Android Camera createCaptureSession
序幕
我们紧接着上一篇openCamera过程继续我们的配流过程学习，也就是createCaptureSession，别眨眼，直接gogogo，出发咯！
开端
这里继续是从app层说起，首先我们先熟悉一下前面章节，再加上本章节内容，上代码！
// 打开相机 private void openCamera() { if (mCameraId == null || mCameraManager == null) { return; } try { // 检查权限 if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) { return; } // 打开相机 mCameraManager.openCamera(mCameraId, mStateCallback, mBackgroundHandler); } catch (CameraAccessException e) { e.printStackTrace(); runOnUiThread(() -> Toast.makeText(this, \"打开相机失败\", Toast.LENGTH_SHORT).show()); } } // 相机设备状态回调 private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() { @Override public void onOpened(@NonNull CameraDevice camera) { // 相机打开成功，保存CameraDevice实例并创建预览会话 mCameraDevice = camera; createCaptureSession(); } @Override public void onDisconnected(@NonNull CameraDevice camera) { camera.close(); mCameraDevice = null; } @Override public void onError(@NonNull CameraDevice camera, int error) { camera.close(); mCameraDevice = null; runOnUiThread(() -> Toast.makeText(Camera2PreviewActivity.this, \"相机打开失败: \" + error, Toast.LENGTH_SHORT).show()); } }; // 创建捕获会话 private void createCaptureSession() { if (mCameraDevice == null || !mTextureView.isAvailable()) { return; } try { // 获取TextureView的SurfaceTexture并创建Surface SurfaceTexture surfaceTexture = mTextureView.getSurfaceTexture(); surfaceTexture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight()); Surface surface = new Surface(surfaceTexture); // 创建预览请求构建器 mPreviewRequestBuilder = mCameraDevice.createCaptureRequest( CameraDevice.TEMPLATE_PREVIEW); // 将Surface作为预览的目标 mPreviewRequestBuilder.addTarget(surface); // 准备输出表面列表（仅包含预览表面） List<Surface> outputSurfaces = new ArrayList(); outputSurfaces.add(surface); // 创建相机捕获会话 mCameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() { @Override public void onConfigured(@NonNull CameraCaptureSession session) { // 会话配置成功 mCaptureSession = session; // 启动预览 startPreviewRequest(); } @Override public void onConfigureFailed(@NonNull CameraCaptureSession session) { runOnUiThread(() -> Toast.makeText(Camera2PreviewActivity.this, \"预览配置失败\", Toast.LENGTH_SHORT).show()); } }, mBackgroundHandler); } catch (CameraAccessException e) { e.printStackTrace(); } }前面openCamera的时候带了一个很重要的参数，也就是mStateCallback，他的作用是用来监听camera open成功失败的一个回调的，当open成功的时候就可以在onOpened()回调里面实现创建捕获会话了，当然如果失败了也会在onError()回调里面实现提示打开相机失败相关提示给用户。
到这里就这篇文章的主角正式登场，开始进入createCaptureSession()流程，继续往下看，它到底做了什么，为啥说这个环节至关重要。
发展
现在我们开始mCameraDevice.createCaptureSession代码跟踪之前需要看下，mCameraDevice从何而来
可以从上面的实例代码可以知道是CameraDevice.StateCallback 的onOpened回调参数赋值的，那CameraDevice又是从哪里来的呢
那就回到上一篇文章openCamera流程里
private CameraDevice openCameraDeviceUserAsync(String cameraId, CameraDevice.StateCallback callback, Executor executor, final int uid, final int oomScoreOffset) throws CameraAccessException { try { cameraUser = cameraService.connectDevice(callbacks, cameraId, mContext.getOpPackageName(), mContext.getAttributionTag(), uid, oomScoreOffset, mContext.getApplicationInfo().targetSdkVersion); } catch (ServiceSpecificException e) { //这里会回调onError，过程不再赘述 deviceImpl.setRemoteFailure(e); } catch (RemoteException e) { //这里会回调onError，过程不再赘述 deviceImpl.setRemoteFailure(e); } //这里会回调onOpened,过程继续看，因为我们要搞清楚上面的mCameraDevice是什么 deviceImpl.setRemoteDevice(cameraUser); return device; }继续
frameworks/base/core/java/android/hardware/camera/impl/CameraDeviceImpl.java
