecameraService = CameraManagerGlobal.get().getCameraService();//向cameraService发送连接请求         cameraUser= cameraService.connectDevice(callbacks, id,                   mContext.getOpPackageName(),uid);}

先看获取CameraService的过程：

CameraManagerGlobal.get().getCameraService();àpublic ICameraService getCameraService() {         connectCameraServiceLocked();}

private void connectCameraServiceLocked() {//这里通过serviceManager来查询cameraservice的句柄，对应的servicename是// private static final String CAMERA_SERVICE_BINDER_NAME ="media.camera";跟前面提到的//cameraservice的启动过程中注册cameraservice到servicemanager时，设置的服务名是一//样的，所以这里得到的就是CameraService的句柄。         IBindercameraServiceBinder =                   ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME);//接下来是把查询到cameraservice句柄这个Ibinder转成ICameraService，在注册//cameraservice时，是把ICameraService转成Ibinder保存的，这里反向转化，由此可以推断//CameraService.cpp一定继承自IBinder，         ICameraServicecameraService = ICameraService.Stub.asInterface(cameraServiceBinder);//这里注册一个监听ICameraServiceListener，当一个新的camera可用时，有相应的回调cameraService.addListener(this);}

接着看下CameraService.cpp是不是继承自IBinder，

CameraService.hclass CameraService : public::android::hardware::BnCameraService,其余省略，CameraService继承自BnCameraService，BnCameraService.h//对应的命名空间：android::hardware::namespace android {namespace hardware {class BnCameraService : public::android::BnInterface<ICameraService>}}

这里的ICameraService是有ICameraService.aidl进过aidl工具自动生成的，ICameraService.aidl文件经转化后生成了ICameraService.java，ICameraService.h，ICameraService.cpp文件，早期版本aidl文件转化后只有.java文件生成。如果*.aidl文件被添加到的Android.mk，它的build Target是库，比如：include $(BUILD_SHARED_LIBRARY)，那么就会自动生成.h，.cpp文件。

继续看BnInterface是不是根IBinder有关系：

IInterface.h

template<typename INTERFACE>

class BnInterface : public INTERFACE, publicBBinder

可以看到BnInterface是一个模板类，这里的INTERFACE就是ICameraService，并且其继承自BBinder，

Frameworks/native/include/binder/Binder.h

class BBinder : public IBinder{}

从这里可以看出BBinder继承自IBinder。

 

从以上继承关系，可以知道connectDevice的调用流程：

CameraManager.java

cameraUser = cameraService.connectDevice(callbacks,id,

            mContext.getOpPackageName(), uid);à

ICameraService.java

这是有ICameraService.aidl自动生成的.java文件

public interface ICameraService extendsandroid.os.IInterface{

         publicstatic abstract class Stub extends android.os.Binder implementsandroid.hardware.ICameraService{

                   privatestatic class Proxy implements android.hardware.ICameraService{

                            @Overridepublic android.hardware.camera2.ICameraDeviceUserconnectDevice(android.hardware.camera2.ICameraDeviceCallbacks callbacks, intcameraId, java.lang.String opPackageName, int clientUid) throwsandroid.os.RemoteException{

                                     mRemote.transact(Stub.TRANSACTION_connectDevice,_data, _reply, 0);à

}

}

}

}

由mRemote.transact()开启跨进程的通信，经由IBinder，BpBinder，IPCThreadState把请求发到Binder驱动，由Binder驱动把请求发到cameraService服务端，针对同一个请求，client和server端的业务码是一致的。

CameraService.cpp的onTransact()方法会被调用：

status_t CameraService::onTransact(uint32_tcode, const Parcel& data, Parcel* reply, uint32_t flags) {

         returnBnCameraService::onTransact(code, data, reply, flags);à

}

ICameraService.cpp

::android::status_tBnCameraService::onTransact(uint32_t _aidl_code, const ::android::Parcel&_aidl_data, ::android::Parcel* _aidl_reply, uint32_t _aidl_flags) {

         caseCall::CONNECTDEVICE:

         ::android::sp<::android::hardware::camera2::ICameraDeviceUser>_aidl_return;

