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Camera Framework 分析

Camera Framework本文主要介绍分析Camera API2相关。

类别文件速查表

类文件目录

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1. Framework Java API1:frameworks/base/core/java/android/hardware/Camera.java 2. Framework Java API2:frameworks/base/core/java/android/hardware/camera2 3. Framework JNI: frameworks/base/core/jni/ 4. AIDL: frameworks/av/camera/aidl 5. Framework Native: frameworks/av/camera  6. Framework Service: frameworks/av/services/camera/libcameraservice

JNI相关

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// frameworks/base/core/jni ./android_hardware_camera2_legacy_LegacyCameraDevice.cpp ./android_hardware_Camera.cpp ./android/graphics/Camera.cpp ./include/android_runtime/android_hardware_camera2_CameraMetadata.h ./android_hardware_camera2_DngCreator.cpp ./android_hardware_camera2_CameraMetadata.cpp ./android_hardware_camera2_legacy_PerfMeasurement.cpp

API 1中，使用jni通过Binder机制和CameraService通信。API 2中，直接在CameraManager.java中通过Binder机制和CameraService通信。

AIDL相关

Framework Camere AIDL是Camera跨过程通信中使用的客户端和服务端AIDL文件、代码都在frameworks/av/camera/其中，目录aidl文件一共有 16 个：

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xmt@server005:~/frameworks/av/camera/aidl/android/hardware$ tree . ├── camera2 │ ├── CaptureRequest.aidl │ ├── ICameraDeviceCallbacks.aidl │ ├── ICameraDeviceUser.aidl │ ├── impl │ │ ├── CameraMetadataNative.aidl │ │ └── CaptureResultExtras.aidl │ ├── params │ │ ├── OutputConfiguration.aidl │ │ ├── VendorTagDescriptor.aidl │ │ └── VendorTagDescriptorCache.aidl │ └── utils │     └── SubmitInfo.aidl ├── CameraInfo.aidl ├── CameraStatus.aidl ├── ICamera.aidl ├── ICameraClient.aidl ├── ICameraService.aidl ├── ICameraServiceListener.aidl └── ICameraServiceProxy.aidl  4 directories, 16 files

frameworks/av/camera/aidl/目录下的aidl有两种类型的文件：

  • 作为Binder中的IInterface可以在跨过程通信中提供的方法
  • 作为Binder中的parcelable跨过程通信数据传输的数据结构

这两种类型的文件很容易区分名称，IInterface所有类型的文件都是以I开头，如:ICameraService.aidl, ICameraDeviceUser.aidl等等。不管是什么类型的。aidl它们都生成相应的文件.java, .h, .cpp分别提供文件Java层和CPP层调用。

IInterface类型文件

IInterface类型文件一共有 7 个，它们的.java, .h, .cpp大部分文件都是自动生成的。

Java文件是在frameworks/base/Android.mk在编译过程中自动定义规则：

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// frameworks/base/Android.mk LOCAL_SRC_FILES  =      ...     ../av/camera/aidl/android/hardware/ICameraService.aidl      ../av/camera/aidl/android/hardware/ICameraServiceListener.aidl      ../av/camera/aidl/android/hardware/ICameraServiceProxy.aidl      ../av/camera/aidl/android/hardware/ICamera.aidl      ../av/camera/aidl/android/hardware/ICameraClient.aidl      ../av/camera/aidl/android/hardware/camera2/ICameraDeviceUser.aidl      ../av/camera/aidl/android/hardware/camera2/ICameraDeviceCallbacks.aidl      ...

在out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/dotdot/生成对应的目录Java文件：

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// out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/dotdot/ av/camera/aidl/android/hardware/ICameraService.java av/camera/aidl/android/hardware/ICameraServiceListener.java av/camera/aidl/android/hardware/ICameraServiceProxy.java av/camera/aidl/android/hardware/ICamera.java av/camera/aidl/android/hardware/ICameraClient.java av/camera/aidl/androd/hardware/camera2/ICameraDeviceUser.java
av/camera/aidl/android/hardware/camera2/ICameraDeviceCallbacks.java

.h, .cpp 文件中，ICamera.aidl, ICameraClient.aidl 两个文件是直接以代码形式手动实现的：

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// 1. ICameraClient.aidl
frameworks/av/camera/aidl/android/hardware/ICameraClient.aidl
frameworks/av/camera/include/camera/android/hardware/ICameraClient.h
frameworks/av/camera/ICameraClient.cpp

// 2. ICamera.aidl
frameworks/av/camera/aidl/android/hardware/ICamera.aidl
frameworks/av/camera/include/camera/android/hardware/ICamera.h
frameworks/av/camera/ICamera.cpp

其他 5 个 aidl 文件是在 frameworks/av/camera/Android.bp 中定义规则，编译时自动生成对应的 .h, .cpp 文件：

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// frameworks/av/camera/Android.bp
cc_library_shared {
    name: "libcamera_client",

    aidl: {
        export_aidl_headers: true,
        local_include_dirs: ["aidl"],
        include_dirs: [
            "frameworks/native/aidl/gui",
        ],
    },

    srcs: [
        // AIDL files for camera interfaces
        // The headers for these interfaces will be 
        // available to any modules that
        // include libcamera_client, at the path "aidl/package/path/BnFoo.h"
        "aidl/android/hardware/ICameraService.aidl",
        "aidl/android/hardware/ICameraServiceListener.aidl",
        "aidl/android/hardware/ICameraServiceProxy.aidl",
        "aidl/android/hardware/camera2/ICameraDeviceCallbacks.aidl",
        "aidl/android/hardware/camera2/ICameraDeviceUser.aidl",


        // Source for camera interface parcelables, 
        // and manually-written interfaces
        "Camera.cpp",
        "CameraMetadata.cpp",
        "CameraParameters.cpp",
        ...
}

在 out/soong/.intermediates/frameworks/av/camera/libcamera_client/ 目录下生成对应的 .h, .cpp 文件，通常在该目录下会同时生成 32 和 64 位两套代码，但实际两份代码是一样的，这里选取 64 位的：

