Android 骁龙Camera拍照流程梳理

本文以SnapdragonCamera为例，分析骁龙Camera的拍照流程，其实现与camera2大致相同。

首先将SnapdragonCamera源码倒入android studio, 具体操作，可查看如何用Android Studio调试Android源码一文。打开camera，点击拍照，ShutterButton类的performClick()方法会被调用。（如何定位点击拍照会调用ShutterButton类的performClick()方法，请参考使用Android Studio中的HierarchyViewer 及UI Automator Viewer定位当前UI界面的代码位置。）

    @Overridepublic boolean performClick() {boolean result = super.performClick();if (mListener != null && getVisibility() == View.VISIBLE) {mListener.onShutterButtonClick();}return result;}

按Ctrl+Alt+B 看onShutterButtonClick()方法是在哪里实现的。如下图，有四个地方调用，由于我们只分析拍照流程，只用查看PhotoModule即可。

在PhotoModule中，onShutterButtonClick()的实现如下

    @Overridepublic synchronized void onShutterButtonClick() {if ((mCameraDevice == null)|| mPaused || mUI.collapseCameraControls()|| !mUI.mMenuInitialized|| (mCameraState == SWITCHING_CAMERA)|| (mCameraState == PREVIEW_STOPPED)|| (mCameraState == LONGSHOT)|| (null == mFocusManager)) return;...if (seconds > 0) {String zsl = mPreferences.getString(CameraSettings.KEY_ZSL,mActivity.getString(R.string.pref_camera_zsl_default));mUI.overrideSettings(CameraSettings.KEY_ZSL, zsl);mUI.startCountDown(seconds, playSound);} else {mSnapshotOnIdle = false;initiateSnap();//关键方法}}

为了便于查看，我们省略掉一些条件判断的代码，最终调用initiateSnap()方法。

  private void initiateSnap(){if(mPreferences.getString(CameraSettings.KEY_SELFIE_FLASH,mActivity.getString(R.string.pref_selfie_flash_default)).equalsIgnoreCase("on") &&mCameraId == CameraHolder.instance().getFrontCameraId()) {mUI.startSelfieFlash();if(selfieThread == null) {selfieThread = new SelfieThread();//若selfieThread == null，SelfieThread中的                                                        selfieThread.start();             //mFocusManager.doSnap()方法被调用}} else {mFocusManager.doSnap();//关键方法}}

接着查看doSnap()方法

    public void doSnap() {if (!mInitialized) return;// If the user has half-pressed the shutter and focus is completed, we// can take the photo right away. If the focus mode is infinity, we can// also take the photo.if (!needAutoFocusCall() || (mState == STATE_SUCCESS || mState == STATE_FAIL)) {capture(); // 关键方法，聚焦完成会调用此方法，} else if (mState == STATE_FOCUSING) {// Half pressing the shutter (i.e. the focus button event) will// already have requested AF for us, so just request capture on// focus here.mState = STATE_FOCUSING_SNAP_ON_FINISH;//开始聚焦未完成时，调用} else if (mState == STATE_IDLE) {// We didn't do focus. This can happen if the user press focus key// while the snapshot is still in progress. The user probably wants// the next snapshot as soon as possible, so we just do a snapshot// without focusing again.capture();//关键方法，没有聚焦时调用}}

我们分析第一种情况，第二种情况，涉及callShutterButtonFocus()的调用流程，这里暂不做分析，接着我们看PhotoModule中capture()函数的实现。