//cameraManager.java中发起connectDevice时是带四个参数，这里加了一个ICameraDeviceUser类型的参数，并把这个出参作为reply的一部分返回给client端，这里的connectDevice才是真正调用到CameraService.cpp中的connectDevice方法。

         ::android::binder::Status_aidl_status(connectDevice(in_callbacks, in_cameraId, in_opPackageName,in_clientUid, &_aidl_return));

//把_aidl_return写入到返回的数据结构中

         _aidl_ret_status=_aidl_reply->writeStrongBinder(::android::hardware::camera2::ICameraDeviceUser::asBinder(_aidl_return));

}

下面先看下怎么返回_aidl_return到client端的，cameraservice先把结果写到_aidl_reply这个parcel中，然后由Binder驱动在发到client端，其中的细节是client端发起请求后会进入睡眠，等server端有了处理结果，把这个结果写到了binder驱动后，client会被Binder驱动唤醒执行读取操作。这里接收结果的客户端是：

ICameraService.java中的Proxy：

public interface ICameraService:: publicstatic abstract class Stub:: private static class Proxy{

         @Overridepublic android.hardware.camera2.ICameraDeviceUserconnectDevice(android.hardware.camera2.ICameraDeviceCallbacks callbacks, intcameraId, java.lang.String opPackageName, int clientUid) throwsandroid.os.RemoteException{

//这句代码是发送请求的开始

                   mRemote.transact(Stub.TRANSACTION_connectDevice,_data, _reply, 0);

//这句就是服务端处理后返回的结果，通过_reply.readStrongBinder()从parcel中读取结果，然后返回值给cameraManager。

                   _result= android.hardware.camera2.ICameraDeviceUser.Stub.asInterface(_reply.readStrongBinder());

                   return_result;

}

}

 

接着看CameraService.cpp中connectDevice都做了什么操作：

CameraService.cpp

Status CameraService::connectDevice(

         constsp<hardware::camera2::ICameraDeviceCallbacks>& cameraCb,

         intcameraId, onst String16& clientPackageName, int clientUid,

         /*out*/sp<hardware::camera2::ICameraDeviceUser>*device){

//这里的device是出参，类型是ICameraDeviceUser，也是有ICameraDeviceUser.aidl自动生成的，这个对象跟CameraDeviceClient的实例client对应，CameraDeviceClient继承了BnCameraDeviceUser进而继承了ICameraDeviceUser，

         sp<CameraDeviceClient>client = nullptr;      

// connectHelper的定义在CameraService.h中

         ret=connectHelper<hardware::camera2::ICameraDeviceCallbacks,CameraDeviceClient>

(cameraCb, id, CAMERA_HAL_API_VERSION_UNSPECIFIED,clientPackageName,

clientUid, USE_CALLING_PID, API_2, /*legacyMode*/ false,/*shimUpdateOnly*/ false,

/*out*/client);

         *device= client;

}

CameraService.h

//这是一个模板方法，CALLBACK是hardware::camera2::ICameraDeviceCallbacks，

//CLIENT是CameraDeviceClient。这个方法主要作用是生成CameraClient实例，并调用其inittialize方法。

template<class CALLBACK, classCLIENT>

binder::StatusCameraService::connectHelper(const sp<CALLBACK>& cameraCb, constString8& cameraId, int halVersion, const String16& clientPackageName,int clientUid, int clientPid, apiLevel effectiveApiLevel, bool legacyMode, boolshimUpdateOnly, /*out*/sp<CLIENT>& device) {

         ret= makeClient(this, cameraCb, clientPackageName, id, facing, clientPid,

                clientUid, getpid(),legacyMode, halVersion, deviceVersion, effectiveApiLevel,

                /*out*/&tmp)

         client= static_cast<CLIENT*>(tmp.get());

         err= client->initialize(mModule)