public void setRemoteDevice(ICameraDeviceUser remoteDevice) throws CameraAccessException { //如果连接没问题的话就会执行一个线程，在这里回调 mDeviceExecutor.execute(mCallOnOpened);} private final Runnable mCallOnOpened = new Runnable() { @Override public void run() { //可以看到传入的就是CameraDeviceImpl本身 mDeviceCallback.onOpened(CameraDeviceImpl.this); } };所以mCameraDevice就是CameraDeviceImpl实例，mCameraDevice.createCaptureSession也就是调用CameraDeviceImpl.java 的createCaptureSession函数
准备工作搞完了，这里开始正式跟踪创建捕获会话过程
frameworks/base/core/java/android/hardware/camera/impl/CameraDeviceImpl.java
@Override public void createCaptureSession(List<Surface> outputs, CameraCaptureSession.StateCallback callback, Handler handler) throws CameraAccessException { List<OutputConfiguration> outConfigurations = new ArrayList(outputs.size()); for (Surface surface : outputs) { outConfigurations.add(new OutputConfiguration(surface)); } createCaptureSessionInternal(null, outConfigurations, callback, checkAndWrapHandler(handler), /*operatingMode*/ICameraDeviceUser.NORMAL_MODE, /*sessionParams*/ null); }这里不着急往下，需要先看下createCaptureSessionInternal传入的几个参数，outConfigurations，callback，其中我们文章开头app端示例代码，这里仅传入了一个surface对象进行预览，其实还可以同时传入预览，拍照两个surface对象，如下：
Arrays.asList(surface, mImageReader.getSurface())正常我们相机肯定不仅仅作为预览的，肯定默认是带了拍照功能的，除此之外还有另一种情况的，比如既有预览，也有录像功能的，一般录像还会存在快照功能的，也就是所谓拍照的功能
这种情况就是需要传入三种suface对象了，如下：
Arrays.asList(surface, mMediaRecoderSurface,mImageReader.getSurface())这种就是一个surface用来预览，一个surface用来给MediaRecorder接收数据，一个用来捕获当前会话帧 ，callback参数是后面创建连接成功之后需要在onConfigured回调里起预览
提一嘴现在常用录制流程如下：
// 1. 创建持久化输入 Surface（供编码器使用）Surface persistentSurface = MediaCodec.createPersistentInputSurface();// 2. 配置 MediaRecorder，关联该 Surface 作为输入MediaRecorder recorder = new MediaRecorder();recorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);// ... 其他配置（输出文件、编码参数等）...recorder.setInputSurface(persistentSurface);recorder.prepare();// 3. 相机配置：将同一个 Surface 作为输出目标CameraDevice cameraDevice = ...; // 已打开的相机CaptureRequest.Builder previewRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);previewRequestBuilder.addTarget(persistentSurface); // 相机帧直接输出到编码器的 Surface// 4. 创建捕获会话，启动录制cameraDevice.createCaptureSession(Collections.singletonList(persistentSurface), new CameraCaptureSession.StateCallback() { @Override public void onConfigured(@NonNull CameraCaptureSession session) { session.setRepeatingRequest(previewRequestBuilder.build(), null, backgroundHandler); recorder.start(); // 开始录制，数据直接从相机流向编码器 } // ... 其他回调 ... }, backgroundHandler);那就继续往下看
private void createCaptureSessionInternal(InputConfiguration inputConfig, List<OutputConfiguration> outputConfigurations, CameraCaptureSession.StateCallback callback, Executor executor, int operatingMode, CaptureRequest sessionParams) throws CameraAccessException { // TODO: dont block for this boolean configureSuccess = true; CameraAccessException pendingException = null; Surface input = null; try { // configure streams and then block until IDLE configureSuccess = configureStreamsChecked(inputConfig, outputConfigurations, operatingMode, sessionParams, createSessionStartTime); if (configureSuccess == true && inputConfig != null) { input = mRemoteDevice.getInputSurface(); } } catch (CameraAccessException e) { configureSuccess = false; pendingException = e; input = null; if (DEBUG) { Log.v(TAG, \"createCaptureSession - failed with exception \", e); } } }这里只关注重点configureStreamsChecked（其实其他省略的也是重点，但这边只关注流程）
