Android -- Camera聚焦流程

@Override
    public void autoFocus() {
        //记录当前聚焦开始时间
        mFocusStartTime = System.currentTimeMillis();
        //设置Camera的回调聚焦
        mCameraDevice.autoFocus(mAutoFocusCallback);
        //设置Camera的状态为Focusing
        setCameraState(FOCUSING);
    }

private void setCameraState(int state) {
        mCameraState = state;
        switch (state) {
            case SNAPSHOT_IN_PROGRESS:
            case FOCUSING:
                enableCameraControls(false);
                break;
            case IDLE:
            case PREVIEW_STOPPED:
                enableCameraControls(true);
                break;
        }
    }

/**
     * 设置几个button或者view不可点击
     * @param enable
     */
    private void enableCameraControls(boolean enable) {
        if (mIndicatorControlContainer != null) {
            mIndicatorControlContainer.setEnabled(enable);
        }
        if (mModePicker != null) mModePicker.setEnabled(enable);
        if (mZoomControl != null) mZoomControl.setEnabled(enable);
        if (mThumbnailView != null) mThumbnailView.setEnabled(enable);
    }

Override
    public void setEnabled(boolean enabled) {
        super.setEnabled(enabled);
        final int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View v = getChildAt(i);
            // Zoom buttons and shutter button are controlled by the activity.
            if (v instanceof AbstractIndicatorButton) {
                v.setEnabled(enabled);
                // Show or hide the indicator buttons during recording.
                if (mCurrentMode == MODE_VIDEO) {
                    v.setVisibility(enabled ? View.VISIBLE : View.INVISIBLE);
                }
            }
        }
        if (mCameraPicker != null) {
            mCameraPicker.setEnabled(enabled);
            if (mCurrentMode == MODE_VIDEO) {
                mCameraPicker.setVisibility(enabled ? View.VISIBLE : View.INVISIBLE);
            }
        }
    }

private final class AutoFocusCallback
            implements android.hardware.Camera.AutoFocusCallback {
        public void onAutoFocus(
                boolean focused, android.hardware.Camera camera) {
            //如果是暂停状态，不聚焦
            if (mPausing) return;
            //算出当前到聚焦开始的时间差
            mAutoFocusTime = System.currentTimeMillis() - mFocusStartTime;
            Log.v(TAG, "mAutoFocusTime = " + mAutoFocusTime + "ms");
            //设置Camera状态为
            setCameraState(IDLE);
            //调用FocusManager中的AutoFocus
            mFocusManager.onAutoFocus(focused);
        }
    }

/**
     * 聚焦
     * @param focused
     */
    public void onAutoFocus(boolean focused) {
        Log.i(TAG, "focus used : " + (System.currentTimeMillis() - focusStart));
        //正在进行聚焦，拍照动作必须再聚焦完之后
        if (mState == STATE_FOCUSING_SNAP_ON_FINISH) {
            // 无论聚焦成功还是失败，都会拍照。如果要进行拍照发声，就无需AF发声了
            if (focused) {
                //聚焦成功
                mState = STATE_SUCCESS;
            } else {
                //聚焦失败
                mState = STATE_FAIL;
            }
            //更新聚焦框UI&&设置人脸识别UI已经各种状态的设置
            updateFocusUI();
            //拍照，mState的状态变为STATE_IDLE
            capture();
        } else if (mState == STATE_FOCUSING) {//如果是聚焦中的状态
            //此状态的发生分为两种，half-pressing按压聚焦或者触摸聚焦被触发，这个时候不要发生拍照动作
            if (focused) {
                //聚焦成功
                mState = STATE_SUCCESS;
                //在连续聚焦状态不要发声，聚焦回调会在拍照前完成，所有状态一直为STATE_FOCUSING
                if (!Parameters.FOCUS_MODE_CONTINUOUS_PICTURE.
                        equals(mFocusMode)) {
                    mListener.playSound(CameraSound.FOCUS_COMPLETE);
                }
            } else {
                //聚焦失败
                mState = STATE_FAIL;
            }
            //更新聚焦&&人脸UI
            updateFocusUI();
            // If this is triggered by touch focus, cancel focus after a
            // while.
            //如果是触摸聚焦，需要延迟一下取消掉聚焦
            if (mFocusArea != null) {
                mHandler.sendEmptyMessageDelayed(RESET_TOUCH_FOCUS, RESET_TOUCH_FOCUS_DELAY);
            }
        } else if (mState == STATE_IDLE) {//空闲
            // User has released the focus key before focus completes.
            // Do nothing.
        }
    }

private class MainHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case RESET_TOUCH_FOCUS: {
                    //取消掉聚焦
                    cancelAutoFocus();
                    //开始人脸识别
                    mListener.startFaceDetection();
                    break;
                }
            }
        }
    }

/**
     * 再重置tap area之前调用mListener.cancelAutofocus，否则，聚焦模式将一直是自动&tap聚焦，并且驱动也不会重置
     */
    private void cancelAutoFocus() {
        //放置聚焦框到屏幕中间
        resetTouchFocus();
        mListener.cancelAutoFocus();
        if (mFaceView != null) mFaceView.resume();
        mState = STATE_IDLE;
        updateFocusUI();
        mHandler.removeMessages(RESET_TOUCH_FOCUS);
    }

