Android Camera数据流分析全程记录（非overlay方式） 2013-11（转）

Android Camera数据流分析全程记录（非overlay方式）  2013-04-03 14:15:55

分类： Android平台

Android Camera数据流分析全程记录

花了不少时间在这个数据流的分析上面，自己毕竟没怎么做过android，这里记录一下自己的见解，任何理解错误还望高人指教，以后还需慢慢纠正
整个分析过程从app的onCreate开始：packages/apps/OMAPCamera/src/com/ti/omap4/android/camera/Camera.java
在onCreate中做了很多的初始化，我们真正关注的是一下几条语句：

 // don't set mSurfaceHolder here. We have it set ONLY within
 // surfaceChanged / surfaceDestroyed, other parts of the code
 // assume that when it is set, the surface is also set.
 SurfaceView preview = (SurfaceView) findViewById(R.id.camera_preview);
 SurfaceHolder holder = preview.getHolder();
 holder.addCallback(this);

在这里我们实例化了一个SurfaceView对象，通过这个对象获取SurfaceHolder对象，实现这个addCallback方法，
其中 SurfaceView的定义在以下路径： frameworks/base/core/java/android/view/SurfaceView.java
其中 SurfaceHolder的定义在以下路径： frameworks/base/core/java/android/view/SurfaceHolder.java

这里看看这个文章的解释，写的很是不错：http://blog.chinaunix.net/uid-9863638-id-1996383.html

SurfaceFlinger 是Android multimedia 的一个部分，在Android 的实现中它是一个service ，提供系统范围内的surface composer 功能，它能够将各种应用程序的2D，3D surface 进行组合。
在具体讲SurfaceFlinger 之前，我们先来看一下有关显示方面的一些基础知识 。

每个应用程序可能对应着一个或者多个图形界面，而每个界面我们就称之为一个surface ，或者说是window ，在上面的图中我们能看到4 个surface ，一个是home 界面，还有就是红、绿、蓝分别代表的3 个surface ，而两个button 实际是home surface 里面的内容。在这里我们能看到我们进行图形显示所需要解决 的问题：
a 、首先每个surface 在屏幕上有它的位置，以及大小，然后每个surface 里面还有要显示的内容，内容，大小，位置 这些元素 在我们改变应用程序的时候都可能会改变，改变时应该如何处理 
b 、然后就各个surface 之间可能有重叠，比如说在上面的简略图中，绿色覆盖了蓝色，而红色又覆盖了绿色和蓝色以及下面的home ，而且还具有一定透明度。这种层之间的关系应该如何描述      
我们首先来看第二个问题，我们可以想象在屏幕平面的垂直方向还有一个Z 轴，所有的surface 根据在Z 轴上的坐标来确定前后，这样就可以描述各个surface 之间的上下覆盖关系了，而这个在Z 轴上的顺序，图形上有个专业术语叫Z-order 。  
对于第一个问题，我们需要一个结构来记录应用程序界面的位置，大小，以及一个buffer 来记录需要显示的内容，所以这就是我们surface 的概念，surface 实际我们可以把它理解成一个容器，这个容器记录着应用程序界面的控制信息，比如说大小啊，位置啊，而它还有buffer 来专门存储需要显示的内容。
在这里还存在一个问题，那就是当存在图形重合的时候应该如何处理呢，而且可能有些surface 还带有透明信息，这里就是我们SurfaceFlinger 需要解决问题，它要把各个surface 组合(compose/merge) 成一个main Surface ，最后将Main Surface 的内容发送给FB/V4l2 Output ，这样屏幕上就能看到我们想要的效果。
在实际中对这些Surface 进行merge 可以采用两种方式，一种就是采用软件的形式来merge ，还一种就是采用硬件的方式，软件的方式就是我们的SurfaceFlinger ，而硬件的方式就是Overlay 。

首先继承SurfaceView并实现SurfaceHolder.Callback接口
使用接口的原因：因为使用SurfaceView 有一个原则，所有的绘图工作必须得在Surface 被创建之后才能开始(Surface—表面，基本上我们可以把它当作显存的一个映射，写入到Surface 的内容可以被直接复制到显存从而显示出来，这使得显示速度会非常快)，而在Surface 被销毁之前必须结束。所以Callback 中的surfaceCreated 和surfaceDestroyed 就成了绘图处理代码的边界。
需要重写的方法
　（1）public void surfaceChanged(SurfaceHolder holder,int format,int width,int height){}//在surface的大小发生改变时激发
　（2）public void surfaceCreated(SurfaceHolder holder){}//在创建时激发，一般在这里调用画图的线程。
　（3）public void surfaceDestroyed(SurfaceHolder holder) {} //销毁时激发，一般在这里将画图的线程停止、释放。
这几个方法在在app中都已经重新实现了，重点分析 surfaceChanged

 public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
         // Make sure we have a surface in the holder before proceeding.
         if (holder.getSurface() == null) {
             Log.d(TAG, "holder.getSurface() == null");
             return;
         }

         Log.v(TAG, "surfaceChanged. w=" + w + ". h=" + h);

         // We need to save the holder for later use, even when the mCameraDevice
         // is null. This could happen if onResume() is invoked after this
         // function.
         mSurfaceHolder = holder;

         // The mCameraDevice will be null if it fails to connect to the camera
         // hardware. In this case we will show a dialog and then finish the
         // activity, so it's OK to ignore it.
         if (mCameraDevice == null) return;

         // Sometimes surfaceChanged is called after onPause or before onResume.
         // Ignore it.
         if (mPausing || isFinishing()) return;

         setSurfaceLayout();

         // Set preview display if the surface is being created. Preview was
         // already started. Also restart the preview if display rotation has
         // changed. Sometimes this happens when the device is held in portrait
         // and camera app is opened. Rotation animation takes some time and
         // display rotation in onCreate may not be what we want.
         if (mCameraState == PREVIEW_STOPPED) {//这里check摄像头是否已经启动，第一次启动摄像头和摄像头已经打开从新进入摄像头实现方法不同
             startPreview(true);
             startFaceDetection();
         } else {
             if (Util.getDisplayRotation(this) != mDisplayRotation) {
                 setDisplayOrientation();
             }
             if (holder.isCreating()) {
                 // Set preview display if the surface is being created and preview
                 // was already started. That means preview display was set to null
                 // and we need to set it now.
                 setPreviewDisplay(holder);
             }
         }

