Android Camera原理之openCamera模块(一)

我们平时开发,知道怎么调度api,怎么调起camera,怎么调用camera的实例来操作camera就可以了,但是这些调度的背后都做了什么事情,我们可能不太清楚,本文打算从openCamera这个调用谈起,展开说下camera调起之后底层是怎么工作的?

Camera操作过程中最重要的四个步骤:

  • CameraManager-->openCamera ---> 打开相机
  • CameraDeviceImpl-->createCaptureSession ---> 创建捕获会话
  • CameraCaptureSession-->setRepeatingRequest ---> 设置预览界面
  • CameraDeviceImpl-->capture ---> 开始捕获图片

1.CameraManager

CameraManager是本地的SystemService集合中一个service,在SystemServiceRegistry中注册:

        registerService(Context.CAMERA_SERVICE, CameraManager.class,
                new CachedServiceFetcher() {
            @Override
            public CameraManager createService(ContextImpl ctx) {
                return new CameraManager(ctx);
            }});

SystemServiceRegistry中有两个HashMap集合来存储本地的SystemService数据,有一点要注意点一些,这和Binder的service不同,他们不是binder service,只是普通的调用模块,集成到一个本地service中,便于管理。

    private static final HashMap, String> SYSTEM_SERVICE_NAMES =
            new HashMap, String>();
    private static final HashMap> SYSTEM_SERVICE_FETCHERS =
            new HashMap>();

2.openCamera函数

CameraManager中两个openCamera(...),只是一个传入Handler,一个传入Executor,是想用线程池来执行Camera中耗时操作。

public void openCamera(@NonNull String cameraId,
            @NonNull final CameraDevice.StateCallback callback, @Nullable Handler handler)

public void openCamera(@NonNull String cameraId,
            @NonNull @CallbackExecutor Executor executor,
            @NonNull final CameraDevice.StateCallback callback)
  • cameraId 是一个标识,标识当前要打开的camera
  • callback 是一个状态回调,当前camera被打开的时候,这个状态回调会被触发的。
  • handler 是传入的一个执行耗时操作的handler
  • executor 操作线程池

了解一下openCamera的调用流程:

Android Camera原理之openCamera模块(一)_第1张图片

openCamera流程.jpg

2.1 openCameraDeviceUserAsync函数

private CameraDevice openCameraDeviceUserAsync(String cameraId,
            CameraDevice.StateCallback callback, Executor executor, final int uid)
            throws CameraAccessException
{
//......
}

返回值是CameraDevice,从《Android Camera模块解析之拍照》中讲解了Camera framework模块中主要类之间的关系,CameraDevice是抽象类,CameraDeviceImpl是其实现类,就是要获取CameraDeviceImpl的实例。
这个函数的主要作用就是到底层获取相机设备的信息,并获取当前指定cameraId的设备实例。
本函数的主要工作可以分为下面五点:

  • 获取当前cameraId指定相机的设备信息
  • 利用获取相机的设备信息创建CameraDeviceImpl实例
  • 调用远程CameraService获取当前相机的远程服务
  • 将获取的远程服务设置到CameraDeviceImpl实例中
  • 返回CameraDeviceImpl实例

2.2 获取当前cameraId指定相机的设备信息

CameraCharacteristics characteristics = getCameraCharacteristics(cameraId);

一句简单的调用,返回值是CameraCharacteristics,CameraCharacteristics提供了CameraDevice的各种属性,可以通过getCameraCharacteristics函数来查询。

