Android Camera数据流分析全程记录（非overlay方式）

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surfaceview，这个surfaceview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->handle = camera_buffer_get_omx_ptr(frame->mBuffer);
                                videoMetadataBuffer->offset = frame->mOffset;
                              }

                            CAMHAL_LOGVB("mDataCbTimestamp : frame->mBuffer=0x%x, videoMetadataBuffer=0x%x, videoMedatadaBufferMemory=0x%x",
                                            frame->mBuffer->opaque, videoMetadataBuffer, videoMedatadaBufferMemory);

                            mDataCbTimestamp(frame->mTimestamp, CAMERA_MSG_VIDEO_FRAME,
                                                videoMedatadaBufferMemory, 0, mCallbackCookie);
                            }
                        else
                            {
                            //TODO: Need to revisit this, should ideally be mapping the TILER buffer using mRequestMemory
                            camera_memory_t* fakebuf = mRequestMemory(-1, sizeof(buffer_handle_t), 1, NULL);
                            if( (NULL == fakebuf) || ( NULL == fakebuf->data) || ( NULL == frame->mBuffer))
                                {
                                CAMHAL_LOGEA("Error! One of the video buffers is NULL");
                                break;
                                }

                            *reinterpret_cast<buffer_handle_t*>(fakebuf->data) = reinterpret_cast<buffer_handle_t>(frame->mBuffer->mapped);
                            mDataCbTimestamp(frame->mTimestamp, CAMERA_MSG_VIDEO_FRAME, fakebuf, 0, mCallbackCookie);
                            fakebuf->release(fakebuf);
                            }
                        }
                    }
                else if(( CameraFrame::SNAPSHOT_FRAME == frame->mFrameType ) &&
                             ( NULL != mCameraHal ) &&
                             ( NULL != mDataCb) &&
                             ( NULL != mNotifyCb)) {
                    //When enabled, measurement data is sent instead of video data
                    if ( !mMeasurementEnabled ) {
                        copyAndSendPreviewFrame(frame, CAMERA_MSG_POSTVIEW_FRAME);
                    } else {
                        mFrameProvider->returnFrame(frame->mBuffer,
                                                    (CameraFrame::FrameType) frame->mFrameType);
                    }
                }
                else if ( ( CameraFrame::PREVIEW_FRAME_SYNC== frame->mFrameType ) &&
                            ( NULL != mCameraHal ) &&
                            ( NULL != mDataCb) &&
                            ( mCameraHal->msgTypeEnabled(CAMERA_MSG_PREVIEW_FRAME)) ) {
                    //When enabled, measurement data is sent instead of video data
                    if ( !mMeasurementEnabled ) {
                        copyAndSendPreviewFrame(frame, CAMERA_MSG_PREVIEW_FRAME);
                    } else {
                         mFrameProvider->returnFrame(frame->mBuffer,
                                                     (CameraFrame::FrameType) frame->mFrameType);
                    }
                }
                else if ( ( CameraFrame::FRAME_DATA_SYNC == frame->mFrameType ) &&
                            ( NULL != mCameraHal ) &&
                            ( NULL != mDataCb) &&
                            ( mCameraHal->msgTypeEnabled(CAMERA_MSG_PREVIEW_FRAME)) ) {
                    copyAndSendPreviewFrame(frame, CAMERA_MSG_PREVIEW_FRAME);
                } else {
                    mFrameProvider->returnFrame(frame->mBuffer,
                                                ( CameraFrame::FrameType ) frame->mFrameType);
                    CAMHAL_LOGDB("Frame type 0x%x is still unsupported!", frame->mFrameType);
                }

                break;

        default:

            break;

        };

exit:

    if ( NULL != frame )
        {
        delete frame;
        }

    LOG_FUNCTION_NAME_EXIT;
}

这里对不同的操作方式做了不同的处理，我们还是先通过preview过程作分析，如上面标注的那样处理，这里看看copyAndSendPreviewFrame的实现方法：

void AppCallbackNotifier::copyAndSendPreviewFrame(CameraFrame* frame, int32_t msgType)
{
    camera_memory_t* picture = NULL;
    CameraBuffer * dest = NULL;

    // scope for lock
    {
        Mutex::Autolock lock(mLock);

        if(mNotifierState != AppCallbackNotifier::NOTIFIER_STARTED) {
            goto exit;
        }

        if (!mPreviewMemory || !frame->mBuffer) {
            CAMHAL_LOGDA("Error! One of the buffer is NULL");
            goto exit;
        }

        dest = &mPreviewBuffers[mPreviewBufCount];

