APP使用相机

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CameraX
Camera2
Camera（已废弃）

CameraX 示例应用

Sample	Description
CameraXBasic	Demonstrates how to use CameraX APIs.
CameraXAdvanced	Demonstrates how to use CameraX APIs with TFLite and others
CameraXVideo	Demonstrates how to use CameraX VideoCapture API.
Camera2Basic	Demonstrates capturing JPEG, RAW and DEPTH images, e.g. unprocessed pixel data directly from the camera sensor.
Camera2SlowMotion	Demonstrates capturing high-speed video in a constrained camera capture session.
Camera2Video	Demonstrates recording video using the Camera2 API and MediaRecorder.
Camera2Extensions	Demonstrates Camera2 extension live preview and still capture.
HdrViewfinder	Demonstrates use of RenderScript to display a live HDR feed from camera frames using Camera2 API.

0. CameraX 概览 | Android Jetpack 的一部分

CameraX 架构
配置选项
实现预览
图片分析
图片拍摄
视频拍摄
供应商扩展
转换输出
用例旋转
实验室测试设备

1. CameraX获取Context.CAMERA_SERVICE服务

CameraXBasic 的setUpCamera()方法第一次调用 ProcessCameraProvider.getInstance() 期间，初始化 CameraX 会cameraFactory.getAvailableCameraIds()枚举和查询设备上可用摄像头的特性。

其中cameraFactory在com/android/example/cameraxbasic/MainApplication.kt中调用CameraXConfig.Builder.fromConfig(Camera2Config.defaultConfig())初始化对象Camera2CameraFactory、CameraXConfig

1.1 获取Context.CAMERA_SERVICE服务

下面获取Context.CAMERA_SERVICE服务，实际获取 SystemServiceRegistry.java中注册的CameraManager.java。通过CameraManagerGlobal连接CameraService

androidx/camera/camera2/internal/Camera2CameraFactory.java
androidx/camera/camera2/internal/compat/CameraManagerCompat.java
androidx/camera/camera2/internal/compat/CameraManagerCompatApi29Impl.java
androidx/camera/camera2/internal/compat/CameraManagerCompatApi28Impl.java
androidx/camera/camera2/internal/compat/CameraManagerCompatBaseImpl.java

frameworks/base/core/java/android/app/SystemServiceRegistry.java

frameworks/base/core/java/android/hardware/camera2/CameraManager.java

public ICameraService getCameraService() {synchronized(mLock) {connectCameraServiceLocked();if (mCameraService == null && !sCameraServiceDisabled) {Log.e(TAG, "Camera service is unavailable");}return mCameraService;}
}private void connectCameraServiceLocked() {// Only reconnect if necessaryif (mCameraService != null || sCameraServiceDisabled) return;Log.i(TAG, "Connecting to camera service");IBinder cameraServiceBinder = ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME);if (cameraServiceBinder == null) {// Camera service is now down, leave mCameraService as nullreturn;}try {cameraServiceBinder.linkToDeath(this, /*flags*/ 0);} catch (RemoteException e) {// Camera service is now down, leave mCameraService as nullreturn;}ICameraService cameraService = ICameraService.Stub.asInterface(cameraServiceBinder);try {CameraMetadataNative.setupGlobalVendorTagDescriptor();} catch (ServiceSpecificException e) {handleRecoverableSetupErrors(e);}try {CameraStatus[] cameraStatuses = cameraService.addListener(this);for (CameraStatus c : cameraStatuses) {onStatusChangedLocked(c.status, c.cameraId);if (c.unavailablePhysicalCameras != null) {for (String unavailPhysicalCamera : c.unavailablePhysicalCameras) {onPhysicalCameraStatusChangedLocked(ICameraServiceListener.STATUS_NOT_PRESENT,c.cameraId, unavailPhysicalCamera);}}}mCameraService = cameraService;} catch(ServiceSpecificException e) {// Unexpected failurethrow new IllegalStateException("Failed to register a camera service listener", e);} catch (RemoteException e) {// Camera service is now down, leave mCameraService as null}try {ConcurrentCameraIdCombination[] cameraIdCombinations =cameraService.getConcurrentCameraIds();for (ConcurrentCameraIdCombination comb : cameraIdCombinations) {mConcurrentCameraIdCombinations.add(comb.getConcurrentCameraIdCombination());}} catch (ServiceSpecificException e) {// Unexpected failurethrow new IllegalStateException("Failed to get concurrent camera id combinations",e);} catch (RemoteException e) {// Camera service died in all probability}
}

1.2 枚举和查询设备上可用摄像头

CameraX 初始化时 cameraFactory.getAvailableCameraIds()枚举和查询设备上可用摄像头的特性。最终调用CameraSelectionOptimizer.getSelectedAvailableCameraIds(this, availableCamerasSelector)通过cameraFactory.getCameraManager().getCameraIdList()获取。

FWK层中CameraManager.java中CameraManagerGlobal的getCameraIdList():connectCameraServiceLocked()连接CameraService服务CAMERA_SERVICE_BINDER_NAME = "media.camera"