    public CameraCharacteristics getCameraCharacteristics(@NonNull String cameraId)
            throws CameraAccessException {
        CameraCharacteristics characteristics = null;
        if (CameraManagerGlobal.sCameraServiceDisabled) {
            throw new IllegalArgumentException("No cameras available on device");
        }
        synchronized (mLock) {
            ICameraService cameraService = CameraManagerGlobal.get().getCameraService();
            if (cameraService == null) {
                throw new CameraAccessException(CameraAccessException.CAMERA_DISCONNECTED,
                        "Camera service is currently unavailable");
            }
            try {
                if (!supportsCamera2ApiLocked(cameraId)) {
                    int id = Integer.parseInt(cameraId);
                    String parameters = cameraService.getLegacyParameters(id);
                    CameraInfo info = cameraService.getCameraInfo(id);
                    characteristics = LegacyMetadataMapper.createCharacteristics(parameters, info);
                } else {
                    CameraMetadataNative info = cameraService.getCameraCharacteristics(cameraId);
                    characteristics = new CameraCharacteristics(info);
                }
            } catch (ServiceSpecificException e) {
                throwAsPublicException(e);
            } catch (RemoteException e) {
                throw new CameraAccessException(CameraAccessException.CAMERA_DISCONNECTED,
                        "Camera service is currently unavailable", e);
            }
        }
        return characteristics;
    }

一个关键的函数----> supportsCamera2ApiLocked(cameraId),这个函数的意思是 当前camera服务是否支持camera2 api,如果支持,返回true,如果不支持,返回false。

    private boolean supportsCameraApiLocked(String cameraId, int apiVersion) {
        /*
         * Possible return values:
         * - NO_ERROR => CameraX API is supported
         * - CAMERA_DEPRECATED_HAL => CameraX API is *not* supported (thrown as an exception)
         * - Remote exception => If the camera service died
         *
         * Anything else is an unexpected error we don't want to recover from.
         */
        try {
            ICameraService cameraService = CameraManagerGlobal.get().getCameraService();
            // If no camera service, no support
            if (cameraService == null) return false;

            return cameraService.supportsCameraApi(cameraId, apiVersion);
        } catch (RemoteException e) {
            // Camera service is now down, no support for any API level
        }
        return false;
    }

调用的CameraService对应的是ICameraService.aidl,对应的实现类在frameworks/av/services/camera/libcameraservice/CameraService.h
下面是CameraManager与CameraService之间的连接关系图示:

Android Camera原理之openCamera模块(一)_第2张图片

CameraService生成.jpg


CameraManagerGlobal是CameraManager中的内部类,服务端在native层,《Android Camera模块解析之拍照》中camera2介绍的时候已经说明了当前cameraservice是放在frameworks/av/services/camera/libcameraservice/中的,编译好了之后会生成一个libcameraservices.so的共享库。熟悉camera代码,首先应该熟悉camera架构的代码。

 

这儿监测的是当前camera架构是基于HAL什么版本的,看下面的switch判断:

  • 当前device是基于HAL1.0 HAL3.0 HAL3.1,并且apiversion不是API_VERSION_2,此时支持,这里要搞清楚了,这里的API_VERSION_2不是api level 2,而是camera1还是camera2.
  • 当前device是基于HAL3.2 HAL3.3 HAL3.4,此时支持
  • 目前android版本,正常情况下都是支持camera2的
Status CameraService::supportsCameraApi(const String16& cameraId, int apiVersion,
        /*out*/ bool *isSupported) {
    ATRACE_CALL();

    const String8 id = String8(cameraId);

    ALOGV("%s: for camera ID = %s", __FUNCTION__, id.string());

    switch (apiVersion) {
        case API_VERSION_1:
        case API_VERSION_2:
            break;
        default:
            String8 msg = String8::format("Unknown API version %d", apiVersion);
            ALOGE("%s: %s", __FUNCTION__, msg.string());
            return STATUS_ERROR(ERROR_ILLEGAL_ARGUMENT, msg.string());
    }

