一、Camera 架构
NOTE：这是 Android Camera API 1 ，Camera 的架构与 Android 整体架构是保持一致的：
Framework ： Camera.java
Android Runtime : android_hardware_Camera.cpp
Library :
Client (Camera.cpp, ICameraClient.cpp, etc...)
Server (CameraService.cpp, ICameraService.cpp, etc...)
HAL : CameraHardwareInterface.h
架构简图:
根据架构简图可以看到，实际上 Camera 的架构与 Android 架构是一一对应的，上层应用调用 Camera 相关的方法后，指令依次通过框架层、运行时环境、本地库、硬件抽象层，最终到达具体设备。设备执行动作后，获得的数据又会沿着反方向依次发送到最上层。
需要注意的是，在本地库这一层中，涉及到一个 C/S 结构：
- 即通过客户端与服务端的交互来传递指令与数据。
- 实际上，只有服务端与 HAL 层进行沟通。
- 由于客户端与服务端是不同的进程，它们之间需要依靠 IPC Binder 机制 来进行通讯。
相关源码位置（Android 7.1 源码）:
Application：（这部分不是学习的重点）
packages/apps/Camera2/src/com/android/camera/***
Framework：
/frameworks/base/core/java/android/hardware/Camera.java
Android Runtime：
frameworks/base/core/jni/android_hardware_Camera.cpp
C/C++ Libraries：
Client：
frameworks/av/camera/CameraBase.cpp
frameworks/av/camera/Camera.cpp
frameworks/av/camera/ICamera.cpp
frameworks/av/camera/aidl/android/hardware/ICamera.aidl
frameworks/av/camera/aidl/android/hardware/ICameraClient.aidl
Server：
frameworks/av/camera/cameraserver/main_cameraserver.cpp
frameworks/av/services/camera/libcameraservice/CameraService.cpp
frameworks/av/services/camera/libcameraservice/api1/CameraClient.cpp
frameworks/av/camera/aidl/android/hardware/ICameraService.aidl
HAL：
HAL 1：(此篇文章分析)
frameworks/av/services/camera/libcameraservice/device1/CameraHardwareInterface.h
HAL 3：（参考：https://www.cnblogs.com/blogs-of-lxl/p/10651611.html ）
frameworks/av/services/camera/libcameraservice/device3/***
二、Camera Open 调用流程
1.Camera.java（Framework层）：frameworks/base/core/java/android/hardware/Camera.java
/***
* Creates a new Camera object to access
* the first back-facing camera on the
* device. If the device does not have a back-facing camera,
* this returns null.
* @see #open(int)
*/
public static Camera open() {
int numberOfCameras = getNumberOfCameras(); //获取 Camera 设备的个数。
CameraInfo cameraInfo = new CameraInfo();
for (int i = 0; i < numberOfCameras; i++) {
getCameraInfo(i, cameraInfo); //依次获取设备信息，
if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) { //如果是获取到后置摄像头（默认），则调用 new Camera(int) 构造对应的摄像头实例。
return new Camera(i);
}
}
return null;
}
Camera(int cameraId)：
/** used by Camera#open, Camera#open(int) */
Camera(int cameraId) {
int err = cameraInitNormal(cameraId); //通过调用 cameraInitNormal(Id) 方法对指定摄像头进行初始化。
if (checkInitErrors(err)) {
if (err == -EACCES) {
throw new RuntimeException("Fail to connect to camera service");
} else if (err == -ENODEV) {
throw new RuntimeException("Camera initialization failed");
}
// Should never hit this.
throw new RuntimeException("Unknown camera error");
}
}
cameraInitNormal(int cameraId)：
private int cameraInitNormal(int cameraId) {
return cameraInitVersion(cameraId,
CAMERA_HAL_API_VERSION_NORMAL_CONNECT); //调用 cameraInitVersion(int cameraId, int halVersion),指定 halVersion 参数
}
cameraInitVersion(int cameraId, int halVersion)：
private int cameraInitVersion(int cameraId,
int halVersion) {
//将各个回调函数置空
mShutterCallback = null;
mRawImageCallback = null;
mJpegCallback = null;
mPreviewCallback = null;
mPostviewCallback = null;
mUsingPreviewAllocation = false;
mZoomListener = null;
Looper looper; //通过 Looper 对事件处理对象进行实例化后，就调用 native_setup 方法进入 JNI（Java Native Interface） 库中调用对应的函数。
if ((looper = Looper.myLooper()) != null) {
mEventHandler = new EventHandler(this, looper);
} else if ((looper = Looper.getMainLooper()) != null) {
mEventHandler = new EventHandler(this, looper);
} else {
mEventHandler = null;
}
return native_setup(new WeakReference<Camera>(this),
cameraId, halVersion,
ActivityThread.currentOpPackageName());
}
至此，open() 方法开始进入 Android Runtime 层。
简图总结：
2. android_hardware_Camera.cpp（Android Runtime）：frameworks/base/core/jni/android_hardware_Camera.cpp
// connect to camera service
static jint android_hardware_Camera_native_setup(JNIEnv *env,
jobject thiz, jobject weak_this,
jint cameraId, jint halVersion,
jstring clientPackageName)
{
// convert jstring to String16(clientPackageName -> clientName) //刚开始要先把 clientPackageName 做一个类型转换，变成 clientName
......
......
sp<Camera> camera; //建立一个 Camera 类型的 StrongPointer(sp)，然后通过 Camera::connect() 或 Camera::connectLegacy()，让客户端与服务端进行连接，并返回相应的 Camera 实例
if (halVersion == CAMERA_HAL_API_VERSION_NORMAL_CONNECT) {
/***** NOTE THIS *****/
// Default path: hal version is don't care, do normal camera connect.
camera = Camera::connect(cameraId, clientName, //进入 C/C++ Libraries 的 C/S 结构中，而 Camera 则属于 Client
Camera::USE_CALLING_UID,
Camera::USE_CALLING_PID);
} else {
jint status = Camera::connectLegacy(cameraId,
halVersion, clientName,
Camera::USE_CALLING_UID, camera);
if (status != NO_ERROR) {
return status;
}
}
if (camera == NULL) {
return -EACCES;
}
//最后对返回的实例进行一些基本的检查，并保存上下文
// make sure camera hardware is alive
if (camera->getStatus() != NO_ERROR) {
return NO_INIT;
}
// save context in opaque field
......
......
}
简图总结：
3.Camera（C/C++ Libraries）：
（1）frameworks/av/include/camera/Camera.h
template <>
struct CameraTraits<Camera>
{
typedef CameraListener TCamListener;
typedef ::android::hardware::ICamera TCamUser;
typedef ::android::hardware::ICameraClient TCamCallbacks;
typedef ::android::binder::Status(::android::hardware::ICameraService::*TCamConnectService)
(const sp<::android::hardware::ICameraClient>&,
int, const String16&, int, int,
/*out*/
sp<::android::hardware::ICamera>*);
static TCamConnectService fnConnectService;
};
（2）framework/av/camera/Camera.cpp
CameraTraits<Camera>::TCamConnectService CameraTraits<Camera>::fnConnectService = //注：fnConnectService是对应到ICameraService::connect函数的 &::android::hardware::ICameraService::connect;
Camera::connect ：
sp<Camera> Camera::connect(int cameraId,
const String16& clientPackageName,
int clientUid, int clientPid)
{
return CameraBaseT::connect(cameraId, //直接调用了 CameraBaseT::connect() 这是定义在 CameraBase.cpp 中的函数。
clientPackageName, clientUid, clientPid);
}
（3）frameworks/av/include/camera/CameraBase.h
template <typename TCam, typename TCamTraits = CameraTraits<TCam> > //TCam对应Camera；TCamTraits对应CameraTraits<Camera>
注意类成员变量声明部分，即可知道 CameraBaseT 对应 CameraBase<Camera>。
sp<TCamUser> mCamera; status_t mStatus; sp<TCamListener> mListener; const int mCameraId; /***** NOTE THIS *****/ typedef CameraBase<TCam> CameraBaseT;
（4）framework/av/camera/CameraBase.cpp
template <typename TCam, typename TCamTraits>
sp<TCam> CameraBase<TCam, TCamTraits>::connect(int cameraId,
const String16& clientPackageName,
int clientUid, int clientPid)
{
ALOGV("%s: connect", __FUNCTION__);
/***** NOTE THIS *****/
sp<TCam> c = new TCam(cameraId); //实例化一个 Camera，通过 Camera 获取 ICameraClient 指针。
sp<TCamCallbacks> cl = c;
const sp<::android::hardware::ICameraService> cs = getCameraService();
binder::Status ret;
if (cs != nullptr) {
/***** NOTE THIS *****/
TCamConnectService fnConnectService = TCamTraits::fnConnectService; //通过 getCameraService() 函数获取 ICameraService。
ret = (cs.get()->*fnConnectService)(cl, cameraId, //通过 ICameraService::connect() 函数获得一个 mCamera， 即 ICamera 实例。
clientPackageName, clientUid,
clientPid, /*out*/ &c->mCamera);
}
if (ret.isOk() && c->mCamera != nullptr) {
/***** NOTE THIS *****/
IInterface::asBinder(c->mCamera)->linkToDeath(c); //将 ICamera 实例与 Binder 建立联系。
c->mStatus = NO_ERROR;
} else {
ALOGW("An error occurred while connecting to camera %d: %s", cameraId,
(cs != nullptr) ? "Service not available" : ret.toString8().string());
c.clear();
}
return c;
}
// establish binder interface to camera service
template <typename TCam, typename TCamTraits>
const sp<::android::hardware::ICameraService> CameraBase<TCam, TCamTraits>::getCameraService()
{
Mutex::Autolock _l(gLock);
/***** NOTE THIS *****/
if (gCameraService.get() == 0) { //gCameraService 是一个 ICameraService,调用get 函数，如果能获取到 ICameraService 则返回。ICameraService
}
/***** NOTE THIS *****/
//若没有返回，则通过 IServiceManager 来获取一个 ICameraService，这个过程中主要是通过 IBinder 来进行数据获取。
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder;
do {
binder = sm->getService(String16(kCameraServiceName));
if (binder != 0) {
break;
}
ALOGW("CameraService not published, waiting...");
usleep(kCameraServicePollDelay);
} while(true);
if (gDeathNotifier == NULL) {
gDeathNotifier = new DeathNotifier();
}
binder->linkToDeath(gDeathNotifier);
/***** NOTE THIS *****/
gCameraService = interface_cast<::android::hardware::ICameraService>(binder);
}
ALOGE_IF(gCameraService == 0, "no CameraService!?");
return gCameraService;
}
4.ICameraService：
- 这一节主要是了解一下关于 Binder 通讯中的一些内部逻辑。
- 实际上在
CameraBase中，所调用的connect对应的是CameraService::connect()。
（1）frameworks/av/camera/aidl/android/hardware/ICameraService.aidl
/**
* Open a camera device through the old camera API
*/
ICamera connect(ICameraClient client,
int cameraId,
String opPackageName,
int clientUid, int clientPid);
（2）out/target/product/generic/obj/SHARED_LIBRARIES/libcamera_client_intermediates/aidl-generated/src/aidl/android/hardware/ICameraService.cpp
