CameraBase基类和Camera类介绍

最新推荐文章于 2025-03-26 01:06:27 发布

原创最新推荐文章于 2025-03-26 01:06:27 发布

· 2.9k 阅读

0 ·

版权

文章标签：

#android

一些语法问题同时被 2 个专栏收录

7 篇文章

订阅专栏

Android Camera专栏

2 篇文章

订阅专栏

本文深入剖析了Android相机框架中的CameraBase基类及其衍生的Camera类。CameraBase利用模板和萃取器获取相机特性，提供了连接、断开、监听等功能。Camera类作为CameraBase的子类，进一步实现了预览、录制、参数设置等具体操作，并通过BnCameraClient进行跨进程通信。此外，文章还涉及到了Binder通信的关键组件。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

CameraBase基类介绍

这个类的定义如下：

template <typename TCam, typename TCamTraits = CameraTraits<TCam> >

class CameraBase : public IBinder::DeathRecipient

{

public:

typedef typename TCamTraits::TCamListener TCamListener;

typedef typename TCamTraits::TCamUser TCamUser;

typedef typename TCamTraits::TCamCallbacks TCamCallbacks;

typedef typename TCamTraits::TCamConnectService TCamConnectService;

static sp<TCam> connect(int cameraId,

const String16& clientPackageName,

int clientUid, int clientPid);

virtual void disconnect();

void setListener(const sp<TCamListener>& listener);

static int getNumberOfCameras();

static status_t getCameraInfo(int cameraId,

/*out*/

struct hardware::CameraInfo* cameraInfo);

sp<TCamUser> remote();

// Status is set to 'UNKNOWN_ERROR' after successful (re)connection

status_t getStatus();

protected:

CameraBase(int cameraId);

virtual ~CameraBase();

// TCamCallbacks implementation

virtual void notifyCallback(int32_t msgType, int32_t ext,

int32_t ext2);

// Common instance variables

Mutex mLock;

virtual void binderDied(const wp<IBinder>& who);

// helper function to obtain camera service handle

static const sp<::android::hardware::ICameraService> getCameraService();

sp<TCamUser> mCamera;

status_t mStatus;

sp<TCamListener> mListener;

const int mCameraId;

typedef CameraBase<TCam> CameraBaseT;

};

从定义来看，这运用了模板，并使用了我们前一章定义的萃取器并设置TCamTraits = CameraTraits<TCam>，这里来获取camera特性。同时为了避免编译错误我们通知

typedef typename TCamTraits::TCamListener TCamListener;

typedef typename TCamTraits::TCamUser TCamUser;

typedef typename TCamTraits::TCamCallbacks TCamCallbacks;

typedef typename TCamTraits::TCamConnectService TCamConnectService;

这些传过来的类型，而不是变量，便于后续的使用。后续当我们使用这个基类的时候由于未指定Tcam，后续需要指定Tcam，类似于CameraBase<TCam>.

这个类继承public IBinder::DeathRecipient通过virtual void binderDied(const wp<IBinder>& who);用来监听binder绑定的进程是否退出。

class DeathRecipient : public virtual RefBase

{

public:

virtual void binderDied(const wp<IBinder>& who) = 0;

};

这里虚函数的实现是在Z:\SA800U_Android9.0_R01_r220\frameworks\av\camera\CameraBase.cpp

内容如下：

template <typename TCam, typename TCamTraits>

void CameraBase<TCam, TCamTraits>::binderDied(const wp<IBinder>& /*who*/) {

ALOGW("mediaserver's remote binder Camera object died");

notifyCallback(CAMERA_MSG_ERROR, CAMERA_ERROR_SERVER_DIED, /*ext2*/0);

}

Camera类介绍

先上定义代码如下：

Z:\SA800U_Android9.0_R01_r220\frameworks\av\include\camera\Camera.h

class Camera :

public CameraBase<Camera>,

public ::android::hardware::BnCameraClient

{

public:

enum {

USE_CALLING_UID = ::android::hardware::ICameraService::USE_CALLING_UID

};

enum {

USE_CALLING_PID = ::android::hardware::ICameraService::USE_CALLING_PID

};

// construct a camera client from an existing remote

static sp<Camera> create(const sp<::android::hardware::ICamera>& camera);

static sp<Camera> connect(int cameraId,

const String16& clientPackageName,

int clientUid, int clientPid);

static status_t connectLegacy(int cameraId, int halVersion,

const String16& clientPackageName,

int clientUid, sp<Camera>& camera);

virtual ~Camera();

status_t reconnect();

status_t lock();

status_t unlock();

// pass the buffered IGraphicBufferProducer to the camera service

status_t setPreviewTarget(const sp<IGraphicBufferProducer>& bufferProducer);

// start preview mode, must call setPreviewTarget first

status_t startPreview();

// stop preview mode

void stopPreview();

// get preview state

bool previewEnabled();

// start recording mode, must call setPreviewTarget first

status_t startRecording();

// stop recording mode

void stopRecording();

// get recording state

bool recordingEnabled();

// release a recording frame

void releaseRecordingFrame(const sp<IMemory>& mem);

// release a recording frame handle

void releaseRecordingFrameHandle(native_handle_t *handle);

// release a batch of recording frame handles

void releaseRecordingFrameHandleBatch(

const std::vector<native_handle_t*> handles);

// autoFocus - status returned from callback

status_t autoFocus();

// cancel auto focus

status_t cancelAutoFocus();

// take a picture - picture returned from callback

status_t takePicture(int msgType);

// set preview/capture parameters - key/value pairs

status_t setParameters(const String8& params);

// get preview/capture parameters - key/value pairs

String8 getParameters() const;

// send command to camera driver

status_t sendCommand(int32_t cmd, int32_t arg1, int32_t arg2);

// Tell camera how to pass video buffers. videoBufferMode is one of VIDEO_BUFFER_MODE_*.