}

CameraService.cpp

Status CameraService::makeClient(constsp<CameraService>& cameraService,

       const sp<IInterface>& cameraCb, const String16& packageName,int cameraId,

       int facing, int clientPid, uid_t clientUid, int servicePid, boollegacyMode,

       int halVersion, int deviceVersion, apiLevel effectiveApiLevel,

       /*out*/sp<BasicClient>* client){

//根据apiversion的不同，这里创建CameraDeviceClient实例。

         *client= new CameraDeviceClient(cameraService, tmp, packageName, cameraId,

                        facing, clientPid,clientUid, servicePid);

}

看下CameraDeviceClient的继承关系，

CameraDeviceClient.h

class CameraDeviceClient :

         publicCamera2ClientBase<CameraDeviceClientBase>,

         publiccamera2::FrameProcessorBase::FilteredListener{}

struct CameraDeviceClientBase :

         publicCameraService::BasicClient,

         publichardware::camera2::BnCameraDeviceUser{}

可以看到CameraDeviceClient继承了CameraService::BasicClient，并且实现了ICameraDeviceUser的这个Binder的api，同时还实现了帧处理线程的监听。

接着看CameraDeviceClient的构造函数：

CameraDeviceClient.cpp

CameraDeviceClient::CameraDeviceClient(constsp<CameraService>& cameraService,

         constsp<hardware::camera2::ICameraDeviceCallbacks>& remoteCallback,

         constString16& clientPackageName, int cameraId, int cameraFacing, int clientPid,

         uid_tclientUid, int servicePid) :

         Camera2ClientBase(cameraService,remoteCallback, clientPackageName,

         cameraId,cameraFacing, clientPid, clientUid, servicePid),

主要是在参数初始化列表中调用了父类Camera2ClientBase的构造函数。

Camera2ClientBase.cpp

Camera2ClientBase是一个模板类，这里的TClientBase是CameraDeviceClientBase，可以从CameraDeviceClient的继承关系看出。除了调用父类TClientBase(CameraDeviceClientBase)的构造函数外，还创建Camera3Device实例。

template <typename TClientBase>

Camera2ClientBase<TClientBase>::Camera2ClientBase(

         constsp<CameraService>& cameraService,  constsp<TCamCallbacks>& remoteCallback,

         constString16& clientPackageName, int cameraId, int cameraFacing, int clientPid,

         uid_tclientUid, int servicePid):

TClientBase(cameraService, remoteCallback,clientPackageName,

       cameraId, cameraFacing, clientPid, clientUid, servicePid),{

         mDevice= new Camera3Device(cameraId);

}

接着把继承的构造函数看完，CameraDeviceClientBase又调用了父类CameraService::BasicClient,的构造函数，BasicClient的构造函数实现代码在CameraService中，主要做的事情是应用权限相关的，这块权限的处理不是很了解。

这一系列构造函数的执行，最重要的还是Camera2ClientBase中的Camera3Device实例的创建及紧接着的initialize方法的调用。

下面看initialize方法的调用流程：

CameraDeviceClient.cpp

status_tCameraDeviceClient::initialize(CameraModule *module){

         res= Camera2ClientBase::initialize(module);

//这里注册了一个监听，mFrameProcessor是一个Thread，是一个输出帧元数据处理线程，

//处理预览回调相关的事情，这个线程会等待camera设备新的帧，然后调用监听接口的方法onResultAvailable，

//这个方法：CameraDeviceClient::onResultAvailable，又会执行回调：

// remoteCb->onResultReceived(result.mMetadata,result.mResultExtras);这个remoteCb是

//hardware::camera2::ICameraDeviceCallbacks类型的，这个callback实例是在

//Cameramanager.java中执行打开camera设备时创建的，然后由CameraService的//connectDevice方法一路传递到CameraDeviceClient这里，所以这个回调实际的实现代码是：

// CameraDeviceImpl.java中的内部类CameraDeviceCallbacks的方法：onResultReceived。

         mFrameProcessor->registerListener(FRAME_PROCESSOR_LISTENER_MIN_ID,

                   FRAME_PROCESSOR_LISTENER_MAX_ID,/*listener*/this, /*sendPartials*/true);

}

Camera2ClientBase.cpp

status_t Camera2ClientBase<TClientBase>::initialize(CameraModule*module){

//这里的mDevice是Camera3Device类的实例。

         res= mDevice->initialize(module);