//这个ICameraService.cpp以及其头文件ICameraService.h都是根据其对应的aidl文件自动生成的。 ::android::binder::Status BpCameraService::connect(const ::android::sp<::android::hardware::ICameraClient>& client, //这里是BpCameraservice，它继承了ICameraService，同时也继承了BpInterface。 int32_t cameraId, const ::android::String16& opPackageName, int32_t clientUid, int32_t clientPid, ::android::sp<::android::hardware::ICamera>* _aidl_return) { ::android::Parcel _aidl_data; //Parcel可以看成是Binder通讯中的信息传递中介，后面将相应的数据写入Parcel ::android::Parcel _aidl_reply; //返回的reply数据判断是否有error::android::status_t _aidl_ret_status = ::android::OK; ::android::binder::Status _aidl_status; _aidl_ret_status = _aidl_data.writeInterfaceToken(getInterfaceDescriptor()); //首先把。 /***** NOTE THIS *****/ if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_ret_status = _aidl_data.writeStrongBinder(::android::hardware::ICameraClient::asBinder(client)); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_ret_status = _aidl_data.writeInt32(cameraId); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_ret_status = _aidl_data.writeString16(opPackageName); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_ret_status = _aidl_data.writeInt32(clientUid); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_ret_status = _aidl_data.writeInt32(clientPid); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } /***** NOTE THIS *****/ _aidl_ret_status = remote()->transact(ICameraService::CONNECT, _aidl_data, &_aidl_reply); //调用远程接口remote()中的处理函数transact()。 if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_ret_status = _aidl_status.readFromParcel(_aidl_reply); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } if (!_aidl_status.isOk()) { return _aidl_status; } _aidl_ret_status = _aidl_reply.readStrongBinder(_aidl_return); if (((_aidl_ret_status) != (::android::OK))) { goto _aidl_error; } _aidl_error: _aidl_status.setFromStatusT(_aidl_ret_status); return _aidl_status; }
BnCameraService::onTransact()：消息处理函数
case Call::CONNECT:
{
::android::sp<::android::hardware::ICameraClient> in_client;
int32_t in_cameraId;
::android::String16 in_opPackageName;
int32_t in_clientUid;
int32_t in_clientPid;
/***** NOTE THIS *****/
::android::sp<::android::hardware::ICamera> _aidl_return;
if (!(_aidl_data.checkInterface(this))) {
_aidl_ret_status = ::android::BAD_TYPE;
break;
}
//接收 Bp 传来的数据
_aidl_ret_status = _aidl_data.readStrongBinder(&in_client);
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
_aidl_ret_status = _aidl_data.readInt32(&in_cameraId);
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
_aidl_ret_status = _aidl_data.readString16(&in_opPackageName);
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
_aidl_ret_status = _aidl_data.readInt32(&in_clientUid);
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
_aidl_ret_status = _aidl_data.readInt32(&in_clientPid);
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
/***** NOTE THIS *****/
::android::binder::Status _aidl_status(connect(in_client, in_cameraId, in_opPackageName, in_clientUid, in_clientPid, &_aidl_return)); //调用了具体的 connect 函数获取 ICamera 并且返
_aidl_ret_status = _aidl_status.writeToParcel(_aidl_reply);
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
if (!_aidl_status.isOk()) {
break;
}
/***** NOTE THIS *****/
_aidl_ret_status = _aidl_reply->writeStrongBinder(::android::hardware::ICamera::asBinder(_aidl_return));
if (((_aidl_ret_status) != (::android::OK))) {
break;
}
}
break;
5.ICamera：
(1)frameworks/av/camera/ICamera.cpp
virtual status_t connect(const sp<ICameraClient>& cameraClient) //BpCamera类中的connect()函数 { Parcel data, reply; data.writeInterfaceToken(ICamera::getInterfaceDescriptor()); data.writeStrongBinder(IInterface::asBinder(cameraClient)); remote()->transact(CONNECT, data, &reply); return reply.readInt32(); }
BnCamera 类中，onTransact 函数则有相应的处理：
case CONNECT: {
CHECK_INTERFACE(ICamera, data, reply);
sp<ICameraClient> cameraClient = interface_cast<ICameraClient>(data.readStrongBinder());
reply->writeInt32(connect(cameraClient));
return NO_ERROR;
} break;
(2)frameworks/av/services/camera/libcameraservice/CameraService.cpp
Status CameraService::connect( const sp<ICameraClient>& cameraClient,
int cameraId,
const String16& clientPackageName,
int clientUid,
int clientPid,
/*out*/
sp<ICamera>* device) {
ATRACE_CALL();
Status ret = Status::ok();
String8 id = String8::format("%d", cameraId);
sp<Client> client = nullptr;
//真正实现逻辑是在 connectHelper() 函数中
ret = connectHelper<ICameraClient,Client>(cameraClient, id,
CAMERA_HAL_API_VERSION_UNSPECIFIED, clientPackageName, clientUid, clientPid, API_1,
/*legacyMode*/ false, /*shimUpdateOnly*/ false,
/*out*/client);
if(!ret.isOk()) {
logRejected(id, getCallingPid(), String8(clientPackageName),
ret.toString8());
return ret;
}
*device = client; //获得一个客户端实例并且通过 *device 返回
return ret;
}
(3)frameworks/av/services/camera/libcameraservice/CameraService.h
sp<BasicClient> clientTmp = nullptr;
std::shared_ptr<resource_policy::ClientDescriptor<String8, sp<BasicClient>>> partial;
if ((err = handleEvictionsLocked(cameraId,
originalClientPid, effectiveApiLevel,
IInterface::asBinder(cameraCb), clientName8,
/*out*/&clientTmp,
/*out*/&partial)) != NO_ERROR) {
/***** do something *****/
}
/***** NOTE THIS *****/
if (clientTmp.get() != nullptr) { //如果客户端实例已经存在于 MediaRecorder ，则直接将其取出返回
// Handle special case for API1 MediaRecorder where the existing client is returned
device = static_cast<CLIENT*>(clientTmp.get());
return ret;
}
// give flashlight a chance to close devices if necessary.
mFlashlight->prepareDeviceOpen(cameraId);
// TODO: Update getDeviceVersion + HAL interface to use strings for Camera IDs
int id = cameraIdToInt(cameraId);
if (id == -1) {
ALOGE("%s: Invalid camera ID %s, cannot get device version from HAL.", __FUNCTION__,
cameraId.string());
return STATUS_ERROR_FMT(ERROR_ILLEGAL_ARGUMENT,
"Bad camera ID \"%s\" passed to camera open", cameraId.string());
}
int facing = -1;
/***** NOTE THIS *****/
int deviceVersion = getDeviceVersion(id, /*out*/&facing); //获取 deviceVersion，然后再调用 makeClient() 函数创建一个客户端。
sp<BasicClient> tmp = nullptr;
if(!(ret = makeClient(this, cameraCb,
clientPackageName, id, facing, clientPid,
clientUid, getpid(), legacyMode, halVersion,
deviceVersion, effectiveApiLevel,
/*out*/&tmp)).isOk()) {
return ret;
}
client = static_cast<CLIENT*>(tmp.get());
LOG_ALWAYS_FATAL_IF(client.get() == nullptr, "%s: CameraService in invalid state",
__FUNCTION__);
/***** NOTE THIS *****/
if ((err = client->initialize(mModule)) != OK) { //调用其 initialize() 函数进行初始化，注意其传入的参数是 mModule，这个参数是连接 Libraries 与 HAL 的关键参数。
/***** do somthing *****/
}
// Update shim paremeters for legacy clients
if (effectiveApiLevel == API_1) {
// Assume we have always received a Client subclass for API1
sp<Client> shimClient = reinterpret_cast<Client*>(client.get());
String8 rawParams = shimClient->getParameters();
CameraParameters params(rawParams);
auto cameraState = getCameraState(cameraId);
if (cameraState != nullptr) {
cameraState->setShimParams(params);
} else {
ALOGE("%s: Cannot update shim parameters for camera %s, no such device exists.",
__FUNCTION__, cameraId.string());
}
}
if (shimUpdateOnly) {
// If only updating legacy shim parameters, immediately disconnect client
mServiceLock.unlock();
client->disconnect();
mServiceLock.lock();
} else {
// Otherwise, add client to active clients list
finishConnectLocked(client, partial);
}
} // lock is destroyed, allow further connect calls
// Important: release the mutex here so the client can call back into the service from its
// destructor (can be at the end of the call)
device = client;
(4)frameworks/av/services/camera/libcameraservice/api1/CameraClient.cpp
status_t CameraClient::initialize(CameraModule *module) {
int callingPid = getCallingPid();
status_t res;
LOG1("CameraClient::initialize E (pid %d, id %d)", callingPid, mCameraId);
// Verify ops permissions
res = startCameraOps();
if (res != OK) {
return res;
}
char camera_device_name[10];
snprintf(camera_device_name, sizeof(camera_device_name), "%d", mCameraId);
/***** NOTE THIS *****/
mHardware = new CameraHardwareInterface(camera_device_name); //获取 CameraHardwareInterface 实例。
res = mHardware->initialize(module);
if (res != OK) {
ALOGE("%s: Camera %d: unable to initialize device: %s (%d)",
__FUNCTION__, mCameraId, strerror(-res), res);
mHardware.clear();
return res;
}
//设置三个回调函数（这里与数据流密切相关）
mHardware->setCallbacks(notifyCallback,
dataCallback,
dataCallbackTimestamp,
(void *)(uintptr_t)mCameraId);
// Enable zoom, error, focus, and metadata messages by default
enableMsgType(CAMERA_MSG_ERROR | CAMERA_MSG_ZOOM | CAMERA_MSG_FOCUS |
CAMERA_MSG_PREVIEW_METADATA | CAMERA_MSG_FOCUS_MOVE);
LOG1("CameraClient::initialize X (pid %d, id %d)", callingPid, mCameraId);
return OK;
}
6.HAL：frameworks/av/services/camera/libcameraservice/device1/CameraHardwareInterface.h
status_t initialize(CameraModule *module)
{
ALOGI("Opening camera %s", mName.string());
camera_info info;
status_t res = module->getCameraInfo(atoi(mName.string()), &info); //通过 module，从 HAL 层的库中调用相关的函数获取 Camera 设备信息
if (res != OK) {
return res;
}
int rc = OK;
//根据模块 API 的版本，判断是用 open 函数还是用 openLegacy，调用 open 后，通过 HAL 库与 Linux Kernel交互
if (module->getModuleApiVersion() >= CAMERA_MODULE_API_VERSION_2_3 &&
info.device_version > CAMERA_DEVICE_API_VERSION_1_0) {
// Open higher version camera device as HAL1.0 device.