    @Overridepublic boolean capture() {// If we are already in the middle of taking a snapshot or the image save request// is full then ignore.if (mCameraDevice == null || mCameraState == SNAPSHOT_IN_PROGRESS|| mCameraState == SWITCHING_CAMERA|| mActivity.getMediaSaveService() == null|| mActivity.getMediaSaveService().isQueueFull()) {return false;}...... //省略相关参数设置，及条件判断代码...if (mCameraState == LONGSHOT) {mLongShotCaptureCountLimit = SystemProperties.getInt("persist.camera.longshot.shotnum", 0);mLongShotCaptureCount = 1;if(mLongshotSave) {mCameraDevice.takePicture(mHandler,new LongshotShutterCallback(),mRawPictureCallback, mPostViewPictureCallback,new LongshotPictureCallback(loc));} else {mCameraDevice.takePicture(mHandler,new LongshotShutterCallback(),mRawPictureCallback, mPostViewPictureCallback,new JpegPictureCallback(loc));}} else {//关键代码mCameraDevice.takePicture(mHandler,new ShutterCallback(!animateBefore),mRawPictureCallback, mPostViewPictureCallback,new JpegPictureCallback(loc));setCameraState(SNAPSHOT_IN_PROGRESS);}mNamedImages.nameNewImage(mCaptureStartTime, mRefocus);if (mSnapshotMode != CameraInfo.CAMERA_SUPPORT_MODE_ZSL) {mFaceDetectionStarted = false;}UsageStatistics.onEvent(UsageStatistics.COMPONENT_CAMERA,UsageStatistics.ACTION_CAPTURE_DONE, "Photo", 0,UsageStatistics.hashFileName(mNamedImages.mQueue.lastElement().title + ".jpg"));return true;}

其中关键代码为mCameraDevice.takePicture(),拍照后会回调JpegPictureCallback中的onPictureTaken()方法。将从底层返回的数据进行处理。

