Android 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Client
	sp<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 route
	sp<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open
	res = 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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