rc = module->openLegacy(mName.string(),
CAMERA_DEVICE_API_VERSION_1_0,
(hw_device_t **)&mDevice);
} else {
rc = module->open(mName.string(), (hw_device_t **)&mDevice);
}
if (rc != OK) {
ALOGE("Could not open camera %s: %d", mName.string(), rc);
return rc;
}
initHalPreviewWindow();
return rc;
}
至此， Camera1的Open调用流程分析完毕。
三、Camera hw_get_module() 相关逻辑
本节由hw_get_module() 函数入手，去探究 Libraries 层是如何调用 HAL 层的库中的函数的，CameraService 是在开机时就会启动，会调用一个名为 onFirstRef() 的成员函数，下面就从这里开始分析。
1. CameraService：framework/av/services/camera/libcameraservice/CameraService.cpp
BnCameraService::onFirstRef(); //首先调用其基类的onFirstRef函数 // Update battery life tracking if service is restarting BatteryNotifier& notifier(BatteryNotifier::getInstance()); //更新notifier（从BatteryNotifier看应该跟电池有关，估计是检测电池电量过低就不开启闪光灯或者相机）。 notifier.noteResetCamera(); notifier.noteResetFlashlight(); camera_module_t *rawModule; /*** NOTE THIS ***/ int err = hw_get_module(CAMERA_HARDWARE_MODULE_ID, //通过hw_get_module函数获取rawModule。 (const hw_module_t **)&rawModule); if (err < 0) { ALOGE("Could not load camera HAL module: %d (%s)", err, strerror(-err)); logServiceError("Could not load camera HAL module", err); return; } /*** NOTE THIS ***/ mModule = new CameraModule(rawModule); //利用rawModule创建mModule的实例，mModule是CameraModule类。 err = mModule->init();
2. hardware:
(1)hardware/libhardware/include/hardware/hardware.h
/** * Name of the hal_module_info */ #define HAL_MODULE_INFO_SYM HMI /** * Name of the hal_module_info as a string */ #define HAL_MODULE_INFO_SYM_AS_STR "HMI"
/** * Get the module info associated with a module by id. * * @return: 0 == success, <0 == error and *module == NULL */ int hw_get_module(const char *id, const struct hw_module_t **module); //作用是通过传入的id来获取模块相关的信息(成功则返回0，出错则返回值小于0且*module == NULL) /** * Get the module info associated with a module instance by class 'class_id' * and instance 'inst'. * * Some modules types necessitate multiple instances. For example audio supports * multiple concurrent interfaces and thus 'audio' is the module class * and 'primary' or 'a2dp' are module interfaces. This implies that the files * providing these modules would be named audio.primary.<variant>.so and * audio.a2dp.<variant>.so * * @return: 0 == success, <0 == error and *module == NULL */ int hw_get_module_by_class(const char *class_id, const char *inst, //作用是通过class_id获取与模块实例相关的信息。 const struct hw_module_t **module);
(2)hardware/libhardware/hardware.c
static const char *variant_keys[] = {
"ro.hardware", /* This goes first so that it can pick up a different
file on the emulator. */
"ro.product.board",
"ro.board.platform",
"ro.arch"
};
int hw_get_module(const char *id, const struct hw_module_t **module)
{
return hw_get_module_by_class(id, NULL, module); //读取库文件，尝试的顺序是：ro.hardware、ro.product.board、ro.board.platform、ro.arch、default
}
...
//通过 load 函数加载模块。
/* First try a property specific to the class and possibly instance */
snprintf(prop_name, sizeof(prop_name), "ro.hardware.%s", name);
if (property_get(prop_name, prop, NULL) > 0) {
if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
goto found;
}
}
/* Loop through the configuration variants looking for a module */
for (i=0 ; i<HAL_VARIANT_KEYS_COUNT; i++) {
if (property_get(variant_keys[i], prop, NULL) == 0) {
continue;
}
if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
goto found;
}
}
/* Nothing found, try the default */
if (hw_module_exists(path, sizeof(path), name, "default") == 0) {
goto found;
}
return -ENOENT;
found:
/* load the module, if this fails, we're doomed, and we should not try
* to load a different variant. */
/*** NOTE THIS ***/
return load(class_id, path, module);
load()：
NOTE：
为了获取动态链接库中的结构体，我们需要用到一个字符串 sym，sym 对应宏 HAL_MODULE_INFO_SYM_AS_STR，即 “HMI”。
动态链接库 .so 文件，是一个 ELF 文件。
ELF：Executable and Linkable Format，可执行链接格式，ELF 文件头保存了一个路线图，用于描述文件的组织结构。
通过 readelf -s 命令，我们可以查看对应的 .so 文件描述，可以看到其中有一个 Name 属性为 HMI ，其对应的位置就是我们所需要的结构体 hw_module_t。
于是通过 HMI 字段，就可以从动态链接库中读取出相应的结构体，从而得以在 Libraries 层中调用 HAL 层的库函数。
static int load(const char *id,
const char *path,
const struct hw_module_t **pHmi)
{
int status = -EINVAL;
void *handle = NULL;
struct hw_module_t *hmi = NULL;
/*
* load the symbols resolving undefined symbols before
* dlopen returns. Since RTLD_GLOBAL is not or'd in with
* RTLD_NOW the external symbols will not be global
*/
/*** NOTE THIS ***/
handle = dlopen(path, RTLD_NOW); //调用 dlopen() 函数获取一个 handle。
if (handle == NULL) {
char const *err_str = dlerror();
ALOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
status = -EINVAL;
goto done;
}
/* Get the address of the struct hal_module_info. */
/*** NOTE THIS ***/
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
hmi = (struct hw_module_t *)dlsym(handle, sym); //调用 dlsym() 函数从动态链接库中获取 hw_module_t 类型的 hmi。
if (hmi == NULL) {
ALOGE("load: couldn't find symbol %s", sym);
status = -EINVAL;
goto done;
}
/* Check that the id matches */
if (strcmp(id, hmi->id) != 0) {
ALOGE("load: id=%s != hmi->id=%s", id, hmi->id);
status = -EINVAL;
goto done;
}
hmi->dso = handle;
/* success */
status = 0;
/*** NOTE THIS ***/
done:
if (status != 0) {
hmi = NULL;
if (handle != NULL) {
dlclose(handle);
handle = NULL;
}
} else {
ALOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
id, path, *pHmi, handle);
}
*pHmi = hmi;
return status;
}
至此，获得了最终的 rawModule，然后回到 onFirstRef() 中继续分析。
3. CameraModule:
（1）frameworks/av/services/camera/libcameraservice/common/CameraModule.cpp
CameraModule::CameraModule(camera_module_t *module) {
if (module == NULL) {
ALOGE("%s: camera hardware module must not be null",
__FUNCTION__);
assert(0);
}
mModule = module; //mModule 是 camera_module_t 类型。
}
init()：
- 调用
mModule的init()函数。 - 如果没有指定的
init()函数，则init流程到这里就可以结束了。
int CameraModule::init() {
ATRACE_CALL();
int res = OK;
if (getModuleApiVersion() >= CAMERA_MODULE_API_VERSION_2_4 &&
mModule->init != NULL) {
ATRACE_BEGIN("camera_module->init");
res = mModule->init();
ATRACE_END();
}
mCameraInfoMap.setCapacity(getNumberOfCameras());
return res;
}
(2)相关代码：
hardware/libhardware/include/hardware/camera_common.h hardware/qcom/camera/QCamera2/QCamera2Factory.h hardware/qcom/camera/QCamera2/QCamera2Factory.cpp hardware/qcom/camera/QCamera2/QCamera2Hal.cpp
简图总结：
上面从 CameraService::onFirstRef() 入手，逐渐理顺了以 hw_get_module() 为中心的一个调用逻辑。实际上，Android HAL 层有一个通用的入口，即宏 HAL_MODULE_INFO_SYM，通过它，可以获取 HAL 层中的模块实例，从而调用 HAL 层所提供的函数。理解了 HAL 层的入口，接下来就可以去对 Camera.startPreview() 的控制流程进行分析，从而再次加深对 Camera 控制流的理解。
四、Camera.startPreview()流程
1.Frameworks：frameworks/base/core/java/android/hardware/Camera.java
/**
* Starts capturing and drawing preview frames to the screen.
* Preview will not actually start until a surface is supplied
* with {@link #setPreviewDisplay(SurfaceHolder)} or
* {@link #setPreviewTexture(SurfaceTexture)}.
*
* <p>If {@link #setPreviewCallback(Camera.PreviewCallback)},
* {@link #setOneShotPreviewCallback(Camera.PreviewCallback)}, or
* {@link #setPreviewCallbackWithBuffer(Camera.PreviewCallback)} were
* called, {@link Camera.PreviewCallback#onPreviewFrame(byte[], Camera)}
* will be called when preview data becomes available.
