Android Camera-CameraX源碼分析
在前面一篇文章中，已經介紹瞭如何使用 CameraX，這篇文章就分析下 CameraX 主要流程的源碼。
本篇分析的源碼版本是1.0.0-alpha06，目前最新的 CameraX 版本是1.0.0-alpha10。java
引用
在 build.gradle 中聲明android
def camerax_version = "1.0.0-alpha06"
implementation "androidx.camera:camera-core:${camerax_version}"
implementation "androidx.camera:camera-camera2:${camerax_version}"
def camerax_view_version = "1.0.0-alpha03"
def camerax_ext_version = "1.0.0-alpha03"
//other
// If you to use the Camera View class
implementation "androidx.camera:camera-view:$camerax_view_version"
// If you to use Camera Extensions
implementation "androidx.camera:camera-extensions:$camerax_ext_version"
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- camera-core：Camera核心庫，設計架構的實現
- camera-camera2：Camera2的配置和操做封裝
- camera-view：自定義的 CameraView 組件
- camera-extensions：Camera的擴展，用於訪問設備專屬供應商效果（例如散景、HDR 及其餘功能）的 API
其中camera-core和camera-camera2是必須使用的庫，使用該庫，能夠輕鬆地使用Camera2 API的功能緩存
CameraX結構
首先看下 CameraX 的屬性：session
private static final CameraX INSTANCE = new CameraX();
final CameraRepository mCameraRepository = new CameraRepository();
private final AtomicBoolean mInitialized = new AtomicBoolean(false);
private final UseCaseGroupRepository mUseCaseGroupRepository = new UseCaseGroupRepository();
private final ErrorHandler mErrorHandler = new ErrorHandler();
private CameraFactory mCameraFactory;
private CameraDeviceSurfaceManager mSurfaceManager;
private UseCaseConfigFactory mDefaultConfigFactory;
private Context mContext;
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主要看其中幾個重要屬性：架構
- CameraRepository：Camera倉庫，保存可用 Camera 的列表
- UseCaseGroupRepository：UseCaseGroupLifecycleController實例倉庫，每一個UseCaseGroupLifecycleController都與一個LifecycleOwner相關聯，該LifecycleOwner調節組中全部用例共享的通用生命週期
- CameraFactory：Camera抽象工廠，Camera2CameraFactory是具體的實現類
- CameraDeviceSurfaceManager：Camera設備與對應數據流管理，具體實現是Camera2DeviceSurfaceManager
- UseCaseConfigFactory：UseCase配置工廠
CameraX主要使用UseCase的概念與相機設備進行交互，目前提供的UseCase：app
- 預覽(Preview)
- 圖片拍攝(ImageCapture)
- 圖片分析(ImageAnalysis)
CameraX初始化
Camera2Initializer
CameraX初始化方法：initide
public static void init(Context context, @NonNull AppConfig appConfig) {
INSTANCE.initInternal(context, appConfig);
}
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init 是經過ContentProvier配置初始化，具體實現類Camera2Initializeroop
public final class Camera2Initializer extends ContentProvider {
private static final String TAG = "Camera2Initializer";
@Override
public boolean onCreate() {
Log.d(TAG, "CameraX initializing with Camera2 ...");
CameraX.init(getContext(), Camera2AppConfig.create(getContext()));
return false;
}
...
}
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在AndroidMainifest.xml會自動生成provider配置，ContentProvider的OnCreate調用比Applicantion的 onCreate調用更早。post
<provider android:name="androidx.camera.camera2.impl.Camera2Initializer" android:exported="false" android:multiprocess="true" android:authorities="${applicationId}.camerax-init" android:initOrder="100" />
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Camera2AppConfig
init 方法傳入的 AppConfig 的 create：gradle
public static AppConfig create(Context context) {
// Create the camera factory for creating Camera2 camera objects
CameraFactory cameraFactory = new Camera2CameraFactory(context);
// Create the DeviceSurfaceManager for Camera2
CameraDeviceSurfaceManager surfaceManager = new Camera2DeviceSurfaceManager(context);
// Create default configuration factory
ExtendableUseCaseConfigFactory configFactory = new ExtendableUseCaseConfigFactory();
configFactory.installDefaultProvider(
ImageAnalysisConfig.class, new ImageAnalysisConfigProvider(cameraFactory, context));
configFactory.installDefaultProvider(
ImageCaptureConfig.class, new ImageCaptureConfigProvider(cameraFactory, context));
configFactory.installDefaultProvider(
VideoCaptureConfig.class, new VideoCaptureConfigProvider(cameraFactory, context));
configFactory.installDefaultProvider(
PreviewConfig.class, new PreviewConfigProvider(cameraFactory, context));
AppConfig.Builder appConfigBuilder =
new AppConfig.Builder()
.setCameraFactory(cameraFactory)
.setDeviceSurfaceManager(surfaceManager)
.setUseCaseConfigFactory(configFactory);
return appConfigBuilder.build();
}
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經過 AppConfig.Builder 進行構建，CameraX中的默認屬性都在這裏初始化。後面具體講到某個 UseCase 的時候，詳細分析下具體的ConfigProvider
CameraX.initInternal
CameraX真正初始化方法：initInternal
private void initInternal(Context context, AppConfig appConfig) {
