Camera的架构与Android系统的整体架构保持一致,如下图所示,本文主要从以下四个方面对其进行说明。
- Framework:Camera.java
- Android Runtime:android_hardware_Camera.cpp
- Library:Camera Client和Camera Service
- HAL:CameraHardwareInterface
一、Framework:Camera.java
Camera是应用层软件直接使用的类,涵盖了启动、预览、拍摄及关闭等操作摄像头的全部接口。Camera.java在Android源码中的路径为:framework/base/core/java/android/hardware。为了说明整个Camera系统的架构,这里暂不横向分析Camera.java的功能,下面从open()方法着手:
/**
* 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();
CameraInfo cameraInfo = new CameraInfo();
for (int i = 0; i < numberOfCameras; i++) {
getCameraInfo(i, cameraInfo);
if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
return new Camera(i);
}
}
return null;
}
open()方法需要注意以下几点:
- getNumberOfCameras为native方法,实现在android_hardware_Camera.cpp中;
- CameraInfo是Camera定义的静态内部类,包含facing、orientation、canDisableShutterSound;
- getCameraInfo内部调用native方法_getCameraInfo获取摄像头信息;
- open()默认启动的是后置摄像头(CAMERA_FACING_BACK)。
Camera(int cameraId) {
mShutterCallback = null;
mRawImageCallback = null;
mJpegCallback = null;
mPreviewCallback = null;
mPostviewCallback = null;
mZoomListener = null;
Looper looper;
if ((looper = Looper.myLooper()) != null) {
mEventHandler = new EventHandler(this, looper);
} else if ((looper = Looper.getMainLooper()) != null) {
mEventHandler = new EventHandler(this, looper);
} else {
mEventHandler = null;
}
String packageName = ActivityThread.currentPackageName();
native_setup(new WeakReference<Camera>(this), cameraId, packageName);
}
调用本地方法native_setup(),由此进入到android_hardware_Camera.cpp(frameworks\base\core\jni)中
private native final void native_setup(Object camera_this, int cameraId,
String packageName);
二、Android Runtime:android_hardware_Camera.cpp
native_setup()被动态注册到JNI,通过JNI调用android_hardware_Camera_native_setup()方法。
// connect to camera service
static void android_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,
jobject weak_this, jint cameraId, jstring clientPackageName)
{
// Convert jstring to String16
const char16_t *rawClientName = env->GetStringChars(clientPackageName, NULL);
jsize rawClientNameLen = env->GetStringLength(clientPackageName);
String16 clientName(rawClientName, rawClientNameLen);
env->ReleaseStringChars(clientPackageName, rawClientName);
sp<Camera> camera = Camera::connect(cameraId, clientName,
Camera::USE_CALLING_UID);
if (camera == NULL) {
jniThrowRuntimeException(env, "Fail to connect to camera service");
return;
}
// make sure camera hardware is alive
if (camera->getStatus() != NO_ERROR) {
jniThrowRuntimeException(env, "Camera initialization failed");
return;
}
jclass clazz = env->GetObjectClass(thiz);
if (clazz == NULL) {
jniThrowRuntimeException(env, "Can't find android/hardware/Camera");
return;
}
// We use a weak reference so the Camera object can be garbage collected.
// The reference is only used as a proxy for callbacks.