}

Camera3Device.cpp

status_tCamera3Device::initialize(CameraModule *module){

//调用CameraModule的open方法打开HAL设备，从这里开始就进入到了HAL层，HAL设备对应的结构体类型是camera3_device_t，module就是CameraModule的实例，这个实例的创建是在CameraService第一次被引用时在其voidCameraService::onFirstRef()函数中，mModule = new CameraModule(rawModule);这部分跟CameraService的启动有关系。

         res= module->open(deviceName.string(),

                   reinterpret_cast<hw_device_t**>(&device));

//初始化HAL层设备，

         res= device->ops->initialize(device, this);

//创建Buffer管理器。

         mBufferManager= new Camera3BufferManager();

 

         res= find_camera_metadata_ro_entry(info.static_camera_characteristics,

                   ANDROID_CONTROL_AE_LOCK_AVAILABLE,&aeLockAvailableEntry);

//开启一个请求队列线程，run方法后它的threadLoop方法就会执行。

         mRequestThread= new RequestThread(this, mStatusTracker, device, aeLockAvailable);

         res= mRequestThread->run(String8::format("C3Dev-%d-ReqQueue",mId).string());

//创建准备流的线程，但是并没有马上运行这个线程，而是等到调用Camera3Device的prepare方法时，根据需要开启线程，什么时候调用了Camera3Device的prepare方法呢？这个我没打log跟，一种可能的情况是当创建一个session时，预分配缓存时调用。

         mPreparerThread= new PreparerThread();

}

-------------------------------------------------------------------------------------------------------------------

到这里Camera设备的打开就完成了。紧接着的就是开启预览。

再回到应用层，CaptureModule.java

上面camera设备打开的过程是从openCameraAndStartPreview中open方法开始的，当camera成功打开后，会回调onCameraOpened，在这个回调中通过camera.startPreview启动预览。

private void openCameraAndStartPreview() {

         mOneCameraOpener.open(cameraId,captureSetting, mCameraHandler, mainThread,

                   imageRotationCalculator,mBurstController, mSoundPlayer,

                   newOpenCallback() {

                            @Override

                            publicvoid onCameraOpened(@Nonnull final OneCamera camera) {

                            mCamera= camera;

                            updatePreviewBufferDimension();

                            updatePreviewBufferSize();

                            camera.startPreview(newSurface(getPreviewSurfaceTexture()),

                                     newCaptureReadyCallback() {

                                               @Override

                                               publicvoid onReadyForCapture() {

//开启预览，要先创建拍照session，如果session成功创建，会回调到这里，说明预览已经准备好了，可以准备拍照了，

                                                        mMainThread.execute(newRunnable() {

         public void run() {

                   onPreviewStarted();

                   onReadyStateChanged(true);

}

}

}

                }); à

                            }

                   },,);

}

OneCameraImpl.java

public void startPreview(SurfacepreviewSurface, CaptureReadyCallback listener) {

         setupAsync(mPreviewSurface,listener);

}

开启异步拍照session

private void setupAsync(final SurfacepreviewSurface, final CaptureReadyCallback listener) {

       mCameraHandler.post(new Runnable() {

           @Override

           public void run() {

               setup(previewSurface,listener);

           }

       });

}

private void setup(Surface previewSurface,final CaptureReadyCallback listener) {

mDevice.createCaptureSession(outputSurfaces,new CameraCaptureSession.StateCallback() {

         public void onConfigured(CameraCaptureSessionsession) {

                   mCaptureSession = session;

         boolean success =repeatingPreview(null);

         if (success) {

                   listener.onReadyForCapture();

         }

}

}

Session的创建是调用到CameraDeviceImpl.java中的createCaptureSession，进而调用configureStreamsChecked配置流，所谓session创建是否成功，就是是否成功配置了输入输出，如果成功了设备会block进入idle，并且回调StateCallbackKK. onIdle()；配置可能会失败，比如格式大小不支持，这时回调StateCallbackKK. onUnconfigured()。不管这个配置成功与否，都会new一个CameraCaptureSessionImpl实例，如果配置是成功的，就会回调上面CameraCaptureSession.StateCallback()中的onConfigured，同时把CameraCaptureSessionImpl实例作为onConfigured的参数传到OneCameraImpl.java中，就是mCaptureSession= session，也就是只有配置成功了，才会接着发出预览的request即repeatingPreview。