if (mInitialized.getAndSet(true)) {
return;
}
mContext = context.getApplicationContext();
mCameraFactory = appConfig.getCameraFactory(null);
if (mCameraFactory == null) {
throw new IllegalStateException(
"Invalid app configuration provided. Missing CameraFactory.");
}
mSurfaceManager = appConfig.getDeviceSurfaceManager(null);
if (mSurfaceManager == null) {
throw new IllegalStateException(
"Invalid app configuration provided. Missing CameraDeviceSurfaceManager.");
}
mDefaultConfigFactory = appConfig.getUseCaseConfigRepository(null);
if (mDefaultConfigFactory == null) {
throw new IllegalStateException(
"Invalid app configuration provided. Missing UseCaseConfigFactory.");
}
mCameraRepository.init(mCameraFactory);
}
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直接從 AppConfig 中獲取到具體實例，mCameraFactory對應的實例是Camera2CameraFactory，mCameraRepository.init(mCameraFactory)進行 Camera 相關的初始化
CameraRepository.init
public void init(CameraFactory cameraFactory) {
synchronized (mCamerasLock) {
try {
Set<String> camerasList = cameraFactory.getAvailableCameraIds();
for (String id : camerasList) {
Log.d(TAG, "Added camera: " + id);
mCameras.put(id, cameraFactory.getCamera(id));
}
...
}
}
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getAvailableCameraIds獲取可用 Camera Id列表，Camera2CameraFactory的getCamera真正初始化Camera
public BaseCamera getCamera(@NonNull String cameraId) {
Camera camera = new Camera(mCameraManager, cameraId,
mAvailabilityRegistry.getAvailableCameraCount(), sHandler);
mAvailabilityRegistry.registerCamera(camera);
return camera;
}
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經過CameraAvailabilityRegistry的registerCamera方法進行Camera註冊
到此爲止，CameraX 相關屬性就初始化完成了
bindToLifecycle
從第一個UseCase預覽(preview)來說解CameraX 生命週期過程，以及數據傳輸流程。
前面一篇文章已經講解過 CameraX 的使用，其中預覽(preivew)，會先聲明PreviewConfig,經過 config 生成Preivew，preview.setOnPreviewOutputUpdateListener設置監聽Camera數據流。這一系列流程可以實現，主要經過CameraX.bindToLifecycle實現
具體流程：
public static void bindToLifecycle(LifecycleOwner lifecycleOwner, UseCase... useCases) {
Threads.checkMainThread();
UseCaseGroupLifecycleController useCaseGroupLifecycleController =
INSTANCE.getOrCreateUseCaseGroup(lifecycleOwner);
UseCaseGroup useCaseGroupToBind = useCaseGroupLifecycleController.getUseCaseGroup();
Collection<UseCaseGroupLifecycleController> controllers =
INSTANCE.mUseCaseGroupRepository.getUseCaseGroups();
//檢查UseCase 只能在一個lifecycle上
for (UseCase useCase : useCases) {
for (UseCaseGroupLifecycleController controller : controllers) {
UseCaseGroup useCaseGroup = controller.getUseCaseGroup();
if (useCaseGroup.contains(useCase) && useCaseGroup != useCaseGroupToBind) {
throw new IllegalStateException(
String.format(
"Use case %s already bound to a different lifecycle.",
useCase));
}
}
}
//onBind監聽回調
for (UseCase useCase : useCases) {
useCase.onBind();
}
calculateSuggestedResolutions(lifecycleOwner, useCases);
for (UseCase useCase : useCases) {
useCaseGroupToBind.addUseCase(useCase);
for (String cameraId : useCase.getAttachedCameraIds()) {
attach(cameraId, useCase);
}
}
useCaseGroupLifecycleController.notifyState();
}
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UseCaseGroupLifecycleController
建立 UseCaseGroupLifecycleController，UseCaseGroup控制器，經過Lifecycle組件進行 start 和 stop 操做
UseCaseGroupLifecycleController useCaseGroupLifecycleController =
INSTANCE.getOrCreateUseCaseGroup(lifecycleOwner);
...
private UseCaseGroupLifecycleController getOrCreateUseCaseGroup(LifecycleOwner lifecycleOwner) {
return mUseCaseGroupRepository.getOrCreateUseCaseGroup(
lifecycleOwner, new UseCaseGroupRepository.UseCaseGroupSetup() {
@Override
public void setup(UseCaseGroup useCaseGroup) {
useCaseGroup.setListener(mCameraRepository);
}
});
}
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經過UseCaseGroupRepository建立UseCaseGroupLifecycleController
UseCaseGroupLifecycleController getOrCreateUseCaseGroup( LifecycleOwner lifecycleOwner, UseCaseGroupSetup groupSetup) {
UseCaseGroupLifecycleController useCaseGroupLifecycleController;
synchronized (mUseCasesLock) {
//若是有緩存，則直接返回，不然進行建立
useCaseGroupLifecycleController = mLifecycleToUseCaseGroupControllerMap.get(
lifecycleOwner);
if (useCaseGroupLifecycleController == null) {
useCaseGroupLifecycleController = createUseCaseGroup(lifecycleOwner);
groupSetup.setup(useCaseGroupLifecycleController.getUseCaseGroup());
}
}
return useCaseGroupLifecycleController;
}
...
private UseCaseGroupLifecycleController createUseCaseGroup(LifecycleOwner lifecycleOwner) {
...