         // If first time initialization is not finished, send a message to do
         // it later. We want to finish surfaceChanged as soon as possible to let
         // user see preview first.
         if (!mFirstTimeInitialized) {
             mHandler.sendEmptyMessage(FIRST_TIME_INIT);
         } else {
             initializeSecondTime();
         }

         SurfaceView preview = (SurfaceView) findViewById(R.id.camera_preview);
         CameraInfo info = CameraHolder.instance().getCameraInfo()[mCameraId];
         boolean mirror = (info.facing == CameraInfo.CAMERA_FACING_FRONT);
         int displayRotation = Util.getDisplayRotation(this);
         int displayOrientation = Util.getDisplayOrientation(displayRotation, mCameraId);

         mTouchManager.initialize(preview.getHeight() / 3, preview.getHeight() / 3,
                preview, this, mirror, displayOrientation);

     }

以上标注部分是关键，现在直接分心startPreview方法，这是第一次打开摄像头的处理函数，进行了一些初始换，而已经处于摄像头打开状态时不必使用startPreview方法，而是用上面的另外一个分支，重新开始显示即可

 private void startPreview(boolean updateAll) {
         if (mPausing || isFinishing()) return;

         mFocusManager.resetTouchFocus();

         mCameraDevice.setErrorCallback(mErrorCallback);

         // If we're previewing already, stop the preview first (this will blank
         // the screen).
         if (mCameraState != PREVIEW_STOPPED) stopPreview();

         setPreviewDisplay(mSurfaceHolder);
         setDisplayOrientation();

         if (!mSnapshotOnIdle) {
             // If the focus mode is continuous autofocus, call cancelAutoFocus to
             // resume it because it may have been paused by autoFocus call.
             if (Parameters.FOCUS_MODE_CONTINUOUS_PICTURE.equals(mFocusManager.getFocusMode())) {
                 mCameraDevice.cancelAutoFocus();
             }
             mFocusManager.setAeAwbLock(false); // Unlock AE and AWB.
         }

         if ( updateAll ) {
             Log.v(TAG, "Updating all parameters!");
             setCameraParameters(UPDATE_PARAM_INITIALIZE | UPDATE_PARAM_ZOOM | UPDATE_PARAM_PREFERENCE);
         } else {
             setCameraParameters(UPDATE_PARAM_MODE);
         }

         //setCameraParameters(UPDATE_PARAM_ALL);

         // Inform the mainthread to go on the UI initialization.
         if (mCameraPreviewThread != null) {
             synchronized (mCameraPreviewThread) {
                 mCameraPreviewThread.notify();
             }
         }

         try {
             Log.v(TAG, "startPreview");
             mCameraDevice.startPreview();
         } catch (Throwable ex) {
             closeCamera();
             throw new RuntimeException("startPreview failed", ex);
         }

         mZoomState = ZOOM_STOPPED;
         setCameraState(IDLE);
         mFocusManager.onPreviewStarted();
         if ( mTempBracketingEnabled ) {
             mFocusManager.setTempBracketingState(FocusManager.TempBracketingStates.ACTIVE);
         }

         if (mSnapshotOnIdle) {
             mHandler.post(mDoSnapRunnable);
         }
     }

这里的思路是：先通过 setPreviewDisplay 方法将surface设定为window-player，这个方法会调用到HAL层，进行很重要的初始化，实现数据的回调

这里我必须得着重着重的进行分析，我一直在寻找是什么决定了overlay的使用与不适用，这里就这个 setPreviewDisplay 方法就是“罪魁祸首 ”
在setPreview方法中传入的参数是 surfa ceview ，这个surfa ceview传到底层HAL层是参数形式发生了改变，但是在我的理解下，就是人换衣服一样，
张三今天换了一身衣服，但这个张三跟昨天穿不同衣服的张三是同一个人，到了HAL层这个参数的形式是 preview_stream_ops  ，下面慢慢你就可以知道了，
在camerahal中的 setPreviewDisplay 方法中，是通过判断传下来的的 preview_stream_ops  参数是否为空决定使用overlay还是不适用overlay的，很重要的
这篇文章只是在这里提及一下，下面不会提及overlay的内容，默认是以不适用overlay的方式分析数据流的整个过程的，这里可千万别混淆了
使用overl的数据回流方式将单独作为一章分析，同时会详细分析使用和不适用overlay的最终决定权

流程如下：app-->frameworks-->通过JNI-->camera client--> camera service-->通过hardware-interface -->hal_module-->HAL
这里十分有必要看一下camera service层的调用过程：

 // set the Surface that the preview will use
 status_t CameraService::Client::setPreviewDisplay(const sp<Surface>& surface) {
     LOG1("setPreviewDisplay(%p) (pid %d)", surface.get(), getCallingPid());

     sp<IBinder> binder(surface != 0 ? surface->asBinder() : 0);
     sp<ANativeWindow> window(surface);
     return setPreviewWindow(binder, window);
 }

这里其实我还是理解的不是很透彻，将我们从app传进来的surface转换为IBinder和ANativiWindow，然后以这两个变量为参数接着调用参数不同的 setPreviewWindow

 status_t CameraService::Client::setPreviewWindow(const sp<IBinder>& binder,
         const sp<ANativeWindow>& window) {
     Mutex::Autolock lock(mLock);
     status_t result = checkPidAndHardware();
     if (result != NO_ERROR) return result;

     // return if no change in surface.
     if (binder == mSurface) {
         return NO_ERROR;
     }

     if (window != 0) {
         result = native_window_api_connect(window.get(), NATIVE_WINDOW_API_CAMERA);
         if (result != NO_ERROR) {
             LOGE("native_window_api_connect failed: %s (%d)", strerror(-result),
                     result);
             return result;
         }
     }

     // If preview has been already started, register preview buffers now.
     if (mHardware->previewEnabled()) {
         if (window != 0) {
             native_window_set_scaling_mode(window.get(),
                     NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
             native_window_set_buffers_transform(window.get(), mOrientation);
             result = mHardware->setPreviewWindow(window);
         }
     }

     if (result == NO_ERROR) {
         // Everything has succeeded. Disconnect the old window and remember the
         // new window.
         disconnectWindow(mPreviewWindow);
         mSurface = binder;
         mPreviewWindow = window;
     } else {
         // Something went wrong after we connected to the new window, so
         // disconnect here.
         disconnectWindow(window);
     }

     return result;
 }

上面先调用到CameraHardwareInterface中的setPreview方法：

 status_t setPreviewWindow(const sp<ANativeWindow>& buf)
     {
         LOGV("%s(%s) buf %p", __FUNCTION__, mName.string(), buf.get());

         if (mDevice->ops->set_preview_window) {
             mPreviewWindow = buf;
 #ifdef OMAP_ENHANCEMENT_CPCAM
             mHalPreviewWindow.user = mPreviewWindow.get();
 #else
             mHalPreviewWindow.user = this;
 #endif
             LOGV("%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;
     }