*/
public native final void startPreview(); //给上层 application 提供一个接口， 进入 Runtime 层。
2.Android Runtime:frameworks/base/core/jni/android_hardware_Camera.cpp
static void android_hardware_Camera_startPreview(JNIEnv *env, jobject thiz)
{
ALOGV("startPreview");
sp<Camera> camera = get_native_camera(env, thiz, NULL); //调用 get_native_camera() 函数获取一个 Camera 实例。
if (camera == 0) return;
if (camera->startPreview() != NO_ERROR) {
jniThrowRuntimeException(env, "startPreview failed");
return;
}
}
sp<Camera> get_native_camera(JNIEnv *env, jobject thiz, JNICameraContext** pContext)
{
sp<Camera> camera;
Mutex::Autolock _l(sLock);
JNICameraContext* context = reinterpret_cast<JNICameraContext*>(env->GetLongField(thiz, fields.context)); //从 DVM 中获取关于 Camera 的上下文。
if (context != NULL) {
camera = context->getCamera(); //从上下文信息中获取 Camera 实例。
}
ALOGV("get_native_camera: context=%p, camera=%p", context, camera.get());
if (camera == 0) {
jniThrowRuntimeException(env,
"Camera is being used after Camera.release() was called");
}
if (pContext != NULL) *pContext = context;
return camera;
}
3. Libraries:
(1)frameworks/av/camera/Camera.cpp
// start preview mode
status_t Camera::startPreview()
{
ALOGV("startPreview");
sp <::android::hardware::ICamera> c = mCamera; //mCamera 即是在 connect 过程中返回的 CameraClient，它具体实现了 startPreview() 接口。
if (c == 0) return NO_INIT;
return c->startPreview();
}
(2)frameworks/av/services/camera/libcameraservice/api1/CameraClient.cpp
// start preview mode
status_t CameraClient::startPreview() {
LOG1("startPreview (pid %d)", getCallingPid());
return startCameraMode(CAMERA_PREVIEW_MODE); //通过 startCameraMode 函数进入具体的实现逻辑。
}
startCameraMode()：
// start preview or recording
status_t CameraClient::startCameraMode(camera_mode mode) { //根据传入的参数 CAMERA_PREVIEW_MODE 确定进入的分支。
LOG1("startCameraMode(%d)", mode);
Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;
switch(mode) {
case CAMERA_PREVIEW_MODE:
if (mSurface == 0 && mPreviewWindow == 0) {
LOG1("mSurface is not set yet.");
// still able to start preview in this case.
}
return startPreviewMode();//调用 startPreviewMode() 。
case CAMERA_RECORDING_MODE:
if (mSurface == 0 && mPreviewWindow == 0) {
ALOGE("mSurface or mPreviewWindow must be set before startRecordingMode.");
return INVALID_OPERATION;
}
return startRecordingMode();
default:
return UNKNOWN_ERROR;
}
}
startPreviewMode()：
status_t CameraClient::startPreviewMode() {
LOG1("startPreviewMode");
status_t result = NO_ERROR;
// if preview has been enabled, nothing needs to be done
if (mHardware->previewEnabled()) {
return NO_ERROR; //如果预览已经存在，则直接返回成功信息。
}
if (mPreviewWindow != 0) {
mHardware->setPreviewScalingMode( //mHardware 是 CameraHardwareInterface 的实例，在 connect 过程的最后被初始化。
NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
mHardware->setPreviewTransform(mOrientation);
}
mHardware->setPreviewWindow(mPreviewWindow); //通过 mHardware 调用 setPreviewWindow() 和 startPreview() 接口。
result = mHardware->startPreview();
if (result == NO_ERROR) {
mCameraService->updateProxyDeviceState( //进入 HAL 层。
ICameraServiceProxy::CAMERA_STATE_ACTIVE,
String8::format("%d", mCameraId));
}
return result;
}
4. HAL:
(1)frameworks/av/services/camera/libcameraservice/device1/CameraHardwareInterface.h
/**
* Returns true if preview is enabled.
*/
int previewEnabled()
{
ALOGV("%s(%s)", __FUNCTION__, mName.string());
if (mDevice->ops->preview_enabled) //mDevice 即是通过 hw_get_module() 相关流程进行初始化的设备实例，它的类型是 camera_device_t 。
return mDevice->ops->preview_enabled(mDevice); //如果 preview 存在，则返回 true 。
return false;
}
setPreviewWindow()：
/** Set the ANativeWindow to which preview frames are sent */
status_t setPreviewWindow(const sp<ANativeWindow>& buf)
{
ALOGV("%s(%s) buf %p", __FUNCTION__, mName.string(), buf.get());
if (mDevice->ops->set_preview_window) { //通过 mDevice->ops 继续向下调用
mPreviewWindow = buf;
if (buf != nullptr) {
if (mPreviewScalingMode != NOT_SET) {
setPreviewScalingMode(mPreviewScalingMode);
}
if (mPreviewTransform != NOT_SET) {
setPreviewTransform(mPreviewTransform);
}
}
mHalPreviewWindow.user = this;
ALOGV("%s &mHalPreviewWindow %p mHalPreviewWindow.user %p", __FUNCTION__,
&mHalPreviewWindow, mHalPreviewWindow.user);
return mDevice->ops->set_preview_window(mDevice,
buf.get() ? &mHalPreviewWindow.nw : 0);
}
return INVALID_OPERATION;
}
startPreview()：
/**
关于 mDevice，结合 Camera.open() 流程与 hw_get_module() 相关逻辑，可以知道它的逻辑是这样的：
在 CameraService 启动时，会调用 onFirstRef() 对 module 进行初始化，获取 module 实例。
在 open 过程中，CameraClient 连接 CameraServer 成功时，会实例化 CameraHardwareInterface，并传入 module 实例对其初始化。
在初始化过程中，通过 module 实例对应的 open 方法，我们获得一个 device 实例，即 mDevice，这对应了具体的摄像头设备。
通过 mDevice 就可以将对应的指令传达到硬件设备。
*/
status_t startPreview()
{
ALOGV("%s(%s)", __FUNCTION__, mName.string());
if (mDevice->ops->start_preview)
return mDevice->ops->start_preview(mDevice);
return INVALID_OPERATION;
}
(2)hardware/libhardware/include/hardware/camera.h
typedef struct camera_device { //这里就声明了要追踪的 camera_device_t 。
/**
* camera_device.common.version must be in the range
* HARDWARE_DEVICE_API_VERSION(0,0)-(1,FF). CAMERA_DEVICE_API_VERSION_1_0 is
* recommended.
*/
hw_device_t common;
camera_device_ops_t *ops;
void *priv;
} camera_device_t;
其中struct camera_device_ops：所有关于 Camera 设备的操作对应的函数指针都在这里声明了。
typedef struct camera_device_ops {
int (*set_preview_window)(struct camera_device *,
struct preview_stream_ops *window);
void (*set_callbacks)(struct camera_device *,
camera_notify_callback notify_cb,
camera_data_callback data_cb,
camera_data_timestamp_callback data_cb_timestamp,
camera_request_memory get_memory,
void *user);
void (*enable_msg_type)(struct camera_device *, int32_t msg_type);
void (*disable_msg_type)(struct camera_device *, int32_t msg_type);
int (*msg_type_enabled)(struct camera_device *, int32_t msg_type);
/**
* Start preview mode.
*/
int (*start_preview)(struct camera_device *);
void (*stop_preview)(struct camera_device *);
int (*preview_enabled)(struct camera_device *);
int (*store_meta_data_in_buffers)(struct camera_device *, int enable);
int (*start_recording)(struct camera_device *);
void (*stop_recording)(struct camera_device *);
int (*recording_enabled)(struct camera_device *);
void (*release_recording_frame)(struct camera_device *,
const void *opaque);
int (*auto_focus)(struct camera_device *);
int (*cancel_auto_focus)(struct camera_device *);
int (*take_picture)(struct camera_device *);
int (*cancel_picture)(struct camera_device *);
int (*set_parameters)(struct camera_device *, const char *parms);
char *(*get_parameters)(struct camera_device *);
void (*put_parameters)(struct camera_device *, char *);
int (*send_command)(struct camera_device *,
int32_t cmd, int32_t arg1, int32_t arg2);
void (*release)(struct camera_device *);
int (*dump)(struct camera_device *, int fd);
} camera_device_ops_t;
（3）hardware/ti/omap4-aah/camera/CameraHal_Module.cpp : 在 open 流程中，就指定了 ops 中指针的对应关系。
memset(camera_device, 0, sizeof(*camera_device));
memset(camera_ops, 0, sizeof(*camera_ops));
camera_device->base.common.tag = HARDWARE_DEVICE_TAG;
camera_device->base.common.version = 0;
camera_device->base.common.module = (hw_module_t *)(module);
camera_device->base.common.close = camera_device_close;
camera_device->base.ops = camera_ops;
camera_ops->set_preview_window = camera_set_preview_window;
camera_ops->set_callbacks = camera_set_callbacks;
camera_ops->enable_msg_type = camera_enable_msg_type;
camera_ops->disable_msg_type = camera_disable_msg_type;