    int deviceVersion = getDeviceVersion(id);
    switch(deviceVersion) {
        case CAMERA_DEVICE_API_VERSION_1_0:
        case CAMERA_DEVICE_API_VERSION_3_0:
        case CAMERA_DEVICE_API_VERSION_3_1:
            if (apiVersion == API_VERSION_2) {
                ALOGV("%s: Camera id %s uses HAL version %d <3.2, doesn't support api2 without shim",
                        __FUNCTION__, id.string(), deviceVersion);
                *isSupported = false;
            } else { // if (apiVersion == API_VERSION_1) {
                ALOGV("%s: Camera id %s uses older HAL before 3.2, but api1 is always supported",
                        __FUNCTION__, id.string());
                *isSupported = true;
            }
            break;
        case CAMERA_DEVICE_API_VERSION_3_2:
        case CAMERA_DEVICE_API_VERSION_3_3:
        case CAMERA_DEVICE_API_VERSION_3_4:
            ALOGV("%s: Camera id %s uses HAL3.2 or newer, supports api1/api2 directly",
                    __FUNCTION__, id.string());
            *isSupported = true;
            break;
        case -1: {
            String8 msg = String8::format("Unknown camera ID %s", id.string());
            ALOGE("%s: %s", __FUNCTION__, msg.string());
            return STATUS_ERROR(ERROR_ILLEGAL_ARGUMENT, msg.string());
        }
        default: {
            String8 msg = String8::format("Unknown device version %x for device %s",
                    deviceVersion, id.string());
            ALOGE("%s: %s", __FUNCTION__, msg.string());
            return STATUS_ERROR(ERROR_INVALID_OPERATION, msg.string());
        }
    }

    return Status::ok();
}

采用camera2 api来获取相机设备的信息。

CameraMetadataNative info = cameraService.getCameraCharacteristics(cameraId);
characteristics = new CameraCharacteristics(info);

Android Camera原理之openCamera模块(一)_第3张图片

getCameraCharacteristics调用流程.jpg

 

其中DeviceInfo3是CameraProviderManager::ProviderInfo::DeviceInfo3,CameraProviderManager中的结构体,最终返回的是CameraMetadata类型,它是一个Parcelable类型,native中对应的代码是frameworks/av/camera/include/camera/CameraMetadata.h,java中对应的是frameworks/base/core/java/android/hardware/camera2/impl/CameraMetadataNative.java,Parcelable类型是可以跨进程传输的。下面是在native中定义CameraMetadata为CameraMetadataNative

namespace hardware {
namespace camera2 {
namespace impl {
using ::android::CameraMetadata;
typedef CameraMetadata CameraMetadataNative;
}
}
}

我们关注其中的一个调用函数:

status_t CameraProviderManager::getCameraCharacteristicsLocked(const std::string &id,
        CameraMetadata* characteristics) const {
    auto deviceInfo = findDeviceInfoLocked(id, /*minVersion*/ {3,0}, /*maxVersion*/ {4,0});
    if (deviceInfo == nullptr) return NAME_NOT_FOUND;

    return deviceInfo->getCameraCharacteristics(characteristics);
}

发现了调用了一个findDeviceInfoLocked(...)函数,返回类型是一个DeviceInfo结构体,CameraProviderManager.h中定义了三个DeviceInfo结构体,除了DeviceInfo之外,还有DeviceInfo1与DeviceInfo3,他们都继承DeviceInfo,其中DeviceInfo1为HALv1服务,DeviceInfo3为HALv3-specific服务,都是提供camera device一些基本信息。这里主要看下findDeviceInfoLocked(...)函数:

CameraProviderManager::ProviderInfo::DeviceInfo* CameraProviderManager::findDeviceInfoLocked(
        const std::string& id,
        hardware::hidl_version minVersion, hardware::hidl_version maxVersion) const {
    for (auto& provider : mProviders) {
        for (auto& deviceInfo : provider->mDevices) {
            if (deviceInfo->mId == id &&
                    minVersion <= deviceInfo->mVersion && maxVersion >= deviceInfo->mVersion) {
                return deviceInfo.get();
            }
        }
    }
    return nullptr;
}