// Need to add observer before creating UseCaseGroupLifecycleController to make sure
// UseCaseGroups can be stopped before the latest active one is started.
lifecycleOwner.getLifecycle().addObserver(createLifecycleObserver());
UseCaseGroupLifecycleController useCaseGroupLifecycleController =
new UseCaseGroupLifecycleController(lifecycleOwner.getLifecycle());
//建立後，放入 map 緩存
synchronized (mUseCasesLock) {
mLifecycleToUseCaseGroupControllerMap.put(lifecycleOwner,
useCaseGroupLifecycleController);
}
return useCaseGroupLifecycleController;
}
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建立UseCaseGroupLifecycleController，並增長Lifecycle生命週期控制：
UseCaseGroupLifecycleController(Lifecycle lifecycle) {
this(lifecycle, new UseCaseGroup());
}
/** Wraps an existing {@link UseCaseGroup} so it is controlled by lifecycle transitions. */
UseCaseGroupLifecycleController(Lifecycle lifecycle, UseCaseGroup useCaseGroup) {
this.mUseCaseGroup = useCaseGroup;
this.mLifecycle = lifecycle;
//綁定Lifecycle
lifecycle.addObserver(this);
}
@OnLifecycleEvent(Lifecycle.Event.ON_START)
public void onStart(LifecycleOwner lifecycleOwner) {
synchronized (mUseCaseGroupLock) {
mUseCaseGroup.start();
}
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
public void onStop(LifecycleOwner lifecycleOwner) {
synchronized (mUseCaseGroupLock) {
mUseCaseGroup.stop();
}
}
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
public void onDestroy(LifecycleOwner lifecycleOwner) {
synchronized (mUseCaseGroupLock) {
mUseCaseGroup.clear();
}
}
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上面的代碼，增長了ON_START，ON_STOP，ON_DESTROY的生命週期監聽
calculateSuggestedResolutions
根據傳入的配置，生成各個UseCase的最佳解決方案。後面的代碼會以Preview這個 UseCase 展開，其餘 UseCase 代碼邏輯相似。
private static void calculateSuggestedResolutions(LifecycleOwner lifecycleOwner, UseCase... useCases) {
// There will only one lifecycleOwner active. Therefore, only collect use cases belong to
// same lifecycleOwner and calculate the suggested resolutions.
...
// Collect new use cases for different camera devices
for (UseCase useCase : useCases) {
String cameraId = null;
try {
cameraId = getCameraWithCameraDeviceConfig(
(CameraDeviceConfig) useCase.getUseCaseConfig());
} catch (CameraInfoUnavailableException e) {
throw new IllegalArgumentException(
"Unable to get camera id for the camera device config.", e);
}
}
...
// Get suggested resolutions and update the use case session configuration
for (String cameraId : newCameraIdUseCaseMap.keySet()) {
Map<UseCase, Size> suggestResolutionsMap =
getSurfaceManager()
.getSuggestedResolutions(
cameraId,
originalCameraIdUseCaseMap.get(cameraId),
newCameraIdUseCaseMap.get(cameraId));
for (UseCase useCase : newCameraIdUseCaseMap.get(cameraId)) {
Size resolution = suggestResolutionsMap.get(useCase);
Map<String, Size> suggestedCameraSurfaceResolutionMap = new HashMap<>();
suggestedCameraSurfaceResolutionMap.put(cameraId, resolution);
//更新配置
useCase.updateSuggestedResolution(suggestedCameraSurfaceResolutionMap);
}
}
}
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每一個 UseCase 會去更新對應配置 updateSuggestedResolution->onSuggestedResolutionUpdated
public void updateSuggestedResolution(Map<String, Size> suggestedResolutionMap) {
Map<String, Size> resolutionMap = onSuggestedResolutionUpdated(suggestedResolutionMap);
...
}
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onSuggestedResolutionUpdated針對不一樣的 UseCase 有不一樣的實現，這裏以Preview爲例
protected Map<String, Size> onSuggestedResolutionUpdated( Map<String, Size> suggestedResolutionMap) {
//獲取前面配置的 config
PreviewConfig config = (PreviewConfig) getUseCaseConfig();
String cameraId = getCameraIdUnchecked(config);
Size resolution = suggestedResolutionMap.get(cameraId);
...