  • 64 位：android_arm64_armv8-a_shared_core
  • 32 位：android_arm_armv7-a-neon_cortex-a53_shared_core
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// 目录 out/soong/.intermediates/frameworks/av/camera/libcamera_client
// 64 位 android_arm64_armv8-a_shared_core/gen/aidl/
android/hardware/ICameraService.h
android/hardware/BnCameraService.h
frameworks/av/camera/aidl/android/hardware/ICameraService.cpp

android/hardware/ICameraServiceListener.h
android/hardware/BnCameraServiceListener.h
frameworks/av/camera/aidl/android/hardware/ICameraServiceListener.cpp

android/hardware/ICameraServiceProxy.h
android/hardware/BnCameraServiceProxy.h
frameworks/av/camera/aidl/android/hardware/ICameraServiceProxy.cpp

android/hardware/camera2/ICameraDeviceUser.h
android/hardware/camera2/BnCameraDeviceUser.h
frameworks/av/camera/aidl/android/hardware/camera2/ICameraDeviceUser.cpp

android/hardware/camera2/ICameraDeviceCallbacks.h
android/hardware/camera2/BnCameraDeviceCallbacks.h
frameworks/av/camera/aidl/android/hardware/camera2/ICameraDeviceCallbacks.cpp

parcelable 类型文件

parcelable 类型文件一共有 9 个，它们都是手动编写的代码。

Java 文件目录为 frameworks/base/core/java/android/hardware/ ：

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// frameworks/base/core/java/android/hardware/
camera2/CaptureRequest.java
camera2/impl/CameraMetadataNative.java
camera2/impl/CaptureResultExtras.java
camera2/params/OutputConfiguration.java
camera2/params/VendorTagDescriptor.java
camera2/params/VendorTagDescriptorCache.java
camera2/utils/SubmitInfo.java
CameraInfo.java
CameraStatus.java

.h, .cpp 文件并不一定是和 aidl 文件名称一一对应的，而是在 aidl 文件中定义的，比如 CameraStatus.aidl 定义如下：

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package android.hardware;

/** @hide */
parcelable CameraStatus cpp_header "camera/CameraBase.h";

parcelable 类型的 aidl 文件对应的 .h, .cpp 文件目录为 frameworks/av/camera ，对应关系整理如下：

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// .h, .cpp 文件目录 frameworks/av/camera
// CaptureRequest.aidl
include/camera/camera2/CaptureRequest.h
camera2/CaptureRequest.cpp

// CameraMetadataNative.aidl
include/camera/CameraMetadata.h
CameraMetadata.cpp

// CaptureResultExtras.aidl
include/camera/CaptureResult.h
CaptureResult.cpp

// OutputConfiguration.aidl
include/camera/camera2/OutputConfiguration.h
camera2/OutputConfiguration.cpp

// VendorTagDescriptor.aidl 和 VendorTagDescriptorCache.aidl
include/camera/VendorTagDescriptor.h
VendorTagDescriptor.cpp

// SubmitInfo.aidl
include/camera/camera2/SubmitInfo.h
camera2/SubmitInfo.cpp

// CameraInfo.aidl 和 CameraStatus.aidl
include/camera/CameraBase.h
CameraBase.cpp

ICameraService 相关

分为客户端向服务端的请求 ICameraService.aidl 和客户端监听服务端的变化 ICameraServiceListener.aidl 。这两个 AIDL 是在 CameraService.cpp 中实现对应功能的。

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interface 
{
    ...
    const int CAMERA_TYPE_BACKWARD_COMPATIBLE = 0;
    const int CAMERA_TYPE_ALL = 1;

    // 返回指定类型的相机设备数量
    int getNumberOfCameras(int type);
    // 根据 id 返回当前相机设备信息
    CameraInfo getCameraInfo(int cameraId);

    ...
    const int CAMERA_HAL_API_VERSION_UNSPECIFIED = -1;
    // api1 + hal1
    ICamera connect(ICameraClient client,
            int cameraId,
            String opPackageName,
            int clientUid, int clientPid);

    // api2 + hal3
    ICameraDeviceUser connectDevice(ICameraDeviceCallbacks callbacks,
            String cameraId,
            String opPackageName,
            int clientUid);

    // api1 + 指定 hal 版本（通常为 hal1）
    ICamera connectLegacy(ICameraClient client,
            int cameraId,
            int halVersion,
            String opPackageName,
            int clientUid);

    // 添加和移除 ICameraServiceListener 监听
    CameraStatus[] addListener(ICameraServiceListener listener);
    void removeListener(ICameraServiceListener listener);

    // 根据 id 返回相机支持的属性
    CameraMetadataNative getCameraCharacteristics(String cameraId);

    // 获取 vendor tag 
    VendorTagDescriptor getCameraVendorTagDescriptor();
    VendorTagDescriptorCache getCameraVendorTagCache();

    // camera api 1 获取参数信息
    String getLegacyParameters(int cameraId);

    const int API_VERSION_1 = 1;
    const int API_VERSION_2 = 2;
    // 指定 id 支持的 API 版本
    boolean supportsCameraApi(String cameraId, int apiVersion);
    // 指定 id 设置手电筒模式
    void setTorchMode(String cameraId, boolean enabled, 
        IBinder clientBinder);

    // 服务端向系统打印系统消息
    const int EVENT_NONE = 0;
    const int EVENT_USER_SWITCHED = 1;
    oneway void notifySystemEvent(int eventId, in int[] args);
}

// 2. ICameraServiceListener.aidl
interface ICameraServiceListener
{
    const int STATUS_NOT_PRESENT      = 0;
    const int STATUS_PRESENT          = 1;
    const int STATUS_ENUMERATING      = 2;
    const int STATUS_NOT_AVAILABLE    = -2;
    const int STATUS_UNKNOWN          = -1;
    // 相机设备状态变化事件
    oneway void onStatusChanged(int status, String cameraId);

    const int TORCH_STATUS_NOT_AVAILABLE = 0;
    const int TORCH_STATUS_AVAILABLE_OFF = 1;
    const int TORCH_STATUS_AVAILABLE_ON  = 2;
    const int TORCH_STATUS_UNKNOWN = -1;
    // 手电筒状态变化事件
    oneway void onTorchStatusChanged(int status, String cameraId);
}