摄像头限制器如果传递给 CameraXConfig.Builder.setAvailableCamerasLimiter() 的 CameraSelector 过滤掉了某个摄像头，则 CameraX 在运行时会假定该摄像头不存在。CameraSelector.DEFAULT_BACK_CAMERA 后置摄像头LENS_FACING_BACK = 1；CameraSelector.DEFAULT_FRONT_CAMERA 前置摄像头LENS_FACING_FRONT = 0。

com/android/example/cameraxbasic/fragments/CameraFragment.kt
androidx/camera/core/CameraX.java
androidx/camera/core/impl/CameraRepository.java

public void init(@NonNull CameraFactory cameraFactory) throws InitializationException {synchronized (mCamerasLock) {try {Set<String> camerasList = cameraFactory.getAvailableCameraIds();for (String id : camerasList) {Logger.d(TAG, "Added camera: " + id);mCameras.put(id, cameraFactory.getCamera(id));}} catch (CameraUnavailableException e) {throw new InitializationException(e);}}
}

androidx/camera/camera2/internal/Camera2CameraFactory.java

public Camera2CameraFactory(@NonNull Context context,@NonNull CameraThreadConfig threadConfig,@Nullable CameraSelector availableCamerasSelector) throws InitializationException {mThreadConfig = threadConfig;mCameraStateRegistry = new CameraStateRegistry(DEFAULT_ALLOWED_CONCURRENT_OPEN_CAMERAS);mCameraManager = CameraManagerCompat.from(context, mThreadConfig.getSchedulerHandler());List<String> optimizedCameraIds = CameraSelectionOptimizer.getSelectedAvailableCameraIds(this, availableCamerasSelector);mAvailableCameraIds = getBackwardCompatibleCameraIds(optimizedCameraIds);
}public Set<String> getAvailableCameraIds() {// Use a LinkedHashSet to preserve orderreturn new LinkedHashSet<>(mAvailableCameraIds);
}

androidx/camera/camera2/internal/CameraSelectionOptimizer.java

static List<String> getSelectedAvailableCameraIds(@NonNull Camera2CameraFactory cameraFactory,@Nullable CameraSelector availableCamerasSelector)throws InitializationException {try {List<String> availableCameraIds = new ArrayList<>();List<String> cameraIdList =Arrays.asList(cameraFactory.getCameraManager().getCameraIdList());if (availableCamerasSelector == null) {for (String id : cameraIdList) {availableCameraIds.add(id);}return availableCameraIds;}// Skip camera ID by heuristic: 0 is back lens facing, 1 is front lens facing.String skippedCameraId;try {Integer lensFacingInteger = availableCamerasSelector.getLensFacing();skippedCameraId = decideSkippedCameraIdByHeuristic(cameraFactory.getCameraManager(), lensFacingInteger, cameraIdList);} catch (IllegalStateException e) {// Don't skip camera if there is any conflict in camera lens facing.skippedCameraId = null;}List<CameraInfo> cameraInfos = new ArrayList<>();for (String id : cameraIdList) {if (id.equals(skippedCameraId)) {continue;}Camera2CameraInfoImpl cameraInfo = cameraFactory.getCameraInfo(id);cameraInfos.add(cameraInfo);}List<CameraInfo> filteredCameraInfos =availableCamerasSelector.filter(cameraInfos);for (CameraInfo cameraInfo : filteredCameraInfos) {String cameraId = ((CameraInfoInternal) cameraInfo).getCameraId();availableCameraIds.add(cameraId);}return availableCameraIds;} catch (CameraAccessExceptionCompat e) {throw new InitializationException(CameraUnavailableExceptionHelper.createFrom(e));} catch (CameraUnavailableException e) {throw new InitializationException(e);}
}

2. 拍照按钮执行

除了setUpCamera()初始化CameraX，其中重要查看updateCameraUi()布局更新；camera_capture_button按钮cameraUiContainerBinding?.cameraCaptureButton?.setOnClickListener设置
com/android/example/cameraxbasic/fragments/CameraFragment.kt