到这里为止，传输的参数已经由最初的surface-->ANativeWindow-->preview_stream_ops, 传递到底层的参数已经发生了本质的变化，后面数据回调的时候还会见到这里变量，现在先记下它
其实我说的本质的变化这里也只能这么说，但往深入追究，这个preview_stream_ops也可以说只是surface的另外一种形式而已
这样才通过hardware调用到hal-module再调用到hal层

 int camera_set_preview_window(struct camera_device * device,
         struct preview_stream_ops *window)
 {
     int rv = -EINVAL;
     ti_camera_device_t* ti_dev = NULL;

     LOGV("%s", __FUNCTION__);

     if(!device)
         return rv;

     ti_dev = (ti_camera_device_t*) device;

     rv = gCameraHals[ti_dev->cameraid]->setPreviewWindow(window);

     return rv;
 }

HAL层调用：

 status_t CameraHal::setPreviewWindow(struct preview_stream_ops *window)
 {
     status_t ret = NO_ERROR;
     CameraAdapter::BuffersDescriptor desc;

     LOG_FUNCTION_NAME;
     mSetPreviewWindowCalled = true;

    //If the Camera service passes a null window, we destroy existing window and free the DisplayAdapter
     if(!window)
     {
         if(mDisplayAdapter.get() != NULL)
         {
             ///NULL window passed, destroy the display adapter if present
             CAMHAL_LOGD("NULL window passed, destroying display adapter");
             mDisplayAdapter.clear();
             ///@remarks If there was a window previously existing, we usually expect another valid window to be passed by the client
             ///@remarks so, we will wait until it passes a valid window to begin the preview again
             mSetPreviewWindowCalled = false;
         }
         CAMHAL_LOGD("NULL ANativeWindow passed to setPreviewWindow");
         return NO_ERROR;
     }else if(mDisplayAdapter.get() == NULL)
     {
         // Need to create the display adapter since it has not been created
         // Create display adapter
         mDisplayAdapter = new ANativeWindowDisplayAdapter();
         ret = NO_ERROR;
         if(!mDisplayAdapter.get() || ((ret=mDisplayAdapter->initialize())!=NO_ERROR))
         {
             if(ret!=NO_ERROR)
             {
                 mDisplayAdapter.clear();
                 CAMHAL_LOGEA("DisplayAdapter initialize failed");
                 LOG_FUNCTION_NAME_EXIT;
                 return ret;
             }
             else
             {
                 CAMHAL_LOGEA("Couldn't create DisplayAdapter");
                 LOG_FUNCTION_NAME_EXIT;
                 return NO_MEMORY;
             }
         }

         // DisplayAdapter needs to know where to get the CameraFrames from inorder to display
         // Since CameraAdapter is the one that provides the frames, set it as the frame provider for DisplayAdapter
         mDisplayAdapter->setFrameProvider(mCameraAdapter);

         // Any dynamic errors that happen during the camera use case has to be propagated back to the application
         // via CAMERA_MSG_ERROR. AppCallbackNotifier is the class that notifies such errors to the application
         // Set it as the error handler for the DisplayAdapter
         mDisplayAdapter->setErrorHandler(mAppCallbackNotifier.get());

         // Update the display adapter with the new window that is passed from CameraService
         ret = mDisplayAdapter->setPreviewWindow(window);
         if(ret!=NO_ERROR)
             {
             CAMHAL_LOGEB("DisplayAdapter setPreviewWindow returned error %d", ret);
             }

         if(mPreviewStartInProgress)
         {
             CAMHAL_LOGDA("setPreviewWindow called when preview running");
             // Start the preview since the window is now available
             ret = startPreview();
         }
     } else {
         // Update the display adapter with the new window that is passed from CameraService
         ret = mDisplayAdapter->setPreviewWindow(window);
         if ( (NO_ERROR == ret) && previewEnabled() ) {
             restartPreview();
         } else if (ret == ALREADY_EXISTS) {
             // ALREADY_EXISTS should be treated as a noop in this case
             ret = NO_ERROR;
         }
     }
     LOG_FUNCTION_NAME_EXIT;

     return ret;

 }

这里配置好显示数据来源，显示到目标，以及错误信息回调方法，最终开始preview

 status_t CameraHal::startPreview() {
     LOG_FUNCTION_NAME;

     // When tunneling is enabled during VTC, startPreview happens in 2 steps:
     // When the application sends the command CAMERA_CMD_PREVIEW_INITIALIZATION,
     // cameraPreviewInitialization() is called, which in turn causes the CameraAdapter
     // to move from loaded to idle state. And when the application calls startPreview,
     // the CameraAdapter moves from idle to executing state.
     //
     // If the application calls startPreview() without sending the command
     // CAMERA_CMD_PREVIEW_INITIALIZATION, then the function cameraPreviewInitialization()
     // AND startPreview() are executed. In other words, if the application calls
     // startPreview() without sending the command CAMERA_CMD_PREVIEW_INITIALIZATION,
     // then the CameraAdapter moves from loaded to idle to executing state in one shot.
     status_t ret = cameraPreviewInitialization();这个地方十分重要，下面会具体分析

     // The flag mPreviewInitializationDone is set to true at the end of the function
     // cameraPreviewInitialization(). Therefore, if everything goes alright, then the
     // flag will be set. Sometimes, the function cameraPreviewInitialization() may
     // return prematurely if all the resources are not available for starting preview.
     // For example, if the preview window is not set, then it would return NO_ERROR.
     // Under such circumstances, one should return from startPreview as well and should
     // not continue execution. That is why, we check the flag and not the return value.
     if (!mPreviewInitializationDone) return ret;

     // Once startPreview is called, there is no need to continue to remember whether
     // the function cameraPreviewInitialization() was called earlier or not. And so
     // the flag mPreviewInitializationDone is reset here. Plus, this preserves the
     // current behavior of startPreview under the circumstances where the application
     // calls startPreview twice or more.
     mPreviewInitializationDone = false;

     //Enable the display adapter if present, actual overlay enable happens when we post the buffer这里说overlay happens,我一直在找的地方，上面棕色标注将来会在详细说说这里
     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");