ICameraServiceProxy.aidl 文件

CameraServiceProxy 服务是在 Java 层注册的：

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interface ICameraServiceProxy
{
    // CameraService 向代理服务发送消息，通知用户更新
    oneway void pingForUserUpdate();

    const int CAMERA_STATE_OPEN = 0;
    const int CAMERA_STATE_ACTIVE = 1;
    const int CAMERA_STATE_IDLE = 2;
    const int CAMERA_STATE_CLOSED = 3;
    const int CAMERA_FACING_BACK = 0;
    const int CAMERA_FACING_FRONT = 1;
    const int CAMERA_FACING_EXTERNAL = 2;

    // CameraService 向代理服务发送消息，通知相机设备状态更新
    oneway void notifyCameraState(String cameraId, int facing, 
            int newCameraState, String clientName);
}

ICamera 相关

Camera API1 才会使用到，分为 ICamera.aidl, ICameraClient.aidl 它们的代码是手动实现的，参考：CameraClient.h/cpp, Camera.h/cpp

ICameraDevice 相关

Camera API2 才会使用到，分为客户端向服务端的请求 ICameraDeviceUser.aidl 和服务端发给客户端的回调 ICameraDeviceCallbacks.aidl 。 表示相机设备具备的能力，能够提供的函数；这两个 AIDL 是在 CameraDeviceClient 中实现对应功能的。

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// 1. ICameraDeviceUser.aidl 
interface ICameraDeviceUser
{
    void disconnect();

    const int NO_IN_FLIGHT_REPEATING_FRAMES = -1;
    // 向设备提交捕获请求
    SubmitInfo submitRequest(in CaptureRequest request, boolean streaming);
    SubmitInfo submitRequestList(in CaptureRequest[] requestList, 
        boolean streaming);
    // 取消置顶 id 的重复请求，并返回上次请求的帧 id
    long cancelRequest(int requestId);

    const int NORMAL_MODE = 0;
    const int CONSTRAINED_HIGH_SPEED_MODE = 1;
    const int VENDOR_MODE_START = 0x8000;

    // 在流处理前执行配置请求
    void beginConfigure();
    // 根据指定输出配置，创建流
    int createStream(in OutputConfiguration outputConfiguration);
    void endConfigure(int operatingMode);
    void deleteStream(int streamId);

    // 创建输入流，返回流 id
    int createInputStream(int width, int height, int format);
    // 返回输入流的 Surface
    Surface getInputSurface();

    // Keep in sync with public API in
    // frameworks/base/core/java/android/hardware/camera2/CameraDevice.java
    const int TEMPLATE_PREVIEW = 1;
    const int TEMPLATE_STILL_CAPTURE = 2;
    const int TEMPLATE_RECORD = 3;
    const int TEMPLATE_VIDEO_SNAPSHOT = 4;
    const int TEMPLATE_ZERO_SHUTTER_LAG = 5;
    const int TEMPLATE_MANUAL = 6;
    // 根据模板创建默认请求，返回相机参数信息
    CameraMetadataNative createDefaultRequest(int templateId);
    // 获取相机参数信息
    CameraMetadataNative getCameraInfo();
    void waitUntilIdle();
    long flush();
    void prepare(int streamId);
    void tearDown(int streamId);
    void prepare2(int maxCount, int streamId);
    void finalizeOutputConfigurations(int streamId, 
        in OutputConfiguration outputConfiguration);
}

// 2. ICameraDeviceCallbacks.aidl
interface ICameraDeviceCallbacks
{
    ...
    oneway void onDeviceError(int errorCode, 
        in CaptureResultExtras resultExtras);
    oneway void onDeviceIdle();
    oneway void onCaptureStarted(in CaptureResultExtras resultExtras, 
        long timestamp);
    oneway void onResultReceived(in CameraMetadataNative result,
                                 in CaptureResultExtras resultExtras);
    oneway void onPrepared(int streamId);
    // 重复请求引起的错误回调
    oneway void onRepeatingRequestError(in long lastFrameNumber,
                                        in int repeatingRequestId);
    oneway void onRequestQueueEmpty();
}

Services 目录下的文件介绍

frameworks/av/services/camera/libcameraserviceAOSP 中这个目录下是 87 个文件，而 Qcom 的基线中增加了 27 个文件，分别为 api1/qticlient2 目录下的 25 个文件，以及 QTICamera2Client.cpp, QTICamera2Client.h 两个文件。

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.
├── Android.mk
├── api1
│   ├── client2
│   └── qticlient2
├── api2
├── CameraFlashlight.cpp
├── CameraFlashlight.h
├── CameraService.cpp
├── CameraService.h
├── common
├── device1
├── device3
├── gui
├── MODULE_LICENSE_APACHE2
├── NOTICE
├── tests
└── utils

从目录结构上可以看出，API1/2 和 HAL1/3 就是在这一层体现的。

API1/API2

APP Java 客户端调用服务端方法时，Camera API1/2 接口对应功能都是在 CameraService 中实现的，而这里的 API1/2 目录对应的就是对上层不同版本接口的处理。

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api1
├── Camera2Client.cpp
├── Camera2Client.h
├── CameraClient.cpp
├── CameraClient.h
├── client2
│   ├── CallbackProcessor.cpp
│   ├── CallbackProcessor.h
│   ├── Camera2Heap.h
│   ├── CaptureSequencer.cpp
│   ├── CaptureSequencer.h
│   ├── FrameProcessor.cpp
│   ├── FrameProcessor.h
│   ├── JpegCompressor.cpp
│   ├── JpegCompressor.h
│   ├── JpegProcessor.cpp
│   ├── JpegProcessor.h
│   ├── Parameters.cpp
│   ├── Parameters.h
│   ├── StreamingProcessor.cpp
│   ├── StreamingProcessor.h
│   ├── ZslProcessor.cpp
│   └── ZslProcessor.h
├── QTICamera2Client.cpp
├── QTICamera2Client.h
└── qticlient2
    ├── CallbackProcessor.cpp
    ├── CallbackProcessor.h
    ├── Camera2Heap.h
    ├── CaptureSequencer.cpp
    ├── CaptureSequencer.h
    ├── FrameProcessor.cpp
    ├── FrameProcessor.h
    ├── JpegCompressor.cpp
    ├── JpegCompressor.h
    ├── JpegProcessor.cpp
    ├── JpegProcessor.h
    ├── Parameters.cpp
    ├── Parameters.h
    ├── QTICaptureSequencer.cpp
    ├── QTICaptureSequencer.h
    ├── QTIFrameProcessor.cpp
    ├── QTIFrameProcessor.h
    ├── QTIParameters.cpp
    ├── QTIParameters.h
    ├── RawProcessor.cpp
    ├── RawProcessor.h
    ├── StreamingProcessor.cpp
    ├── StreamingProcessor.h
    ├── ZslProcessor.cpp
    └── ZslProcessor.h
api2
├── CameraDeviceClient.cpp
└── CameraDeviceClient.h

