本篇仅学习从应用层到framework的过程，jni以下部分暂不讨论。因为一个优秀的相机应用，核心永远是它的图像处理部分（即Hal层中的3A算法部分），而MTK相关内容未开源。我们从按下拍照键开始做时序图如下：
camera-takephoto.png
上图可以分成三个部分，第一部分就是接口的回调与实现，第二部分是不同模块execute执行指令部分，第三个部分是数据保存生成jpeg文件。我们这里说一下时序图上未记录的一些东西：
PhotoActor.java
@Override
public void onShutterButtonClick(ShutterButton button) {
int cameraState = mCameraActivity.getCameraState();
ViewState currentViewState = mICameraAppUi.getViewState();
Log.i(TAG, "[onShutterButtonClick] cameraState = " + cameraState
+ ", currentViewState = " + currentViewState);
if (ViewState.VIEW_STATE_LOMOEFFECT_SETTING == currentViewState
|| ViewState.VIEW_STATE_CONTINUOUS_CAPTURE == currentViewState
|| ViewState.VIEW_STATE_CAMERA_CLOSED == currentViewState) {
return;
}
if (mICameraAppUi.updateRemainStorage() > 0) {
if (!(CameraActivity.STATE_SWITCHING_CAMERA == cameraState || CameraActivity.STATE_PREVIEW_STOPPED == cameraState)) {
if (mSelfTimerManager.startSelfTimer()) {
Log.i(TAG, "[onShutterButtonClick] start self timer");
mModuleManager.onSelfTimerState(true);
mICameraAppUi.setSwipeEnabled(false);
mICameraAppUi.setViewState(ViewState.VIEW_STATE_CAPTURE);
mIsSelftimerCounting = true;
return;
} else {
mIsSelftimerCounting = false;
}
mModuleManager.onPhotoShutterButtonClick();
}
} else {
Log.i(TAG, "remain storage is less than 0");
mICameraAppUi.showRemaining();
}
}
这里面有两个函数未记入时序图，一个updateRemainStorage()，其最终实现位于RemainingManager用来计算当前的剩余空间，空间不足自然无法拍照保存，另一个是mSelfTimerManager.startSelfTimer()用来做倒计时拍照的功能。
ModuleManager.java
public boolean onPhotoShutterButtonClick() {
mAdditionManager.execute(ActionType.ACTION_PHOTO_SHUTTER_BUTTON_CLICK, false);
return mICameraMode.execute(ActionType.ACTION_PHOTO_SHUTTER_BUTTON_CLICK);
}
在这个地方开始执行execute，mAdditionManager是什么呢？我们进入这个类，看一下它的execute方法：
public boolean execute(AdditionActionType type, Object... arg) {
Log.i(TAG, "[execute],addition action type = " + type);
boolean result = false;
for (ICameraAddition addition : mModeAddition) {
result = addition.execute(type, arg) || result;
}
return result;
}
mModeAddition表示当前的拍摄模式，其值定义如下：
public void setCurrentMode(CameraModeType type) {
Log.i(TAG, "[setCurrentMode]type = " + type);
switch (type) {
case EXT_MODE_PHOTO:
mModeAddition = mPhotoAddtion;
break;
case EXT_MODE_VIDEO:
mModeAddition = mVideoAddtion;
break;
case EXT_MODE_PHOTO_PIP:
mModeAddition = mPipPhotoAddition;
break;
case EXT_MODE_VIDEO_PIP:
mModeAddition = mPipVideoAddition;
break;
case EXT_MODE_FACE_BEAUTY:
mModeAddition = mFaceBeautyAddition;
break;
case EXT_MODE_STEREO_CAMERA:
mModeAddition = mRefocusAddition;
break;
default:
mModeAddition = mDummyAddtion;
break;
}
}
我们从相关各个类的关系来看下：
camera-addition.png
CameraAddition的子类除了图中的还有其它，这里只画出了在AdditionManager初始化时用到的子类。整个addition包是由mtk新加的code，从ICameraAddition该接口的定义来看，大概是将不同的ACTION_TYPE传递到不同的MODE下进行Camera的操作。
回到前面mICameraMode.execute()，根据不同的mode进入相关类，我们这里肯定是执行PhotoMode的execute方法。顺序执行到如下方法：
private void onShutterButtonClick() {
boolean isEnoughSpace = mIFileSaver.isEnoughSpace();
Log.i(TAG, "[onShutterButtonClick]isEnoughSpace = " + isEnoughSpace + ",mCameraClosed = "
+ mCameraClosed + ",mCurrentState = " + getModeState());
// Do not take the picture if there is not enough storage or camera is not available.