这儿的是mProviders是ProviderInfo类型的列表,这个ProviderInfo也是CameraProviderManager.h中定义的结构体,并且上面3种DeviceInfo都是定义在ProviderInfo里面的。下面给出了ProviderInfo的代码大纲,裁剪了很多代码,但是我们还是能看到核心的代码:ProviderInfo是管理当前手机的camera device设备的,通过addDevice保存在mDevices中,接下来我们看下这个addDevice是如何工作的。

    struct ProviderInfo :
            virtual public hardware::camera::provider::V2_4::ICameraProviderCallback,
            virtual public hardware::hidl_death_recipient
    {
    //......
        ProviderInfo(const std::string &providerName,
                sp& interface,
                CameraProviderManager *manager);
        ~ProviderInfo();

        status_t initialize();

        const std::string& getType() const;

        status_t addDevice(const std::string& name,
                hardware::camera::common::V1_0::CameraDeviceStatus initialStatus =
                hardware::camera::common::V1_0::CameraDeviceStatus::PRESENT,
                /*out*/ std::string *parsedId = nullptr);

        // ICameraProviderCallbacks interface - these lock the parent mInterfaceMutex
        virtual hardware::Return cameraDeviceStatusChange(
                const hardware::hidl_string& cameraDeviceName,
                hardware::camera::common::V1_0::CameraDeviceStatus newStatus) override;
        virtual hardware::Return torchModeStatusChange(
                const hardware::hidl_string& cameraDeviceName,
                hardware::camera::common::V1_0::TorchModeStatus newStatus) override;

        // hidl_death_recipient interface - this locks the parent mInterfaceMutex
        virtual void serviceDied(uint64_t cookie, const wp& who) override;

        // Basic device information, common to all camera devices
        struct DeviceInfo {
            //......
        };
        std::vector> mDevices;
        std::unordered_set mUniqueCameraIds;
        int mUniqueDeviceCount;

        // HALv1-specific camera fields, including the actual device interface
        struct DeviceInfo1 : public DeviceInfo {
            //......
        };

        // HALv3-specific camera fields, including the actual device interface
        struct DeviceInfo3 : public DeviceInfo {
            //......
        };

    private:
        void removeDevice(std::string id);
    };
  • mProviders是如何添加的?
  • addDevice是如何工作的?

mProviders添加的流程:
1.CameraService --> onFirstRef()
2.CameraService --> enumerateProviders()
3.CameraProviderManager --> initialize(this)
initialize(...)函数原型是:

status_t initialize(wp listener,
            ServiceInteractionProxy *proxy = &sHardwareServiceInteractionProxy);

第2个参数默认是sHardwareServiceInteractionProxy类型,

    struct ServiceInteractionProxy {
        virtual bool registerForNotifications(
                const std::string &serviceName,
                const sp
                ¬ification) = 0;
        virtual sp getService(
                const std::string &serviceName) = 0;
        virtual ~ServiceInteractionProxy() {}
    };

    // Standard use case - call into the normal generated static methods which invoke
    // the real hardware service manager
    struct HardwareServiceInteractionProxy : public ServiceInteractionProxy {
        virtual bool registerForNotifications(
                const std::string &serviceName,
                const sp
                ¬ification) override {
            return hardware::camera::provider::V2_4::ICameraProvider::registerForNotifications(
                    serviceName, notification);
        }
        virtual sp getService(
                const std::string &serviceName) override {
            return hardware::camera::provider::V2_4::ICameraProvider::getService(serviceName);
        }
    };

hardware::camera::provider::V2_4::ICameraProvider::getService(serviceName)出处在./hardware/interfaces/camera/provider/2.4/default/CameraProvider.cpp,传入的参数可能是下面两种的一个:
const std::string kLegacyProviderName("legacy/0"); 代表 HALv1
const std::string kExternalProviderName("external/0"); 代码HALv3-specific