BasicClient 有三个重要的子类：

  • CameraClient 如果平台仅支持 HAL 1，即 CAMERA_DEVICE_API_VERSION_1_0 ；使用 API 1/2 + HAL 1 都会对应该客户端。
  • Camera2Client 如果平台支持 HAL 3 ，即 CAMERA_DEVICE_API_VERSION_3_0 及以上版本；使用 API 1 + HAL 3 对应的客户端。Camera2Client 会将 API1 中的接口转换为 API2 中对应的功能。
  • CameraDeviceClient 如果平台支持 HAL 3 ，使用 API 2 + HAL 3 对应的客户端。

平台仅支持 HAL 1 时，API 2 在 openCamera 时，通过 CameraDeviceUserShim 将 API 2 转换为 API 1 ，即 HAL 1 + API 1 向下发起请求。LegacyCameraDevice 会将 CAMERA API2 转换为 CAMERA API1 ，而 CameraDeviceUserShim 封装了 LegacyCameraDevice 。

QTICamera2Client

Qcom 的基线中增加了 27 个文件，分别为 api1/qticlient2 目录下的 25 个文件，以及 QTICamera2Client.cpp, QTICamera2Client.h 两个文件。 而 QTICamera2Client 是高通针对 API1 做的优化？在什么情况下会转换为 QTICamera2Client 呢？看如下源码：

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// 1. Camera2Client.h
class Camera2Client :
        public Camera2ClientBase<CameraService::Client>
{

friend class QTICamera2Client;
#endif
...

    sp<camera2::RawProcessor> mRawProcessor;
#endif
...

    sp<QTICamera2Client> mQTICamera2Client;
#endif
...
}

// 2. Camera2Client.cpp
template<typename TProviderPtr>
status_t Camera2Client::initializeImpl(TProviderPtr providerPtr)
{
...

    mQTICamera2Client = new QTICamera2Client(this);
#endif
...

    mRawProcessor = new RawProcessor(this, mCaptureSequencer);
    threadName = String8::format("C2-%d-RawProc", mCameraId);
    mRawProcessor->run(threadName.string());
#endif
...
}

QTICamera2Client 是高通对 API 1 中 Camera2Client 做的一层封装，添加了部分功能，主要是向上提供 raw 数据。

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// 1. QTICamera2Client.h
class QTICamera2Client: public virtual RefBase{
private:
    wp<Camera2Client> mParentClient;
    status_t stopPreviewExtn();

public:
    QTICamera2Client(sp<Camera2Client> client);
    ~QTICamera2Client();
    ...
}

// 2. QTICamera2Client.cpp
QTICamera2Client::QTICamera2Client(sp<Camera2Client> client):
        mParentClient(client) {
}

device1/device3

device1/device3 可以理解为 Framework 层对应 HAL 层的 HAL 1/3 。

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device1
├── CameraHardwareInterface.cpp
└── CameraHardwareInterface.h
device3
├── Camera3BufferManager.cpp
├── Camera3BufferManager.h
├── Camera3Device.cpp
├── Camera3Device.h
├── Camera3DummyStream.cpp
├── Camera3DummyStream.h
├── Camera3InputStream.cpp
├── Camera3InputStream.h
├── Camera3IOStreamBase.cpp
├── Camera3IOStreamBase.h
├── Camera3OutputStream.cpp
├── Camera3OutputStream.h
├── Camera3OutputStreamInterface.h
├── Camera3SharedOutputStream.cpp
├── Camera3SharedOutputStream.h
├── Camera3StreamBufferFreedListener.h
├── Camera3StreamBufferListener.h
├── Camera3Stream.cpp
├── Camera3Stream.h
├── Camera3StreamInterface.h
├── Camera3StreamSplitter.cpp
├── Camera3StreamSplitter.h
├── StatusTracker.cpp
└── StatusTracker.h
  • API1/device1/HAL1 的连接过程
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// API1: CameraClient.h
sp<CameraHardwareInterface>     mHardware;
// device1: CameraHardwareInterface.h
sp<hardware::camera::device::V1_0::ICameraDevice> mHidlDevice;
// 这里的 ICameraDevice 即为 HAL1

API1 的客户端 CameraClient 对应的 device1: CameraHardwareInterface，而它直接包含了 HAL1 中 ICameraDevice 。

  • API1/3/device3/HAL3 的连接过程 
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    // API1: Camera2Client.h
class Camera2Client :
    public Camera2ClientBase<CameraService::Client>{...}

// API2: CameraDeviceClient.h
class CameraDeviceClient :
    public Camera2ClientBase<CameraDeviceClientBase>,
    public camera2::FrameProcessorBase::FilteredListener{...}

// Camera2ClientBase.h
sp<CameraDeviceBase>  mDevice;

// Camera2ClientBase.cpp
template <typename TClientBase>
Camera2ClientBase<TClientBase>::Camera2ClientBase(
    const sp<CameraService>& cameraService,
    const sp<TCamCallbacks>& remoteCallback,
    const String16& clientPackageName,
    const String8& cameraId,
    int cameraFacing,
    int clientPid,
    uid_t clientUid,
    int servicePid):
    TClientBase(cameraService, remoteCallback, clientPackageName,
            cameraId, cameraFacing, clientPid, clientUid, servicePid),
    mSharedCameraCallbacks(remoteCallback),
    mDeviceVersion(cameraService->getDeviceVersion(
            TClientBase::mCameraIdStr)),
    mDeviceActive(false)
{
    ...
    mInitialClientPid = clientPid;
    // 只要是 HAL3 ，则 device 都是对应的 Camera3Device
    mDevice = new Camera3Device(cameraId);
    ...
}

从源码可以看出，不管是 API1/2 ，只要是 HAL 3 ，Camera2Client, CameraDeviceClient 两个客户端对应的都是 device3: Camera3Device 。

Camera3Device::HalInterface 内部类，用于和 HAL 层通信，实现了 HAL 层 ICameraDeviceSession.hal 部分代码：