/**
     * 触摸，，这里会发生触摸聚焦
     * @param e
     * @return
     */
    public boolean onTouch(MotionEvent e) {
        //没有初始化或者拍照前的聚焦的状态，直接返回
        if (!mInitialized || mState == STATE_FOCUSING_SNAP_ON_FINISH) return false;

        //让用户可以取消掉之前未消失的触摸聚焦
        if ((mFocusArea != null) && (mState == STATE_FOCUSING ||
                    mState == STATE_SUCCESS || mState == STATE_FAIL)) {
            cancelAutoFocus();
        }

        // Initialize variables.
        int x = Math.round(e.getX());
        int y = Math.round(e.getY());
        int focusWidth = mFocusIndicatorRotateLayout.getWidth();
        int focusHeight = mFocusIndicatorRotateLayout.getHeight();
        int previewWidth = mPreviewFrame.getWidth();
        int previewHeight = mPreviewFrame.getHeight();
        if (mFocusArea == null) {
            mFocusArea = new ArrayList<Area>();
            mFocusArea.add(new Area(new Rect(), 1));
            mMeteringArea = new ArrayList<Area>();
            mMeteringArea.add(new Area(new Rect(), 1));
        }

        //将坐标转换为驱动的格式。AE面积更大,因为曝光会敏感和容易，或者说曝光不足,如果面积太小了。
        calculateTapArea(focusWidth, focusHeight, 1f, x, y, previewWidth, previewHeight,
                mFocusArea.get(0).rect);
        calculateTapArea(focusWidth, focusHeight, 1.5f, x, y, previewWidth, previewHeight,
                mMeteringArea.get(0).rect);

        // Use margin to set the focus indicator to the touched area.
        RelativeLayout.LayoutParams p =
                (RelativeLayout.LayoutParams) mFocusIndicatorRotateLayout.getLayoutParams();
        int left = Util.clamp(x - focusWidth / 2, 0, previewWidth - focusWidth);
        int top = Util.clamp(y - focusHeight / 2, 0, previewHeight - focusHeight);
        p.setMargins(left, top, 0, 0);
        // Disable "center" rule because we no longer want to put it in the center.
        int[] rules = p.getRules();
        rules[RelativeLayout.CENTER_IN_PARENT] = 0;
        mFocusIndicatorRotateLayout.requestLayout();

        //停止人脸识别，因为要进行识别聚焦和测量area
        mListener.stopFaceDetection();

        //设置聚焦区域&测量区域
        mListener.setFocusParameters();
        //如果支持触摸聚焦&&手指抬起
        if (mFocusAreaSupported && (e.getAction() == MotionEvent.ACTION_UP)) {
            autoFocus();
        } else {  // Just show the indicator in all other cases.
            updateFocusUI();
            // Reset the metering area in 3 seconds.
            mHandler.removeMessages(RESET_TOUCH_FOCUS);
            mHandler.sendEmptyMessageDelayed(RESET_TOUCH_FOCUS, RESET_TOUCH_FOCUS_DELAY);
        }

        return true;
    }

doSnap()：空闲状态可以执行拍照
onAutoFocus(boolean focused)：用户再聚焦完成前放掉了聚焦按钮，所以不做任何事。
onPreviewStarted()，onPreviewStopped()：状态都变为空闲
cancelAutoFocus()：取消聚焦，状态变为空闲
updateFocusUI()：如果空闲&有聚焦区域，显示聚焦框框

onShutterUp()：如果是focusmode为自动聚焦，状态为正在聚焦，则取消掉聚焦
doSnap()：如果是正在聚焦状态，将状态改为聚焦完拍照状态
onAutoFocus(boolean focused)：判断focused，为true变为聚焦成功状态，为false变为聚焦失败状态
onTouch(MotionEvent e)：如果正在聚焦&之前有手动聚焦了，则取消掉之前的聚焦
autoFocus()：状态变为聚焦状态
updateFocusUI()：显示聚焦的框框

onShutterUp()：状态不是聚焦完拍照，可以设置FocusParameters
onAutoFocus(boolean focused)：判断focused，为true变为聚焦成功状态，为false变为聚焦失败状态，更新聚焦框UI
onTouch(MotionEvent e)：直接不继续操作下去
updateFocusUI()：显示聚焦的框框

onShutterDown()：如果是自动聚焦mode，并且不为聚焦成功状态，执行聚焦
onShutterUp()： 如果是自动聚焦mode，并且为聚焦成功状态，执行取消聚焦
doSnap()：拍照
onTouch(MotionEvent e)：让用户可以取消掉之前未消失的触摸聚焦
updateFocusUI()：聚焦框框显示成功

onShutterDown()：如果是自动聚焦mode，并且不为聚焦失败状态，执行聚焦
onShutterUp()： 如果是自动聚焦mode，并且为聚焦失败状态，执行取消聚焦
doSnap()：拍照
onTouch(MotionEvent e)：让用户可以取消掉之前未消失的触摸聚焦
updateFocusUI()：聚焦框框显示失败