if (!isEnoughSpace || isCameraNotAvailable()) {
Log.w(TAG, "[onShutterButtonClick]return.");
return;
}
Log.i(TAG,
"[CMCC Performance test][Camera][Camera] camera capture start ["
+ System.currentTimeMillis() + "]");
if (mIFocusManager != null) {
mIFocusManager.focusAndCapture();
}
}
这里FileSaverImpl会判断一次剩余空间的大小，在前面第一次判断剩余空间时，将avaliableSpace保存到Storage，而在这里会将该值取出再次判断。而当相机处于不可用状态时也将放弃拍照而直接返回。
private boolean isCameraNotAvailable() {
ModeState modeState = getModeState();
Log.d(TAG, "isCameraNotAvailable modeState " + modeState);
return (ModeState.STATE_CAPTURING == modeState || ModeState.STATE_SAVING == modeState ||
ModeState.STATE_CLOSED == modeState) ? true : false;
}
准确的来说，应该不是相机不可用，而是当相机处于CAPTURING、SAVING、CLOSED这三种状态时暂时看作相机不可用。如果不是这三种状态，则开始聚焦拍照。然后，接口回调到PhotoMode中的capture()方法：
@Override
public boolean capture() {
Log.i(TAG, "[capture]...");
long start = System.currentTimeMillis();
mCaptureStartTime = System.currentTimeMillis();
mPostViewPictureCallbackTime = 0;
mJpegImageData = null;
mIFileSaver.init(FILE_TYPE.JPEG, 0, null, -1);
mICameraAppUi.setSwipeEnabled(false);
mICameraAppUi.showRemaining();
mCameraCategory.takePicture();
setModeState(ModeState.STATE_CAPTURING);
Log.d(TAG, "[capture] Capture time = " + (System.currentTimeMillis() - start));
return true;
}
这里各种工作准备就绪后初始化FileSaver相关准备进行文件保存，然后更新UI显示当前的剩余空间，然后调用了内部类的方法再通过代理调用到了Camera。
protected class CameraCategory {
public void takePicture() {
if (!mAdditionManager.execute(AdditionActionType.ACTION_TAKEN_PICTURE)) {
mICameraDevice.takePicture(mShutterCallback, mRawPictureCallback,
null, mJpegPictureCallback);
mICameraAppUi.setViewState(ViewState.VIEW_STATE_CAPTURE);
}
}
}
我们的文件保存在哪进行的呢，看下这个mJpegPictureCallback：
private final PictureCallback mJpegPictureCallback = new PictureCallback() {
@Override
public void onPictureTaken(byte[] jpegData, Camera camera) {
Log.i(TAG, "[mJpegPictureCallback]onPictureTaken");
...
// Calculate the width and the height of the jpeg.
if (!mIModuleCtrl.isImageCaptureIntent()) {
mIFileSaver.savePhotoFile(jpegData, null, mCaptureStartTime,
mIModuleCtrl.getLocation(), 0, null);
} else {
mJpegImageData = jpegData;
if (!mIModuleCtrl.isQuickCapture()) {
mICameraAppUi.showReview(null, null);
mICameraAppUi.switchShutterType(ShutterButtonType.SHUTTER_TYPE_OK_CANCEL);
} else {
doAttach();
}
}
...
}
};
SaveRequest将保存照片的各种信息：
@Override
public boolean savePhotoFile(byte[] photoData, String fileName, long date,
Location location, int tag, OnFileSavedListener listener) {
Log.i(TAG, "[savePhotoFile]title =" + fileName);
if (null == mSaveRequest || null == photoData) {
Log.w(TAG, "[savePhotoFile]fail,mSaveRequest = " + mSaveRequest);
return false;
}
mListener = listener;
if (mSaveRequest.getDataSize() > 0) {
Log.i(TAG, "[savePhotoFile]Current SaveRequest is used, copy new one!");
mSaveRequest = mFileSaver.copyPhotoRequest(mSaveRequest);
}
mSaveRequest.setData(photoData);
mSaveRequest.setFileName(fileName);
mSaveRequest.setTag(tag);
mSaveRequest.updateDataTaken(date);
mSaveRequest.setLocation(location);
mSaveRequest.setListener(mFileSaverListener);
mSaveRequest.addRequest();
return true;
}
SaveRequest是一个接口，其实现在FileSaver的内部类RequestOperator，而该内部类同时又是一个抽象类，其子类同样是位于FileSaver的内部类VideoOperator、PanoOperator、PhotoOperator，因此这里的addRequet方法最终由PhotoOperator实现，它又将调用外部类FileSaver的addSaveRequest()方法，而这个请求在这里将交给FileSaverService来处理：
// run in main thread
public void addSaveRequest(SaveRequest request) {
Log.i(TAG, "[addSaveRequest]...begin,the queue number is = " + mQueue.size()
+ "mContinuousSaveTask:" + mContinuousSaveTask);