ICameraProvider* HIDL_FETCH_ICameraProvider(const char* name) {
    if (strcmp(name, kLegacyProviderName) == 0) {
        CameraProvider* provider = new CameraProvider();
        if (provider == nullptr) {
            ALOGE("%s: cannot allocate camera provider!", __FUNCTION__);
            return nullptr;
        }
        if (provider->isInitFailed()) {
            ALOGE("%s: camera provider init failed!", __FUNCTION__);
            delete provider;
            return nullptr;
        }
        return provider;
    } else if (strcmp(name, kExternalProviderName) == 0) {
        ExternalCameraProvider* provider = new ExternalCameraProvider();
        return provider;
    }
    ALOGE("%s: unknown instance name: %s", __FUNCTION__, name);
    return nullptr;
}

addDevice是如何工作的?
1.CameraProviderManager::ProviderInfo::initialize()初始化的时候是检查当前的camera device,检查的执行函数是:

    std::vector devices;
    hardware::Return ret = mInterface->getCameraIdList([&status, &devices](
            Status idStatus,
            const hardware::hidl_vec& cameraDeviceNames) {
        status = idStatus;
        if (status == Status::OK) {
            for (size_t i = 0; i < cameraDeviceNames.size(); i++) {
                devices.push_back(cameraDeviceNames[i]);
            }
        } });

最终调用到./hardware/interfaces/camera/provider/2.4/default/CameraProvider.cpp中的getCameraIdList函数:CAMERA_DEVICE_STATUS_PRESENT表明当前的camera是可用的,mCameraStatusMap存储了所有的camera 设备列表。

Return CameraProvider::getCameraIdList(getCameraIdList_cb _hidl_cb)  {
    std::vector deviceNameList;
    for (auto const& deviceNamePair : mCameraDeviceNames) {
        if (mCameraStatusMap[deviceNamePair.first] == CAMERA_DEVICE_STATUS_PRESENT) {
            deviceNameList.push_back(deviceNamePair.second);
        }
    }
    hidl_vec hidlDeviceNameList(deviceNameList);
    _hidl_cb(Status::OK, hidlDeviceNameList);
    return Void();
}

我们理一下整体的调用结构:

Android Camera原理之openCamera模块(一)_第4张图片

Camera分层体系.jpg

 

1.上面谈的camera2 api就是在framework层的,在应用程序进程中。
2.CameraService,是camera2 api binder IPC通信方式调用到服务端的,camera相关的操作都在在服务端进行。所在的位置就是./frameworks/av/services/camera/下面
3.服务端也只是一个桥梁,service也会调用到HAL,硬件抽象层,具体位置在./hardware/interfaces/camera/provider/2.4
4.camera driver,底层的驱动层了,这是真正操作硬件的地方。

2.3 利用获取相机的设备信息创建CameraDeviceImpl实例

android.hardware.camera2.impl.CameraDeviceImpl deviceImpl =
                    new android.hardware.camera2.impl.CameraDeviceImpl(
                        cameraId,
                        callback,
                        executor,
                        characteristics,
                        mContext.getApplicationInfo().targetSdkVersion);

创建CameraDevice实例,传入了刚刚获取的characteristics参数(camera设备信息赋值为CameraDevice实例)。这个实例接下来还是使用,使用的时候再谈一下。

2.4 调用远程CameraService获取当前相机的远程服务

                    // 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");
                    }
                    cameraUser = cameraService.connectDevice(callbacks, cameraId,
                            mContext.getOpPackageName(), uid);

这个函数的主要目的就是连接当前的cameraDevice设备。调用到CameraService::connectDevice中。

Android Camera原理之openCamera模块(一)_第5张图片

connectDevice调用流程.jpg

Status CameraService::connectDevice(
        const sp& cameraCb,
        const String16& cameraId,
        const String16& clientPackageName,
        int clientUid,
        /*out*/
        sp* device) {

    ATRACE_CALL();
    Status ret = Status::ok();
    String8 id = String8(cameraId);
    sp client = nullptr;
    ret = connectHelper(cameraCb, id,
            /*api1CameraId*/-1,
            CAMERA_HAL_API_VERSION_UNSPECIFIED, clientPackageName,
            clientUid, USE_CALLING_PID, API_2,
            /*legacyMode*/ false, /*shimUpdateOnly*/ false,
            /*out*/client);

    if(!ret.isOk()) {
        logRejected(id, getCallingPid(), String8(clientPackageName),
                ret.toString8());
        return ret;
    }