// Returns OK if the specified video buffer mode is supported. If videoBufferMode is

// VIDEO_BUFFER_MODE_BUFFER_QUEUE, setVideoTarget() must be called before starting

// video recording.

status_t setVideoBufferMode(int32_t videoBufferMode);

// Set the video buffer producer for camera to use in VIDEO_BUFFER_MODE_BUFFER_QUEUE

// mode.

status_t setVideoTarget(const sp<IGraphicBufferProducer>& bufferProducer);

void setListener(const sp<CameraListener>& listener);

void setRecordingProxyListener(const sp<ICameraRecordingProxyListener>& listener);

// Configure preview callbacks to app. Only one of the older

// callbacks or the callback surface can be active at the same time;

// enabling one will disable the other if active. Flags can be

// disabled by calling it with CAMERA_FRAME_CALLBACK_FLAG_NOOP, and

// Target by calling it with a NULL interface.

void setPreviewCallbackFlags(int preview_callback_flag);

status_t setPreviewCallbackTarget(

const sp<IGraphicBufferProducer>& callbackProducer);

sp<ICameraRecordingProxy> getRecordingProxy();

// ICameraClient interface

virtual void notifyCallback(int32_t msgType, int32_t ext, int32_t ext2);

virtual void dataCallback(int32_t msgType, const sp<IMemory>& dataPtr,

camera_frame_metadata_t *metadata);

virtual void dataCallbackTimestamp(nsecs_t timestamp, int32_t msgType, const sp<IMemory>& dataPtr);

virtual void recordingFrameHandleCallbackTimestamp(nsecs_t timestamp, native_handle_t* handle);

virtual void recordingFrameHandleCallbackTimestampBatch(

const std::vector<nsecs_t>& timestamps,

const std::vector<native_handle_t*>& handles);

class RecordingProxy : public BnCameraRecordingProxy

{

public:

explicit RecordingProxy(const sp<Camera>& camera);

// ICameraRecordingProxy interface

virtual status_t startRecording(const sp<ICameraRecordingProxyListener>& listener);

virtual void stopRecording();

virtual void releaseRecordingFrame(const sp<IMemory>& mem);

virtual void releaseRecordingFrameHandle(native_handle_t* handle);

virtual void releaseRecordingFrameHandleBatch(

const std::vector<native_handle_t*>& handles);

private:

sp<Camera> mCamera;

};

protected:

explicit Camera(int cameraId);

Camera(const Camera&);

Camera& operator=(const Camera);

sp<ICameraRecordingProxyListener> mRecordingProxyListener;

friend class CameraBase;

};

可以看到这个类继承两个父类，其中CameraBase已经讲过了不必多述，

接下来讲一下另一个父类BnCameraClient。

BnCameraClient

这个类是用来进行binder通信的，最终我们Camera是作为客户端需要调用binder服务端CameraService执行我们需要的动作，这里牵扯到跨进程通信，Camera Service在安卓启动过程中就会被系统拉起来等待客户端的调用。

首先看下这个类的定义：

Z:\SA800U_Android9.0_R01_r220\frameworks\av\include\camera\android\hardware\ICameraClient.h

class BnCameraClient: public android::BnInterface<ICameraClient>

{

public:

virtual status_t onTransact( uint32_t code,

const Parcel& data,

Parcel* reply,

uint32_t flags = 0);

};

可以看到这个类又继承自BnInterface并传入了IcameraClient作为其模板类型，我们先来看看这个BnInterface的定义

template<typename INTERFACE>

class BnInterface : public INTERFACE, public Bbinder

{

public:

virtual sp<IInterface> queryLocalInterface(const String16& _descriptor);

virtual const String16& getInterfaceDescriptor() const;

protected:

virtual IBinder* onAsBinder();

};

可以看到这个类继承自INTERFACE模板参数以及继承自Bbinder，那么返回去也会就是BnCameraClient同样会继承IcameraClient，BnInterface为一个通用模板类，安卓framework native中很多服务都用到这个类，这个主要是用来进行binder通信。其中BBinder启动重要作用。

class BBinder : public Ibinder

这个类继承自Ibinder.

这部分涉及到安卓native的binder跨进程通信。

我们回到IcameraClient它的定义跟BnCameraClient在同一个文件中，定义一些CameraClient的一些功能，BnCameraClient作为跨进程服务者存在，所以它只定义一个onTransact函数。

这里使用虚函数来定义，给子类实现多态性。

这样我们大体的类关系可以梳理一下如下图：