Android(安卓)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。）

    @Override    public 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

    @Override    public 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。

    @Override    public 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。

    @Override        public 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 picture                        String 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 outputs                    if (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() {                            @Override                            public 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

@Overrideprotected Uri doInBackground(Void... v) {    if (width == 0 || height == 0) {        // Decode bounds        BitmapFactory.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。

    @Override        protected 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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