//設置 config
updateConfigAndOutput(config, resolution);
return suggestedResolutionMap;
}
...
private void updateConfigAndOutput(PreviewConfig config, Size resolution) {
String cameraId = getCameraIdUnchecked(config);
//初始化pipeline
mSessionConfigBuilder = createPipeline(config, resolution);
attachToCamera(cameraId, mSessionConfigBuilder.build());
updateOutput(mSurfaceTextureHolder.getSurfaceTexture(), resolution);
}
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Preview.createPipeline
建立Preview管道，經過 PreviewConfig 的配置，建立對應的顯示Surface和SessionConfig
SessionConfig.Builder createPipeline(PreviewConfig config, Size resolution) {
Threads.checkMainThread();
SessionConfig.Builder sessionConfigBuilder = SessionConfig.Builder.createFrom(config);
final CaptureProcessor captureProcessor = config.getCaptureProcessor(null);
//擴展的 extensions實現
if (captureProcessor != null) {
CaptureStage captureStage = new CaptureStage.DefaultCaptureStage();
// TODO: To allow user to use an Executor for the processing.
...
} else {
final ImageInfoProcessor processor = config.getImageInfoProcessor(null);
if (processor != null) {
sessionConfigBuilder.addCameraCaptureCallback(new CameraCaptureCallback() {
@Override
public void onCaptureCompleted( @NonNull CameraCaptureResult cameraCaptureResult) {
super.onCaptureCompleted(cameraCaptureResult);
if (processor.process(
new CameraCaptureResultImageInfo(cameraCaptureResult))) {
notifyUpdated();
}
}
});
}
//默認的 Surface
CheckedSurfaceTexture checkedSurfaceTexture = new CheckedSurfaceTexture(resolution);
mSurfaceTextureHolder = checkedSurfaceTexture;
sessionConfigBuilder.addSurface(checkedSurfaceTexture);
}
...
}
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這裏就能夠看到咱們熟悉的味道，在Camera2中 用到的Surface，Session相關配置，後面會用到相關配置。
在CheckedSurfaceTexture中會建立FixedSizeSurfaceTexture用來顯示圖像。
Preview.updateOutput
增長數據的監聽
void updateOutput(SurfaceTexture surfaceTexture, Size resolution) {
PreviewConfig useCaseConfig = (PreviewConfig) getUseCaseConfig();
...
PreviewOutput newOutput =
PreviewOutput.create(surfaceTexture, resolution, relativeRotation);
// Only update the output if something has changed
if (!Objects.equals(mLatestPreviewOutput, newOutput)) {
SurfaceTexture oldTexture =
(mLatestPreviewOutput == null)
? null
: mLatestPreviewOutput.getSurfaceTexture();
OnPreviewOutputUpdateListener outputListener = getOnPreviewOutputUpdateListener();
...
if (outputListener != null) {
mSurfaceDispatched = true;
updateListener(outputListener, newOutput);
}
}
}
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根據Preview設置的setOnPreviewOutputUpdateListener，獲取到對應的Listener，經過updateListener方法回調數據。
private void updateListener(OnPreviewOutputUpdateListener listener, PreviewOutput output) {
...
mOutputUpdateExecutor.execute(() -> listener.onUpdated(output));
...
}
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notifyState
調用UseCaseGroupLifecycleController的notifyState，激活 UseCase 狀態，在UseCaseGroupLifecycleController中有增長生命週期的監聽，在ON_START狀態會調用mUseCaseGroup.start方法。
void notifyState() {
synchronized (mUseCaseGroupLock) {
if (mLifecycle.getCurrentState().isAtLeast(State.STARTED)) {
mUseCaseGroup.start();
}
for (UseCase useCase : mUseCaseGroup.getUseCases()) {
useCase.notifyState();
}
}
}
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UseCaseGroup.start
void start() {
synchronized (mListenerLock) {
if (mListener != null) {
mListener.onGroupActive(this);
}
mIsActive = true;
}
}
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啓動 start 狀態，調用CameraRepository的onGroupActive方法：
public void onGroupActive(UseCaseGroup useCaseGroup) {
synchronized (mCamerasLock) {
Map<String, Set<UseCase>> cameraIdToUseCaseMap = useCaseGroup.getCameraIdToUseCaseMap();
for (Map.Entry<String, Set<UseCase>> cameraUseCaseEntry :
cameraIdToUseCaseMap.entrySet()) {
BaseCamera camera = getCamera(cameraUseCaseEntry.getKey());
attachUseCasesToCamera(camera, cameraUseCaseEntry.getValue());
}
}
}
...
private void attachUseCasesToCamera(BaseCamera camera, Set<UseCase> useCases) {
camera.addOnlineUseCase(useCases);
}
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camera.addOnlineUseCase關聯UseCase 和 Camera。
Camera.addOnlineUseCase
public void addOnlineUseCase(@NonNull final Collection<UseCase> useCases) {
if (useCases.isEmpty()) {
return;
}
// Attaches the surfaces of use case to the Camera (prevent from surface abandon crash)
// addOnlineUseCase could be called with duplicate use case, so we need to filter out
// use cases that are either pending for addOnline or are already online.