camera_ops->msg_type_enabled = camera_msg_type_enabled;
camera_ops->start_preview = camera_start_preview;
camera_ops->stop_preview = camera_stop_preview;
camera_ops->preview_enabled = camera_preview_enabled;
camera_ops->store_meta_data_in_buffers = camera_store_meta_data_in_buffers;
camera_ops->start_recording = camera_start_recording;
camera_ops->stop_recording = camera_stop_recording;
camera_ops->recording_enabled = camera_recording_enabled;
camera_ops->release_recording_frame = camera_release_recording_frame;
camera_ops->auto_focus = camera_auto_focus;
camera_ops->cancel_auto_focus = camera_cancel_auto_focus;
camera_ops->take_picture = camera_take_picture;
camera_ops->cancel_picture = camera_cancel_picture;
camera_ops->set_parameters = camera_set_parameters;
camera_ops->get_parameters = camera_get_parameters;
camera_ops->put_parameters = camera_put_parameters;
camera_ops->send_command = camera_send_command;
camera_ops->release = camera_release;
camera_ops->dump = camera_dump;
*device = &camera_device->base.common;
// -------- TI specific stuff --------
camera_device->cameraid = cameraid;
camera_start_preview()：
int camera_start_preview(struct camera_device * device)
{
CAMHAL_LOG_MODULE_FUNCTION_NAME;
int rv = -EINVAL;
ti_camera_device_t* ti_dev = NULL;
if(!device)
return rv;
ti_dev = (ti_camera_device_t*) device;
rv = gCameraHals[ti_dev->cameraid]->startPreview(); //gCameraHals 是 CameraHal * 。
return rv;
}
(4)hardware/ti/omap4-aah/camera/CameraHal.cpp : 将 Camera Hardware Interface 映射到 V4L2。
status_t CameraHal::startPreview() {
LOG_FUNCTION_NAME;
status_t ret = cameraPreviewInitialization(); //首先调用了 cameraPreviewInitialization() 函数进行初始化。
if (!mPreviewInitializationDone) return ret;
mPreviewInitializationDone = false;
if(mDisplayAdapter.get() != NULL) {
CAMHAL_LOGDA("Enabling display");
int width, height;
mParameters.getPreviewSize(&width, &height);
#if PPM_INSTRUMENTATION || PPM_INSTRUMENTATION_ABS
ret = mDisplayAdapter->enableDisplay(width, height, &mStartPreview);
#else
ret = mDisplayAdapter->enableDisplay(width, height, NULL);
#endif
if ( ret != NO_ERROR ) {
CAMHAL_LOGEA("Couldn't enable display");
CAMHAL_ASSERT_X(false,
"At this stage mCameraAdapter->mStateSwitchLock is still locked, "
"deadlock is guaranteed");
goto error;
}
}
CAMHAL_LOGDA("Starting CameraAdapter preview mode");
ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_START_PREVIEW); //通过 CameraAdapter 发送 CAMERA_START_PREVIEW 指令，若成功执行，则完成流程。
if(ret!=NO_ERROR) {
CAMHAL_LOGEA("Couldn't start preview w/ CameraAdapter");
goto error;
}
CAMHAL_LOGDA("Started preview");
mPreviewEnabled = true;
mPreviewStartInProgress = false;
return ret;
error:
CAMHAL_LOGEA("Performing cleanup after error");
//Do all the cleanup
freePreviewBufs();
mCameraAdapter->sendCommand(CameraAdapter::CAMERA_STOP_PREVIEW);
if(mDisplayAdapter.get() != NULL) {
mDisplayAdapter->disableDisplay(false);
}
mAppCallbackNotifier->stop();
mPreviewStartInProgress = false;
mPreviewEnabled = false;
LOG_FUNCTION_NAME_EXIT;
return ret;
}
cameraPreviewInitialization()：
- 代码中不断使用
mCameraAdapter->sendCommand()来发送指令，并获取一些数据。 - 指令发送到对应的
Adapter（如V4L Adapter），就会调用相应的函数进行处理。
////////////
/**
@brief Set preview mode related initialization
-> Camera Adapter set params
-> Allocate buffers
-> Set use buffers for preview
@param none
@return NO_ERROR
@todo Update function header with the different errors that are possible
*/
status_t CameraHal::cameraPreviewInitialization()
{
status_t ret = NO_ERROR;
CameraAdapter::BuffersDescriptor desc;
CameraFrame frame;
unsigned int required_buffer_count;
unsigned int max_queueble_buffers;
#if PPM_INSTRUMENTATION || PPM_INSTRUMENTATION_ABS
gettimeofday(&mStartPreview, NULL);
#endif
LOG_FUNCTION_NAME;
if (mPreviewInitializationDone) {
return NO_ERROR;
}
if ( mPreviewEnabled ){
CAMHAL_LOGDA("Preview already running");
LOG_FUNCTION_NAME_EXIT;
return ALREADY_EXISTS;
}
if ( NULL != mCameraAdapter ) {
ret = mCameraAdapter->setParameters(mParameters); //通过 Adapter 设置相关参数；
}
if ((mPreviewStartInProgress == false) && (mDisplayPaused == false)){
ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_QUERY_RESOLUTION_PREVIEW,( int ) &frame);
if ( NO_ERROR != ret ){
CAMHAL_LOGEB("Error: CAMERA_QUERY_RESOLUTION_PREVIEW %d", ret);
return ret;
}
///Update the current preview width and height
mPreviewWidth = frame.mWidth;
mPreviewHeight = frame.mHeight;
}
///If we don't have the preview callback enabled and display adapter,
if(!mSetPreviewWindowCalled || (mDisplayAdapter.get() == NULL)){
CAMHAL_LOGD("Preview not started. Preview in progress flag set");
mPreviewStartInProgress = true;
ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_SWITCH_TO_EXECUTING);
if ( NO_ERROR != ret ){
CAMHAL_LOGEB("Error: CAMERA_SWITCH_TO_EXECUTING %d", ret);
return ret;
}
return NO_ERROR;
}
if( (mDisplayAdapter.get() != NULL) && ( !mPreviewEnabled ) && ( mDisplayPaused ) )
{
CAMHAL_LOGDA("Preview is in paused state");
mDisplayPaused = false;
mPreviewEnabled = true;
if ( NO_ERROR == ret )
{
ret = mDisplayAdapter->pauseDisplay(mDisplayPaused);
if ( NO_ERROR != ret )
{
CAMHAL_LOGEB("Display adapter resume failed %x", ret);
}
}
//restart preview callbacks
if(mMsgEnabled & CAMERA_MSG_PREVIEW_FRAME)
{
mAppCallbackNotifier->enableMsgType (CAMERA_MSG_PREVIEW_FRAME);
}
signalEndImageCapture();
return ret;
}
required_buffer_count = atoi(mCameraProperties->get(CameraProperties::REQUIRED_PREVIEW_BUFS));
///Allocate the preview buffers
ret = allocPreviewBufs(mPreviewWidth, mPreviewHeight, mParameters.getPreviewFormat(), required_buffer_count, max_queueble_buffers); //申请 Buffers 空间；
if ( NO_ERROR != ret )
{
CAMHAL_LOGEA("Couldn't allocate buffers for Preview");
goto error;
}
if ( mMeasurementEnabled )
{
ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_QUERY_BUFFER_SIZE_PREVIEW_DATA,
( int ) &frame,
required_buffer_count);
if ( NO_ERROR != ret )
{
return ret;
}
///Allocate the preview data buffers
ret = allocPreviewDataBufs(frame.mLength, required_buffer_count);
if ( NO_ERROR != ret ) {
CAMHAL_LOGEA("Couldn't allocate preview data buffers");
goto error;
}
if ( NO_ERROR == ret )
{
//在申请 Buffers 空间成功后设置相应的成员。
desc.mBuffers = mPreviewDataBuffers;
desc.mOffsets = mPreviewDataOffsets;
desc.mFd = mPreviewDataFd;
desc.mLength = mPreviewDataLength;
desc.mCount = ( size_t ) required_buffer_count;
desc.mMaxQueueable = (size_t) required_buffer_count;
mCameraAdapter->sendCommand(CameraAdapter::CAMERA_USE_BUFFERS_PREVIEW_DATA,
( int ) &desc);
}
}
///Pass the buffers to Camera Adapter
desc.mBuffers = mPreviewBuffers;
desc.mOffsets = mPreviewOffsets;
desc.mFd = mPreviewFd;
desc.mLength = mPreviewLength;
desc.mCount = ( size_t ) required_buffer_count;
desc.mMaxQueueable = (size_t) max_queueble_buffers;
ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_USE_BUFFERS_PREVIEW,
( int ) &desc);
if ( NO_ERROR != ret )
{
CAMHAL_LOGEB("Failed to register preview buffers: 0x%x", ret);
freePreviewBufs();
return ret;
}
///Start the callback notifier
ret = mAppCallbackNotifier->start(); //开启回调通知。
if( ALREADY_EXISTS == ret )
{
//Already running, do nothing
CAMHAL_LOGDA("AppCallbackNotifier already running");
ret = NO_ERROR;
}
else if ( NO_ERROR == ret ) {
CAMHAL_LOGDA("Started AppCallbackNotifier..");
mAppCallbackNotifier->setMeasurements(mMeasurementEnabled);
}
else
{
CAMHAL_LOGDA("Couldn't start AppCallbackNotifier");
goto error;
}
if (ret == NO_ERROR) mPreviewInitializationDone = true;
//将 Buffers 对应到相应的回调函数中，以供上层 APP 获取预览所需的数据。
