Android Camera FW到Camera Hal调用流程

本文主要是介绍Android Camera FW到Camera Hal调用流程，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1. 首先是调用framework层的Camera.java(frameworks\base\core\java\android\hardware)的takePicture方法

2. 接着会调用到JNI层的android_hardware_Camera.cpp(frameworks\base\core\jni)的android_hardware_Camera_takePicture方法，其中会通过get_native_camera获取一个Camera对象。

3. 上述Camera对象的定义在Camera.h(frameworks\av\include\camera)，camera.h同时定义了CameraInfo。Camera对象继承自publicBnCameraClient,DeathRecipient。Camera对象的真正实现是在Camera.cpp(frameworks\av\camera) 。BnCameraClient是作为CameraService回调而存在的。Camera对象内含有一个mCameraService变量用于保存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文件中，ICameraClient和ICameraService都继承自IInterface，也就是Binder通信的基础，此外ICamera.h也继承自IInterface

class ICameraClient:public IInterface

class ICameraService :public IInterface

class ICamera: publicIInterface

然后发现BnCameraClient继承自BnInterface<ICameraClient>，作为ICameraClient的服务器端存在：

class BnCameraClient: publicBnInterface<ICameraClient>

BnCameraService继承自BnInterface<ICameraService>，作为ICameraService的服务器端存在：

class BnCameraService: publicBnInterface<ICameraService>

BnCamera继承自BnInterface<ICamera>，作为ICamera的服务器端存在：

class BnCamera: public BnInterface<ICamera>

对应的上述三个分别存在一个作为Binder客户端的类存在，为Bp***：

class BpCameraClient:public BpInterface<ICameraClient>

class BpCameraService:public BpInterface<ICameraService>

class BpCamera: publicBpInterface<ICamera>

上述三个的实现分别在ICameraClient.cpp、ICameraService.cpp、ICamera.cpp,在这三支文件中分别实现了三组Binder的Server端和Client端，Camera常用的方法都在ICamera中实现。

5. Camera.cpp文件connect方法在JNI层去setupCamera的时候会调用，JNI层是在上层opencamera的时候被调用的，在camera.cpp的connect方法中获取一个ICamera对象来完成对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文件中可以看到CameraService定义内部类Client，CameraClient继承此类，在CameraService中持有对mClient对象的一个数组，这个数组也是Camera.cpp客户端调用connect方法后需要返回的Binder引用对象

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());

并且Google好像有开发新的API2.0，在此处通过判断不同的version实例化不同的CameraClient的Binder引用对象回去，目前Camera2文件夹有Burst等实现

7. 在CameraService层的CameraClient对象的定义中，持有CameraHardwareInterface对象的引用mHardware.在CameraClient的initilize方法中会创建此对象，在对象的构造方法中传入需要打开的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 defaultenableMsgType(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 defaultenableMsgType(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，会加载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方法的实现在hardware/libhardware/Hardware.c文件中实现

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

{

return hw_get_module_by_class(id, NULL,module);

}

Camera_module_t的结构体定义在camera_common.h文件中

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的定义在hardware.h文件中，hw_module_t持有对hw_module_methods_t引用，其中有定义一个open指针