// It's ok for two thread to run here, since it‘ll do nothing if use case is already
// pending.
synchronized (mPendingLock) {
for (UseCase useCase : useCases) {
boolean isOnline = isUseCaseOnline(useCase);
if (mPendingForAddOnline.contains(useCase) || isOnline) {
continue;
}
notifyAttachToUseCaseSurfaces(useCase);
mPendingForAddOnline.add(useCase);
}
}
...
updateCaptureSessionConfig();
resetCaptureSession(/*abortInFlightCaptures=*/false);
if (mState == InternalState.OPENED) {
openCaptureSession();
} else {
open();
}
updateCameraControlPreviewAspectRatio(useCases);
}
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在addOnlineUseCase方法中，open會去打開Camera設備。
Camera.open
public void open() {
...
switch (mState) {
case INITIALIZED:
openCameraDevice();
break;
case CLOSING:
setState(InternalState.REOPENING);
// If session close has not yet completed, then the camera is still open. We
// can move directly back into an OPENED state.
// If session close is already complete, then the camera is closing. We'll reopen
// the camera in the camera state callback.
// If the camera device is currently in an error state, we need to close the
// camera before reopening, so we cannot directly reopen.
if (!isSessionCloseComplete() && mCameraDeviceError == ERROR_NONE) {
Preconditions.checkState(mCameraDevice != null,
"Camera Device should be open if session close is not complete");
setState(InternalState.OPENED);
openCaptureSession();
}
break;
default:
Log.d(TAG, "open() ignored due to being in state: " + mState);
}
}
...
void openCameraDevice() {
// Check that we have an available camera to open here before attempting
// to open the camera again.
if (!mCameraAvailability.isCameraAvailable()) {
Log.d(TAG, "No cameras available. Waiting for available camera before opening camera: "
+ mCameraId);
setState(InternalState.PENDING_OPEN);
return;
} else {
setState(InternalState.OPENING);
}
...
//真正打開相機
mCameraManager.openCamera(mCameraId, mExecutor, createDeviceStateCallback());
...
}
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接下來就是Camera2的預覽流程
Camera
CameraX封裝了Camera2的標準預覽流程，這些類都是在 CameraX 庫中
CameraDevice.StateCallback
openCameraDevice的stateCallback
final class StateCallback extends CameraDevice.StateCallback {
@Override
public void onOpened(CameraDevice cameraDevice) {
Log.d(TAG, "CameraDevice.onOpened(): " + cameraDevice.getId());
mCameraDevice = cameraDevice;
mCameraDeviceError = ERROR_NONE;
switch (mState) {
case CLOSING:
case RELEASING:
// No session should have yet been opened, so close camera directly here.
Preconditions.checkState(isSessionCloseComplete());
mCameraDevice.close();
mCameraDevice = null;
break;
case OPENING:
case REOPENING:
setState(InternalState.OPENED);
openCaptureSession();
break;
default:
throw new IllegalStateException(
"onOpened() should not be possible from state: " + mState);
}
}
...
}
...
void openCaptureSession() {
...
mCaptureSession.open(validatingBuilder.build(), mCameraDevice);
...
}
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CaptureSession.open
建立CaptureSession
void open(SessionConfig sessionConfig, CameraDevice cameraDevice) throws CameraAccessException, DeferrableSurface.SurfaceClosedException {
synchronized (mStateLock) {
switch (mState) {
case UNINITIALIZED:
throw new IllegalStateException(
"open() should not be possible in state: " + mState);
case INITIALIZED:
//Camera中傳入的essionConfig，默認有TEMPLATE_PREVIEW的 surface 實現
List<DeferrableSurface> surfaces = sessionConfig.getSurfaces();
...
//狀態更新
notifySurfaceAttached();
mState = State.OPENING;
...
SessionConfigurationCompat sessionConfigCompat =
new SessionConfigurationCompat(
SessionConfigurationCompat.SESSION_REGULAR,
outputConfigList,
getExecutor(),
comboCallback);
CaptureRequest captureRequest =
Camera2CaptureRequestBuilder.buildWithoutTarget(
captureConfigBuilder.build(),
cameraDevice);
if (captureRequest != null) {
sessionConfigCompat.setSessionParameters(captureRequest);
}
//建立CaptureSession，CameraDeviceCompat根據 Android 版本有不一樣的實現
CameraDeviceCompat.createCaptureSession(cameraDevice, sessionConfigCompat);
...