    @Overridepublic void onPictureTaken(byte [] jpegData, CameraProxy camera) {mUI.stopSelfieFlash();mUI.enableShutter(true);if (mUI.isPreviewCoverVisible()) {// When take picture request is sent before starting preview, onPreviewFrame()// callback doesn't happen so removing preview cover here, instead.mUI.hidePreviewCover();}if (mInstantCaptureSnapShot == true) {Log.v(TAG, "Instant capture picture taken!");mInstantCaptureSnapShot = false;}if (mPaused) {return;}if (mIsImageCaptureIntent) {if (!mRefocus) {stopPreview();}} else if (mSceneMode == CameraUtil.SCENE_MODE_HDR) {mUI.showSwitcher();mUI.setSwipingEnabled(true);}mReceivedSnapNum = mReceivedSnapNum + 1;mJpegPictureCallbackTime = System.currentTimeMillis();if(mSnapshotMode == CameraInfo.CAMERA_SUPPORT_MODE_ZSL) {Log.v(TAG, "JpegPictureCallback : in zslmode");mParameters = mCameraDevice.getParameters();mBurstSnapNum = mParameters.getInt("num-snaps-per-shutter");}Log.v(TAG, "JpegPictureCallback: Received = " + mReceivedSnapNum +"Burst count = " + mBurstSnapNum);// If postview callback has arrived, the captured image is displayed// in postview callback. If not, the captured image is displayed in// raw picture callback.if (mPostViewPictureCallbackTime != 0) {mShutterToPictureDisplayedTime =mPostViewPictureCallbackTime - mShutterCallbackTime;mPictureDisplayedToJpegCallbackTime =mJpegPictureCallbackTime - mPostViewPictureCallbackTime;} else {mShutterToPictureDisplayedTime =mRawPictureCallbackTime - mShutterCallbackTime;mPictureDisplayedToJpegCallbackTime =mJpegPictureCallbackTime - mRawPictureCallbackTime;}Log.v(TAG, "mPictureDisplayedToJpegCallbackTime = "+ mPictureDisplayedToJpegCallbackTime + "ms");mFocusManager.updateFocusUI(); // Ensure focus indicator is hidden.boolean needRestartPreview = !mIsImageCaptureIntent&& !mPreviewRestartSupport&& (mCameraState != LONGSHOT)&& (mSnapshotMode != CameraInfo.CAMERA_SUPPORT_MODE_ZSL)&& (mReceivedSnapNum == mBurstSnapNum);if (needRestartPreview) {setupPreview();if (CameraUtil.FOCUS_MODE_CONTINUOUS_PICTURE.equals(mFocusManager.getFocusMode())) {mCameraDevice.cancelAutoFocus();}} else if ((mReceivedSnapNum == mBurstSnapNum)&& (mCameraState != LONGSHOT)){mFocusManager.resetTouchFocus();if (CameraUtil.FOCUS_MODE_CONTINUOUS_PICTURE.equals(mFocusManager.getFocusMode())) {mCameraDevice.cancelAutoFocus();}mUI.resumeFaceDetection();if (!mIsImageCaptureIntent) {setCameraState(IDLE);}startFaceDetection();}mLastPhotoTakenWithRefocus = mRefocus;if (mRefocus) {final String[] NAMES = { "00.jpg", "01.jpg", "02.jpg", "03.jpg","04.jpg", "DepthMapImage.y", "AllFocusImage.jpg" };try {FileOutputStream out = mActivity.openFileOutput(NAMES[mReceivedSnapNum - 1],Context.MODE_PRIVATE);out.write(jpegData, 0, jpegData.length);out.close();} catch (Exception e) {}}if (!mRefocus || (mRefocus && mReceivedSnapNum == 7)) {ExifInterface exif = Exif.getExif(jpegData);int orientation = Exif.getOrientation(exif);if(mCameraId == CameraHolder.instance().getFrontCameraId()) {IconListPreference selfieMirrorPref = (IconListPreference) mPreferenceGroup.findPreference(CameraSettings.KEY_SELFIE_MIRROR);if (selfieMirrorPref != null && selfieMirrorPref.getValue() != null &&selfieMirrorPref.getValue().equalsIgnoreCase("enable")) {jpegData = flipJpeg(jpegData);exif = Exif.getExif(jpegData);  //将图片信息存入Exif中exif.addOrientationTag(orientation);}}if (!mIsImageCaptureIntent) {// Burst snapshot. Generate new image name.if (mReceivedSnapNum > 1) {mNamedImages.nameNewImage(mCaptureStartTime, mRefocus);}// Calculate the width and the height of the jpeg.Size s = mParameters.getPictureSize();int width, height;if ((mJpegRotation + orientation) % 180 == 0) {width = s.width;height = s.height;} else {width = s.height;height = s.width;}String pictureFormat = mParameters.get(KEY_PICTURE_FORMAT);if (pictureFormat != null && !pictureFormat.equalsIgnoreCase(PIXEL_FORMAT_JPEG)) {// overwrite width and height if raw pictureString pair = mParameters.get(KEY_QC_RAW_PICUTRE_SIZE);if (pair != null) {int pos = pair.indexOf('x');if (pos != -1) {width = Integer.parseInt(pair.substring(0, pos));height = Integer.parseInt(pair.substring(pos + 1));}}}NamedEntity name = mNamedImages.getNextNameEntity();String title = (name == null) ? null : name.title;long date = (name == null) ? -1 : name.date;// Handle debug mode outputsif (mDebugUri != null) {// If using a debug uri, save jpeg there.saveToDebugUri(jpegData);// Adjust the title of the debug image shown in mediastore.if (title != null) {title = DEBUG_IMAGE_PREFIX + title;}}if (title == null) {Log.e(TAG, "Unbalanced name/data pair");} else {if (date == -1) {date = mCaptureStartTime;}if (mHeading >= 0) {// heading direction has been updated by the sensor.ExifTag directionRefTag = exif.buildTag(ExifInterface.TAG_GPS_IMG_DIRECTION_REF,ExifInterface.GpsTrackRef.MAGNETIC_DIRECTION);ExifTag directionTag = exif.buildTag(ExifInterface.TAG_GPS_IMG_DIRECTION,new Rational(mHeading, 1));exif.setTag(directionRefTag);exif.setTag(directionTag);}String mPictureFormat = mParameters.get(KEY_PICTURE_FORMAT);mActivity.getMediaSaveService().addImage(jpegData, title, date, mLocation, width, height,orientation, exif, mOnMediaSavedListener,mContentResolver, mPictureFormat);//将图片数据写入到文件和数据库中if (mRefocus && mReceivedSnapNum == 7) {mUI.showRefocusToast(mRefocus);}}// Animate capture with real jpeg data instead of a preview frame.if (mCameraState != LONGSHOT) {Size pic_size = mParameters.getPictureSize();if ((pic_size.width <= 352) && (pic_size.height<= 288)) {mUI.setDownFactor(2); //Downsample by 2 for CIF & below} else {mUI.setDownFactor(4);}if (mAnimateCapture) {mUI.animateCapture(jpegData);}} else {// In long shot mode, we do not want to update the preview thumbnail// for each snapshot, instead, keep the last jpeg data and orientation,// use it to show the final one at the end of long shot.mLastJpegData = jpegData;mLastJpegOrientation = orientation;}} else {stopPreview();mJpegImageData = jpegData;if (!mQuickCapture) {mUI.showCapturedImageForReview(jpegData, orientation, false);} else {onCaptureDone();}}if(!mLongshotActive) {mActivity.updateStorageSpaceAndHint(new CameraActivity.OnStorageUpdateDoneListener() {@Overridepublic void onStorageUpdateDone(long storageSpace) {mUI.updateRemainingPhotos(--mRemainingPhotos);}});} else {mUI.updateRemainingPhotos(--mRemainingPhotos);}long now = System.currentTimeMillis();mJpegCallbackFinishTime = now - mJpegPictureCallbackTime;Log.v(TAG, "mJpegCallbackFinishTime = "+ mJpegCallbackFinishTime + "ms");if (mReceivedSnapNum == mBurstSnapNum) {mJpegPictureCallbackTime = 0;}if (mHiston && (mSnapshotMode ==CameraInfo.CAMERA_SUPPORT_MODE_ZSL)) {mActivity.runOnUiThread(new Runnable() {public void run() {if (mGraphView != null) {mGraphView.setVisibility(View.VISIBLE);mGraphView.PreviewChanged();}}});}if (mSnapshotMode == CameraInfo.CAMERA_SUPPORT_MODE_ZSL &&mCameraState != LONGSHOT &&mReceivedSnapNum == mBurstSnapNum &&!mIsImageCaptureIntent) {cancelAutoFocus();}}}