synchronized (mQueue) {
mQueue.add(request);
}
if (mContinuousSaveTask == null) {
mContinuousSaveTask = new SaveTask();
mTaskNumber++;
mContinuousSaveTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
Log.i(TAG, "[addSaveRequest]execute continuous AsyncTask.");
}
Log.i(TAG, "[addSaveRequest]...end,the queue number is = " + mQueue.size());
}
因为需要写文件，这里开启了一个AsyncTask来处理耗时操作：
@Override
protected Void doInBackground(Void... v) {
Log.i(TAG, "[SaveTask]doInBackground...,queue is empty = " + mQueue.isEmpty());
FileSaverListener lastFileSaverListener = null;
while (!mQueue.isEmpty()) {
r = mQueue.get(0);
//different cameraActivity use different listener
// notify old listener save done info
if (lastFileSaverListener != null
&& r.getFileSaverListener() != lastFileSaverListener) {
r.getFileSaverListener().onSaveDone();
}
if (Storage.isStorageReady()) {
r.saveRequest();
}
r.notifyListener();
// LinkedList is not saved list, so mQueue should be sync in
// multi thread
synchronized (mQueue) {
mQueue.remove(0);
}
synchronized (mListnerObject) {
r.getFileSaverListener().onFileSaved(r);
}
lastFileSaverListener = r.getFileSaverListener();
}
mContinuousSaveTask = null;
mTaskNumber--;
synchronized (mListnerObject) {
r.getFileSaverListener().onSaveDone();
}
Log.i(TAG, "[SaveTask]doInBackground...,end ");
return null;
}
通知相关Listener保存成功。SD卡准备好的话，具体的写文件操作重新交给SaveRequest（由java特性确定最后由PhotoOperator实现）
@Override
public synchronized void saveRequest() {
if (mData == null) {
Log.w(TAG, "[saveRequest]mData is null,return!");
return;
}
int orientation = Exif.getOrientation(mData);
// M: ConShots
mGroupId = Exif.getGroupId(mData);
mGroupIndex = Exif.getGroupIndex(mData);
mFocusValueHigh = Exif.getFocusValueHigh(mData);
mFocusValueLow = Exif.getFocusValueLow(mData);
mOrientation = orientation;
mDataSize = mData.length;
if (null != mFileName) {
mTitle = mFileName.substring(0, mFileName.indexOf('.'));
} else {
mTitle = createName(mFileType, mDateTaken, mGroupIndex);
mFileName = Storage.generateFileName(mTitle, mTempPictureType);
Log.i(TAG, "[saveRequest]PhotoOperator,mFileName = " + mFileName);
}
mFilePath = Storage.generateFilepath(mFileName);
mTempFilePath = mFilePath + TEMP_SUFFIX;
saveImageToSDCard(mTempFilePath, mFilePath, mData);
// camera decouple
mMimeType = Storage.generateMimetype(mTitle, mTempPictureType);
checkDataProperty();
saveImageToDatabase(this);
}
private void saveImageToSDCard(String tempFilePath, String filePath, byte[] data) {
FileOutputStream out = null;
try {
// Write to a temporary file and rename it to the final name.
// This
// avoids other apps reading incomplete data.
Log.d(TAG, "[saveImageToSDCard]begin add the data to SD Card");
out = new FileOutputStream(tempFilePath);
out.write(data);
out.close();
new File(tempFilePath).renameTo(new File(filePath));
} catch (IOException e) {
Log.e(TAG, "[saveImageToSDCard]Failed to write image,ex:", e);
} finally {
if (out != null) {
try {
out.close();
} catch (IOException e) {
Log.e(TAG, "[saveImageToSDCard]IOException:", e);
}
}
}
Log.i(TAG, "[saveImageToSDCard]end of add the data to SD Card");
}
我们看到最后的文件生成就是一个new File的过程，这说明我们在PictureCallback里面拿到的数据一定是已经过3A算法处理后的数据，而不是Camera设备得到的原始数据。最后我们看下FileSaver相关类的关系图：
camera-filesaver.png
为方便看图，这里没有加入VideoOperator和PanoOperator这两个内部类。我们在PictureCallback中将数据保存为文件的时候，直接操作的是IFileSaver这个接口，其实现是FileSaverImpl，然后该类中有两个成员变量mSaveRequest和mVideoSaveRequest（接口SaveRequest的对象），执行它们的addRequest()方法也就是执行FileSaver的内部类RequestOperator的想着方法，而由于其抽象类型的原因最终又将来到其子类PhotoOperator的相关方法，与我们上面的时序图一致。