mAppCallbackNotifier->startPreviewCallbacks(mParameters, mPreviewBuffers, mPreviewOffsets, mPreviewFd, mPreviewLength, required_buffer_count);
return ret;
error:
CAMHAL_LOGEA("Performing cleanup after error");
//Do all the cleanup
freePreviewBufs();
mCameraAdapter->sendCommand(CameraAdapter::CAMERA_STOP_PREVIEW);
if(mDisplayAdapter.get() != NULL)
{
mDisplayAdapter->disableDisplay(false);
}
mAppCallbackNotifier->stop();
mPreviewStartInProgress = false;
mPreviewEnabled = false;
LOG_FUNCTION_NAME_EXIT;
return ret;
}
(5)hardware/ti/omap4-aah/camera/BaseCameraAdapter.cpp : 各常量分别对应不同的命令。
const LUT cameraCommandsUserToHAL[] = {
{ "CAMERA_START_PREVIEW", CameraAdapter::CAMERA_START_PREVIEW },
{ "CAMERA_STOP_PREVIEW", CameraAdapter::CAMERA_STOP_PREVIEW },
{ "CAMERA_START_VIDEO", CameraAdapter::CAMERA_START_VIDEO },
{ "CAMERA_STOP_VIDEO", CameraAdapter::CAMERA_STOP_VIDEO },
{ "CAMERA_START_IMAGE_CAPTURE", CameraAdapter::CAMERA_START_IMAGE_CAPTURE },
{ "CAMERA_STOP_IMAGE_CAPTURE", CameraAdapter::CAMERA_STOP_IMAGE_CAPTURE },
{ "CAMERA_PERFORM_AUTOFOCUS", CameraAdapter::CAMERA_PERFORM_AUTOFOCUS },
{ "CAMERA_CANCEL_AUTOFOCUS", CameraAdapter::CAMERA_CANCEL_AUTOFOCUS },
{ "CAMERA_PREVIEW_FLUSH_BUFFERS", CameraAdapter::CAMERA_PREVIEW_FLUSH_BUFFERS },
{ "CAMERA_START_SMOOTH_ZOOM", CameraAdapter::CAMERA_START_SMOOTH_ZOOM },
{ "CAMERA_STOP_SMOOTH_ZOOM", CameraAdapter::CAMERA_STOP_SMOOTH_ZOOM },
{ "CAMERA_USE_BUFFERS_PREVIEW", CameraAdapter::CAMERA_USE_BUFFERS_PREVIEW },
{ "CAMERA_SET_TIMEOUT", CameraAdapter::CAMERA_SET_TIMEOUT },
{ "CAMERA_CANCEL_TIMEOUT", CameraAdapter::CAMERA_CANCEL_TIMEOUT },
{ "CAMERA_START_BRACKET_CAPTURE", CameraAdapter::CAMERA_START_BRACKET_CAPTURE },
{ "CAMERA_STOP_BRACKET_CAPTURE", CameraAdapter::CAMERA_STOP_BRACKET_CAPTURE },
{ "CAMERA_QUERY_RESOLUTION_PREVIEW", CameraAdapter::CAMERA_QUERY_RESOLUTION_PREVIEW },
{ "CAMERA_QUERY_BUFFER_SIZE_IMAGE_CAPTURE", CameraAdapter::CAMERA_QUERY_BUFFER_SIZE_IMAGE_CAPTURE },
{ "CAMERA_QUERY_BUFFER_SIZE_PREVIEW_DATA", CameraAdapter::CAMERA_QUERY_BUFFER_SIZE_PREVIEW_DATA },
{ "CAMERA_USE_BUFFERS_IMAGE_CAPTURE", CameraAdapter::CAMERA_USE_BUFFERS_IMAGE_CAPTURE },
{ "CAMERA_USE_BUFFERS_PREVIEW_DATA", CameraAdapter::CAMERA_USE_BUFFERS_PREVIEW_DATA },
{ "CAMERA_TIMEOUT_EXPIRED", CameraAdapter::CAMERA_TIMEOUT_EXPIRED },
{ "CAMERA_START_FD", CameraAdapter::CAMERA_START_FD },
{ "CAMERA_STOP_FD", CameraAdapter::CAMERA_STOP_FD },
{ "CAMERA_SWITCH_TO_EXECUTING", CameraAdapter::CAMERA_SWITCH_TO_EXECUTING },
{ "CAMERA_USE_BUFFERS_VIDEO_CAPTURE", CameraAdapter::CAMERA_USE_BUFFERS_VIDEO_CAPTURE },
#ifdef OMAP_ENHANCEMENT_CPCAM
{ "CAMERA_USE_BUFFERS_REPROCESS", CameraAdapter::CAMERA_USE_BUFFERS_REPROCESS },
{ "CAMERA_START_REPROCESS", CameraAdapter::CAMERA_START_REPROCESS },
#endif
};
BaseCameraAdapter::sendCommand()：利用 switch 将不同的命令对应到各自的逻辑中。
case CameraAdapter::CAMERA_START_PREVIEW: //BaseCameraAdapter::startPreview()具体操作在其子类中实现，后面通过子类V4LCameraAdapter继续分析。 { CAMHAL_LOGDA("Start Preview"); if ( ret == NO_ERROR ) { ret = setState(operation); } if ( ret == NO_ERROR ) { ret = startPreview(); } if ( ret == NO_ERROR ) { ret = commitState(); } else { ret |= rollbackState(); } break; }
（6）hardware/ti/omap4-aah/camera/inc/V4LCameraAdapter/V4LCameraAdapter.h
private:
class PreviewThread : public android::Thread {
V4LCameraAdapter* mAdapter; //类 V4LCameraAdapter 继承了 BaseCameraAdapter
public:
PreviewThread(V4LCameraAdapter* hw) : //该线程不断执行 Adapter 中的 previewThread() 函数。
Thread(false), mAdapter(hw) { }
virtual void onFirstRef() {
run("CameraPreviewThread", android::PRIORITY_URGENT_DISPLAY);
}
virtual bool threadLoop() {
mAdapter->previewThread();
// loop until we need to quit
return true;
}
};
//Used for calculation of the average frame rate during preview
status_t recalculateFPS();
char * GetFrame(int &index);
int previewThread();
（7）hardware/ti/omap4-aah/camera/V4LCameraAdapter/V4LCameraAdapter.cpp
startPreview()：
status_t V4LCameraAdapter::startPreview()
{
status_t ret = NO_ERROR;
LOG_FUNCTION_NAME;
android::AutoMutex lock(mPreviewBufsLock);
if(mPreviewing) {
ret = BAD_VALUE;
goto EXIT;
}
for (int i = 0; i < mPreviewBufferCountQueueable; i++) {
mVideoInfo->buf.index = i;
mVideoInfo->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
mVideoInfo->buf.memory = V4L2_MEMORY_MMAP;
ret = v4lIoctl(mCameraHandle, VIDIOC_QBUF, &mVideoInfo->buf); //通过 v4lIoctl() 函数从硬件获取需要的数据，并存入 Buffers。
if (ret < 0) {
CAMHAL_LOGEA("VIDIOC_QBUF Failed");
goto EXIT;
}
nQueued++;
}
ret = v4lStartStreaming();// Create and start preview thread for receiving buffers from V4L Camera
if(!mCapturing) {
mPreviewThread = new PreviewThread(this); //启动一个 PreviewThread，用于接收从 V4L 摄像头设备传回的数据。
CAMHAL_LOGDA("Created preview thread");
}
//Update the flag to indicate we are previewing（设置标志，表明预览功能已开启）
mPreviewing = true;
mCapturing = false;
EXIT:
LOG_FUNCTION_NAME_EXIT;
return ret;
}
previewThread()：
int V4LCameraAdapter::previewThread()
{
status_t ret = NO_ERROR;
int width, height;
CameraFrame frame;
void *y_uv[2];
int index = 0;
int stride = 4096;
char *fp = NULL;
mParams.getPreviewSize(&width, &height);
if (mPreviewing) {
fp = this->GetFrame(index);
if(!fp) {
ret = BAD_VALUE;
goto EXIT;
}
CameraBuffer *buffer = mPreviewBufs.keyAt(index);
CameraFrame *lframe = (CameraFrame *)mFrameQueue.valueFor(buffer);
if (!lframe) {
ret = BAD_VALUE;
goto EXIT;
}
debugShowFPS();
if ( mFrameSubscribers.size() == 0 ) {
ret = BAD_VALUE;
goto EXIT;
}
y_uv[0] = (void*) lframe->mYuv[0];
//y_uv[1] = (void*) lframe->mYuv[1];
//y_uv[1] = (void*) (lframe->mYuv[0] + height*stride);
convertYUV422ToNV12Tiler ( (unsigned char*)fp, (unsigned char*)y_uv[0], width, height); //获取设备传回的数据，并进行一些格式转换操作.
CAMHAL_LOGVB("##...index= %d.;camera buffer= 0x%x; y= 0x%x; UV= 0x%x.",index, buffer, y_uv[0], y_uv[1] );
#ifdef SAVE_RAW_FRAMES
unsigned char* nv12_buff = (unsigned char*) malloc(width*height*3/2);
//Convert yuv422i to yuv420sp(NV12) & dump the frame to a file
convertYUV422ToNV12 ( (unsigned char*)fp, nv12_buff, width, height);
saveFile( nv12_buff, ((width*height)*3/2) );
free (nv12_buff);
#endif
//给帧数据进行一些必要的参数设置，如帧大小、时间戳等。
frame.mFrameType = CameraFrame::PREVIEW_FRAME_SYNC;
frame.mBuffer = buffer;
frame.mLength = width*height*3/2;
frame.mAlignment = stride;
frame.mOffset = 0;
frame.mTimestamp = systemTime(SYSTEM_TIME_MONOTONIC);
frame.mFrameMask = (unsigned int)CameraFrame::PREVIEW_FRAME_SYNC;
if (mRecording)
{
frame.mFrameMask |= (unsigned int)CameraFrame::VIDEO_FRAME_SYNC;
mFramesWithEncoder++;
}
ret = setInitFrameRefCount(frame.mBuffer, frame.mFrameMask);
if (ret != NO_ERROR) {
CAMHAL_LOGDB("Error in setInitFrameRefCount %d", ret);
} else {
ret = sendFrameToSubscribers(&frame); //将帧数据发送给用户
}
}
EXIT:
return ret;
}
(8)hardware/ti/omap4-aah/camera/AppCallbackNotifier.cpp：预览功能初始化的部分，调用到了 AppCallbackNotifier 类的函数。
status_t AppCallbackNotifier::startPreviewCallbacks(android::CameraParameters ¶ms, CameraBuffer *buffers, uint32_t *offsets, int fd, size_t length, size_t count)
{
unsigned int *bufArr;
int size = 0;
LOG_FUNCTION_NAME;
android::AutoMutex lock(mLock);
if ( NULL == mFrameProvider )
{
CAMHAL_LOGEA("Trying to start video recording without FrameProvider");
return -EINVAL;
}
if ( mPreviewing )
{
CAMHAL_LOGDA("+Already previewing");
return NO_INIT;
}
int w,h;
///Get preview size
params.getPreviewSize(&w, &h);
// save preview pixel format, size and stride
mPreviewWidth = w;
mPreviewHeight = h;
mPreviewStride = 4096;