}
}
}
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在Camera2的使用中，CameraDevice的createCaptureSession能夠建立預覽畫面，CameraX的CaptureSession很好的封裝了這些實現。
在CaptureSession.open傳入的SessionConfig，是在Camera2AppConfig.create建立的時候生成
public static AppConfig create(Context context) {
// Create the camera factory for creating Camera2 camera objects
CameraFactory cameraFactory = new Camera2CameraFactory(context);
// PreviewConfig 配置
configFactory.installDefaultProvider(
PreviewConfig.class, new PreviewConfigProvider(cameraFactory, context));
AppConfig.Builder appConfigBuilder =
new AppConfig.Builder()
.setCameraFactory(cameraFactory)
.setDeviceSurfaceManager(surfaceManager)
.setUseCaseConfigFactory(configFactory);
return appConfigBuilder.build();
}
//PreviewConfigProvider配置getConfig
@Override
public PreviewConfig getConfig(LensFacing lensFacing) {
PreviewConfig.Builder builder =
PreviewConfig.Builder.fromConfig(Preview.DEFAULT_CONFIG.getConfig(lensFacing));
// SessionConfig containing all intrinsic properties needed for Preview
SessionConfig.Builder sessionBuilder = new SessionConfig.Builder();
// createCaptureSession中的 preview 設置
sessionBuilder.setTemplateType(CameraDevice.TEMPLATE_PREVIEW);
// Add options to UseCaseConfig
builder.setDefaultSessionConfig(sessionBuilder.build());
builder.setSessionOptionUnpacker(Camera2SessionOptionUnpacker.INSTANCE);
CaptureConfig.Builder captureBuilder = new CaptureConfig.Builder();
captureBuilder.setTemplateType(CameraDevice.TEMPLATE_PREVIEW);
builder.setDefaultCaptureConfig(captureBuilder.build());
builder.setCaptureOptionUnpacker(Camera2CaptureOptionUnpacker.INSTANCE);
...
}
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CameraDeviceCompat.createCaptureSession的CameraCaptureSession回調
final class StateCallback extends CameraCaptureSession.StateCallback {
@Override
public void onConfigured(@NonNull CameraCaptureSession session) {
synchronized (mStateLock) {
switch (mState) {
case UNINITIALIZED:
case INITIALIZED:
case OPENED:
case RELEASED:
throw new IllegalStateException(
"onConfigured() should not be possible in state: " + mState);
case OPENING:
...
// Issue capture request of enableSession if exists.
if (mSessionConfig != null) {
Config implOptions = mSessionConfig.getImplementationOptions();
CameraEventCallbacks eventCallbacks = new Camera2Config(
implOptions).getCameraEventCallback(
CameraEventCallbacks.createEmptyCallback());
//可配置CameraEventCallback的EnableSession回調
List<CaptureConfig> list =
eventCallbacks.createComboCallback().onEnableSession();
if (!list.isEmpty()) {
issueCaptureRequests(setupConfiguredSurface(list));
}
}
//
issueRepeatingCaptureRequests();
issueBurstCaptureRequest();
break;
...
}
}
}
}
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CaptureSession.issueRepeatingCaptureRequests
開啓Camera預覽
void issueRepeatingCaptureRequests() {
...
CaptureConfig captureConfig = mSessionConfig.getRepeatingCaptureConfig();
...
// The override priority for implementation options
// P1 CameraEventCallback onRepeating options
// P2 SessionConfig options
CaptureConfig.Builder captureConfigBuilder = CaptureConfig.Builder.from(captureConfig);
//建立CaptureRequest
CaptureRequest captureRequest = Camera2CaptureRequestBuilder.build(
captureConfigBuilder.build(), mCameraCaptureSession.getDevice(),
mConfiguredSurfaceMap);
if (captureRequest == null) {
Log.d(TAG, "Skipping issuing empty request for session.");
return;
}
//設置Capture回調
CameraCaptureSession.CaptureCallback comboCaptureCallback =
createCamera2CaptureCallback(
captureConfig.getCameraCaptureCallbacks(),
mCaptureCallback);
CameraCaptureSessionCompat.setSingleRepeatingRequest(mCameraCaptureSession,
captureRequest, mExecutor, comboCaptureCallback);
}
複製代碼
CameraCaptureSessionCompat.setSingleRepeatingRequest 也是區分 Android 版本
private static CameraCaptureSessionCompatImpl chooseImplementation() {
if (Build.VERSION.SDK_INT >= 28) {
return new CameraCaptureSessionCompatApi28Impl();
}
return new CameraCaptureSessionCompatBaseImpl();
}
//CameraCaptureSessionCompatBaseImpl，和平時使用的同樣
public int setSingleRepeatingRequest(@NonNull CameraCaptureSession captureSession, @NonNull CaptureRequest request, @NonNull Executor executor, @NonNull CameraCaptureSession.CaptureCallback listener) throws CameraAccessException {
Preconditions.checkNotNull(captureSession);