             // FIXME: At this stage mStateSwitchLock is locked and unlock is supposed to be called
             // only from mCameraAdapter->sendCommand(CameraAdapter::CAMERA_START_PREVIEW)
             // below. But this will never happen because of goto error. Thus at next
             // startPreview() call CameraHAL will be deadlocked.
             // Need to revisit mStateSwitch lock, for now just abort the process.
             CAMHAL_ASSERT_X(false,
                 "At this stage mCameraAdapter->mStateSwitchLock is still locked, "
                 "deadlock is guaranteed");

             goto error;
         }

     }

     CAMHAL_LOGDA("Starting CameraAdapter preview mode");
     //Send START_PREVIEW command to adapter
     ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_START_PREVIEW);//从这里开始调用到BaseCameraAdapter

     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;
 }

BaseCameraAdapter实现了父类的sendcommand方法：

 case CameraAdapter::CAMERA_START_PREVIEW:
             {

                 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;

             }

这里我们接着分析startPreview方法，之前的文章中已经分析过，这里调用的startPreview方法不是BaseCameraAdapter中的startPreview,而是调用的V4LCameraAdapter中的startPreview方法：

 status_t V4LCameraAdapter::startPreview()
 {
     status_t ret = NO_ERROR;

     LOG_FUNCTION_NAME;
     Mutex::Autolock 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);//申请内存空间
         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);//开始preview线程
         CAMHAL_LOGDA("Created preview thread");
     }

     //Update the flag to indicate we are previewing
     mPreviewing = true;
     mCapturing = false;

 EXIT:
     LOG_FUNCTION_NAME_EXIT;
     return ret;
 }

 status_t V4LCameraAdapter::v4lStartStreaming () {
     status_t ret = NO_ERROR;
     enum v4l2_buf_type bufType;

     if (!mVideoInfo->isStreaming) {
         bufType = V4L2_BUF_TYPE_VIDEO_CAPTURE;

         ret = v4lIoctl (mCameraHandle, VIDIOC_STREAMON, &bufType);开始preview
         if (ret < 0) {
             CAMHAL_LOGEB("StartStreaming: Unable to start capture: %s", strerror(errno));
             return ret;
         }
         mVideoInfo->isStreaming = true;
     }
     return ret;
 }

现在我们就看看开启的preview线程都在干什么：

 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;
         }
         //从这里开始以我的理解是进行数据的转换和保存操作
         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);
         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

         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);
         }
     }
 EXIT:

     return ret;
 }

就上面这段代码做一下说明，这里在我看来就是整个数据回流过程的中转站了，上面棕色部分buffer中拿到就就是底层driver返回回来的视频数据了，
那么我不是很明白的是，driver中的视频数据是怎么和 mPreviewBufs 还有index关联在一起的，并且这里可以通过 buffer  =  mPreviewBufs . keyAt ( index ) 获取到CameraBuffer，这里待会会详细探究一下
先接着往下说，获取到视频数据之后，如果需要，会将数据经过转换保存到file中方便之后使用，
最后使用得到的camerabuffer填充CameraFrame，这个结构至关重要，在我的理解，最终是通过 sendFrameToSubscribers ( & frame ) ; 方法将数据回流的

这里就先追踪一下 driver中的视频数据是怎么和 mPreviewBufs 还有index关联在一起的
到了这里就不得不提及上面已经说的一个很重要的方法，先看看这个方法：
他是startPreview的第一步， cameraPreviewInitialization

 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);配置参数到CameraAdapter
     }

     if ((mPreviewStartInProgress == false) && (mDisplayPaused == false)){
       ret = mCameraAdapter->sendCommand(CameraAdapter::CAMERA_QUERY_RESOLUTION_PREVIEW,( int ) &frame);//通过这个command获取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;//初始化宽和高
       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);

     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 )
             {
             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;
         }

     mAppCallbackNotifier->startPreviewCallbacks(mParameters, mPreviewBuffers, mPreviewOffsets, mPreviewFd, mPreviewLength, required_buffer_count);
     ///Start the callback notifier
     ret = mAppCallbackNotifier->start();

     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;
     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;
 }

这里先为preview buffer申请内存，并将preview set进cameraAdapter通过方法 mCameraAdapter - > sendCommand ( CameraAdapter : : CAMERA_USE_BUFFERS_PREVIEW , (   int   )   & desc )
在sendcommand中实现如下：

             case CameraAdapter::CAMERA_USE_BUFFERS_PREVIEW:
                 CAMHAL_LOGDA("Use buffers for preview");
                 desc = ( BuffersDescriptor * ) value1;

                 if ( NULL == desc )
                     {
                     CAMHAL_LOGEA("Invalid preview buffers!");
                     return -EINVAL;
                     }

                 if ( ret == NO_ERROR )
                     {
                     ret = setState(operation);
                     }

                 if ( ret == NO_ERROR )
                     {
                     Mutex::Autolock lock(mPreviewBufferLock);
                     mPreviewBuffers = desc->mBuffers;
                     mPreviewBuffersLength = desc->mLength;
                     mPreviewBuffersAvailable.clear();
                     mSnapshotBuffersAvailable.clear();
                     for ( uint32_t i = 0 ; i < desc->mMaxQueueable ; i++ )
                         {
                         mPreviewBuffersAvailable.add(&mPreviewBuffers[i], 0);这里实现了mPreviewBuffersAvailable与mPreviewBuffers的关联
                         }
                     // initial ref count for undeqeueued buffers is 1 since buffer provider
                     // is still holding on to it
                     for ( uint32_t i = desc->mMaxQueueable ; i < desc->mCount ; i++ )
                         {
                         mPreviewBuffersAvailable.add(&mPreviewBuffers[i], 1);
                         }
                     }

                 if ( NULL != desc )
                     {
                     ret = useBuffers(CameraAdapter::CAMERA_PREVIEW,
                                      desc->mBuffers,
                                      desc->mCount,
                                      desc->mLength,
                                      desc->mMaxQueueable);
                     }

                 if ( ret == NO_ERROR )
                     {
                     ret = commitState();
                     }
                 else
                     {
                     ret |= rollbackState();
                     }

                 break;