        CAMHAL_LOGVB("%d:copy2Dto1D(%p, %p, %d, %d, %d, %d, %d,%s)",
                     __LINE__,
                      dest,
                      frame->mBuffer,
                      mPreviewWidth,
                      mPreviewHeight,
                      mPreviewStride,
                      2,
                      frame->mLength,
                      mPreviewPixelFormat);

        /* FIXME map dest */
        if ( NULL != dest && dest->mapped != NULL ) {
            // data sync frames don't need conversion
            if (CameraFrame::FRAME_DATA_SYNC == frame->mFrameType) {
                if ( (mPreviewMemory->size / MAX_BUFFERS) >= frame->mLength ) {
                    memcpy(dest->mapped, (void*) frame->mBuffer->mapped, frame->mLength);
                } else {
                    memset(dest->mapped, 0, (mPreviewMemory->size / MAX_BUFFERS));
                }
            } else {
              if ((NULL == frame->mYuv[0]) || (NULL == frame->mYuv[1])){
                CAMHAL_LOGEA("Error! One of the YUV Pointer is NULL");
                goto exit;
              }
              else{
                copy2Dto1D(dest->mapped,
                           frame->mYuv,
                           mPreviewWidth,
                           mPreviewHeight,
                           mPreviewStride,
                           frame->mOffset,
                           2,
                           frame->mLength,
                           mPreviewPixelFormat);
              }
            }
        }
    }

 exit:
    mFrameProvider->returnFrame(frame->mBuffer, (CameraFrame::FrameType) frame->mFrameType);

    if((mNotifierState == AppCallbackNotifier::NOTIFIER_STARTED) &&
       mCameraHal->msgTypeEnabled(msgType) &&
       (dest != NULL) && (dest->mapped != NULL)) {
        AutoMutex locker(mLock);
        if ( mPreviewMemory )
            mDataCb(msgType, mPreviewMemory, mPreviewBufCount, NULL, mCallbackCookie);
    }

    // increment for next buffer
    mPreviewBufCount = (mPreviewBufCount + 1) % AppCallbackNotifier::MAX_BUFFERS;
}

具体中间的实现过程这里就先不做具体分析，我们只看最后这一个标注的方法mDataCb，他的定义是这样的
camera_data_callback   mDataCb;
这个方法的实现很关键，其实他是在cameraservice中实现，过程如下：
1.cameraservice中调用mHardware->setCallbacks(notifyCallback,dataCallback, dataCallbackTimestamp, (void *)cameraId);
2.camerahardwareinterface中调用mDevice->ops->set_callbacks(mDevice,__notify_cb,__data_cb, __data_cb_timestamp, __get_memory, this);
3.camerahal_module中调用gCameraHals[ti_dev->cameraid]->setCallbacks(notify_cb, data_cb, data_cb_timestamp, get_memory, user);
4.camerahal中调用mAppCallbackNotifier->setCallbacks(this,notify_cb, data_cb, data_cb_timestamp, get_memory, user);
5.这里就到了appcallbacknotifier中，我们就看看这个setcallbacks的实现吧

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)
{
    Mutex::Autolock 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;
}

这里可以很清楚的看到mDataCb就是指向cameraservice中定义的回调函数，也就是通过这种机制，最终底层获取的数据现在已经传递到cameraservice层了
不过这里还是要很注意一点，我上面我说的mDataCb就是指向cameraservice中定义的回调函数也是不准确的说法，准确的说法应该是mDataCb的实现方法最红会调用到cameraservice中定义的回调函数，
这里还是花点时间说明一下这个回调过程：
mDataCb其实真正知道的是camerahardwareinterface中定义的__data_cb实现，这是由以下调用决定的
mDevice->ops->set_callbacks(mDevice,
                                   __notify_cb,
                                   __data_cb,
                                   __data_cb_timestamp,
                                   __get_memory,
                                   this);
下面来看看的__data_cb定义

static void __data_cb(int32_t msg_type,
                          const camera_memory_t *data, unsigned int index,
                          camera_frame_metadata_t *metadata,
                          void *user)
    {
        LOGV("%s", __FUNCTION__);
        CameraHardwareInterface *__this =
                static_cast<CameraHardwareInterface *>(user);
        sp<CameraHeapMemory> mem(static_cast<CameraHeapMemory *>(data->handle));
        if (index >= mem->mNumBufs) {
            LOGE("%s: invalid buffer index %d, max allowed is %d", __FUNCTION__,
                 index, mem->mNumBufs);
            return;
        }
        __this->mDataCb(msg_type, mem->mBuffers[index], metadata, __this->mCbUser);
    }

而这里这个mDataCb又是哪里来的

/** 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;
        mDataCb = data_cb;
        mDataCbTimestamp = data_cb_timestamp;
        mCbUser = user;