sp<JNICameraContext> context = new JNICameraContext(env, weak_this, clazz, camera);
context->incStrong((void*)android_hardware_Camera_native_setup);
camera->setListener(context);
// save context in opaque field
env->SetIntField(thiz, fields.context, (int)context.get());
}
android_hardware_Camera_native_setup()方法通过调用Camera::connect()方法请求连接CameraService服务。入参中:
- clientName是通过将clientPackageName从jstring转换为String16格式得到;
- Camera::USE_CALLING_UID是定义在Camera.h中的枚举类型,其值为ICameraService::USE_CALLING_UID(同样为枚举类型,值为-1)。
Camera::connect()位于Camera.cpp(frameworks\av\camera)中,由此进入到Library层。
三、Library:Camera Client和Camera Service
如上述架构图中所示,ICameraService.h、ICameraClient.h和ICamera.h(frameworks\av\include\camera)三个类定义了Camera的接口和架构,ICameraService.cpp和Camera.cpp两个文件用于Camera架构的实现,Camera的具体功能在下层调用硬件相关的接口来实现。Camera.h是Camera系统对上层的接口。
具体的,Camera类继承模板类CameraBase,Camera::connect()调用了CameraBase.cpp中的connect()方法。
sp<Camera> Camera::connect(int cameraId, const String16& clientPackageName,
int clientUid)
{
return CameraBaseT::connect(cameraId, clientPackageName, clientUid);
}
CameraBase实际上又继承了IBinder的DeathRecipient内部类,DeathRecipient虚拟继承自RefBase。RefBase是Android中的引用计数基础类,其中定义了incStrong、decStrong、incWeak和decWeak等涉及sp/wp的指针操作函数,当然这扯远了。
template <typename TCam>
struct CameraTraits {
};
template <typename TCam, typename TCamTraits = CameraTraits<TCam> >
class CameraBase : public IBinder::DeathRecipient
{
public:
static sp<TCam> connect(int cameraId,
const String16& clientPackageName,
int clientUid);
……
}
class DeathRecipient : public virtual RefBase { public: virtual void binderDied(const wp<IBinder>& who) = 0; };
回到Camera::connect()的实现上,其中,new TCam(cameraId)生成BnCameraClient对象,BnCameraClient定义在ICameraClient.h文件中,继承自模板类BnInterface。getCameraService()方法返回CameraService的服务代理BpCameraService,BpCameraService同样继承自模板类BnInterface。然后通过Binder通信发送CONNECT命令,当BnCameraService收到CONNECT命令后调用CameraService的connect()成员函数来做相应的处理。frameworks\av\camera\CameraBase.cpp
template <typename TCam, typename TCamTraits> sp<TCam> CameraBase<TCam, TCamTraits>::connect(int cameraId, const String16& clientPackageName, int clientUid) { ALOGV("%s: connect", __FUNCTION__); sp<TCam> c = new TCam(cameraId); sp<TCamCallbacks> cl = c; const sp<ICameraService>& cs = getCameraService(); if (cs != 0) { c->mCamera = cs->connect(cl, cameraId, clientPackageName, clientUid); } if (c->mCamera != 0) { c->mCamera->asBinder()->linkToDeath(c); c->mStatus = NO_ERROR; } else { c.clear(); } return c; }
class BnCameraService: public BnInterface<ICameraService> { public: virtual status_t onTransact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags = 0); };
注:connect()函数在BpCameraService和BnCameraService的父类ICameraService中声明为纯虚函数,在BpCameraService和CameraService中分别给出了实现,BpCameraService作为代理类,提供接口给客户端,真正实现在BnCameraService的子类CameraService中。
在BpCameraService中,connect()函数实现如下:
frameworks\av\camera\ICameraService.cpp
// connect to camera service virtual sp<ICamera> connect(const sp<ICameraClient>& cameraClient, int cameraId, const String16 &clientPackageName, int clientUid) { Parcel data, reply; data.writeInterfaceToken(ICameraService::getInterfaceDescriptor()); data.writeStrongBinder(cameraClient->asBinder()); data.writeInt32(cameraId); data.writeString16(clientPackageName); data.writeInt32(clientUid); remote()->transact(BnCameraService::CONNECT, data, &reply); return interface_cast<ICamera>(reply.readStrongBinder()); }
首先将传递过来的Camera对象cameraClient转换成IBinder类型,将调用的参数写到Parcel(可理解为Binder通信的管道)中,通过BpBinder的transact()函数发送消息,然后由BnCameraService去响应该连接,最后就是等待服务端返回,如果成功则生成一个BpCamera实例。
真正的服务端响应实现在BnCameraService的onTransact()函数中,其负责解包收到的Parcel并执行client端的请求的方法。