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// Camera3Device.h
class Camera3Device :
    ...
    class HalInterface : public camera3::Camera3StreamBufferFreedListener {
      public:
        ...
        // Calls into the HAL interface

        // Caller takes ownership of requestTemplate
        status_t constructDefaultRequestSettings(
                camera3_request_template_t templateId,
                /*out*/ camera_metadata_t **requestTemplate);
        status_t configureStreams(
            /*inout*/ camera3_stream_configuration *config);
        status_t processCaptureRequest(camera3_capture_request_t *request);
        status_t flush();
        status_t close();
        ...
    }
    ...
}

cameraserver 进程

cameraserver 进程的源码在 frameworks/av/camera/cameraserver 目录下，该目录只有三个文件：

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.
├── Android.mk              
├── cameraserver.rc         // rc 文件
└── main_cameraserver.cpp   // 主进程

cameraserver 进程在启动时，做了三件事：

  • 设置 Socket 通信时，对端关闭读取时进程不退出，返回错误信息（Socket 用在了哪？）
  • HIDL 通信初始化
  • Native Binder 初始化，CameraService 向 service_manager 注册服务
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// frameworks/av/camera/cameraserver/main_cameraserver.cpp
int main(int argc __unused, char** argv __unused)
{
    // 1. Socket 通信时，对端关闭读取时进程不退出，返回错误信息
    signal(SIGPIPE, SIG_IGN);

    // 2. HIDL 通信初始化
    // Set 3 threads for HIDL calls
    hardware::configureRpcThreadpool(3, /*willjoin*/ false);

    // 3. Native Binder 初始化，CameraService 是具体的服务
    sp<ProcessState> proc(ProcessState::self());
    sp<IServiceManager> sm = defaultServiceManager();
    ALOGI("ServiceManager: %p", sm.get());
    CameraService::instantiate();
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();
}

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// init 进程启动名字为 cameraserver 的进程及对应路径
service cameraserver /system/bin/cameraserver
    // class 表示类别，同一类别的进程同时启动
    class main
    // 用户名
    user cameraserver
    // 分组
    group audio camera input drmrpc
    ioprio rt 4
    writepid /dev/cpuset/camera-daemon/tasks /dev/stune/top-app/tasks

CameraService 启动服务注册流程图：0109-android-camera-4-framework-CameraService-addService.png

CameraService 服务

CameraService 服务的名称为：media.camera ，主要有两个功能：

  • 作为服务端 实现 AIDL 对应功能，当 API1/2 客户端发出请求后，作为服务端响应并处理这些功能。
  • 作为客户端 实现 HIDL 回调，用于响应 HAL 层发回的回调。并且通过 CameraProviderManager 和 HAL 层实现双向通信。

服务名称

CameraService 继承了 BinderService<CameraService> ，将 CameraService::instantiate(); 代码展开：

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// BinderService.h
template<typename SERVICE>
class BinderService
{
public:
    static status_t publish(bool allowIsolated = false) {
        sp<IServiceManager> sm(defaultServiceManager());
        return sm->addService(
                String16(SERVICE::getServiceName()),
                new SERVICE(), allowIsolated);
    }
    ...
    static void instantiate() { publish(); }
    ...
}

// IServiceManager.h
class IServiceManager : public IInterface
{
public:
    ...
    virtual status_t addService( const String16& name,
            const sp<IBinder>& service,
            bool allowIsolated = false) = 0;
    ...
}

// CameraService.h
class CameraService :
    public BinderService<CameraService>,
    public virtual ::android::hardware::BnCameraService,
    public virtual IBinder::DeathRecipient,
    public camera_module_callbacks_t,
    public virtual CameraProviderManager::StatusListener
{
    ...
    // Implementation of BinderService<T>
    static char const* getServiceName() { return "media.camera"; }
    ...
}

从继承关系及 CameraService.h 源码，getServiceName 设置了 CameraService 服务的名称为 media.camera 。

注册流程图

CameraService 注册流程，查看原图

源码分析

先来看 CameraService.h 头文件相关定义：

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// CameraService.h
class CameraService :
    public BinderService<CameraService>,
    public virtual ::android::hardware::BnCameraService,
    public virtual IBinder::DeathRecipient,
    public camera_module_callbacks_t,
    public virtual CameraProviderManager::StatusListener
{

    static char const* getServiceName() { return "media.camera"; }
}
  • BinderService 继承了 BinderService ，用于注册服务。服务名称为 media.camera 。
  • camera_module_callbacks_t 继承了 camera_module_callbacks_t ，它是在 HAL 中定义的，用于 HAL 向 Framework 发送通知。
  • StatusListener 继承了 StatusListener ，它是在 CameraProviderManager.h 中定义的，用于 CameraProviderManager 向 CameraService 发送通知。

现在查看 CameraService 的构造方法，因为在注册服务时 BinderService 会对 CameraService 强指针引用，所以会调用对应函数 onFirstRef ：

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// CameraService.cpp
CameraService::CameraService() :
        mEventLog(DEFAULT_EVENT_LOG_LENGTH),
        mNumberOfCameras(0), mNumberOfNormalCameras(0),
        mSoundRef(0), mInitialized(false) {
    // camera_module_callbacks_t 结构体的函数指针赋值
    this->camera_device_status_change = 
        android::camera_device_status_change;
    this->torch_mode_status_change = android::torch_mode_status_change;
    ...
}

void CameraService::onFirstRef()
{
    ...
    BatteryNotifier& notifier(BatteryNotifier::getInstance());
    notifier.noteResetCamera();
    notifier.noteResetFlashlight();

    status_t res = INVALID_OPERATION;

    // 实例化 CameraProviderManager ，并连接 Hardware
    res = enumerateProviders();
    if (res == OK) {
        mInitialized = true;
    }

    // CameraServiceProxy 服务是 Java 代码注册的
    // 但是 CameraService 启动时间很早，CameraServiceProxy 可能还并没有注册
    // 实际调试结果也是，这段代码实际不会调用 CameraServiceProxy 对应方法
    CameraService::pingCameraServiceProxy();
}

构造函数中非常简单，仅仅是将 camera_module_callbacks_t 结构体的函数指针赋值；在 onFirstRef 中，主要通过 enumerateProviders 来实例化对应的 CameraProviderManager 并连接 HAL ，最后去 ping 一次 CameraServiceProxy 代理服务，实际上是 ping 不通的，因为 CameraService.cpp 一定是比 CameraServiceProxy.java 启动的早。