OneCameraImpl.java

private boolean repeatingPreview(Objecttag) {

         CaptureRequest.Builderbuilder = mDevice.

                   createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);

         mCaptureSession.setRepeatingRequest(builder.build(),mCaptureCallback,

                   mCameraHandler);

}

如果request成功build，就可以准备拍照了。

CameraCaptureSessionImpl.java

public synchronized intsetRepeatingRequest(CaptureRequest request, CaptureCallback callback,

         Handlerhandler) throws CameraAccessException {

//这里会把提交的request的requestID入队，因为session的创建要配置camera设备的内部管道，要分配内存缓冲区，很耗时，所以capture request提交后会先入队，等session ready就开始执行capture

         returnaddPendingSequence(mDeviceImpl.setRepeatingRequest(request,

                   createCaptureCallbackProxy(handler,callback), mDeviceHandler));

}

其中的参数createCaptureCallbackProxy(handler, callback)是指定了回调从CameraDeviceImpl.CaptureCallback到CameraCaptureSession.CaptureCallback的，比较重要的一个方法是它的onCaptureCompleted。其中callback是OneCameraImpl.java中的mCaptureCallback。

继续看Request的创建提交。

CameraDeviceImpl.java

public intsetRepeatingRequest(CaptureRequest request, CaptureCallback callback,

         Handlerhandler) throws CameraAccessException {

         returnsubmitCaptureRequest(requestList, callback, handler, /*streaming*/true);

}

private intsubmitCaptureRequest(List<CaptureRequest> requestList, CaptureCallbackcallback,

         Handlerhandler, boolean repeating) throws CameraAccessException {

         requestInfo= mRemoteDevice.submitRequestList(requestArray, repeating);

         if(callback != null) {

         mCaptureCallbackMap.put(requestInfo.getRequestId(),

                   new CaptureCallbackHolder(

                   callback, requestList,handler, repeating, mNextSessionId - 1));

}

}

通过ICameraDeviceUserWrapper的实例mRemoteDevice提交request，

ICameraDeviceUserWrapper.java

public SubmitInfosubmitRequest(CaptureRequest request, boolean streaming){

         returnmRemoteDevice.submitRequest(request, streaming);

}

这里的mRemoteDevice类型是ICameraDeviceUser，这个实例是通过cameraService的connectDevice方法返回的。

前面我们说过ICameraDeviceUser对应了CameraDeviceClient，CameraDeviceClient对应了CameraService的内部类Client。

ICameraDeviceUser.java，ICameraDeviceUser.cpp都是aidl文件自动生成的。

这样request就借助aidl的跨进程从ICameraDeviceUser.java到了CameraDeviceClient.cpp这边，进而跟cameraservice建立了联系。

继续看submitCaptureRequest对callback的处理，把callback做了一个包装放在了mCaptureCallbackMap中跟requestID做了关联，那么什么时候回调了这个callback呢？

前面在说CameraDeviceClient.cpp的初始化时提到，mFrameProcessor是一个输出帧元数据处理线程，处理预览回调相关的事情，这个线程会等待caemra设备新的帧，然后然后调用监听接口的方

法onResultAvailable，这个方法：CameraDeviceClient::onResultAvailable，又会执行回调：remoteCb->onResultReceived(result.mMetadata,result.mResultExtras);这个remoteCb是hardware::camera2::ICameraDeviceCallbacks类型的，这个callback实例是在Cameramanager.java中执行打开camera设备时创建的，然后由CameraService的connectDevice方法一路传递到CameraDeviceClient这里，所以这个回调实际的实现代码是：