调用V4LCameraAdapter中的useBuffers方法，然后他会接着调用UseBuffersPreview方法：

 status_t V4LCameraAdapter::UseBuffersPreview(CameraBuffer *bufArr, int num)
 {
     int ret = NO_ERROR;
     LOG_FUNCTION_NAME;

     if(NULL == bufArr) {
         ret = BAD_VALUE;
         goto EXIT;
     }

     ret = v4lInitMmap(num);
     if (ret == NO_ERROR) {
         for (int i = 0; i < num; i++) {
             //Associate each Camera internal buffer with the one from Overlay
             mPreviewBufs.add(&bufArr[i], i);//这里实现了mPreviewBufs和desc->mBuffers的关联
             CAMHAL_LOGDB("Preview- buff [%d] = 0x%x ",i, mPreviewBufs.keyAt(i));
         }

         // Update the preview buffer count
         mPreviewBufferCount = num;
     }
 EXIT:
     LOG_FUNCTION_NAME_EXIT;
     return ret;
 }

在这里我们还是很有必要去深入研究一下 mAppCallbackNotifier 这个变量的初始化过程，他决定很多回调函数的初始化
的初始化是在哪里实现的呢？？在在camerahal文件的initial中初始化的

 /**
    @brief Initialize the Camera HAL

    Creates CameraAdapter, AppCallbackNotifier, DisplayAdapter and MemoryManager

    @param None
    @return NO_ERROR - On success
          NO_MEMORY - On failure to allocate memory for any of the objects
    @remarks Camera Hal internal function

  */

 status_t CameraHal::initialize(CameraProperties::Properties* properties)
 {
     LOG_FUNCTION_NAME;

     int sensor_index = 0;
     const char* sensor_name = NULL;

     ///Initialize the event mask used for registering an event provider for AppCallbackNotifier
     ///Currently, registering all events as to be coming from CameraAdapter
     int32_t eventMask = CameraHalEvent::ALL_EVENTS;

     // Get my camera properties
     mCameraProperties = properties;

     if(!mCameraProperties)
     {
         goto fail_loop;
     }

     // Dump the properties of this Camera
     // will only print if DEBUG macro is defined
     mCameraProperties->dump();

     if (strcmp(CameraProperties::DEFAULT_VALUE, mCameraProperties->get(CameraProperties::CAMERA_SENSOR_INDEX)) != 0 )
         {
         sensor_index = atoi(mCameraProperties->get(CameraProperties::CAMERA_SENSOR_INDEX));
         }

     if (strcmp(CameraProperties::DEFAULT_VALUE, mCameraProperties->get(CameraProperties::CAMERA_NAME)) != 0 ) {
         sensor_name = mCameraProperties->get(CameraProperties::CAMERA_NAME);
     }
     CAMHAL_LOGDB("Sensor index= %d; Sensor name= %s", sensor_index, sensor_name);

     if (strcmp(sensor_name, V4L_CAMERA_NAME_USB) == 0) {
 #ifdef V4L_CAMERA_ADAPTER
         mCameraAdapter = V4LCameraAdapter_Factory(sensor_index);
 #endif
     }
     else {
 #ifdef OMX_CAMERA_ADAPTER
         mCameraAdapter = OMXCameraAdapter_Factory(sensor_index);
 #endif
     }

     if ( ( NULL == mCameraAdapter ) || (mCameraAdapter->initialize(properties)!=NO_ERROR))
         {
         CAMHAL_LOGEA("Unable to create or initialize CameraAdapter");
         mCameraAdapter = NULL;
         goto fail_loop;
         }

     mCameraAdapter->incStrong(mCameraAdapter);
     mCameraAdapter->registerImageReleaseCallback(releaseImageBuffers, (void *) this);
     mCameraAdapter->registerEndCaptureCallback(endImageCapture, (void *)this);

     if(!mAppCallbackNotifier.get())
         {
         /// Create the callback notifier
         mAppCallbackNotifier = new AppCallbackNotifier();
         if( ( NULL == mAppCallbackNotifier.get() ) || ( mAppCallbackNotifier->initialize() != NO_ERROR))
             {
             CAMHAL_LOGEA("Unable to create or initialize AppCallbackNotifier");
             goto fail_loop;
             }
         }

     if(!mMemoryManager.get())
         {
         /// Create Memory Manager
         mMemoryManager = new MemoryManager();
         if( ( NULL == mMemoryManager.get() ) || ( mMemoryManager->initialize() != NO_ERROR))
             {
             CAMHAL_LOGEA("Unable to create or initialize MemoryManager");
             goto fail_loop;
             }
         }

     ///Setup the class dependencies...

     ///AppCallbackNotifier has to know where to get the Camera frames and the events like auto focus lock etc from.
     ///CameraAdapter is the one which provides those events
     ///Set it as the frame and event providers for AppCallbackNotifier
     ///@remarks setEventProvider API takes in a bit mask of events for registering a provider for the different events
     /// That way, if events can come from DisplayAdapter in future, we will be able to add it as provider
     /// for any event
     mAppCallbackNotifier->setEventProvider(eventMask, mCameraAdapter);
     mAppCallbackNotifier->setFrameProvider(mCameraAdapter);

     ///Any dynamic errors that happen during the camera use case has to be propagated back to the application
     ///via CAMERA_MSG_ERROR. AppCallbackNotifier is the class that notifies such errors to the application
     ///Set it as the error handler for CameraAdapter
     mCameraAdapter->setErrorHandler(mAppCallbackNotifier.get());

     ///Start the callback notifier
     if(mAppCallbackNotifier->start() != NO_ERROR)
       {
         CAMHAL_LOGEA("Couldn't start AppCallbackNotifier");
         goto fail_loop;
       }

     CAMHAL_LOGDA("Started AppCallbackNotifier..");
     mAppCallbackNotifier->setMeasurements(mMeasurementEnabled);

     ///Initialize default parameters
     initDefaultParameters();


     if ( setParameters(mParameters) != NO_ERROR )
         {
         CAMHAL_LOGEA("Failed to set default parameters?!");
         }

     // register for sensor events
     mSensorListener = new SensorListener();
     if (mSensorListener.get()) {
         if (mSensorListener->initialize() == NO_ERROR) {
             mSensorListener->setCallbacks(orientation_cb, this);
             mSensorListener->enableSensor(SensorListener::SENSOR_ORIENTATION);
         } else {
             CAMHAL_LOGEA("Error initializing SensorListener. not fatal, continuing");
             mSensorListener.clear();
             mSensorListener = NULL;
         }
     }

     LOG_FUNCTION_NAME_EXIT;

     return NO_ERROR;

     fail_loop:

         ///Free up the resources because we failed somewhere up
         deinitialize();
         LOG_FUNCTION_NAME_EXIT;

         return NO_MEMORY;

 }

这里实例化了一些对象，我真正关注的是 mAppCallbackNotifier 这个对象，实例化这个对象，并且initialize，并且设置EventProvider和FrameProvider
我们就看一下setFrameProvider这个方法都做了什么事情，

 void AppCallbackNotifier::setFrameProvider(FrameNotifier *frameNotifier)
 {
     LOG_FUNCTION_NAME;
     ///@remarks There is no NULL check here. We will check
     ///for NULL when we get the start command from CameraAdapter
     mFrameProvider = new FrameProvider(frameNotifier, this, frameCallbackRelay);
     if ( NULL == mFrameProvider )
         {
         CAMHAL_LOGEA("Error in creating FrameProvider");
         }
     else
         {
         //Register only for captured images and RAW for now
         //TODO: Register for and handle all types of frames
         mFrameProvider->enableFrameNotification(CameraFrame::IMAGE_FRAME);
         mFrameProvider->enableFrameNotification(CameraFrame::RAW_FRAME);
         }

     LOG_FUNCTION_NAME_EXIT;
 }

实例化一个FrameProvider对象，并且enable响应notification，这里实例化的对象里面的参数中有一个frameCallbackRely是一个回调函数，这里我们暂且回过头看看previewthread中的那个方法 sendFrameToSubscribers
这个方法只是调用了下面这个方法实现：

 status_t BaseCameraAdapter::__sendFrameToSubscribers(CameraFrame* frame,
                                                      KeyedVector<int, frame_callback> *subscribers,
                                                      CameraFrame::FrameType frameType)
 {
     size_t refCount = 0;
     status_t ret = NO_ERROR;
     frame_callback callback = NULL;

     frame->mFrameType = frameType;

     if ( (frameType == CameraFrame::PREVIEW_FRAME_SYNC) ||
          (frameType == CameraFrame::VIDEO_FRAME_SYNC) ||
          (frameType == CameraFrame::SNAPSHOT_FRAME) ){
         if (mFrameQueue.size() > 0){
           CameraFrame *lframe = (CameraFrame *)mFrameQueue.valueFor(frame->mBuffer);
           frame->mYuv[0] = lframe->mYuv[0];
           frame->mYuv[1] = frame->mYuv[0] + (frame->mLength + frame->mOffset)*2/3;
         }
         else{
           CAMHAL_LOGDA("Empty Frame Queue");
           return -EINVAL;
         }
       }

     if (NULL != subscribers) {
         refCount = getFrameRefCount(frame->mBuffer, frameType);

         if (refCount == 0) {
             CAMHAL_LOGDA("Invalid ref count of 0");
             return -EINVAL;
         }

         if (refCount > subscribers->size()) {
             CAMHAL_LOGEB("Invalid ref count for frame type: 0x%x", frameType);
             return -EINVAL;
         }

         CAMHAL_LOGVB("Type of Frame: 0x%x address: 0x%x refCount start %d",
                      frame->mFrameType,
                      ( uint32_t ) frame->mBuffer,
                      refCount);

         for ( unsigned int i = 0 ; i < refCount; i++ ) {
             frame->mCookie = ( void * ) subscribers->keyAt(i);
             callback = (frame_callback) subscribers->valueAt(i);

             if (!callback) {
                 CAMHAL_LOGEB("callback not set for frame type: 0x%x", frameType);
                 return -EINVAL;
             }

             callback(frame);
         }
     } else {
         CAMHAL_LOGEA("Subscribers is null??");
         return -EINVAL;
     }

     return ret;
 }

最重要的部分我在上面已经表示出来，通过subscribers这个全局KeyedVector变量找到相应的frame->mCookie和callback方法，
这里所要获取到的callback方法就是上面setFrameProvider时引入的 frameCallbackRelay 这个函数，我们看看这个函数的具体实现

 void AppCallbackNotifier::frameCallbackRelay(CameraFrame* caFrame)
 {
     LOG_FUNCTION_NAME;
     AppCallbackNotifier *appcbn = (AppCallbackNotifier*) (caFrame->mCookie);
     appcbn->frameCallback(caFrame);
     LOG_FUNCTION_NAME_EXIT;
 }

 void AppCallbackNotifier::frameCallback(CameraFrame* caFrame)
 {
     ///Post the event to the event queue of AppCallbackNotifier
     TIUTILS::Message msg;
     CameraFrame *frame;

     LOG_FUNCTION_NAME;

     if ( NULL != caFrame )
         {

         frame = new CameraFrame(*caFrame);
         if ( NULL != frame )
             {
               msg.command = AppCallbackNotifier::NOTIFIER_CMD_PROCESS_FRAME;
               msg.arg1 = frame;
               mFrameQ.put(&msg);
             }
         else
             {
             CAMHAL_LOGEA("Not enough resources to allocate CameraFrame");
             }

         }

     LOG_FUNCTION_NAME_EXIT;
 }

这个回调函数只是将数据装载入mag这个消息结构体，比且把这个消息put到mFrameQ这个全局消息中心，app就是从这个消息中心把数据取走的
我们可以看一下在 AppCallbackNotifier初始化的时候就调用了initialize做一下初始设置

 /**
   * NotificationHandler class
   */

 ///Initialization function for AppCallbackNotifier
 status_t AppCallbackNotifier::initialize()
 {
     LOG_FUNCTION_NAME;

     mPreviewMemory = 0;

     mMeasurementEnabled = false;

     mNotifierState = NOTIFIER_STOPPED;

     ///Create the app notifier thread
     mNotificationThread = new NotificationThread(this);
     if(!mNotificationThread.get())
         {
         CAMHAL_LOGEA("Couldn't create Notification thread");
         return NO_MEMORY;
         }

     ///Start the display thread
     status_t ret = mNotificationThread->run("NotificationThread", PRIORITY_URGENT_DISPLAY);
     if(ret!=NO_ERROR)
         {
         CAMHAL_LOGEA("Couldn't run NotificationThread");
         mNotificationThread.clear();
         return ret;
         }

     mUseMetaDataBufferMode = true;
     mRawAvailable = false;

     mRecording = false;
     mPreviewing = false;

     LOG_FUNCTION_NAME_EXIT;

     return ret;
 }

这个初始化的方法里面最重要就是开启了一个线程，用来监听HAL层发送来的一切消息，并在其中将消息或者数据告诉app，看看这个线程的具体实现

 bool AppCallbackNotifier::notificationThread()
 {
     bool shouldLive = true;
     status_t ret;