status_t BnCameraService::onTransact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) { switch(code) { case GET_NUMBER_OF_CAMERAS: { CHECK_INTERFACE(ICameraService, data, reply); reply->writeInt32(getNumberOfCameras()); return NO_ERROR; } break; case GET_CAMERA_INFO: { CHECK_INTERFACE(ICameraService, data, reply); CameraInfo cameraInfo; memset(&cameraInfo, 0, sizeof(cameraInfo)); status_t result = getCameraInfo(data.readInt32(), &cameraInfo); reply->writeInt32(cameraInfo.facing); reply->writeInt32(cameraInfo.orientation); reply->writeInt32(result); return NO_ERROR; } break; case CONNECT: { CHECK_INTERFACE(ICameraService, data, reply); sp<ICameraClient> cameraClient = interface_cast<ICameraClient>(data.readStrongBinder()); int32_t cameraId = data.readInt32(); const String16 clientName = data.readString16(); int32_t clientUid = data.readInt32(); sp<ICamera> camera = connect(cameraClient, cameraId, clientName, clientUid); reply->writeStrongBinder(camera->asBinder()); return NO_ERROR; } break; case CONNECT_PRO: { CHECK_INTERFACE(ICameraService, data, reply); sp<IProCameraCallbacks> cameraClient = interface_cast<IProCameraCallbacks>(data.readStrongBinder()); int32_t cameraId = data.readInt32(); const String16 clientName = data.readString16(); int32_t clientUid = data.readInt32(); sp<IProCameraUser> camera = connect(cameraClient, cameraId, clientName, clientUid); reply->writeStrongBinder(camera->asBinder()); return NO_ERROR; } break; case ADD_LISTENER: { CHECK_INTERFACE(ICameraService, data, reply); sp<ICameraServiceListener> listener = interface_cast<ICameraServiceListener>(data.readStrongBinder()); reply->writeInt32(addListener(listener)); return NO_ERROR; } break; case REMOVE_LISTENER: { CHECK_INTERFACE(ICameraService, data, reply); sp<ICameraServiceListener> listener = interface_cast<ICameraServiceListener>(data.readStrongBinder()); reply->writeInt32(removeListener(listener)); return NO_ERROR; } break; default: return BBinder::onTransact(code, data, reply, flags); } }
主要的处理包括:
- 通过data中Camera的Binder对象生成Camera客户代理BpCameraClient实例;
- 将生成的BpCameraClient对象作为参数传递到CameraService(/frameworks/av/services/camera /libcameraservice/CameraService.cpp)的connect()函数中,该函数会返回一个BpCamera实例;
- 将在上述实例对象以IBinder的形式打包到Parcel中返回。
status_t CameraClient::initialize(camera_module_t *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); mHardware = new CameraHardwareInterface(camera_device_name); res = mHardware->initialize(&module->common); if (res != OK) { ALOGE("%s: Camera %d: unable to initialize device: %s (%d)", __FUNCTION__, mCameraId, strerror(-res), res); mHardware.clear(); return NO_INIT; } mHardware->setCallbacks(notifyCallback, dataCallback, dataCallbackTimestamp, (void *)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; }
上述函数中,主要注意以下流程:
- 加粗的代码CameraHardwareInterface新建了了一个Camera硬件接口,当然,camera_device_name为摄像头设备名;
- mHardware->initialize(&module->common)调用底层硬件的初始化方法;
- mHardware->setCallbacks将CamerService处的回调函数注册到HAL处。
CameraHardwareInterface定义了Camera的硬件抽象特征,由此进入到HAL。
四、HAL:CameraHardwareInterface
CameraHardwareInterface的作用在于链接Camera Server和V4L2,通过实现CameraHardwareInterface可以屏蔽不同的driver对Camera Server的影响。CameraHardwareInterface同样虚拟继承自RefBase。
CameraHardwareInterface中包含了控制通道和数据通道,控制通道用于处理预览和视频获取的开始/停止、拍摄照片、自动对焦等功能,数据通道通过回调函数来获得预览、视频录制、自动对焦等数据。当需要支持新的硬件时就需要继承于CameraHardwareInterface ,来实现对应的功能。CameraHardwareInterface提供的public方法如下:class CameraHardwareInterface : public virtual RefBase { public: CameraHardwareInterface(const char *name) { mDevice = 0; mName = name; } …… }
在前一节中,initialize()函数调用了mHardware->initialize和mHardware->setCallbacks,下面来看下CameraHardwareInterface.h对其的实现。
status_t initialize(hw_module_t *module)
{
ALOGI("Opening camera %s", mName.string());
int rc = module->methods->open(module, mName.string(),
(hw_device_t **)&mDevice);
if (rc != OK) {
ALOGE("Could not open camera %s: %d", mName.string(), rc);
return rc;
}
initHalPreviewWindow();
return rc;
}
在initialize()方法中,通过module->methods->open打开摄像头模组,initHalPreviewWindow()用于初始化Preview的相关流opspreview_stream_ops,初始化hal的预览窗口。