CameraDeviceImpl.java中的内部类CameraDeviceCallbacks的方法：onResultReceived。

我们看CameraDeviceImpl.java的onResultReceived方法：

CameraDeviceImpl.java

public voidonResultReceived(CameraMetadataNative result,

         CaptureResultExtrasresultExtras) throws RemoteException {

//根据requestId，取得holder

         intrequestId = resultExtras.getRequestId();

         finalCaptureCallbackHolder holder =

                   CameraDeviceImpl.this.mCaptureCallbackMap.get(requestId);

         finalCaptureRequest request = holder.getRequest(resultExtras.getSubsequenceId());

//通过holder得到callback执行回调，同时传入数据resultAsCapture。

         holder.getCallback().onCaptureProgressed(CameraDeviceImpl.this,

request, resultAsCapture);

         holder.getCallback().onCaptureCompleted(CameraDeviceImpl.this,

request, resultAsCapture);

}

这样就把底层的数据传到Framework，进一步传到了应用层。

另外获取元数据，也可以通过ImageLoader。

在实例化Camera实例时，获取ImageReader对象，同时设置它的监听，当有一张新的图片可用时，回调其onImageAvailable接口，在这个onImageAvailable接口中，读取、存储元数据。

OneCameraImpl.javaprivate final ImageReader mCaptureImageReader;    ImageReader.OnImageAvailableListener mCaptureImageListener =            new ImageReader.OnImageAvailableListener() {                @Override                public void onImageAvailable(ImageReader reader) {                    // Add the image data to the latest in-flight capture.                    // If all the data for that capture is complete, store the                    // image data.                    InFlightCapture capture = null;                    synchronized (mCaptureQueue) {                        if (mCaptureQueue.getFirst().setImage(reader.acquireLatestImage())                                .isCaptureComplete()) {                            capture = mCaptureQueue.removeFirst();                        }                    }                    if (capture != null) {                        onCaptureCompleted(capture);                    }                }            };

获取ImageReader实例，设置监听。

OneCameraImpl(CameraDevice device, CameraCharacteristics characteristics, Size pictureSize) {        mCaptureImageReader = ImageReader.newInstance(pictureSize.getWidth(),                pictureSize.getHeight(),                sCaptureImageFormat, 2);        mCaptureImageReader.setOnImageAvailableListener(mCaptureImageListener, mCameraHandler);}

拍照完成时，会回调onCaptureCompleted。

private void onCaptureCompleted(InFlightCapture capture) {        // Experimental support for writing RAW. We do not have a usable JPEG        // here, so we don't use the usual capture session mechanism and instead        // just store the RAW file in its own directory.        // TODO: If we make this a real feature we should probably put the DNGs        // into the Camera directly.//可以存储元数据        if (sCaptureImageFormat == ImageFormat.RAW_SENSOR) {            if (!RAW_DIRECTORY.exists()) {                if (!RAW_DIRECTORY.mkdirs()) {                    throw new RuntimeException("Could not create RAW directory.");                }            }            File dngFile = new File(RAW_DIRECTORY, capture.session.getTitle() + ".dng");            writeDngBytesAndClose(capture.image, capture.totalCaptureResult,                    mCharacteristics, dngFile);        } else {//也可以存储jpg。            // Since this is not an HDR+ session, we will just save the            // result.            byte[] imageBytes = acquireJpegBytesAndClose(capture.image);            saveJpegPicture(imageBytes, capture.parameters, capture.session,                    capture.totalCaptureResult);        }        broadcastReadyState(true);        capture.parameters.callback.onPictureTaken(capture.session);}

调用writeDngBytesAndClose存储元数据，

 private static void writeDngBytesAndClose(Image image, TotalCaptureResult captureResult,            CameraCharacteristics characteristics, File dngFile) {        try (DngCreator dngCreator = new DngCreator(characteristics, captureResult);                FileOutputStream outputStream = new FileOutputStream(dngFile)) {            // TODO: Add DngCreator#setThumbnail and add the DNG to the normal            // filmstrip.            dngCreator.writeImage(outputStream, image);            outputStream.close();            image.close();        } catch (IOException e) {            Log.e(TAG, "Could not store DNG file", e);            return;        }        Log.i(TAG, "Successfully stored DNG file: " + dngFile.getAbsolutePath());    }