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// CameraService.cpp
status_t CameraService::enumerateProviders() {
    ...
    // 实例化 CameraProviderManager
    if (nullptr == mCameraProviderManager.get()) {
        mCameraProviderManager = new CameraProviderManager();
        res = mCameraProviderManager->initialize(this);
        ...
    }

    mNumberOfCameras = mCameraProviderManager->getCameraCount();
    mNumberOfNormalCameras =
            mCameraProviderManager->getAPI1CompatibleCameraCount();
    mCameraProviderManager->setUpVendorTags();

    if (nullptr == mFlashlight.get()) {
        mFlashlight = new CameraFlashlight(mCameraProviderManager, this);
    }
    res = mFlashlight->findFlashUnits();
    ...
    for (auto& cameraId : mCameraProviderManager->getCameraDeviceIds()){
        ...
        onDeviceStatusChanged(id8, CameraDeviceStatus::PRESENT);
        ...
    }

    return OK;
}

如果 mCameraProviderManager 为空，则实例化并调用 initialize ；接着实例化 CameraFlashlight ；先看头文件 CameraProviderManager.h 中定义的几个重要数据结构和函数：

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// CameraProviderManager.h
class CameraProviderManager : 
    virtual public hidl::manager::V1_0::IServiceNotification {
public:
    ...
    // 定义纯虚函数
    struct ServiceInteractionProxy {
        virtual bool registerForNotifications(
                const std::string &serviceName,
                const sp<hidl::manager::V1_0::IServiceNotification>
                &notification) = 0;
        virtual sp<hardware::camera::provider::V2_4::ICameraProvider> 
                getService(const std::string &serviceName) = 0;
        virtual ~ServiceInteractionProxy() {}
    };

    // 调用 ICameraProvider 实现这些方法
    struct HardwareServiceInteractionProxy : 
            public ServiceInteractionProxy {
        virtual bool registerForNotifications(
                const std::string &serviceName,
                const sp<hidl::manager::V1_0::IServiceNotification>
                &notification) override {
            return hardware::camera::provider::V2_4::
                    ICameraProvider::registerForNotifications(
                    serviceName, notification);
        }
        virtual sp<hardware::camera::provider::V2_4::ICameraProvider>
                getService(const std::string &serviceName) override {
            return hardware::camera::provider::V2_4::
                    ICameraProvider::getService(serviceName);
        }
    };

    struct StatusListener : virtual public RefBase {
        ~StatusListener() {}
        virtual void onDeviceStatusChanged(const String8 &cameraId,
                hardware::camera::common::V1_0::CameraDeviceStatus 
                newStatus) = 0;
        virtual void onTorchStatusChanged(const String8 &cameraId,
                hardware::camera::common::V1_0::TorchModeStatus 
                newStatus) = 0;
        virtual void onNewProviderRegistered() = 0;
    };

    virtual hardware::Return<void> onRegistration(
            const hardware::hidl_string& fqName,
            const hardware::hidl_string& name,
            bool preexisting) override;

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

private:
  static HardwareServiceInteractionProxy sHardwareServiceInteractionProxy;
  • ServiceInteractionProxy 定义了几个纯虚函数，用于向 HAL 系统服务中注册 registerForNotifications 监听 ICameraProvider.hal 的消息；getService 返回 ICameraProvider 的实例。
  • HardwareServiceInteractionProxyServiceInteractionProxy 的实现结构体，具体调用 ICameraProvider 对应的 registerForNotifications, getService ；也就是 CameraProviderManager 持有 ICameraProvider 的远程实例。
  • onRegistrationregisterForNotifications 的回调函数，注册成功后回调。
  • StatusListener 状态监听接口，这些接口是在 CameraService 中实现的；用于 CameraProviderManager 回调 CameraService 。
  • sHardwareServiceInteractionProxy 静态变量，是初始化 initialize 函数形参 ServiceInteractionProxy 的默认值。

从 CameraService 中调用 CameraProviderManager::initialize 时，传入的是 CameraService 的实例，仅仅一个参数，所以 ServiceInteractionProxy 使用的是默认的 sHardwareServiceInteractionProxy 实例。

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// CameraProviderManager.cpp
// 实例化 HAL 代理
CameraProviderManager::HardwareServiceInteractionProxy
CameraProviderManager::sHardwareServiceInteractionProxy{};

status_t CameraProviderManager::initialize(
        wp<CameraProviderManager::StatusListener> listener,
        ServiceInteractionProxy* proxy) {
    ...
    mListener = listener;
    mServiceProxy = proxy;

    bool success = mServiceProxy->registerForNotifications(
        /* instance name, empty means no filter */ "",
        this);
    ...

    addProviderLocked(kLegacyProviderName, /*expected*/ false);
    return OK;
}

CameraProviderManager::initialize 中主要是初始化赋值 mListener, mServiceProxy ，并通过 sHardwareServiceInteractionProxy->registerForNotifications 向 HIDL 服务管理注册了自己，最后调用 addProviderLocked 。

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// CameraProviderManager.cpp
status_t CameraProviderManager::addProviderLocked(
        const std::string& newProvider, bool expected) {
    for (const auto& providerInfo : mProviders) {
        if (providerInfo->mProviderName == newProvider) {
            ALOGW(...);
            return ALREADY_EXISTS;
        }
    }

    // HIDL 通信，通过 ICameraProvider 和 HAL 层通信
    sp<provider::V2_4::ICameraProvider> interface;
    interface = mServiceProxy->getService(newProvider);

    if (interface == nullptr) {
        ...
    }

    sp<ProviderInfo> providerInfo =
            new ProviderInfo(newProvider, interface, this);
    status_t res = providerInfo->initialize();
    if (res != OK) {
        return res;
    }

    mProviders.push_back(providerInfo);

    return OK;
}

addProviderLocked 中有如下信息：

  • 通过代理获取 ICameraProvider 实例，用于和 HAL 通信
  • 新建 ProviderInfo 并初始化，保存 ICameraProvider 实例
  • mProviders 保存所有的 ProviderInfo （实测只有一个实例元素，名称为 legacy/0）
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// CameraProviderManager.h
struct ProviderInfo :
    virtual public 
        hardware::camera::provider::V2_4::ICameraProviderCallback,
    virtual public hardware::hidl_death_recipient
{
    const std::string mProviderName;
    const sp<hardware::camera::provider::V2_4::ICameraProvider> 
        mInterface;
    const metadata_vendor_id_t mProviderTagid;
    ...
}