        LOGV("%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);
        }
    }

找里大家清楚的看到了mDataCb就指向cameraservice中定义的datacallback方法，这个过程只是稍微绕了下圈

这里还是继续分析吧，看看数据到底是怎样送到app的，下面看看cameraservice中的这个datacallback方法的定义

void CameraService::Client::dataCallback(int32_t msgType,
        const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata, void* user) {
    LOG2("dataCallback(%d)", msgType);

    sp<Client> client = getClientFromCookie(user);
    if (client == 0) return;
    if (!client->lockIfMessageWanted(msgType)) return;

    if (dataPtr == 0 && metadata == NULL) {
        LOGE("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;
#ifdef OMAP_ENHANCEMENT
        case CAMERA_MSG_COMPRESSED_BURST_IMAGE:
            client->handleCompressedBurstPicture(dataPtr);
            break;
#endif
        default:
            client->handleGenericData(msgType, dataPtr, metadata);
            break;
    }
}

preview数据是通过上面的client->handlePreviewData(msgType, dataPtr, metadata);方法继续往上走的，通过这种方式，数据由cameras层---->cameraclient层
接着看看cameraclent的实现

// 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);
    }
}

这里的listener到底是什么，还记得初始化的时候，在jni里面有设置listenerm吗？我们还是从新再看一下吧：frameworks/base/core/jni/android_hardware_Camera.cpp

// connect to camera service
static void android_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,
    jobject weak_this, jint cameraId)
{
    sp<Camera> camera = Camera::connect(cameraId);

    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(thiz);
    camera->setListener(context);

    // save context in opaque field
    env->SetIntField(thiz, fields.context, (int)context.get());
}

由上面可以看出JNICameraContext是个监听类，同时set这个监听类，这个类的定义在：frameworks/base/core/jni/android_hardware_Camera.cpp

// provides persistent context for calls from native code to Java
class JNICameraContext: public CameraListener
{
public:
    JNICameraContext(JNIEnv* env, jobject weak_this, jclass clazz, const sp<Camera>& camera);
    ~JNICameraContext() { release(); }
    virtual void notify(int32_t msgType, int32_t ext1, int32_t ext2);
    virtual void postData(int32_t msgType, const sp<IMemory>& dataPtr,
                          camera_frame_metadata_t *metadata);
    virtual void postDataTimestamp(nsecs_t timestamp, int32_t msgType, const sp<IMemory>& dataPtr);
    void postMetadata(JNIEnv *env, int32_t msgType, camera_frame_metadata_t *metadata);
    void addCallbackBuffer(JNIEnv *env, jbyteArray cbb, int msgType);
    void setCallbackMode(JNIEnv *env, bool installed, bool manualMode);
    sp<Camera> getCamera() { Mutex::Autolock _l(mLock); return mCamera; }
    bool isRawImageCallbackBufferAvailable() const;
    void release();

private:
    void copyAndPost(JNIEnv* env, const sp<IMemory>& dataPtr, int msgType);
    void clearCallbackBuffers_l(JNIEnv *env, Vector<jbyteArray> *buffers);
    void clearCallbackBuffers_l(JNIEnv *env);
    jbyteArray getCallbackBuffer(JNIEnv *env, Vector<jbyteArray> *buffers, size_t bufferSize);

    jobject mCameraJObjectWeak; // weak reference to java object
    jclass mCameraJClass; // strong reference to java class
    sp<Camera> mCamera; // strong reference to native object
    jclass mFaceClass; // strong reference to Face class
    jclass mRectClass; // strong reference to Rect class
    Mutex mLock;

    /*
     * Global reference application-managed raw image buffer queue.
     *
     * Manual-only mode is supported for raw image callbacks, which is
     * set whenever method addCallbackBuffer() with msgType =
     * CAMERA_MSG_RAW_IMAGE is called; otherwise, null is returned
     * with raw image callbacks.
     */
    Vector<jbyteArray> mRawImageCallbackBuffers;

    /*
     * Application-managed preview buffer queue and the flags
     * associated with the usage of the preview buffer callback.
     */
    Vector<jbyteArray> mCallbackBuffers; // Global reference application managed byte[]
    bool mManualBufferMode; // Whether to use application managed buffers.
    bool mManualCameraCallbackSet; // Whether the callback has been set, used to
                                         // reduce unnecessary calls to set the callback.
};

