<Android Framework 之路>Android5.1 Camera Framework（三）
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上一次讲解了一下startPreview过程，主要是为了画出一条大致的从上到下的线条，今天我们看一下Camera在Framework的sendCommand和dataCallback，这部分属于衔接过程，可以看到上下是如何交流沟通的。
首先，sendCommand
Camera.java中并没有sendCommand方法，在Camera.cpp中存在sendCommand函数，所以这个sendCommand是从android_hardware_interface.cpp中开始使用的
android_hardware_Camera.cpp (base\core\jni)
startSmoothZoom
android_hardware_Camera_startSmoothZoom
——>CAMERA_CMD_START_SMOOTH_ZOOM
stopSmoothZoom
android_hardware_Camera_stopSmoothZoom
——>CAMERA_CMD_STOP_SMOOTH_ZOOM
setDisplayOrientation
android_hardware_Camera_setDisplayOrientation
——>CAMERA_CMD_SET_DISPLAY_ORIENTATION
_enableShutterSound
android_hardware_Camera_enableShutterSound
——>CAMERA_CMD_ENABLE_SHUTTER_SOUND
_startFaceDetection
android_hardware_Camera_startFaceDetection
——>CAMERA_CMD_START_FACE_DETECTION
_stopFaceDetection
android_hardware_Camera_stopFaceDetection
——>CAMERA_CMD_STOP_FACE_DETECTION
enableFocusMoveCallback
android_hardware_Camera_enableFocusMoveCallback
——>CAMERA_CMD_ENABLE_FOCUS_MOVE_MSG
诸如此类的命令类型定义在Camera.h (system\core\include\system)
enum {
CAMERA_CMD_START_SMOOTH_ZOOM = 1,
CAMERA_CMD_STOP_SMOOTH_ZOOM = 2,
CAMERA_CMD_SET_DISPLAY_ORIENTATION = 3,
CAMERA_CMD_ENABLE_SHUTTER_SOUND = 4,
CAMERA_CMD_PLAY_RECORDING_SOUND = 5,
CAMERA_CMD_START_FACE_DETECTION = 6,
CAMERA_CMD_STOP_FACE_DETECTION = 7,
CAMERA_CMD_ENABLE_FOCUS_MOVE_MSG = 8,
CAMERA_CMD_PING = 9,
CAMERA_CMD_SET_VIDEO_BUFFER_COUNT = 10,
};
以上者几种操作都是采用sendCommand()的函数来实现的，对应的命令类型也列举出来了，HAL层会根据这个消息类型做出判断，然后做出对应的操作。
来看下sendCommand的实现：
Camera.cpp (frameworks\av\camera)
// send command to camera driverstatus_t Camera::sendCommand(int32_t cmd, int32_t arg1, int32_t arg2){ ALOGV("sendCommand"); sp <ICamera> c = mCamera; if (c == 0) return NO_INIT; return c->sendCommand(cmd, arg1, arg2); //三个参数，第一个是消息类型，后面两个参数有时候使用有时不使用，这里应该是具有扩展性的，如果需要添加更多的参数，上下接口同时修改就可以了。}然后通过Binder机制，
virtual status_t sendCommand(int32_t cmd, int32_t arg1, int32_t arg2) { ALOGV("sendCommand"); Parcel data, reply; data.writeInterfaceToken(ICamera::getInterfaceDescriptor()); data.writeInt32(cmd); data.writeInt32(arg1); data.writeInt32(arg2); remote()->transact(SEND_COMMAND, data, &reply); return reply.readInt32(); }status_t BnCamera::onTransact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){ ...... case SEND_COMMAND: { ALOGV("SEND_COMMAND"); CHECK_INTERFACE(ICamera, data, reply); int command = data.readInt32(); int arg1 = data.readInt32(); int arg2 = data.readInt32(); reply->writeInt32(sendCommand(command, arg1, arg2)); return NO_ERROR; } break;}然后调用到
status_t CameraClient::sendCommand(int32_t cmd, int32_t arg1, int32_t arg2) { ...... if (cmd == CAMERA_CMD_SET_DISPLAY_ORIENTATION) { // Mirror the preview if the camera is front-facing. orientation = getOrientation(arg1, mCameraFacing == CAMERA_FACING_FRONT); if (orientation == -1) return BAD_VALUE; if (mOrientation != orientation) { mOrientation = orientation; if (mPreviewWindow != 0) { native_window_set_buffers_transform(mPreviewWindow.get(), mOrientation); } } return OK; } else if (cmd == CAMERA_CMD_ENABLE_SHUTTER_SOUND) { switch (arg1) { //这里就是对参数arg1的使用，通过参数来开关拍照声音 case 0: return enableShutterSound(false); case 1: return enableShutterSound(true); default: return BAD_VALUE; } return OK; } else if (cmd == CAMERA_CMD_PLAY_RECORDING_SOUND) { //录像声音 mCameraService->playSound(CameraService::SOUND_RECORDING); } else if (cmd == CAMERA_CMD_SET_VIDEO_BUFFER_COUNT) { // Silently ignore this command return INVALID_OPERATION; } else if (cmd == CAMERA_CMD_PING) { // If mHardware is 0, checkPidAndHardware will return error. return OK; } //以上是framework可以处理的命令 return mHardware->sendCommand(cmd, arg1, arg2); //HAL层处理}在HAL层中处理的消息类型主要是打开和停止人脸检测过程，