mPreviewPixelFormat = CameraHal::getPixelFormatConstant(params.getPreviewFormat());
size = CameraHal::calculateBufferSize(mPreviewPixelFormat, w, h);
mPreviewMemory = mRequestMemory(-1, size, AppCallbackNotifier::MAX_BUFFERS, NULL);
if (!mPreviewMemory) {
return NO_MEMORY;
}
for (int i=0; i < AppCallbackNotifier::MAX_BUFFERS; i++) {
mPreviewBuffers[i].type = CAMERA_BUFFER_MEMORY;
mPreviewBuffers[i].opaque = (unsigned char*) mPreviewMemory->data + (i*size);
mPreviewBuffers[i].mapped = mPreviewBuffers[i].opaque;
}
if ( mCameraHal->msgTypeEnabled(CAMERA_MSG_PREVIEW_FRAME ) ) {
mFrameProvider->enableFrameNotification(CameraFrame::PREVIEW_FRAME_SYNC);
}
if ( mCameraHal->msgTypeEnabled(CAMERA_MSG_POSTVIEW_FRAME) ) {
mFrameProvider->enableFrameNotification(CameraFrame::SNAPSHOT_FRAME); //同步预览帧
}
mPreviewBufCount = 0;
mPreviewing = true;
LOG_FUNCTION_NAME_EXIT;
return NO_ERROR;
}
以上回调函数在这里设置：
void AppCallbackNotifier::setCallbacks(CameraHal* cameraHal,
camera_notify_callback notify_cb,
camera_data_callback data_cb,
camera_data_timestamp_callback data_cb_timestamp,
camera_request_memory get_memory,
void *user)
{
android::AutoMutex lock(mLock);
LOG_FUNCTION_NAME;
mCameraHal = cameraHal;
mNotifyCb = notify_cb;
mDataCb = data_cb;
mDataCbTimestamp = data_cb_timestamp;
mRequestMemory = get_memory;
mCallbackCookie = user;
LOG_FUNCTION_NAME_EXIT;
}
notifyEvent()：
case CameraHalEvent::EVENT_METADATA: //预览元数据
metaEvtData = evt->mEventData->metadataEvent;
if ( ( NULL != mCameraHal ) &&
( NULL != mNotifyCb) &&
( mCameraHal->msgTypeEnabled(CAMERA_MSG_PREVIEW_METADATA) ) )
{
// WA for an issue inside CameraService
camera_memory_t *tmpBuffer = mRequestMemory(-1, 1, 1, NULL); //申请一个 camera_memory_t 对应的 Buffers 空间后，就调用回调函数将元数据往上层进行传输了。
mDataCb(CAMERA_MSG_PREVIEW_METADATA,
tmpBuffer,
0,
metaEvtData->getMetadataResult(),
mCallbackCookie);
metaEvtData.clear();
if ( NULL != tmpBuffer ) {
tmpBuffer->release(tmpBuffer);
}
}
break;
简图总结： HAL 层中，CameraHardwareInterface 是通用的入口，而真正实现与驱动层的对接是与平台相关，不同平台有不同的实现方案。
五、Camera.takePicture()流程
Camera API 1 中，数据流主要是通过函数回调的方式，依照从下往上的方向，逐层 return 到 Applications 中。
1.Open 时设置回调：frameworks/av/services/camera/libcameraservice/device1/CameraHardwareInterface.h
/** Set the notification and data callbacks */
void setCallbacks(notify_callback notify_cb,
data_callback data_cb,
data_callback_timestamp data_cb_timestamp,
void* user)
{
mNotifyCb = notify_cb; //设置 notify 回调，这用来通知数据已经更新。
mDataCb = data_cb; //置 data 回调以及 dataTimestamp 回调，对应的是函数指针 mDataCb 与 mDataCvTimestamp 。
mDataCbTimestamp = data_cb_timestamp;
mCbUser = user;
ALOGV("%s(%s)", __FUNCTION__, mName.string());
if (mDevice->ops->set_callbacks) { //注：设置 mDevice->ops 对应回调函数时，传入的不是之前设置的函数指针，而是 __data_cb 这样的函数。在该文件中，实现了 __data_cb ，将回调函数做了一层封装。
mDevice->ops->set_callbacks(mDevice,
__notify_cb,
__data_cb,
__data_cb_timestamp,
__get_memory,
this);
}
}
__data_cb()：对原 callback 函数简单封装，附加了一个防止数组越界判断。
static void __data_cb(int32_t msg_type,
const camera_memory_t *data, unsigned int index,
camera_frame_metadata_t *metadata,
void *user)
{
ALOGV("%s", __FUNCTION__);
CameraHardwareInterface *__this =
static_cast<CameraHardwareInterface *>(user);
sp<CameraHeapMemory> mem(static_cast<CameraHeapMemory *>(data->handle));
if (index >= mem->mNumBufs) {
ALOGE("%s: invalid buffer index %d, max allowed is %d", __FUNCTION__,
index, mem->mNumBufs);
return;
}
__this->mDataCb(msg_type, mem->mBuffers[index], metadata, __this->mCbUser);
}
2.控制流：
（1）frameworks/base/core/java/android/hardware/Camera.java
takePicture()：
public final void takePicture(ShutterCallback shutter, PictureCallback raw,
PictureCallback postview, PictureCallback jpeg) {
mShutterCallback = shutter; //设置快门回调。
mRawImageCallback = raw; //设置各种类型的图片数据回调。
mPostviewCallback = postview;
mJpegCallback = jpeg;
// If callback is not set, do not send me callbacks.
int msgType = 0;
if (mShutterCallback != null) {
msgType |= CAMERA_MSG_SHUTTER;
}
if (mRawImageCallback != null) {
msgType |= CAMERA_MSG_RAW_IMAGE;
}
if (mPostviewCallback != null) {
msgType |= CAMERA_MSG_POSTVIEW_FRAME;
}
if (mJpegCallback != null) {
msgType |= CAMERA_MSG_COMPRESSED_IMAGE;
}
native_takePicture(msgType); //调用 JNI takePicture 方法,传入的参数 msgType 是根据相应 CallBack 是否存在而确定的，每种 Callback 应该对应一个二进制中的数位（如 1，10，100 中 1 的位置）
mFaceDetectionRunning = false;
}
3.Android Runtime：frameworks/base/core/jni/android_hardware_Camera.cpp
static void android_hardware_Camera_takePicture(JNIEnv *env, jobject thiz, jint msgType)
{
ALOGV("takePicture");
JNICameraContext* context;
sp<Camera> camera = get_native_camera(env, thiz, &context); //获取已经打开的 camera 实例，调用其 takePicture() 接口。
if (camera == 0) return;
/*
* When CAMERA_MSG_RAW_IMAGE is requested, if the raw image callback
* buffer is available, CAMERA_MSG_RAW_IMAGE is enabled to get the
* notification _and_ the data; otherwise, CAMERA_MSG_RAW_IMAGE_NOTIFY
* is enabled to receive the callback notification but no data.
*
* Note that CAMERA_MSG_RAW_IMAGE_NOTIFY is not exposed to the
* Java application.
*
注意，在这个函数中，对于 RAW_IMAGE 有一些附加操作：
如果设置了 RAW 的 callback ，则要检查上下文中，是否能找到对应 Buffer。
若无法找到 Buffer ，则将 CAMERA_MSG_RAW_IMAGE 的信息去掉，换成 CAMERA_MSG_RAW_IMAGE_NOTIFY。
替换后，就只会获得 notification 的消息，而没有对应的图像数据。
*/
if (msgType & CAMERA_MSG_RAW_IMAGE) {
ALOGV("Enable raw image callback buffer");
if (!context->isRawImageCallbackBufferAvailable()) {
ALOGV("Enable raw image notification, since no callback buffer exists");
msgType &= ~CAMERA_MSG_RAW_IMAGE;
msgType |= CAMERA_MSG_RAW_IMAGE_NOTIFY;
}
}
if (camera->takePicture(msgType) != NO_ERROR) {
jniThrowRuntimeException(env, "takePicture failed");
return;
}
}
4.C/C++ Libraries
(1)frameworks/av/camera/Camera.cpp
// take a picture
status_t Camera::takePicture(int msgType)
{
ALOGV("takePicture: 0x%x", msgType);
sp <::android::hardware::ICamera> c = mCamera;
if (c == 0) return NO_INIT;
return c->takePicture(msgType); //获取一个 ICamera，调用其 takePicture 接口。
}
(2)frameworks/av/camera/ICamera.cpp
// take a picture - returns an IMemory (ref-counted mmap)
status_t takePicture(int msgType)
{
ALOGV("takePicture: 0x%x", msgType);
Parcel data, reply;
data.writeInterfaceToken(ICamera::getInterfaceDescriptor());
data.writeInt32(msgType);
remote()->transact(TAKE_PICTURE, data, &reply); //利用 Binder 机制发送相应指令到服务端,实际调用到的是 CameraClient::takePicture() 函数。
status_t ret = reply.readInt32();
return ret;
}
(3)frameworks/av/services/camera/libcameraservice/api1/CameraClient.cpp
// take a picture - image is returned in callback
status_t CameraClient::takePicture(int msgType) {
LOG1("takePicture (pid %d): 0x%x", getCallingPid(), msgType);
Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;
if ((msgType & CAMERA_MSG_RAW_IMAGE) && //注:CAMERA_MSG_RAW_IMAGE 指令与 CAMERA_MSG_RAW_IMAGE_NOTIFY 指令不能同时有效，需要进行对应的检查。
(msgType & CAMERA_MSG_RAW_IMAGE_NOTIFY)) {
ALOGE("CAMERA_MSG_RAW_IMAGE and CAMERA_MSG_RAW_IMAGE_NOTIFY"
" cannot be both enabled");
return BAD_VALUE;
}
// We only accept picture related message types
// and ignore other types of messages for takePicture().
int picMsgType = msgType //对传入的指令过滤，只留下与 takePicture() 操作相关的。
& (CAMERA_MSG_SHUTTER |
CAMERA_MSG_POSTVIEW_FRAME |
CAMERA_MSG_RAW_IMAGE |
CAMERA_MSG_RAW_IMAGE_NOTIFY |
CAMERA_MSG_COMPRESSED_IMAGE);
enableMsgType(picMsgType);
return mHardware->takePicture(); //调用 CameraHardwareInterface 中的 takePicture() 接口。
}
5.数据流:由于数据流是通过 callback 函数实现的，所以探究其流程的时候我是从底层向上层进行分析的
(1)HAL:frameworks/av/services/camera/libcameraservice/device1/CameraHardwareInterface.h
/**
* Take a picture.