static struct hw_module_methods_t camera_module_methods = {
open: camera_device_open
};
camera_module_t HAL_MODULE_INFO_SYM = {
common: {
tag: HARDWARE_MODULE_TAG,
version_major: 1,
version_minor: 0,
id: CAMERA_HARDWARE_MODULE_ID,
name: "Freescale CameraHal Module",
author: "Freescale",
methods: &camera_module_methods,
dso: NULL, /* remove compilation warnings */
reserved: { 0 }, /* remove compilation warnings */
},
get_number_of_cameras: camera_get_number_of_cameras,
get_camera_info: camera_get_camera_info,
};
/* open device handle to one of the cameras
*
* assume camera service will keep singleton of each camera
* so this function will always only be called once per camera instance
*/
int camera_device_open(const hw_module_t *module,
const char *name,
hw_device_t **device)
{
int rv = 0;
int num_cameras = 0;
int cameraid;
fsl_camera_device_t *camera_device = NULL;
camera_device_ops_t *camera_ops = NULL;
CameraHal *camera = NULL;
char *SelectedCameraName;
android::Mutex::Autolock lock(gCameraHalDeviceLock);
ALOGI("camera_device open: %s", name);
if (name != NULL) {
cameraid = atoi(name);
num_cameras = camera_get_number_of_cameras();
if (cameraid > num_cameras)
{
ALOGE("camera service provided cameraid out of bounds, "
"cameraid = %d, num supported = %d",
cameraid, num_cameras);
rv = -EINVAL;
goto fail;
}
camera_device = (fsl_camera_device_t *)malloc(sizeof(*camera_device));
if (!camera_device)
{
ALOGE("camera_device allocation fail");
rv = -ENOMEM;
goto fail;
}
camera_ops = (camera_device_ops_t *)malloc(sizeof(*camera_ops));
if (!camera_ops)
{
ALOGE("camera_ops allocation fail");
rv = -ENOMEM;
goto fail;
}
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;
camera_device->cameraid = cameraid;
camera = new CameraHal(cameraid);
if (!camera)
{
ALOGE("Couldn't create instance of CameraHal class");
rv = -ENOMEM;
goto fail;
}
if (camera->initialize(sCameraInfo[cameraid]) < 0) {
rv = -EINVAL;
goto fail;
}
gCameraHals[cameraid] = camera;
gCamerasOpen++;
}
return rv;
fail:
if (camera_device) {
free(camera_device);
camera_device = NULL;
}
if (camera_ops) {
free(camera_ops);
camera_ops = NULL;
}
if (camera) {
delete camera;
camera = NULL;
}
*device = NULL;
return rv;
}
hardware\imx\mx6\libcamera\CameraHal.cpp
status_t CameraHal::initialize(const CameraInfo& info)
{
status_t ret = NO_ERROR;
FLOG_RUNTIME("initialize name:%s, path:%s", info.name, info.devPath);
mDeviceAdapter = DeviceAdapter::Create(info);
if (mDeviceAdapter == NULL) {
FLOGE("CameraHal: DeviceAdapter create failed");
return BAD_VALUE;
}
ret = mDeviceAdapter->initialize(info);
if (ret) {
FLOGE("CameraHal: DeviceAdapter initialize failed");
return ret;
}
mCameraBridge = new CameraBridge();
if (mCameraBridge == NULL) {
FLOGE("CameraHal: new CameraBridge failed");
return BAD_VALUE;
}
ret = mCameraBridge->initialize();
if (ret) {
FLOGE("CameraHal: CameraBridge initialize failed");
return ret;
}
mCameraBridge->getSupportedRecordingFormat(mSupportedRecordingFormat,
MAX_VPU_SUPPORT_FORMAT);
mCameraBridge->getSupportedPictureFormat(mSupportedPictureFormat,
MAX_PICTURE_SUPPORT_FORMAT);
ret = mDeviceAdapter->initParameters(mParameters,
mSupportedRecordingFormat,
MAX_VPU_SUPPORT_FORMAT,
mSupportedPictureFormat,
MAX_PICTURE_SUPPORT_FORMAT);
if (ret) {
FLOGE("CameraHal: DeviceAdapter initParameters failed");
return ret;
}
ret = mCameraBridge->initParameters(mParameters);
if (ret) {
FLOGE("CameraHal: CameraBridge initParameters failed");
return ret;
}
mDeviceAdapter->setErrorListener(mCameraBridge.get());
mCameraBridge->setCameraFrameProvider(mDeviceAdapter.get());
mCameraBridge->setCameraEventProvider(CameraEvent::EVENT_INVALID,
mDeviceAdapter.get());
mBufferProvider = NULL;
return ret;
}
这里主要是硬件抽象层对接驱动层代码,DeviceAdapter::initialize类打开设备节点。