public boolean configureStreamsChecked(InputConfiguration inputConfig, List<OutputConfiguration> outputs, int operatingMode, CaptureRequest sessionParams, long createSessionStartTime) throws CameraAccessException { mRemoteDevice.beginConfigure(); // Delete all streams first (to free up HW resources) for (Integer streamId : deleteList) { mRemoteDevice.deleteStream(streamId); mConfiguredOutputs.delete(streamId); } // Add all new streams for (OutputConfiguration outConfig : outputs) { if (addSet.contains(outConfig)) { int streamId = mRemoteDevice.createStream(outConfig); mConfiguredOutputs.put(streamId, outConfig); } } int offlineStreamIds[]; if (sessionParams != null) { offlineStreamIds = mRemoteDevice.endConfigure(operatingMode, sessionParams.getNativeCopy(), createSessionStartTime); } else { offlineStreamIds = mRemoteDevice.endConfigure(operatingMode, null, createSessionStartTime); } return success; }直接看mRemoteDevice.endConfigure，最关键的流程
高潮
frameworks/av/services/camera/libcameraservice/api2/CameraDeviceClient.cpp
binder::Status CameraDeviceClient::endConfigure(int operatingMode, const hardware::camera2::impl::CameraMetadataNative& sessionParams, int64_t startTimeMs, std::vector<int>* offlineStreamIds /*out*/) { //省略n行代码，只跟最关键的 status_t err = mDevice->configureStreams(sessionParams, operatingMode); return res; }以下是一些列函数调用跳转，忽略其他干扰，直接看最终函数目的地
frameworks/av/services/camera/libcameraservice/device3/Camera3Device.cpp
status_t Camera3Device::configureStreams(const CameraMetadata& sessionParams, int operatingMode) { ATRACE_CALL(); ALOGV(\"%s: E\", __FUNCTION__); Mutex::Autolock il(mInterfaceLock); Mutex::Autolock l(mLock); // In case the client doesn\'t include any session parameter, try a // speculative configuration using the values from the last cached // default request. if (sessionParams.isEmpty() && ((mLastTemplateId > 0) && (mLastTemplateId < CAMERA_TEMPLATE_COUNT)) && (!mRequestTemplateCache[mLastTemplateId].isEmpty())) { ALOGV(\"%s: Speculative session param configuration with template id: %d\", __func__, mLastTemplateId); return filterParamsAndConfigureLocked(mRequestTemplateCache[mLastTemplateId], operatingMode); } return filterParamsAndConfigureLocked(sessionParams, operatingMode);}status_t Camera3Device::filterParamsAndConfigureLocked(const CameraMetadata& sessionParams, int operatingMode) { return configureStreamsLocked(operatingMode, filteredParams);}status_t Camera3Device::configureStreamsLocked(int operatingMode, const CameraMetadata& sessionParams, bool notifyRequestThread) { res = mInterface->configureStreams(sessionBuffer, &config, bufferSizes); return OK; }看到这里就知道了，又是跟之前一样，又该通过HIDL直接跳转了,那就跳吧，我也累了，等不及了
hardware/interfaces/camera/device/3.2/default/CameraDeviceSession.cpp
Return<void> CameraDeviceSession::configureStreams( const StreamConfiguration& requestedConfiguration, ICameraDeviceSession::configureStreams_cb _hidl_cb) { // 这里的mDevice是camera_device_t* 类型,可以直接去HAL的so库里找实现不用折腾 status_t ret = mDevice->ops->configure_streams(mDevice, &stream_list);}看了上一篇就知道在这里找了，立马就找到了
hardware/qcom/camera/msm8998/QCamera2/HAL3/QCamera3HWI.cpp
int QCamera3HardwareInterface::configure_streams( const struct camera3_device *device, camera3_stream_configuration_t *stream_list){ LOGD(\"E\"); QCamera3HardwareInterface *hw = reinterpret_cast<QCamera3HardwareInterface *>(device->priv); if (!hw) { LOGE(\"NULL camera device\"); return -ENODEV; } int rc = hw->configureStreams(stream_list); LOGD(\"X\"); return rc;}然后咔咔一顿掏
status_t OutputBufferDispatcher::configureStreams(camera3_stream_configuration_t *streamList){ std::lock_guard<std::mutex> lock(mLock); mStreamBuffers.clear(); if (!streamList) { ALOGE(\"%s: streamList is nullptr.\", __FUNCTION__); return -EINVAL; } // Create a \"frame-number -> buffer\" map for each stream. for (uint32_t i = 0; i < streamList->num_streams; i++) { mStreamBuffers.emplace(streamList->streams[i], std::map<uint32_t, Buffer>()); } return OK;}不对，掏错了，这个才是真的，不睡觉真的眼花了，看来需要个冰廓落提提神了