*/
status_t takePicture()
{
ALOGV("%s(%s)", __FUNCTION__, mName.string());
if (mDevice->ops->take_picture)
return mDevice->ops->take_picture(mDevice); //通过 mDevice 中设置的函数指针，调用 HAL 层中具体平台对应的 takePicture 操作的实现逻辑。
return INVALID_OPERATION;
}
__data_cb()：该回调函数是在同文件中实现的 setCallbacks() 函数中设置的，Camera 设备获得数据后，就会往上传输，在 HAL 层中会调用到这个回调函数。
static void __data_cb(int32_t msg_type,
const camera_memory_t *data, unsigned int index,
camera_frame_metadata_t *metadata,
void *user)
{
ALOGV("%s", __FUNCTION__);
CameraHardwareInterface *__this =
static_cast<CameraHardwareInterface *>(user);
sp<CameraHeapMemory> mem(static_cast<CameraHeapMemory *>(data->handle));
if (index >= mem->mNumBufs) {
ALOGE("%s: invalid buffer index %d, max allowed is %d", __FUNCTION__,
index, mem->mNumBufs);
return;
}
__this->mDataCb(msg_type, mem->mBuffers[index], metadata, __this->mCbUser); // mDataCb 指针对应的是 CameraClient 类中实现的 dataCallback()。
}
(2)C/C++ Libraries:
frameworks/av/services/camera/libcameraservice/api1/CameraClient.cpp
void CameraClient::dataCallback(int32_t msgType, //该回调在initialize()函数中设置到CameraHardwareInterface中。 const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata, void* user) { LOG2("dataCallback(%d)", msgType); sp<CameraClient> client = static_cast<CameraClient*>(getClientFromCookie(user).get()); //启动这个回调后，就从Cookie中获取已连接的客户端。 if (client.get() == nullptr) return; if (!client->lockIfMessageWanted(msgType)) return; if (dataPtr == 0 && metadata == NULL) { ALOGE("Null data returned in data callback"); client->handleGenericNotify(CAMERA_MSG_ERROR, UNKNOWN_ERROR, 0); return; } switch (msgType & ~CAMERA_MSG_PREVIEW_METADATA) { //根据msgType，启动对应的handle操作。 case CAMERA_MSG_PREVIEW_FRAME: client->handlePreviewData(msgType, dataPtr, metadata); break; case CAMERA_MSG_POSTVIEW_FRAME: client->handlePostview(dataPtr); break; case CAMERA_MSG_RAW_IMAGE: client->handleRawPicture(dataPtr); break; case CAMERA_MSG_COMPRESSED_IMAGE: client->handleCompressedPicture(dataPtr); break; default: client->handleGenericData(msgType, dataPtr, metadata); break; } }
handleRawPicture()：
// picture callback - raw image ready
void CameraClient::handleRawPicture(const sp<IMemory>& mem) {
disableMsgType(CAMERA_MSG_RAW_IMAGE);
ssize_t offset;
size_t size;
sp<IMemoryHeap> heap = mem->getMemory(&offset, &size);
sp<hardware::ICameraClient> c = mRemoteCallback; //在 open 流程中，connect() 函数调用时，mRemoteCallback 已经设置为一个客户端实例，其对应的是 ICameraClient 的强指针。
mLock.unlock();
if (c != 0) {
c->dataCallback(CAMERA_MSG_RAW_IMAGE, mem, NULL); //基于 Binder 机制来启动客户端的 dataCallback客户端的，dataCallback 是实现在 Camera 类中。
}
}
frameworks/av/camera/Camera.cpp
// callback from camera service when frame or image is ready
void Camera::dataCallback(int32_t msgType, const sp<IMemory>& dataPtr,
camera_frame_metadata_t *metadata)
{
sp<CameraListener> listener;
{
Mutex::Autolock _l(mLock);
listener = mListener;
}
if (listener != NULL) {
listener->postData(msgType, dataPtr, metadata); //调用 CameraListener 的 postData 接口(android_hardware_Camera.cpp中实现)，将数据继续向上传输。
}
}
（3）Android Runtime ：frameworks/base/core/jni/android_hardware_Camera.cpp
void JNICameraContext::postData(int32_t msgType, const sp<IMemory>& dataPtr,
camera_frame_metadata_t *metadata) //postData是 JNICameraContext 类的成员函数，该类继承了 CameraListener。
{
// VM pointer will be NULL if object is released
Mutex::Autolock _l(mLock);
JNIEnv *env = AndroidRuntime::getJNIEnv(); //首先获取虚拟机指针
if (mCameraJObjectWeak == NULL) {
ALOGW("callback on dead camera object");
return;
}
int32_t dataMsgType = msgType & ~CAMERA_MSG_PREVIEW_METADATA; //然后过滤掉 CAMERA_MSG_PREVIEW_METADATA 信息
// return data based on callback type
switch (dataMsgType) {
case CAMERA_MSG_VIDEO_FRAME:
// should never happen
break;
// For backward-compatibility purpose, if there is no callback
// buffer for raw image, the callback returns null.
case CAMERA_MSG_RAW_IMAGE:
ALOGV("rawCallback");
if (mRawImageCallbackBuffers.isEmpty()) {
env->CallStaticVoidMethod(mCameraJClass, fields.post_event,
mCameraJObjectWeak, dataMsgType, 0, 0, NULL);
} else {
copyAndPost(env, dataPtr, dataMsgType); //关键是在于 copyAndPost() 函数
}
break;
// There is no data.
case 0:
break;
default:
ALOGV("dataCallback(%d, %p)", dataMsgType, dataPtr.get());
copyAndPost(env, dataPtr, dataMsgType);
break;
}
// post frame metadata to Java
if (metadata && (msgType & CAMERA_MSG_PREVIEW_METADATA)) {
postMetadata(env, CAMERA_MSG_PREVIEW_METADATA, metadata);
}
}
copyAndPost()：
void JNICameraContext::copyAndPost(JNIEnv* env, const sp<IMemory>& dataPtr, int msgType)
{
jbyteArray obj = NULL;
// allocate Java byte array and copy data
if (dataPtr != NULL) { //首先确认 Memory 中数据是否存在
ssize_t offset;
size_t size;
sp<IMemoryHeap> heap = dataPtr->getMemory(&offset, &size);
ALOGV("copyAndPost: off=%zd, size=%zu", offset, size);
uint8_t *heapBase = (uint8_t*)heap->base();
if (heapBase != NULL) {
const jbyte* data = reinterpret_cast<const jbyte*>(heapBase + offset);
if (msgType == CAMERA_MSG_RAW_IMAGE) {
obj = getCallbackBuffer(env, &mRawImageCallbackBuffers, size);
} else if (msgType == CAMERA_MSG_PREVIEW_FRAME && mManualBufferMode) {
obj = getCallbackBuffer(env, &mCallbackBuffers, size);
if (mCallbackBuffers.isEmpty()) {
ALOGV("Out of buffers, clearing callback!");
mCamera->setPreviewCallbackFlags(CAMERA_FRAME_CALLBACK_FLAG_NOOP);
mManualCameraCallbackSet = false;
if (obj == NULL) {
return;
}
}
} else {
ALOGV("Allocating callback buffer");
obj = env->NewByteArray(size);
}
if (obj == NULL) {
ALOGE("Couldn't allocate byte array for JPEG data");
env->ExceptionClear();
} else {
env->SetByteArrayRegion(obj, 0, size, data);
}
} else {
ALOGE("image heap is NULL");
}
}
// post image data to Java
env->CallStaticVoidMethod(mCameraJClass, fields.post_event, //将图像传给 Java 端
mCameraJObjectWeak, msgType,0, 0, obj);
if (obj) {
env->DeleteLocalRef(obj);
}
}
(4)frameworks/base/core/java/android/hardware/Camera.java
private static void postEventFromNative(Object camera_ref, //继承了Handler类 int what, int arg1, int arg2, Object obj) { Camera c = (Camera)((WeakReference)camera_ref).get(); //首先确定Camera是否已经实例化。 if (c == null) return; if (c.mEventHandler != null) { Message m = c.mEventHandler.obtainMessage(what, arg1, arg2, obj); //通过Camera的成员mEventHandler的obtainMessage方法将从Native环境中获得的数据封装成Message类的一个实例, c.mEventHandler.sendMessage(m); //然后调用sendMessage()方法将数据传出。 } }
@Override
public void handleMessage(Message msg) { //继承了 Handler 类
switch(msg.what) {
case CAMERA_MSG_SHUTTER:
if (mShutterCallback != null) {
mShutterCallback.onShutter();
}
return;
case CAMERA_MSG_RAW_IMAGE:
if (mRawImageCallback != null) {
mRawImageCallback.onPictureTaken((byte[])msg.obj, mCamera);
}
return;
case CAMERA_MSG_COMPRESSED_IMAGE:
if (mJpegCallback != null) {
mJpegCallback.onPictureTaken((byte[])msg.obj, mCamera);
}
return;
case CAMERA_MSG_PREVIEW_FRAME:
PreviewCallback pCb = mPreviewCallback;
if (pCb != null) {
if (mOneShot) {
// Clear the callback variable before the callback
// in case the app calls setPreviewCallback from
// the callback function
mPreviewCallback = null;
} else if (!mWithBuffer) {
// We're faking the camera preview mode to prevent
// the app from being flooded with preview frames.
// Set to oneshot mode again.
setHasPreviewCallback(true, false);
}
pCb.onPreviewFrame((byte[])msg.obj, mCamera);
}
return;
case CAMERA_MSG_POSTVIEW_FRAME:
if (mPostviewCallback != null) {
mPostviewCallback.onPictureTaken((byte[])msg.obj, mCamera); //通过调用这个方法，底层传输到此的数据最终发送到最上层的 Java 应用中，上层应用通过解析 Message 得到图像数据。
}
return;
case CAMERA_MSG_FOCUS:
AutoFocusCallback cb = null;
synchronized (mAutoFocusCallbackLock) {
cb = mAutoFocusCallback;
}
if (cb != null) {
boolean success = msg.arg1 == 0 ? false : true;
cb.onAutoFocus(success, mCamera);
}
return;
case CAMERA_MSG_ZOOM:
if (mZoomListener != null) {
mZoomListener.onZoomChange(msg.arg1, msg.arg2 != 0, mCamera);
}
return;
case CAMERA_MSG_PREVIEW_METADATA:
if (mFaceListener != null) {
mFaceListener.onFaceDetection((Face[])msg.obj, mCamera);
}
return;
case CAMERA_MSG_ERROR :
Log.e(TAG, "Error " + msg.arg1);
if (mErrorCallback != null) {
mErrorCallback.onError(msg.arg1, mCamera);
}
return;
case CAMERA_MSG_FOCUS_MOVE:
if (mAutoFocusMoveCallback != null) {
mAutoFocusMoveCallback.onAutoFocusMoving(msg.arg1 == 0 ? false : true, mCamera);
}
return;
default:
Log.e(TAG, "Unknown message type " + msg.what);
return;
}
}
简图总结：
总结：
不管是控制流还是数据流，都是要通过五大层次依次执行下一步的。控制流是将命令从顶层流向底层，而数据流则是将底层的数据流向顶层。如果要自定义一个对数据进行处理的 C++ 功能库，并将其加入相机中，可以通过对 HAL 层进行一些修改，将 RAW 图像流向自己的处理库，再将处理后的 RAW 图像传回 HAL 层（需要在 HAL 层对 RAW 格式进行一些处理才能把图像上传），最后通过正常的回调流程把图像传到顶层应用中。