     LOG_FUNCTION_NAME;

     //CAMHAL_LOGDA("Notification Thread waiting for message");
     ret = TIUTILS::MessageQueue::waitForMsg(&mNotificationThread->msgQ(),
                                             &mEventQ,
                                             &mFrameQ,
                                             AppCallbackNotifier::NOTIFIER_TIMEOUT);

     //CAMHAL_LOGDA("Notification Thread received message");

     if (mNotificationThread->msgQ().hasMsg()) {
         ///Received a message from CameraHal, process it
         CAMHAL_LOGDA("Notification Thread received message from Camera HAL");
         shouldLive = processMessage();
         if(!shouldLive) {
           CAMHAL_LOGDA("Notification Thread exiting.");
           return shouldLive;
         }
     }

     if(mEventQ.hasMsg()) {
         ///Received an event from one of the event providers
         CAMHAL_LOGDA("Notification Thread received an event from event provider (CameraAdapter)");
         notifyEvent();
      }

     if(mFrameQ.hasMsg()) {
        ///Received a frame from one of the frame providers
        //CAMHAL_LOGDA("Notification Thread received a frame from frame provider (CameraAdapter)");
        notifyFrame();
     }

     LOG_FUNCTION_NAME_EXIT;
     return shouldLive;
 }

这里等待到有消息时，我们直接分析我需要的，preview，如果检测到mFrameQ中有消息，则调用notifyFrame方法

 void AppCallbackNotifier::notifyFrame()
 {
     ///Receive and send the frame notifications to app
     TIUTILS::Message msg;
     CameraFrame *frame;
     MemoryHeapBase *heap;
     MemoryBase *buffer = NULL;
     sp<MemoryBase> memBase;
     void *buf = NULL;

     LOG_FUNCTION_NAME;

     {
         Mutex::Autolock lock(mLock);
         if(!mFrameQ.isEmpty()) {
             mFrameQ.get(&msg);
         } else {
             return;
         }
     }

     bool ret = true;

     frame = NULL;
     switch(msg.command)
         {
         case AppCallbackNotifier::NOTIFIER_CMD_PROCESS_FRAME:

                 frame = (CameraFrame *) msg.arg1;
                 if(!frame)
                     {
                     break;
                     }

                 if ( (CameraFrame::RAW_FRAME == frame->mFrameType )&&
                     ( NULL != mCameraHal ) &&
                     ( NULL != mDataCb) &&
                     ( NULL != mNotifyCb ) )
                     {

                     if ( mCameraHal->msgTypeEnabled(CAMERA_MSG_RAW_IMAGE) )
                         {
 #ifdef COPY_IMAGE_BUFFER
                         copyAndSendPictureFrame(frame, CAMERA_MSG_RAW_IMAGE);
 #else
                         //TODO: Find a way to map a Tiler buffer to a MemoryHeapBase
 #endif
                         }
                     else {
                         if ( mCameraHal->msgTypeEnabled(CAMERA_MSG_RAW_IMAGE_NOTIFY) ) {
                             mNotifyCb(CAMERA_MSG_RAW_IMAGE_NOTIFY, 0, 0, mCallbackCookie);
                         }
                         mFrameProvider->returnFrame(frame->mBuffer,
                                                     (CameraFrame::FrameType) frame->mFrameType);
                     }

                     mRawAvailable = true;

                     }
                 else if ( (CameraFrame::IMAGE_FRAME == frame->mFrameType) &&
                           (NULL != mCameraHal) &&
                           (NULL != mDataCb) &&
                           (CameraFrame::ENCODE_RAW_YUV422I_TO_JPEG & frame->mQuirks) )
                     {

                     int encode_quality = 100, tn_quality = 100;
                     int tn_width, tn_height;
                     unsigned int current_snapshot = 0;
                     Encoder_libjpeg::params *main_jpeg = NULL, *tn_jpeg = NULL;
                     void* exif_data = NULL;
                     const char *previewFormat = NULL;
                     camera_memory_t* raw_picture = mRequestMemory(-1, frame->mLength, 1, NULL);

                     if(raw_picture) {
                         buf = raw_picture->data;
                     }

                     CameraParameters parameters;
                     char *params = mCameraHal->getParameters();
                     const String8 strParams(params);
                     parameters.unflatten(strParams);

                     encode_quality = parameters.getInt(CameraParameters::KEY_JPEG_QUALITY);
                     if (encode_quality < 0 || encode_quality > 100) {
                         encode_quality = 100;
                     }

                     tn_quality = parameters.getInt(CameraParameters::KEY_JPEG_THUMBNAIL_QUALITY);
                     if (tn_quality < 0 || tn_quality > 100) {
                         tn_quality = 100;
                     }

                     if (CameraFrame::HAS_EXIF_DATA & frame->mQuirks) {
                         exif_data = frame->mCookie2;
                     }

                     main_jpeg = (Encoder_libjpeg::params*)
                                     malloc(sizeof(Encoder_libjpeg::params));

                     // Video snapshot with LDCNSF on adds a few bytes start offset
                     // and a few bytes on every line. They must be skipped.
                     int rightCrop = frame->mAlignment/2 - frame->mWidth;

                     CAMHAL_LOGDB("Video snapshot right crop = %d", rightCrop);
                     CAMHAL_LOGDB("Video snapshot offset = %d", frame->mOffset);

                     if (main_jpeg) {
                         main_jpeg->src = (uint8_t *)frame->mBuffer->mapped;
                         main_jpeg->src_size = frame->mLength;
                         main_jpeg->dst = (uint8_t*) buf;
                         main_jpeg->dst_size = frame->mLength;
                         main_jpeg->quality = encode_quality;
                         main_jpeg->in_width = frame->mAlignment/2; // use stride here
                         main_jpeg->in_height = frame->mHeight;
                         main_jpeg->out_width = frame->mAlignment/2;
                         main_jpeg->out_height = frame->mHeight;
                         main_jpeg->right_crop = rightCrop;
                         main_jpeg->start_offset = frame->mOffset;
                         if ( CameraFrame::FORMAT_YUV422I_UYVY & frame->mQuirks) {
                             main_jpeg->format = TICameraParameters::PIXEL_FORMAT_YUV422I_UYVY;
                         }
                         else { //if ( CameraFrame::FORMAT_YUV422I_YUYV & frame->mQuirks)
                             main_jpeg->format = CameraParameters::PIXEL_FORMAT_YUV422I;
                         }
                     }