QCamera2HWI.cpp (\device\asus\flo\camera\qcamera2\hal)
int QCamera2HardwareInterface::sendCommand(int32_t command, int32_t /*arg1*/, int32_t /*arg2*/){ int rc = NO_ERROR; switch (command) { case CAMERA_CMD_START_FACE_DETECTION: case CAMERA_CMD_STOP_FACE_DETECTION: //开关人脸检测 rc = setFaceDetection(command == CAMERA_CMD_START_FACE_DETECTION? true : false); break; default: rc = NO_ERROR; break; } return rc;}综上，如上就是sendCommand的过程
然后，回调Callback
从之前的文章可以看到callback主要有三种类型
notifyCallback
dataCallback
dataTimestampCallback
这个过程我们就不能按照之前的从上至下的跟过程了，这次需要反着来，从HAL层回调到
CameraHardwareInterface.h (frameworks\av\services\camera\libcameraservice\device1)
static void __notify_cb(int32_t msg_type, int32_t ext1, int32_t ext2, void *user) { ALOGV("%s", __FUNCTION__); CameraHardwareInterface *__this = static_cast<CameraHardwareInterface *>(user); __this->mNotifyCb(msg_type, ext1, ext2, __this->mCbUser); } 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); ...... __this->mDataCb(msg_type, mem->mBuffers[index], metadata, __this->mCbUser); } static void __data_cb_timestamp(nsecs_t timestamp, int32_t msg_type, const camera_memory_t *data, unsigned index, void *user) { ALOGV("%s", __FUNCTION__); CameraHardwareInterface *__this = static_cast<CameraHardwareInterface *>(user); ...... __this->mDataCbTimestamp(timestamp, msg_type, mem->mBuffers[index], __this->mCbUser); }其中的mNotifyCb，mDataCb，mDataCbTimestamp是在CameraClient::initialize函数中设置的
void setCallbacks(notify_callback notify_cb, data_callback data_cb, data_callback_timestamp data_cb_timestamp, void* user) { mNotifyCb = notify_cb; mDataCb = data_cb; mDataCbTimestamp = data_cb_timestamp; mCbUser = user; ALOGV("%s(%s)", __FUNCTION__, mName.string()); if (mDevice->ops->set_callbacks) { mDevice->ops->set_callbacks(mDevice, __notify_cb, __data_cb, __data_cb_timestamp, __get_memory, this); } }回调自然是到CameraClient中去找了
void CameraClient::notifyCallback(int32_t msgType, int32_t ext1, int32_t ext2, void* user) { ......}void CameraClient::dataCallback(int32_t msgType, const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata, void* user) { LOG2("dataCallback(%d)", msgType); Mutex* lock = getClientLockFromCookie(user); if (lock == NULL) return; Mutex::Autolock alock(*lock); CameraClient* client = static_cast<CameraClient*>(getClientFromCookie(user)); if (client == NULL) 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) { 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; }}void CameraClient::dataCallbackTimestamp(nsecs_t timestamp, int32_t msgType, const sp<IMemory>& dataPtr, void* user) { ......}这里主要看下dataCallback的过程吧，
switch (msgType & ~CAMERA_MSG_PREVIEW_METADATA) { case CAMERA_MSG_PREVIEW_FRAME: //预览帧数据 client->handlePreviewData(msgType, dataPtr, metadata); break; case CAMERA_MSG_POSTVIEW_FRAME: //postview image client->handlePostview(dataPtr); break; case CAMERA_MSG_RAW_IMAGE: //原始数据 client->handleRawPicture(dataPtr); break; case CAMERA_MSG_COMPRESSED_IMAGE: //真实图片 client->handleCompressedPicture(dataPtr); break; default: client->handleGenericData(msgType, dataPtr, metadata); break; }这里最后会调用到
c->dataCallback，然后根据消息类型来做处理，然后在通过binder机制