// Listener for button used to capture photo
cameraUiContainerBinding?.cameraCaptureButton?.setOnClickListener {// Get a stable reference of the modifiable image capture use caseimageCapture?.let { imageCapture ->// Create output file to hold the imageval photoFile = createFile(outputDirectory, FILENAME, PHOTO_EXTENSION)// Setup image capture metadataval metadata = Metadata().apply {// Mirror image when using the front cameraisReversedHorizontal = lensFacing == CameraSelector.LENS_FACING_FRONT}// Create output options object which contains file + metadataval outputOptions = ImageCapture.OutputFileOptions.Builder(photoFile).setMetadata(metadata).build()// Setup image capture listener which is triggered after photo has been takenimageCapture.takePicture(outputOptions, cameraExecutor, object : ImageCapture.OnImageSavedCallback {override fun onError(exc: ImageCaptureException) {Log.e(TAG, "Photo capture failed: ${exc.message}", exc)}override fun onImageSaved(output: ImageCapture.OutputFileResults) {val savedUri = output.savedUri ?: Uri.fromFile(photoFile)Log.d(TAG, "Photo capture succeeded: $savedUri")// We can only change the foreground Drawable using API level 23+ APIif (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {// Update the gallery thumbnail with latest picture takensetGalleryThumbnail(savedUri)}// Implicit broadcasts will be ignored for devices running API level >= 24// so if you only target API level 24+ you can remove this statementif (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) {requireActivity().sendBroadcast(Intent(android.hardware.Camera.ACTION_NEW_PICTURE, savedUri))}// If the folder selected is an external media directory, this is// unnecessary but otherwise other apps will not be able to access our// images unless we scan them using [MediaScannerConnection]val mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(savedUri.toFile().extension)MediaScannerConnection.scanFile(context,arrayOf(savedUri.toFile().absolutePath),arrayOf(mimeType)) { _, uri ->Log.d(TAG, "Image capture scanned into media store: $uri")}}})// We can only change the foreground Drawable using API level 23+ APIif (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {// Display flash animation to indicate that photo was capturedfragmentCameraBinding.root.postDelayed({fragmentCameraBinding.root.foreground = ColorDrawable(Color.WHITE)fragmentCameraBinding.root.postDelayed({ fragmentCameraBinding.root.foreground = null }, ANIMATION_FAST_MILLIS)}, ANIMATION_SLOW_MILLIS)}}
}

3. 前置/后置摄像头切换

查看updateCameraUi()布局更新；camera_switch_button按钮cameraUiContainerBinding?.cameraSwitchButton?.let设置，CameraSelector.LENS_FACING_BACK、CameraSelector.LENS_FACING_FRONT 前后置属性，bindCameraUseCases()更新预览preview、捕获imageCapture和分析imageAnalyzer用例；observeCameraState(camera?.cameraInfo!!)监听Camera状态

com/android/example/cameraxbasic/fragments/CameraFragment.kt

// Setup for button used to switch cameras
cameraUiContainerBinding?.cameraSwitchButton?.let {// Disable the button until the camera is set upit.isEnabled = false// Listener for button used to switch cameras. Only called if the button is enabledit.setOnClickListener {lensFacing = if (CameraSelector.LENS_FACING_FRONT == lensFacing) {CameraSelector.LENS_FACING_BACK} else {CameraSelector.LENS_FACING_FRONT}// Re-bind use cases to update selected camerabindCameraUseCases()}
}/** Declare and bind preview, capture and analysis use cases */
private fun bindCameraUseCases() {// Get screen metrics used to setup camera for full screen resolutionval metrics = windowManager.getCurrentWindowMetrics().boundsLog.d(TAG, "Screen metrics: ${metrics.width()} x ${metrics.height()}")val screenAspectRatio = aspectRatio(metrics.width(), metrics.height())Log.d(TAG, "Preview aspect ratio: $screenAspectRatio")val rotation = fragmentCameraBinding.viewFinder.display.rotation// CameraProviderval cameraProvider = cameraProvider?: throw IllegalStateException("Camera initialization failed.")// CameraSelectorval cameraSelector = CameraSelector.Builder().requireLensFacing(lensFacing).build()// Previewpreview = Preview.Builder()// We request aspect ratio but no resolution.setTargetAspectRatio(screenAspectRatio)// Set initial target rotation.setTargetRotation(rotation).build()// ImageCaptureimageCapture = ImageCapture.Builder().setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY)// We request aspect ratio but no resolution to match preview config, but letting// CameraX optimize for whatever specific resolution best fits our use cases.setTargetAspectRatio(screenAspectRatio)// Set initial target rotation, we will have to call this again if rotation changes// during the lifecycle of this use case.setTargetRotation(rotation).build()// ImageAnalysisimageAnalyzer = ImageAnalysis.Builder()// We request aspect ratio but no resolution.setTargetAspectRatio(screenAspectRatio)// Set initial target rotation, we will have to call this again if rotation changes// during the lifecycle of this use case.setTargetRotation(rotation).build()// The analyzer can then be assigned to the instance.also {it.setAnalyzer(cameraExecutor, LuminosityAnalyzer { luma ->// Values returned from our analyzer are passed to the attached listener// We log image analysis results here - you should do something useful// instead!Log.d(TAG, "Average luminosity: $luma")})}// Must unbind the use-cases before rebinding themcameraProvider.unbindAll()try {// A variable number of use-cases can be passed here -// camera provides access to CameraControl & CameraInfocamera = cameraProvider.bindToLifecycle(this, cameraSelector, preview, imageCapture, imageAnalyzer)// Attach the viewfinder's surface provider to preview use casepreview?.setSurfaceProvider(fragmentCameraBinding.viewFinder.surfaceProvider)observeCameraState(camera?.cameraInfo!!)} catch (exc: Exception) {Log.e(TAG, "Use case binding failed", exc)}
}