                     tn_width = parameters.getInt(CameraParameters::KEY_JPEG_THUMBNAIL_WIDTH);
                     tn_height = parameters.getInt(CameraParameters::KEY_JPEG_THUMBNAIL_HEIGHT);
                     previewFormat = parameters.getPreviewFormat();

                     if ((tn_width > 0) && (tn_height > 0) && ( NULL != previewFormat )) {
                         tn_jpeg = (Encoder_libjpeg::params*)
                                       malloc(sizeof(Encoder_libjpeg::params));
                         // if malloc fails just keep going and encode main jpeg
                         if (!tn_jpeg) {
                             tn_jpeg = NULL;
                         }
                     }

                     if (tn_jpeg) {
                         int width, height;
                         parameters.getPreviewSize(&width,&height);
                         current_snapshot = (mPreviewBufCount + MAX_BUFFERS - 1) % MAX_BUFFERS;
                         tn_jpeg->src = (uint8_t *)mPreviewBuffers[current_snapshot].mapped;
                         tn_jpeg->src_size = mPreviewMemory->size / MAX_BUFFERS;
                         tn_jpeg->dst_size = calculateBufferSize(tn_width,
                                                                 tn_height,
                                                                 previewFormat);
                         tn_jpeg->dst = (uint8_t*) malloc(tn_jpeg->dst_size);
                         tn_jpeg->quality = tn_quality;
                         tn_jpeg->in_width = width;
                         tn_jpeg->in_height = height;
                         tn_jpeg->out_width = tn_width;
                         tn_jpeg->out_height = tn_height;
                         tn_jpeg->right_crop = 0;
                         tn_jpeg->start_offset = 0;
                         tn_jpeg->format = CameraParameters::PIXEL_FORMAT_YUV420SP;;
                     }

                     sp<Encoder_libjpeg> encoder = new Encoder_libjpeg(main_jpeg,
                                                       tn_jpeg,
                                                       AppCallbackNotifierEncoderCallback,
                                                       (CameraFrame::FrameType)frame->mFrameType,
                                                       this,
                                                       raw_picture,
                                                       exif_data, frame->mBuffer);
                     gEncoderQueue.add(frame->mBuffer->mapped, encoder);
                     encoder->run();
                     encoder.clear();
                     if (params != NULL)
                       {
                         mCameraHal->putParameters(params);
                       }
                     }
                 else if ( ( CameraFrame::IMAGE_FRAME == frame->mFrameType ) &&
                              ( NULL != mCameraHal ) &&
                              ( NULL != mDataCb) )
                     {

                     // CTS, MTS requirements: Every 'takePicture()' call
                     // who registers a raw callback should receive one
                     // as well. This is not always the case with
                     // CameraAdapters though.
                     if (!mCameraHal->msgTypeEnabled(CAMERA_MSG_RAW_IMAGE)) {
                         dummyRaw();
                     } else {
                         mRawAvailable = false;
                     }

 #ifdef COPY_IMAGE_BUFFER
                     {
                         Mutex::Autolock lock(mBurstLock);
 #if defined(OMAP_ENHANCEMENT)
                         if ( mBurst )
                         {
                             copyAndSendPictureFrame(frame, CAMERA_MSG_COMPRESSED_BURST_IMAGE);
                         }
                         else
 #endif
                         {
                             copyAndSendPictureFrame(frame, CAMERA_MSG_COMPRESSED_IMAGE);
                         }
                     }
 #else
                      //TODO: Find a way to map a Tiler buffer to a MemoryHeapBase
 #endif
                     }
                 else if ( ( CameraFrame::VIDEO_FRAME_SYNC == frame->mFrameType ) &&
                              ( NULL != mCameraHal ) &&
                              ( NULL != mDataCb) &&
                              ( mCameraHal->msgTypeEnabled(CAMERA_MSG_VIDEO_FRAME) ) )
                     {
                     AutoMutex locker(mRecordingLock);
                     if(mRecording)
                         {
                         if(mUseMetaDataBufferMode)
                             {
                             camera_memory_t *videoMedatadaBufferMemory =
                                              mVideoMetadataBufferMemoryMap.valueFor(frame->mBuffer->opaque);
                             video_metadata_t *videoMetadataBuffer = (video_metadata_t *) videoMedatadaBufferMemory->data;

                             if( (NULL == videoMedatadaBufferMemory) || (NULL == videoMetadataBuffer) || (NULL == frame->mBuffer) )
                                 {
                                 CAMHAL_LOGEA("Error! One of the video buffers is NULL");
                                 break;
                                 }

                             if ( mUseVideoBuffers )
                               {
                                 CameraBuffer *vBuf = mVideoMap.valueFor(frame->mBuffer->opaque);
                                 GraphicBufferMapper &mapper = GraphicBufferMapper::get();
                                 Rect bounds;
                                 bounds.left = 0;
                                 bounds.top = 0;
                                 bounds.right = mVideoWidth;
                                 bounds.bottom = mVideoHeight;

                                 void *y_uv[2];
                                 mapper.lock((buffer_handle_t)vBuf, CAMHAL_GRALLOC_USAGE, bounds, y_uv);
                                 y_uv[1] = y_uv[0] + mVideoHeight*4096;

                                 structConvImage input = {frame->mWidth,
                                                           frame->mHeight,
                                                           4096,
                                                           IC_FORMAT_YCbCr420_lp,
                                                           (mmByte *)frame->mYuv[0],
                                                           (mmByte *)frame->mYuv[1],
                                                           frame->mOffset};

                                 structConvImage output = {mVideoWidth,
                                                           mVideoHeight,
                                                           4096,
                                                           IC_FORMAT_YCbCr420_lp,
                                                           (mmByte *)y_uv[0],
                                                           (mmByte *)y_uv[1],
                                                           0};

                                 VT_resizeFrame_Video_opt2_lp(&input, &output, NULL, 0);
                                 mapper.unlock((buffer_handle_t)vBuf->opaque);
                                 videoMetadataBuffer->metadataBufferType = (int) kMetadataBufferTypeCameraSource;
                                 /* FIXME remove cast */
                                 videoMetadataBuffer->handle = (void *)vBuf->opaque;
                                 videoMetadataBuffer->offset = 0;
                               }
                             else
                               {
                                 videoMetadataBuffer->metadataBufferType = (int) kMetadataBufferTypeCameraSource;
                                 videoMetadataBuffer->