Android Camera AP到Camera Hal調用流程

1.       首先是調用framework層的Camera.java(frameworks\base\core\java\android\hardware)的takePicture方法

2.       接著會調用到JNI層的android_hardware_Camera.cpp(frameworks\base\core\jni)的android_hardware_Camera_takePicture方法，其中會通過get_native_camera擷取一個Camera對象。

3.       上述Camera對象的定義在Camera.h(frameworks\av\include\camera)，camera.h同時定義了CameraInfo。Camera對象繼承自publicBnCameraClient,DeathRecipient。Camera對象的真正實現是在Camera.cpp(frameworks\av\camera)  
。BnCameraClient是作為CameraService回調而存在的。Camera對象內含有一個mCameraService變數用於儲存CameraService引用。

class Camera :
public BnCameraClient,public IBinder::DeathRecipient

constsp<ICameraService>& Camera::getCameraService()

{

    Mutex::Autolock _l(mLock);

    if (mCameraService.get() == 0) {

        sp<IServiceManager> sm = defaultServiceManager();

        sp<IBinder> binder;

        do {

            binder =sm->getService(String16("media.camera"));

            if (binder != 0)

                break;

            ALOGW("CameraService notpublished, waiting...");

            usleep(500000); // 0.5 s

        } while(true);

        if (mDeathNotifier == NULL) {

            mDeathNotifier = newDeathNotifier();

        }

        binder->linkToDeath(mDeathNotifier);

        mCameraService =interface_cast<ICameraService>(binder);

    }

4.       在ICameraClient.h和ICameraService.h檔案中，ICameraClient和ICameraService都繼承自IInterface，也就是Binder通訊的基礎，此外ICamera.h也繼承自IInterface

class ICameraClient:public IInterface

class ICameraService :public IInterface

class ICamera: publicIInterface

然後發現BnCameraClient繼承自BnInterface<ICameraClient>，作為ICameraClient的伺服器端存在：

class BnCameraClient: publicBnInterface<ICameraClient>

BnCameraService繼承自BnInterface<ICameraService>，作為ICameraService的伺服器端存在：

class BnCameraService: publicBnInterface<ICameraService>

BnCamera繼承自BnInterface<ICamera>，作為ICamera的伺服器端存在：

class BnCamera: public BnInterface<ICamera>

對應的上述三個分別存在一個作為Binder用戶端的類存在，為Bp***：

class BpCameraClient:public BpInterface<ICameraClient>

class BpCameraService:public BpInterface<ICameraService>

class BpCamera: publicBpInterface<ICamera>

上述三個的實現分別在ICameraClient.cpp、ICameraService.cpp、ICamera.cpp,在這三支檔案中分別實現了三組Binder的Server端和Client端，Camera常用的方法都在ICamera中實現。

5.       Camera.cpp檔案connect方法在JNI層去setupCamera的時候會調用，JNI層是在上層opencamera的時候被調用的，在camera.cpp的connect方法中擷取一個ICamera對象來完成對Camera的真正操作。

sp<Camera>Camera::connect(int cameraId)

{

    ALOGV("connect");

    sp<Camera> c = new Camera();

    const sp<ICameraService>& cs =getCameraService();

    if (cs != 0) {

        c->mCamera = cs->connect(c, cameraId);

    }

    if (c->mCamera != 0) {

       c->mCamera->asBinder()->linkToDeath(c);

        c->mStatus = NO_ERROR;

    } else {

        c.clear();

    }

    return c;

}

6.       在CameraService.h檔案中可以看到CameraService定義內部類Client，CameraClient繼承此類，在CameraService中持有對mClient對象的一個數組，這個數組也是Camera.cpp用戶端調用connect方法後需要返回的Binder引用對象

 class Client : public BnCamera

class CameraClient : public CameraService::Client

wp<Client>         mClient[MAX_CAMERAS];

    switch(deviceVersion) {

      case CAMERA_DEVICE_API_VERSION_1_0:

        client = new CameraClient(this,cameraClient, cameraId,

                info.facing, callingPid, getpid());

        break;

      case CAMERA_DEVICE_API_VERSION_2_0:

        client = new Camera2Client(this,cameraClient, cameraId,

                info.facing, callingPid,getpid());