ProviderInfo 继承了 ICameraProviderCallback, hidl_death_recipient ，它会处理来着 ICameraProvider 的回调。

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// CameraProviderManager.cpp
CameraProviderManager::ProviderInfo::ProviderInfo(
        const std::string &providerName,
        sp<provider::V2_4::ICameraProvider>& interface,
        CameraProviderManager *manager) :
        mProviderName(providerName),
        mInterface(interface),
        mProviderTagid(generateVendorTagId(providerName)),
        mUniqueDeviceCount(0),
        mManager(manager) {
    (void) mManager;
}

status_t CameraProviderManager::ProviderInfo::initialize() {
    status_t res = parseProviderName(mProviderName, &mType, &mId);
    ...
    // 设置回调
    hardware::Return<Status> status = mInterface->setCallback(this);
    ...
    // HIDL 连接
    hardware::Return<bool> linked = 
        mInterface->linkToDeath(this, /*cookie*/ mId);
    ...
    // Get initial list of camera devices, if any
    std::vector<std::string> devices;
    // 获取 CameraIdList ，实际是获取的一组设备名
    hardware::Return<void> ret = 
        mInterface->getCameraIdList([&status, &devices](
            Status idStatus,
            const hardware::hidl_vec<hardware::hidl_string>& 
                cameraDeviceNames) {
        status = idStatus;
        if (status == Status::OK) {
            for (size_t i = 0; i < cameraDeviceNames.size(); i++) {
                devices.push_back(cameraDeviceNames[i]);
            }
        } });
    ...
    for (auto& device : devices) {
        std::string id;
        // 添加从 HAL 返回的每个设备名
        status_t res = addDevice(device,
            hardware::camera::common::V1_0::CameraDeviceStatus::PRESENT,
            &id);
        ...
    }
    ...
    return OK;
}

ProviderInfo::initialize 初始化，主要是从 HAL 获取设备名后，添加具体的设备信息。

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// CameraProviderManager.h
struct DeviceInfo {
    const std::string mName;  // Full instance name
    const std::string mId;    // ID section of full name
    const hardware::hidl_version mVersion;
    const metadata_vendor_id_t mProviderTagid;
    ...
protected:
    bool mHasFlashUnit;
    template<class InterfaceT>
    static status_t setTorchMode(InterfaceT& interface, bool enabled);
};

// HALv1-specific camera fields, including the actual device interface
struct DeviceInfo1 : public DeviceInfo {
    typedef hardware::camera::device::V1_0::ICameraDevice InterfaceT;
    const sp<InterfaceT> mInterface;
    ...
private:
    CameraParameters2 mDefaultParameters;
};

// HALv3-specific camera fields, including the actual device interface
struct DeviceInfo3 : public DeviceInfo {
    typedef hardware::camera::device::V3_2::ICameraDevice InterfaceT;
    const sp<InterfaceT> mInterface;
    ...
private:
    CameraMetadata mCameraCharacteristics;
};

头文件中可以看出，DeviceInfo 有两个子类，分别对应 HAL 1 和 HAL 3 ，并将具体的 ICameraDevice 版本保存到 mInterface 中；所以设备添加时也会根据不同版本分别添加：

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// CameraProviderManager.cpp
status_t CameraProviderManager::ProviderInfo::addDevice(
        const std::string& name,
        CameraDeviceStatus initialStatus, 
        /*out*/ std::string* parsedId) {
    ...
    status_t res = parseDeviceName(name, &major, &minor, &type, &id);
    ...
    std::unique_ptr<DeviceInfo> deviceInfo;
    switch (major) {
        case 1:
            deviceInfo = initializeDeviceInfo<DeviceInfo1>(
                name, mProviderTagid, id, minor);
            break;
        case 3:
            deviceInfo = initializeDeviceInfo<DeviceInfo3>(
                name, mProviderTagid, id, minor);
            break;
        default:
            ALOGE(...);
            return BAD_VALUE;
    }
    ...
    return OK;
}

template<class DeviceInfoT>
std::unique_ptr<CameraProviderManager::ProviderInfo::DeviceInfo>
    CameraProviderManager::ProviderInfo::initializeDeviceInfo(
        const std::string &name, const metadata_vendor_id_t tagId,
        const std::string &id, uint16_t minorVersion) const {
    Status status;

    auto cameraInterface =
            getDeviceInterface<typename DeviceInfoT::InterfaceT>(name);
    if (cameraInterface == nullptr) return nullptr;

    CameraResourceCost resourceCost;
    cameraInterface->getResourceCost([&status, &resourceCost](
        Status s, CameraResourceCost cost) {
                status = s;
                resourceCost = cost;
            });
    ...
    return std::unique_ptr<DeviceInfo>(
        new DeviceInfoT(name, tagId, id, minorVersion, resourceCost,
                cameraInterface));
}

根据传入的 deviceName 解析版本号、类型、设备 Id （前后摄），并根据 major 版本号（表示 HAL 1 或者 HAL 3） 分别初始化对应的 DeviceInfo ；在 initializeDeviceInfo 中通过 getDeviceInterface 获取对应的 ICameraDevice 版本，在对应版本 DeviceInfo 实例化时保存；也就是将 DeviceInfo 和 HAL 层的 ICameraDevice 绑定。