其中， mActivity.getMediaSaveService().addImage();方法将返回的图片数据存入文件和数据库中。MediaSaveService中的addImage()方法如下

    public void addImage(final byte[] data, String title, long date, Location loc,int width, int height, int orientation, ExifInterface exif,OnMediaSavedListener l, ContentResolver resolver, String pictureFormat) {if (isQueueFull()) {Log.e(TAG, "Cannot add image when the queue is full");return;}ImageSaveTask t = new ImageSaveTask(data, title, date,(loc == null) ? null : new Location(loc),width, height, orientation, exif, resolver, l, pictureFormat);mMemoryUse += data.length;if (isQueueFull()) {onQueueFull();}t.execute();}

最后通过ImageSaveTask异步任务，实现图片的存储，接着看ImageSaveTask中的doInBackground()方法

@Override
protected Uri doInBackground(Void... v) {if (width == 0 || height == 0) {// Decode boundsBitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeByteArray(data, 0, data.length, options);width = options.outWidth;height = options.outHeight;}return Storage.addImage(resolver, title, date, loc, orientation, exif, data, width, height, pictureFormat);
}

最后调用Storage.addImage()方法

   // Save the image with a given mimeType and add it the MediaStore.public static Uri addImage(ContentResolver resolver, String title, long date,Location location, int orientation, ExifInterface exif, byte[] jpeg, int width,int height, String mimeType) {String path = generateFilepath(title, mimeType);int size = writeFile(path, jpeg, exif, mimeType); //存文件// Try to get the real image size after add exif.File f = new File(path);if (f.exists() && f.isFile()) {size = (int) f.length();}return addImage(resolver, title, date, location, orientation,size, path, width, height, mimeType);//存数据库}

存完之后调用ImageSaveTask中的onPostExecute()方法，通知图片已经存完。

    @Overrideprotected void onPostExecute(Uri uri) {if (listener != null) listener.onMediaSaved(uri);boolean previouslyFull = isQueueFull();mMemoryUse -= data.length;if (isQueueFull() != previouslyFull) onQueueAvailable();}

以上是对拍照流程的简单分析，只是大致做了梳理，有很多细节为涉及，以后再慢慢讨论。

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