    *device = client;
    return ret;
}
  • connectDevice函数的第5个参数就是当前binder ipc的返回值,我们connectDevice之后,会得到一个cameraDeviceClient对象,这个对象会返回到应用程序进程中。我们接下来主要看看这个对象是如何生成的。
  • validateConnectLocked:检查当前的camera device是否可用,这儿的判断比较简单,只是简单判断当前设备是否存在。
  • handleEvictionsLocked:处理camera独占情况,主要的工作是当前的cameradevice如果已经被其他的设备使用了,或者是否有比当前调用优先级更高的调用等等,在执行完这个函数之后,才能完全判断当前的camera device是可用的,并且开始获取camera device的一些信息开始工作了。
  • CameraFlashlight-->prepareDeviceOpen:此时准备连接camera device 了,需要判断一下如果当前的camera device有可用的flashlight,那就要开始准备好了,但是flashlight被占用的那就没有办法了。只是一个通知作用。
  • getDeviceVersion:判断一下当前的camera device的version 版本,主要判断在CameraProviderManager::getHighestSupportedVersion函数中,这个函数中将camera device支持的最高和最低版本查清楚,然后我们判断当前的camera facing,只有两种情况CAMERA_FACING_BACK = 0与CAMERA_FACING_FRONT = 1,这些都是先置判断条件,只有这些检查都通过,说明当前camera device是确实可用的。
  • makeClient:是根据当前的CAMERA_DEVICE_API_VERSION来判断的,当前最新的HAL架构都是基于HALv3的,所以我们采用的client都是CameraDeviceClient
Status CameraService::makeClient(const sp& cameraService,
        const sp& cameraCb, const String16& packageName, const String8& cameraId,
        int api1CameraId, int facing, int clientPid, uid_t clientUid, int servicePid,
        bool legacyMode, int halVersion, int deviceVersion, apiLevel effectiveApiLevel,
        /*out*/sp* client) {

    if (halVersion < 0 || halVersion == deviceVersion) {
        // Default path: HAL version is unspecified by caller, create CameraClient
        // based on device version reported by the HAL.
        switch(deviceVersion) {
          case CAMERA_DEVICE_API_VERSION_1_0:
            if (effectiveApiLevel == API_1) {  // Camera1 API route
                sp tmp = static_cast(cameraCb.get());
                *client = new CameraClient(cameraService, tmp, packageName,
                        api1CameraId, facing, clientPid, clientUid,
                        getpid(), legacyMode);
            } else { // Camera2 API route
                ALOGW("Camera using old HAL version: %d", deviceVersion);
                return STATUS_ERROR_FMT(ERROR_DEPRECATED_HAL,
                        "Camera device \"%s\" HAL version %d does not support camera2 API",
                        cameraId.string(), deviceVersion);
            }
            break;
          case CAMERA_DEVICE_API_VERSION_3_0:
          case CAMERA_DEVICE_API_VERSION_3_1:
          case CAMERA_DEVICE_API_VERSION_3_2:
          case CAMERA_DEVICE_API_VERSION_3_3:
          case CAMERA_DEVICE_API_VERSION_3_4:
            if (effectiveApiLevel == API_1) { // Camera1 API route
                sp tmp = static_cast(cameraCb.get());
                *client = new Camera2Client(cameraService, tmp, packageName,
                        cameraId, api1CameraId,
                        facing, clientPid, clientUid,
                        servicePid, legacyMode);
            } else { // Camera2 API route
                sp tmp =
                        static_cast(cameraCb.get());
                *client = new CameraDeviceClient(cameraService, tmp, packageName, cameraId,
                        facing, clientPid, clientUid, servicePid);
            }
            break;
          default:
            // Should not be reachable
            ALOGE("Unknown camera device HAL version: %d", deviceVersion);
            return STATUS_ERROR_FMT(ERROR_INVALID_OPERATION,
                    "Camera device \"%s\" has unknown HAL version %d",
                    cameraId.string(), deviceVersion);
        }
    } else {
        // A particular HAL version is requested by caller. Create CameraClient
        // based on the requested HAL version.
        if (deviceVersion > CAMERA_DEVICE_API_VERSION_1_0 &&
            halVersion == CAMERA_DEVICE_API_VERSION_1_0) {
            // Only support higher HAL version device opened as HAL1.0 device.
            sp tmp = static_cast(cameraCb.get());
            *client = new CameraClient(cameraService, tmp, packageName,
                    api1CameraId, facing, clientPid, clientUid,
                    servicePid, legacyMode);
        } else {
            // Other combinations (e.g. HAL3.x open as HAL2.x) are not supported yet.
            ALOGE("Invalid camera HAL version %x: HAL %x device can only be"
                    " opened as HAL %x device", halVersion, deviceVersion,
                    CAMERA_DEVICE_API_VERSION_1_0);
            return STATUS_ERROR_FMT(ERROR_ILLEGAL_ARGUMENT,
                    "Camera device \"%s\" (HAL version %d) cannot be opened as HAL version %d",
                    cameraId.string(), deviceVersion, halVersion);
        }
    }
    return Status::ok();
}

