Android(安卓)P Camera架构

Camera架构

一、APP层
获取摄像头ID列表：getCameraIdList()
打开摄像头：openCamera();

二、frameworks层：
CameraManager：
代码路径：\frameworks\base\core\java\android\hardware\camera2\CameraManager.java

private CameraDevice openCameraDeviceUserAsync(String cameraId,        CameraDevice.StateCallback callback, Executor executor, final int uid)        throws CameraAccessException {//省略一部分代码//...   // Use cameraservice's cameradeviceclient implementation for HAL3.2+ devices   ICameraService cameraService = CameraManagerGlobal.get().getCameraService();   if (cameraService == null) {       throw new ServiceSpecificException(           ICameraService.ERROR_DISCONNECTED,           "Camera service is currently unavailable");   }   //通过CameraService连接摄像头设备   cameraUser = cameraService.connectDevice(callbacks, cameraId,           mContext.getOpPackageName(), uid);//省略一部分代码//... }

三、C++ Libraries层代码：
CameraService
代码路径：frameworks\av\services\camera\libcameraservice\CameraService.cpp

// CameraService::connectDevice流程{//省略一部分代码//...// 创建不同HAL版本对应的相机Clientsp<BasicClient> tmp = nullptr;if(!(ret = makeClient(this, cameraCb, clientPackageName,        cameraId, api1CameraId, facing,        clientPid, clientUid, getpid(), legacyMode,        halVersion, deviceVersion, effectiveApiLevel,        /*out*/&tmp)).isOk()) {    return ret;}//省略一部分代码//...}// 根据HAL版本创建对应的相机Clinet，这里以创建最新版本的CAMERA_DEVICE_API_VERSION_3_4版本，// 以Camera2 API为例的版本Status CameraService::makeClient() {//省略一部分代码//...// Camera2 API routesp<hardware::camera2::ICameraDeviceCallbacks> tmp = static_cast<hardware::camera2::ICameraDeviceCallbacks*>(cameraCb.get());*client = new CameraDeviceClient(cameraService, tmp, packageName, cameraId, facing, clientPid, clientUid, servicePid);//省略一部分代码//...}

frameworks\av\services\camera\libcameraservice\api2\CameraDeviceClient.cpp
frameworks\av\services\camera\libcameraservice\common\Camera2ClientBase.cpp
frameworks\av\services\camera\libcameraservice\device3\Camera3Device.cpp

status_t Camera3Device::initialize(sp<CameraProviderManager> manager) {//在初始化时，调用了 CameraProviderManager 的 openSession 方法，开启了远端的 Session    sp<ICameraDeviceSession> session;    ATRACE_BEGIN("CameraHal::openSession");    status_t res = manager->openSession(mId.string(), this,            /*out*/ &session);    ATRACE_END();    if (res != OK) {        SET_ERR_L("Could not open camera session: %s (%d)", strerror(-res), res);        return res;    }//生成HIDL接口层对象mInterface = new HalInterface(session, queue);}

frameworks\av\services\camera\libcameraservice\common\CameraProviderManager.cpp

//V3_2::ICameraDeviceCallback 调用V3.2版本的HIDL接口status_t CameraProviderManager::openSession(const std::string &id,        const sp<hardware::camera::device::V3_2::ICameraDeviceCallback>& callback,        /*out*/        sp<hardware::camera::device::V3_2::ICameraDeviceSession> *session) {    std::lock_guard<std::mutex> lock(mInterfaceMutex);    auto deviceInfo = findDeviceInfoLocked(id,            /*minVersion*/ {3,0}, /*maxVersion*/ {4,0});    if (deviceInfo == nullptr) return NAME_NOT_FOUND;    auto *deviceInfo3 = static_cast<ProviderInfo::DeviceInfo3*>(deviceInfo);    Status status;    hardware::Return<void> ret;    //通过HIDL层接口调用open()    ret = deviceInfo3->mInterface->open(callback, [&status, &session]            (Status s, const sp<device::V3_2::ICameraDeviceSession>& cameraSession) {                status = s;                if (status == Status::OK) {                    *session = cameraSession;                }            });    if (!ret.isOk()) {        ALOGE("%s: Transaction error opening a session for camera device %s: %s",                __FUNCTION__, id.c_str(), ret.description().c_str());        return DEAD_OBJECT;    }    return mapToStatusT(status);}

四、HIDL层和HAL层
文件路径：
hardware\interfaces\camera\device\3.2\default\CameraDevice.cpp

Return<void> CameraDevice::open(const sp<ICameraDeviceCallback>& callback, open_cb _hidl_cb)  {/** Open HAL device */status_t res;camera3_device_t *device;ATRACE_BEGIN("camera3->open");//调用CameraModule中的openres = mModule->open(mCameraId.c_str(), reinterpret_cast<hw_device_t**>(&device));ATRACE_END();}

hardware\interfaces\camera\common\1.0\default\CameraModule.cpp

int CameraModule::open(const char* id, struct hw_device_t** device) {    int res;    ATRACE_BEGIN("camera_module->open");    //mModule是一个camera_module_t对象，此openfa方法将调用Driver层代码进行打开摄像头操作    res = filterOpenErrorCode(mModule->common.methods->open(&mModule->common, id, device));    ATRACE_END();    return res;}

//camera_module_t涉及到CAMERA_HARDWARE_MODULE_ID的创建和绑定
camera_module_t文件路径：hardware\libhardware\include\hardware\camera_common.h

五、Driver层
Driver层是硬件厂商定制的，所以，不同的芯片厂商，Driver层代码不一样。

驱动层执行一些跟摄像头设备相关和图形显示，视频数据的一些操作，涉及到一些设备文件操作。

主要方法和解析如下：
// open camera dev nodes, etc
int32_t ret = mVideoStream->openDev(mDevPath);
主要执行：

// name为"/dev/video0"摄像头设备，mDev = open(name, O_RDWR);

// flush camera dev nodes.
return mVideoStream->flushDev();
主要执行：

   // 这里执行了两个重要的操作VIDIOC_DQBUF和VIDIOC_QBUF，取出摄像头视频图像Buffer    ret = ioctl(mDev, VIDIOC_DQBUF, &cfilledbuffer);    if (ret < 0) {        ALOGE("%s: VIDIOC_DQBUF Failed: %s (%d)", __func__, strerror(errno), errno);        return BAD_VALUE;    }    ret = ioctl(mDev, VIDIOC_QBUF, &cfilledbuffer);    if (ret < 0) {        ALOGE("%s: VIDIOC_QBUF Failed: %s (%d)", __func__, strerror(errno), errno);        return BAD_VALUE;    }

// close camera dev nodes, etc
mVideoStream->closeDev();
主要执行：

// 关闭摄像头设备close(mDev);

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