标注部分是我们在上面用到的postData，我们看一看postData的实现过程：

void JNICameraContext::postData(int32_t msgType, const sp<IMemory>& dataPtr,
                                camera_frame_metadata_t *metadata)
{
    // VM pointer will be NULL if object is released
    Mutex::Autolock _l(mLock);
    JNIEnv *env = AndroidRuntime::getJNIEnv();
    if (mCameraJObjectWeak == NULL) {
        LOGW("callback on dead camera object");
        return;
    }

    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:
            LOGV("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:
            LOGV("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);
    }
}

我们接着看看这个copyAndPost方法：

void JNICameraContext::copyAndPost(JNIEnv* env, const sp<IMemory>& dataPtr, int msgType)
{
    jbyteArray obj = NULL;

    // allocate Java byte array and copy data
    if (dataPtr != NULL) {
        ssize_t offset;
        size_t size;
        sp<IMemoryHeap> heap = dataPtr->getMemory(&offset, &size);
        LOGV("copyAndPost: off=%ld, size=%d", 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()) {
                    LOGV("Out of buffers, clearing callback!");
                    mCamera->setPreviewCallbackFlags(CAMERA_FRAME_CALLBACK_FLAG_NOOP);
                    mManualCameraCallbackSet = false;

                    if (obj == NULL) {
                        return;
                    }
                }
            } else {
                LOGV("Allocating callback buffer");
                obj = env->NewByteArray(size);
            }

            if (obj == NULL) {
                LOGE("Couldn't allocate byte array for JPEG data");
                env->ExceptionClear();
            } else {
                env->SetByteArrayRegion(obj, 0, size, data);
            }
        } else {
            LOGE("image heap is NULL");
        }
    }

    // post image data to Java
    env->CallStaticVoidMethod(mCameraJClass, fields.post_event,
            mCameraJObjectWeak, msgType, 0, 0, obj);
    if (obj) {
        env->DeleteLocalRef(obj);
    }
}

以上先建立一个byte数组obj，将data缓存数据存储进obj数组，CallStaticVoidMethod是C调用java函数，最后执行实在Camera.java(框架）的postEventFromNative（）
从这里开始，回调函数进入到camera framework层
frameworks/base/core/java/android/hardware/Camera.java

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);
        }
    }

sendMessage之后由handle进行处理，定义同样在framework层

private class EventHandler extends Handler
    {
        private 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:
                if (mPreviewCallback != null) {
                    PreviewCallback cb = mPreviewCallback;
                    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);
                    }
                    cb.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:
                if (mAutoFocusCallback != null) {
                    mAutoFocusCallback.onAutoFocus(msg.arg1 == 0 ? false : true, 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;

            default:
                Log.e(TAG, "Unknown message type " + msg.what);
                return;
            }
        }
    }

上面可以看出，这里处理了所有的回调，快门回调mShutterCallback.onShutter()，RawImageCallback.onPictureTaken（）拍照数据回调，自动对焦回调等。。
默认是没有previewcallback这个回调的，除非你的app设置了setPreviewCallback，可以看出preview的数据还是可以向上层回调，只是系统默认不回调，这里再说深一些：
由上面绿色标注的地方可以看出，我们需要做以下事情，检查PreviewCallback 这个在framework中定义的接口有没有设置了setPreviewCallback，设置则调用，这里接口中
的onPreviewFrame方法需要开发者自己实现，这里默认是没有实现的，需要特殊使用的要自己添加，这里是自己的理解，看一下PreviewCallback 接口的定义：frameworks/base/core/java/android/hardware/Camera.java

/**
     * Callback interface used to deliver copies of preview frames as
     * they are displayed.
     *
     * @see #setPreviewCallback(Camera.PreviewCallback)
     * @see #setOneShotPreviewCallback(Camera.PreviewCallback)
     * @see #setPreviewCallbackWithBuffer(Camera.PreviewCallback)
     * @see #startPreview()
     */
    public interface PreviewCallback
    {
        /**
         * Called as preview frames are displayed. This callback is invoked
         * on the event thread {@link #open(int)} was called from.
         *
         * @param data the contents of the preview frame in the format defined
         * by {@link android.graphics.ImageFormat}, which can be queried
         * with {@link android.hardware.Camera.Parameters#getPreviewFormat()}.
         * If {@link android.hardware.Camera.Parameters#setPreviewFormat(int)}
         * is never called, the default will be the YCbCr_420_SP
         * (NV21) format.
         * @param camera the Camera service object.
         */
        void onPreviewFrame(byte[] data, Camera camera);
    };

另数据采集区与显示区两个缓存区buffer preview数据的投递，以完成preview实时显示是在HAL层完成的。

到这里为止，整个过程大致走了一遍，中间必定有很多不多，这也只是自己的学习记录，难免有自己错误的见解，待修正

待续。。。。。