// generic data callback from camera service to app with image data void dataCallback(int32_t msgType, const sp<IMemory>& imageData, camera_frame_metadata_t *metadata) { ALOGV("dataCallback"); Parcel data, reply; data.writeInterfaceToken(ICameraClient::getInterfaceDescriptor()); data.writeInt32(msgType); data.writeStrongBinder(imageData->asBinder()); if (metadata) { data.writeInt32(metadata->number_of_faces); data.write(metadata->faces, sizeof(camera_face_t) * metadata->number_of_faces); } remote()->transact(DATA_CALLBACK, data, &reply, IBinder::FLAG_ONEWAY); }status_t BnCameraClient::onTransact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){ switch(code) { ...... case DATA_CALLBACK: { ALOGV("DATA_CALLBACK"); CHECK_INTERFACE(ICameraClient, data, reply); int32_t msgType = data.readInt32(); sp<IMemory> imageData = interface_cast<IMemory>(data.readStrongBinder()); camera_frame_metadata_t *metadata = NULL; if (data.dataAvail() > 0) { metadata = new camera_frame_metadata_t; metadata->number_of_faces = data.readInt32(); metadata->faces = (camera_face_t *) data.readInplace( sizeof(camera_face_t) * metadata->number_of_faces); } dataCallback(msgType, imageData, metadata); if (metadata) delete metadata; return NO_ERROR; } break; ......}这里转到Camera.cpp
// callback from camera service when frame or image is readyvoid 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); }}通过listener的方式来往上层甩数据，那么问题来了，这个listener是什么时候设置的？
回想一下第一篇FWK分析博客中的native_setup过程中有这么一段
sp<JNICameraContext> context = new JNICameraContext(env, weak_this, clazz, camera); context->incStrong((void*)android_hardware_Camera_native_setup); camera->setListener(context);就是在这里设置的listener,JNICameraContext继承CameraListener，复写父类的方法
class JNICameraContext: public CameraListener{ ...... }class CameraListener: virtual public RefBase{public: virtual void notify(int32_t msgType, int32_t ext1, int32_t ext2) = 0; virtual void postData(int32_t msgType, const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata) = 0; virtual void postDataTimestamp(nsecs_t timestamp, int32_t msgType, const sp<IMemory>& dataPtr) = 0;};承接上面那一段，这里我们只看postData()
android_hardware_Camera.cpp (frameworks\base\core\jni)
void JNICameraContext::postData(int32_t msgType, const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata){ ...... int32_t dataMsgType = msgType & ~CAMERA_MSG_PREVIEW_METADATA; // 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); } 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);//这里有人脸数据 }}这里涉及到的
env->CallStaticVoidMethod(mCameraJClass, fields.post_event,
mCameraJObjectWeak, dataMsgType, 0, 0, NULL);
copyAndPost(env, dataPtr, dataMsgType);
postMetadata(env, CAMERA_MSG_PREVIEW_METADATA, metadata);
直接或间接的使用到fileds.post_event函数，这里是JNI中的方法注册，
fields.post_event = env->GetStaticMethodID(clazz, “postEventFromNative”,
“(Ljava/lang/Object;IIILjava/lang/Object;)V”);
这个是在register_android_hardware_Camera()函数中调用的，这里不做过多停留，这个实际会调用到
Camera.java (frameworks\base\core\java\android\hardware)
private static void postEventFromNative(Object camera_ref, int what, int arg1, int arg2, Object obj) { Camera c = (Camera)((WeakReference)camera_ref).get(); if (c == null) return; if (c.mEventHandler != null) { Message m = c.mEventHandler.obtainMessage(what, arg1, arg2, obj); c.mEventHandler.sendMessage(m); } }这里也是采用了JAVA中很常用的handler message处理
private class EventHandler extends Handler { private final Camera mCamera; public EventHandler(Camera c, Looper looper) { super(looper); mCamera = c; } @Override public void handleMessage(Message msg) { 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); } 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; } } }到这里基本上就是上层的处理了，callback都是在相机应用中设置的，然后各种数据就在相机应用中得到对应的处理。
具体的每一个数据怎么处理，这里我们不做分析，后续有需要，可以在细讲一下，旨在弄清楚代码是怎么走的。
本文中代码使用的是Android5.1原始代码，欢迎大家留言交流。
版权声明：本文为博主原创文章，未经博主允许不得转载。
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