看这个官方注释应该是稳了
/*=========================================================================== * FUNCTION : configureStreams * * DESCRIPTION: Reset HAL camera device processing pipeline and set up new input * and output streams. * * PARAMETERS : * @stream_list : streams to be configured * * RETURN : * *==========================================================================*/int QCamera3HardwareInterface::configureStreams( camera3_stream_configuration_t *streamList){ ATRACE_CAMSCOPE_CALL(CAMSCOPE_HAL3_CFG_STRMS); int rc = 0; // Acquire perfLock before configure streams mPerfLockMgr.acquirePerfLock(PERF_LOCK_START_PREVIEW); rc = configureStreamsPerfLocked(streamList); mPerfLockMgr.releasePerfLock(PERF_LOCK_START_PREVIEW); return rc;}这下面这个函数也是让我叹为观止，没见过这么长的，谷歌是真不怕我更加看不清了嘛，下面代码已经大量删减
/*=========================================================================== * FUNCTION : configureStreamsPerfLocked * * DESCRIPTION: configureStreams while perfLock is held. * * PARAMETERS : * @stream_list : streams to be configured * * RETURN : int32_t type of status * NO_ERROR -- success * none-zero failure code *==========================================================================*/int QCamera3HardwareInterface::configureStreamsPerfLocked( camera3_stream_configuration_t *streamList){ //这里会将所有的流停掉，为了保证流的合法性，完整性，后面申请的时候再重新start /* first invalidate all the steams in the mStreamList * if they appear again, they will be validated */ for (List<stream_info_t*>::iterator it = mStreamInfo.begin(); it != mStreamInfo.end(); it++) { QCamera3ProcessingChannel *channel = (QCamera3ProcessingChannel*)(*it)->stream->priv; if (channel) { channel->stop(); } (*it)->status = INVALID; } if (mRawDumpChannel) { mRawDumpChannel->stop(); delete mRawDumpChannel; mRawDumpChannel = NULL; } if (mHdrPlusRawSrcChannel) { mHdrPlusRawSrcChannel->stop(); delete mHdrPlusRawSrcChannel; mHdrPlusRawSrcChannel = NULL; } if (mSupportChannel) mSupportChannel->stop(); if (mAnalysisChannel) { mAnalysisChannel->stop(); } if (mMetadataChannel) { /* If content of mStreamInfo is not 0, there is metadata stream */ mMetadataChannel->stop(); } //这里检查状态，没有配置完成就继续完成配流操作 // Check state switch (mState) { case INITIALIZED: case CONFIGURED: case STARTED: /* valid state */ break; default: LOGE(\"Invalid state %d\", mState); pthread_mutex_unlock(&mMutex); return -ENODEV; } //下面又重新初始化，配流实际就是建立路由连接，等待后续请求时候获取数据 //更新状态，此时已完成配流 // Update state mState = CONFIGURED; // Create analysis stream all the time, even when h/w support is not available if (!onlyRaw) { mAnalysisChannel = new QCamera3SupportChannel( mCameraHandle->camera_handle, mChannelHandle, mCameraHandle->ops, &analysisInfo.analysis_padding_info, analysisFeatureMask, CAM_STREAM_TYPE_ANALYSIS, &analysisDim, (analysisInfo.analysis_format == CAM_FORMAT_Y_ONLY ? CAM_FORMAT_Y_ONLY : CAM_FORMAT_YUV_420_NV21), analysisInfo.hw_analysis_supported, gCamCapability[mCameraId]->color_arrangement, this, 0); // force buffer count to 0 } //创建不同通路，以及设置各种流配置 //RAW DUMP channel if (mEnableRawDump && isRawStreamRequested == false){ cam_dimension_t rawDumpSize; rawDumpSize = getMaxRawSize(mCameraId); cam_feature_mask_t rawDumpFeatureMask = CAM_QCOM_FEATURE_NONE; setPAAFSupport(rawDumpFeatureMask, CAM_STREAM_TYPE_RAW, gCamCapability[mCameraId]->color_arrangement); mRawDumpChannel = new QCamera3RawDumpChannel(mCameraHandle->camera_handle, mChannelHandle, mCameraHandle->ops, rawDumpSize, &padding_info, this, rawDumpFeatureMask); if (!mRawDumpChannel) { LOGE(\"Raw Dump channel cannot be created\"); pthread_mutex_unlock(&mMutex); return -ENOMEM; } } if (!onlyRaw && isSupportChannelNeeded(streamList, mStreamConfigInfo)) { mSupportChannel = new QCamera3SupportChannel( mCameraHandle->camera_handle, mChannelHandle, mCameraHandle->ops, &gCamCapability[mCameraId]->padding_info, callbackFeatureMask, CAM_STREAM_TYPE_CALLBACK, &QCamera3SupportChannel::kDim, CAM_FORMAT_YUV_420_NV21, supportInfo.hw_analysis_supported, gCamCapability[mCameraId]->color_arrangement, this, 0); } if ((mOpMode == CAMERA3_STREAM_CONFIGURATION_CONSTRAINED_HIGH_SPEED_MODE) && !m_bIsVideo) { mDummyBatchChannel = new QCamera3RegularChannel(mCameraHandle->camera_handle, mChannelHandle, mCameraHandle->ops, captureResultCb, setBufferErrorStatus, &gCamCapability[mCameraId]->padding_info, this, &mDummyBatchStream, CAM_STREAM_TYPE_VIDEO, dummyFeatureMask, mMetadataChannel); } if ((mOpMode == CAMERA3_STREAM_CONFIGURATION_CONSTRAINED_HIGH_SPEED_MODE) && !m_bIsVideo) { mDummyBatchChannel = new QCamera3RegularChannel(mCameraHandle->camera_handle, mChannelHandle, mCameraHandle->ops, captureResultCb, setBufferErrorStatus, &gCamCapability[mCameraId]->padding_info, this, &mDummyBatchStream, CAM_STREAM_TYPE_VIDEO, dummyFeatureMask, mMetadataChannel); }}后续这些实例Channel，在预览或者拍照时，会调用到processCaptureRequest 初始化并启动，这是后话，可以先了解一下
int QCamera3HardwareInterface::processCaptureRequest( camera3_capture_request_t *request, List<InternalRequest> &internallyRequestedStreams){ if (mRawDumpChannel) { rc = mRawDumpChannel->initialize(IS_TYPE_NONE); if (rc != NO_ERROR) { LOGE(\"Error: Raw Dump Channel init failed\"); pthread_mutex_unlock(&mMutex); goto error_exit; } } if (mHdrPlusRawSrcChannel) { rc = mHdrPlusRawSrcChannel->initialize(IS_TYPE_NONE); if (rc != NO_ERROR) { LOGE(\"Error: HDR+ RAW Source Channel init failed\"); pthread_mutex_unlock(&mMutex); goto error_exit; } } if (mSupportChannel) { rc = mSupportChannel->initialize(IS_TYPE_NONE); if (rc < 0) { LOGE(\"Support channel initialization failed\"); pthread_mutex_unlock(&mMutex); goto error_exit; } } if (mAnalysisChannel) { rc = mAnalysisChannel->initialize(IS_TYPE_NONE); if (rc < 0) { LOGE(\"Analysis channel initialization failed\"); pthread_mutex_unlock(&mMutex); goto error_exit; } } if (mDummyBatchChannel) { rc = mDummyBatchChannel->setBatchSize(mBatchSize); if (rc < 0) { LOGE(\"mDummyBatchChannel setBatchSize failed\"); pthread_mutex_unlock(&mMutex); goto error_exit; } rc = mDummyBatchChannel->initialize(IS_TYPE_NONE); if (rc < 0) { LOGE(\"mDummyBatchChannel initialization failed\"); pthread_mutex_unlock(&mMutex); goto error_exit; } } if (mState == CONFIGURED && mChannelHandle) { //Then start them. LOGH(\"Start META Channel\"); rc = mMetadataChannel->start(); if (rc < 0) { LOGE(\"META channel start failed\"); pthread_mutex_unlock(&mMutex); return rc; } if (mAnalysisChannel) { rc = mAnalysisChannel->start(); if (rc < 0) { LOGE(\"Analysis channel start failed\"); mMetadataChannel->stop(); pthread_mutex_unlock(&mMutex); return rc; } } if (mSupportChannel) { rc = mSupportChannel->start(); if (rc < 0) { LOGE(\"Support channel start failed\"); mMetadataChannel->stop(); /* Although support and analysis are mutually exclusive today adding it in anycase for future proofing */ if (mAnalysisChannel) { mAnalysisChannel->stop(); } pthread_mutex_unlock(&mMutex); return rc; } } }尾声
从最后这边可以知道配流主要干了几个事情：
1.建立从传感器到各输出目标的通路；
2.分配硬件缓冲区
3.维护会话状态，为后续的捕获请求提供基础。
配流还是得结合起预览一起看，还有谷歌原生的代码真的太有操作了，后面空了再瞄一下，品鉴一下谷歌代码的魅力~