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// CameraProviderManager.cpp
CameraProviderManager::ProviderInfo::DeviceInfo3::DeviceInfo3(
        const std::string& name,
        const metadata_vendor_id_t tagId, const std::string &id,
        uint16_t minorVersion,
        const CameraResourceCost& resourceCost,
        sp<InterfaceT> interface) :
        DeviceInfo(name, tagId, id, 
            hardware::hidl_version{3, minorVersion}, resourceCost),
        mInterface(interface) {
    // Get camera characteristics and initialize flash unit availability
    Status status;
    hardware::Return<void> ret;
    // 获取 Camera 设备配置信息
    ret = mInterface->getCameraCharacteristics([&status, this](Status s,
                device::V3_2::CameraMetadata metadata) {
            status = s;
            if (s == Status::OK) {
                camera_metadata_t *buffer =
                    reinterpret_cast<camera_metadata_t*>(metadata.data());
                size_t expectedSize = metadata.size();
                int res = validate_camera_metadata_structure(buffer, 
                    &expectedSize);
                if (res==OK||res==CAMERA_METADATA_VALIDATION_SHIFTED) {
                    set_camera_metadata_vendor_id(buffer, mProviderTagid);
                    mCameraCharacteristics = buffer;
                } else {
                    ALOGE(...);
                    status = Status::INTERNAL_ERROR;
                }
            }
        });
    ...
    camera_metadata_entry flashAvailable =
            mCameraCharacteristics.find(ANDROID_FLASH_INFO_AVAILABLE);
    if (flashAvailable.count == 1 &&
            flashAvailable.data.u8[0] == ANDROID_FLASH_INFO_AVAILABLE_TRUE) {
        mHasFlashUnit = true;
    } else {
        mHasFlashUnit = false;
    }
}

这里分析的是 DeviceInfo3 的构造函数，它会向 HAL 层请求当前设备的配置信息，并保存 mCameraCharacteristics ，后续查看属性时都会通过这个变量查询。CameraService::enumerateProviders 中，首先新建并初始化 CameraProviderManager ，其持有和 HAL 通信的实例；接着新建并初始化 CameraFlashlight ，用于控制闪光灯。先看头文件：

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// CameraFlashlight.h
class FlashControlBase : public virtual VirtualLightRefBase {
public:
    ...
    virtual status_t hasFlashUnit(const String8& cameraId,
                bool *hasFlash) = 0;
    virtual status_t setTorchMode(const String8& cameraId,
                bool enabled) = 0;
};

// HAL 3 闪光灯控制
class ProviderFlashControl : public FlashControlBase {
public:
    ...
    // FlashControlBase
    status_t hasFlashUnit(const String8& cameraId, bool *hasFlash);
    status_t setTorchMode(const String8& cameraId, bool enabled);
private:
    sp<CameraProviderManager> mProviderManager;
...
};

// HAL 1 闪光灯控制，通过 CameraHardwareInterface 向下调用
class CameraHardwareInterfaceFlashControl : public FlashControlBase {
public:
    ...
    // FlashControlBase
    status_t setTorchMode(const String8& cameraId, bool enabled);
    status_t hasFlashUnit(const String8& cameraId, bool *hasFlash);
private:
    sp<CameraProviderManager> mProviderManager;
    const camera_module_callbacks_t *mCallbacks;
    sp<CameraHardwareInterface> mDevice;
    String8 mCameraId;
    CameraParameters mParameters;
    ...
}

class CameraFlashlight : public virtual VirtualLightRefBase {
public:
    ...
    bool hasFlashUnit(const String8& cameraId);
    status_t setTorchMode(const String8& cameraId, bool enabled);
private:
    sp<FlashControlBase> mFlashControl;
    sp<CameraProviderManager> mProviderManager;
    const camera_module_callbacks_t *mCallbacks;

头文件定义的几个信息：

  • CameraHardwareInterfaceFlashControlHAL 1 闪光灯控制类，通过 CameraHardwareInterface 向下调用。
  • ProviderFlashControlHAL 3 闪光灯控制类。
  • FlashControlBase 基类。
  • CameraProviderManager 主要用于 ProviderFlashControl 向下发送信息。
  • camera_module_callbacks_tHAL 层的回调。
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// CameraFlashlight.cpp
CameraFlashlight::CameraFlashlight(
        sp<CameraProviderManager> providerManager,
        camera_module_callbacks_t* callbacks) :
        mProviderManager(providerManager),
        mCallbacks(callbacks),
        mFlashlightMapInitialized(false) {
}

status_t CameraFlashlight::findFlashUnits() {
    ...
    mFlashControl.clear();
    for (auto &id : cameraIds) {
        ssize_t index = mHasFlashlightMap.indexOfKey(id);
        if (0 <= index) {
            continue;
        }

        bool hasFlash = false;
        res = createFlashlightControl(id);
        ...
    }
    ...
    return OK;
}

status_t CameraFlashlight::createFlashlightControl(
        const String8& cameraId) {
    ...
    if (mProviderManager->supportSetTorchMode(cameraId.string())) {
        mFlashControl = new ProviderFlashControl(mProviderManager);
    } else {
        // Only HAL1 devices do not support setTorchMode
        mFlashControl =
            new CameraHardwareInterfaceFlashControl(mProviderManager,
            *mCallbacks);
    }
    return OK;
}

CameraFlashlight 的构造函数仅仅初始化了几个本地变量，CameraService 中调用 CameraFlashlight::findFlashUnits 时，会根据 HAL 1/3 分别来创建对应的闪光灯控制类。至此整个 CameraService 注册流程结束。

小结

CameraService 初始化和注册流程中，实例化了两个对象：

  • CameraProviderManager mCameraProviderManager 对象
  • Flashlight mFlashlight 对象

CameraProviderManager 初始化完后：

  • mProviders 保存了 ProviderInfo 对象；并关联了 ICameraProvider ，用于和 HAL 通信
  • ProviderInfo 中 mDevices 保存了所有的 DeviceInfo1, DeviceInfo3 设备信息，并关联 ICameraDevice 实例，用于直接通信
  • DeviceInfo1 中保存了 CameraParameters2 mDefaultParameters 参数信息
  • DeviceInfo3 中保存了 CameraMetadata mCameraCharacteristics 参数信息

CameraFlashlight 新建和初始化后：

  • 如果是 HAL 1 会实例化控制类 CameraHardwareInterfaceFlashControl
  • 如果是 HAL 3 会实例化控制类 ProviderFlashControl

Camera Open 流程

API

Camera API 2 开启摄像头设备时，通过 CameraManager.openCamera 来打开：

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// CameraManager.java
@RequiresPermission(android.Manifest.permission.CAMERA)
public void openCamera(@NonNull String cameraId,
        @NonNull final CameraDevice.StateCallback callback,
        @Nullable Handler handler)
        throws CameraAccessException {

    openCameraForUid(cameraId, callback, handler, USE_CALLING_UID);
}
  • String cameraId 表示前后摄的 ID ，通常 0 表示后摄。
  • CameraDevice.StateCallback callback 打开设备时，状态回调接口。
  • Handler handler 表示回调接口在哪

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