Android Camera原理之openCamera模块(一)_第6张图片

CameraClient.jpg

CameraClient与Camera2Client是之前系统版本使用的camera client对象,现在都使用CameraDeviceClient了
BnCamera --> ./frameworks/av/camera/include/camera/android/hardware/ICamera.h
ICamera --> ./frameworks/av/camera/include/camera/android/hardware/ICamera.h
BnCameraDeviceUser --> android/hardware/camera2/BnCameraDeviceUser.h 这是ICameraDeviceUser.aidl自动生成的binder 对象。所以最终得到的client对象就是ICameraDeviceUser.Stub对象。

2.5 将获取的远程服务设置到CameraDeviceImpl实例中

deviceImpl.setRemoteDevice(cameraUser);
device = deviceImpl;

这个cameraUser就是cameraservice端设置的ICameraDeviceUser.Stub对象,

    public void setRemoteDevice(ICameraDeviceUser remoteDevice) throws CameraAccessException {
        synchronized(mInterfaceLock) {
            // TODO: Move from decorator to direct binder-mediated exceptions
            // If setRemoteFailure already called, do nothing
            if (mInError) return;

            mRemoteDevice = new ICameraDeviceUserWrapper(remoteDevice);

            IBinder remoteDeviceBinder = remoteDevice.asBinder();
            // For legacy camera device, remoteDevice is in the same process, and
            // asBinder returns NULL.
            if (remoteDeviceBinder != null) {
                try {
                    remoteDeviceBinder.linkToDeath(this, /*flag*/ 0);
                } catch (RemoteException e) {
                    CameraDeviceImpl.this.mDeviceExecutor.execute(mCallOnDisconnected);

                    throw new CameraAccessException(CameraAccessException.CAMERA_DISCONNECTED,
                            "The camera device has encountered a serious error");
                }
            }

            mDeviceExecutor.execute(mCallOnOpened);
            mDeviceExecutor.execute(mCallOnUnconfigured);
        }
    }

这个mRemoteDevice是应用程序进程和android camera service端之间链接的桥梁,上层操作camera的方法会通过调用mRemoteDevice来调用到camera service端来实现操作底层camera驱动的目的。

小结

本文通过我们熟知的openCamera函数讲起,openCamera串起应用程序和cameraService之间的联系,通过研究cameraservice代码,我们知道了底层是如何通过HAL调用camera驱动设备的。下面会逐渐深入讲解camera底层知识,不足之处,敬请谅解。

转载于:https://my.oschina.net/u/920274/blog/3078082

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