// Wrap the executor in the callback
CameraCaptureSession.CaptureCallback cb =
new CameraCaptureSessionCompat.CaptureCallbackExecutorWrapper(executor, listener);
return captureSession.setRepeatingRequest(
request, cb, MainThreadAsyncHandler.getInstance());
}
//CameraCaptureSessionCompatApi28Impl，新版本 API 有些變化
public int setSingleRepeatingRequest(@NonNull CameraCaptureSession captureSession, @NonNull CaptureRequest request, @NonNull Executor executor, @NonNull CameraCaptureSession.CaptureCallback listener) throws CameraAccessException {
Preconditions.checkNotNull(captureSession);
// Call through directly to executor API
return captureSession.setSingleRepeatingRequest(request, executor, listener);
}
複製代碼
從Camera的開啓到預覽，以及讀取各類配置，整個過程到此就完成了，接下來介紹如何拍照，這個流程相對來講比較簡單
ImageCapture.takePicture
拍照的流程：
sendImageCaptureRequest
建立 ImageCaptureRequest，設置cameraId、targetRatio、回調等
private void sendImageCaptureRequest( @Nullable Executor listenerExecutor, OnImageCapturedListener listener) {
String cameraId = getCameraIdUnchecked(mConfig);
// Get the relative rotation or default to 0 if the camera info is unavailable
int relativeRotation = 0;
try {
CameraInfoInternal cameraInfoInternal = CameraX.getCameraInfo(cameraId);
relativeRotation =
cameraInfoInternal.getSensorRotationDegrees(
mConfig.getTargetRotation(Surface.ROTATION_0));
} catch (CameraInfoUnavailableException e) {
Log.e(TAG, "Unable to retrieve camera sensor orientation.", e);
}
Rational targetRatio = mConfig.getTargetAspectRatioCustom(null);
targetRatio = ImageUtil.rotate(targetRatio, relativeRotation);
mImageCaptureRequests.offer(
new ImageCaptureRequest(relativeRotation, targetRatio, listenerExecutor, listener));
if (mImageCaptureRequests.size() == 1) {
issueImageCaptureRequests();
}
}
複製代碼
takePictureInternal
void issueImageCaptureRequests() {
if (mImageCaptureRequests.isEmpty()) {
return;
}
takePictureInternal();
}
...
//拍照流程
private void takePictureInternal() {
//自定義 Future 調用鏈
FutureChain.from(preTakePicture(state))
.transformAsync{
...
return ImageCapture.this.issueTakePicture(state);
})
.transformAsync{
...
return ImageCapture.this.postTakePicture(state);
})
.addCallback(
...
onTakePictureFinish(null);
)
}
複製代碼
自定義了整個拍照工做流，經過issueTakePicture進行拍照，postTakePicture是拍照成功，釋放資源，取消3A。下面重點看下issueTakePicture流程
issueTakePicture
ListenableFuture<Void> issueTakePicture(TakePictureState state) {
...
getCurrentCameraControl().submitCaptureRequests(captureConfigs);
...
}
複製代碼
經過CameraControl提交Capture 請求，CameraControl具體實現是Camera2CameraControl。
submitCaptureRequests
public void submitCaptureRequests(@NonNull final List<CaptureConfig> captureConfigs) {
mExecutor.execute(new Runnable() {
@Override
public void run() {
submitCaptureRequestsInternal(captureConfigs);
}
});
}
...
void submitCaptureRequestsInternal(final List<CaptureConfig> captureConfigs) {
mControlUpdateListener.onCameraControlCaptureRequests(captureConfigs);
//mControlUpdateListener是Camera 的回調，onCameraControlCaptureRequests 真正實如今 Camera 中
}
//Camera.java
public void onCameraControlUpdateSessionConfig(@NonNull SessionConfig sessionConfig) {
mCameraControlSessionConfig = sessionConfig;
updateCaptureSessionConfig();
}
...
private void updateCaptureSessionConfig() {
...
SessionConfig sessionConfig = validatingBuilder.build();
mCaptureSession.setSessionConfig(sessionConfig);
...
}
}
Camera 獲取 Capture的SessionConfig，經過`CaptureSession`進行狀態控制
複製代碼
CaptureSession.setSessionConfig
void setSessionConfig(SessionConfig sessionConfig) {
synchronized (mStateLock) {
switch (mState) {
case UNINITIALIZED:
throw new IllegalStateException(
"setSessionConfig() should not be possible in state: " + mState);
case INITIALIZED:
case OPENING:
mSessionConfig = sessionConfig;
break;
case OPENED:
mSessionConfig = sessionConfig;
if (!mConfiguredSurfaceMap.keySet().containsAll(sessionConfig.getSurfaces())) {
Log.e(TAG, "Does not have the proper configured lists");
return;
}
Log.d(TAG, "Attempting to submit CaptureRequest after setting");
issueRepeatingCaptureRequests();
break;
case CLOSED:
case RELEASING:
case RELEASED:
throw new IllegalStateException(
"Session configuration cannot be set on a closed/released session.");
}
}
}
複製代碼
在Camera的OPENED狀態，則進行拍照流程
issueRepeatingCaptureRequests
void issueRepeatingCaptureRequests() {
...