並且Google好像有開發新的API2.0，在此處通過判斷不同的version執行個體化不同的CameraClient的Binder引用對象回去，目前Camera2檔案夾有Burst等實現

7.       在CameraService層的CameraClient對象的定義中，持有CameraHardwareInterface對象的引用mHardware.在CameraClient的initilize方法中會建立此對象，在對象的構造方法中傳入需要開啟的Camera的ID。

sp<CameraHardwareInterface>     mHardware;

status_t CameraClient::initialize(camera_module_t *module) {

    int callingPid = getCallingPid();

    LOG1("CameraClient::initialize E (pid%d, id %d)", callingPid, mCameraId);

 

    char camera_device_name[10];

    status_t res;

    snprintf(camera_device_name, sizeof(camera_device_name),"%d",
mCameraId);

    mHardware = new CameraHardwareInterface(camera_device_name);

    res = mHardware->initialize(&module->common);

    if (res != OK) {

        ALOGE("%s: Camera %d: unable toinitialize device: %s (%d)",

                __FUNCTION__, mCameraId,strerror(-res), res);

        mHardware.clear();

        return NO_INIT;

    }

    mHardware->setCallbacks(notifyCallback,

           dataCallback,

           dataCallbackTimestamp,

            (void*)mCameraId);

    //Enable zoom, error, focus, and metadata messages by default

    enableMsgType(CAMERA_MSG_ERROR | CAMERA_MSG_ZOOM | CAMERA_MSG_FOCUS |

                 CAMERA_MSG_PREVIEW_METADATA | CAMERA_MSG_FOCUS_MOVE);

//!++

#ifdef  MTK_CAMERA_BSP_SUPPORT

    // Enable MTK-extended messages by default

    enableMsgType(MTK_CAMERA_MSG_EXT_NOTIFY |MTK_CAMERA_MSG_EXT_DATA);

#endif

//!--

    LOG1("CameraClient::initialize X (pid%d, id %d)", callingPid, mCameraId);

    return OK;

}

8.       在CameraService的onFirstRef方法中，會載入CameraHal  Module

void CameraService:: onFirstRef()

{

    BnCameraService::onFirstRef();

 

    if (hw_get_module(CAMERA_HARDWARE_MODULE_ID,

                (const hw_module_t**)&mModule) < 0) {

        ALOGE("Could not load camera HALmodule");

        mNumberOfCameras = 0;

    }

    else {

        mNumberOfCameras =mModule->get_number_of_cameras();

        if (mNumberOfCameras > MAX_CAMERAS){

            ALOGE("Number of cameras(%d)> MAX_CAMERAS(%d).",

                    mNumberOfCameras, MAX_CAMERAS);

            mNumberOfCameras = MAX_CAMERAS;

        }

        for (int i = 0; i <mNumberOfCameras; i++) {

            setCameraFree(i);

        }

    }

}

hw_get_module方法的實現在hardware/libhardware/Hardware.c檔案中實現

int hw_get_module(constchar *id, const struct hw_module_t **module)

{

    return hw_get_module_by_class(id, NULL,module);

}

Camera_module_t的結構體定義在camera_common.h檔案中

typedef structcamera_module {

    hw_module_t common;

    int (*get_number_of_cameras)(void);

    int (*get_camera_info)(int camera_id,struct camera_info *info);

} camera_module_t;

Hw_module_t的定義在hardware.h檔案中，hw_module_t持有對hw_module_methods_t引用，其中有定義一個open指標

typedef structhw_module_methods_t {

    /** Open a specific device */

    int (*open)(const struct hw_module_t*module, const char* id,

            struct hw_device_t** device);

 

} hw_module_methods_t;

而載入CamDevice的操作是在CameraHardwareInterface的init方法中調用open

        int rc =module->methods->open(module, mName.string(),

                                       (hw_device_t **)&mDevice);