CameraCaptureSession.CaptureCallback comboCaptureCallback =
createCamera2CaptureCallback(
captureConfig.getCameraCaptureCallbacks(),
mCaptureCallback);
CameraCaptureSessionCompat.setSingleRepeatingRequest(mCameraCaptureSession,
captureRequest, mExecutor, comboCaptureCallback);
...
}
複製代碼
CameraCaptureSessionCompat根據 Android 版本有CameraCaptureSessionCompatBaseImpl和CameraCaptureSessionCompatApi28Impl兩種實現，最終經過CameraCaptureSession實現真正的拍照。
拍照完成後，經過最開始設置的 Listener 進行回調
ImageCapture.createPipeline
在 Preview 那小節，講解過 bindToLifecycle 流程，這裏的ImageCapture也是一個UseCase。在CameraX中的calculateSuggestedResolutions方法，最終會調用到各個UseCase的onSuggestedResolutionUpdated方法。在ImageCapture的onSuggestedResolutionUpdated方法，經過createPipeline建立了拍照數據的回調
SessionConfig.Builder createPipeline(ImageCaptureConfig config, Size resolution) {
...
//和 Camera2的流程一致
mProcessingImageResultThread = new HandlerThread("OnImageAvailableHandlerThread");
mProcessingImageResultThread.start();
mProcessingImageResultHandler = new Handler(mProcessingImageResultThread.getLooper());
...
mImageReader.setOnImageAvailableListener(
new ImageReaderProxy.OnImageAvailableListener() {
@Override
public void onImageAvailable(ImageReaderProxy imageReader) {
ImageProxy image = null;
try {
image = imageReader.acquireLatestImage();
} catch (IllegalStateException e) {
Log.e(TAG, "Failed to acquire latest image.", e);
} finally {
if (image != null) {
// Call the head request listener to process the captured image.
ImageCaptureRequest imageCaptureRequest;
if ((imageCaptureRequest = mImageCaptureRequests.peek()) != null) {
SingleCloseImageProxy wrappedImage = new SingleCloseImageProxy(
image);
wrappedImage.addOnImageCloseListener(mOnImageCloseListener);
//ImageCaptureRequest設置 Listener
imageCaptureRequest.dispatchImage(wrappedImage);
} else {
// Discard the image if we have no requests.
image.close();
}
}
}
}
},
mProcessingImageResultHandler);
...
}
複製代碼
ImageReader設置了 Camera 數據會調用，並經過ImageCaptureRequest的dispatchImage方法進行分發
ImageCaptureRequest.dispatchImage
void dispatchImage(final ImageProxy image) {
try {
mListenerExecutor.execute(new Runnable() {
@Override
public void run() {
Size sourceSize = new Size(image.getWidth(), image.getHeight());
if (ImageUtil.isAspectRatioValid(sourceSize, mTargetRatio)) {
image.setCropRect(
ImageUtil.computeCropRectFromAspectRatio(sourceSize,
mTargetRatio));
}
//真正的回調
mListener.onCaptureSuccess(image, mRotationDegrees);
}
});
} catch (RejectedExecutionException e) {
Log.e(TAG, "Unable to post to the supplied executor.");
// Unable to execute on the supplied executor, close the image.
image.close();
}
}
複製代碼
mListener是一個封裝Listener，在ImageCapture中實現
Listener
Listener的關係圖：
+-----------------------+
| |
|ImageCapture. |
|OnImageCapturedListener|
| |
+-----------+-----------+
|
|
+-----------v-----------+ +----------------------+
| | | |
| ImageSaver. | | ImageCapture. |
| OnImageSavedListener +------> OnImageSavedListener |
| | | |
+-----------------------+ +----------------------+
複製代碼
OnImageCapturedListener的實現，其中經過ImageSaver設置的OnImageSavedListener回調到最上層的OnImageSavedListener
OnImageCapturedListener imageCaptureCallbackWrapper =
new OnImageCapturedListener() {
@Override
public void onCaptureSuccess(ImageProxy image, int rotationDegrees) {
CameraXExecutors.ioExecutor()
.execute(
new ImageSaver(
image,
saveLocation,
rotationDegrees,
metadata.isReversedHorizontal,
metadata.isReversedVertical,
metadata.location,
executor,
imageSavedListenerWrapper));
}
...
};
// ImageSaver是一個 Runnable，主要 run 的實現
final class ImageSaver implements Runnable {
...
@Override
public void run() {
...
//圖像處理
...
if (saveError != null) {
postError(saveError, errorMessage, exception);
} else {
postSuccess();
}
}
...
private void postSuccess() {
mExecutor.execute(new Runnable() {
@Override
public void run() {
//最外層回調
mListener.onImageSaved(mFile);
}
});
}
}
複製代碼
整個拍照流程和數據回調就講解完畢了。
經過對 CameraX的 Preview 和 ImageCapture的分析，CameraX對Camera2進行完整的封裝，統一參數配置，自動計算Resolution，簡化Camera2的開發，並增長了生命週期控制，對外只暴露了簡單接口。
使用該庫，只須要簡單的幾行代碼就能夠實現之前Camera2複雜的操做。
參考
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