Camera2 API Touch to Focus

Question

i looked through the various questions concerning touch to focus, but i could not find the "best" or "right" solution. I put some answers together and came up with this implementation:

mTextureView.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View view, MotionEvent motionEvent) {
        float positionX = (int) motionEvent.getX();
        float positionY = (int) motionEvent.getY();

        //Build the Rectangle, where the focus should be applied.
        Rect focusRect = calculateFocusRect(motionEvent.getX(), motionEvent.getY());
        MeteringRectangle meteringRectangle = new MeteringRectangle(focusRect, 500);
        final MeteringRectangle[] meterRecArray = { meteringRectangle };

        mPreviewCaptureRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);

        //Set a captureRequest to cancel focus.
        try {
            mCameraCaptureSession.capture(mPreviewCaptureRequestBuilder.build(), mSessionCaptureCallback, mBackgroundHandler);
            mState = STATE_PREVIEW;
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }

        //Set the focusRegion.
        mPreviewCaptureRequestBuilder.set(CaptureRequest.CONTROL_AF_REGIONS, meterRecArray);
        mPreviewCaptureRequestBuilder.set(CaptureRequest.CONTROL_AE_REGIONS, meterRecArray);
        mPreviewCaptureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);

        //Restart the Preview, so changes apply.
        try {
            mCameraCaptureSession.abortCaptures();
            mCameraCaptureSession.setRepeatingRequest(mPreviewCaptureRequestBuilder.build(), mSessionCaptureCallback, mBackgroundHandler);
        } catch (CameraAccessException e) {
            Log.e("Camera", "RepeatingRequest Failed");
            e.printStackTrace();
        }

        return false;
    }
});

Building the Rectangle is managed like this:

//Calculate a Rectangle, where the user touched the screen.
private MeteringRectangle[] calculateFocusRect(float x, float y) {
    //Size of the Rectangle.
    int areaSize = 200;

    int left = clamp((int) x - areaSize / 2, 0, mTextureView.getWidth() - areaSize);
    int top = clamp((int) y - areaSize / 2, 0, mTextureView.getHeight() - areaSize);

    RectF rectF = new RectF(left, top, left + areaSize, top + areaSize);
    Rect focusRect = new Rect(Math.round(rectF.left), Math.round(rectF.top), Math.round(rectF.right), Math.round(rectF.bottom));
    MeteringRectangle meteringRectangle = new MeteringRectangle(focusRect, 1);

    return new MeteringRectangle[] {meteringRectangle};
}

//Clamp the inputs.
private int clamp(int x, int min, int max) {
    if (x > max) {
        return max;
    }
    if (x < min) {
        return min;
    }
    return x;
}

But it just doesent seem to work right. After tapping, the camera often seems to get stuck in an endless scan. Or it focuses and right as it gets the focus, it jumps back to the previous focus and the image ends up blurry.

Any idea what the problem might be?

Answer 1

When you set the focus region,use the below code and it should work:

        mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,CaptureRequest.CONTROL_AF_MODE_AUTO);
        mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,CaptureRequest.CONTROL_AF_TRIGGER_START);
        mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE,CaptureRequest.CONTROL_AE_MODE_ON);

As far as I know, if you set the CONTROL_AF_MODE to CONTROL_AF_MODE_CONTINUOUS_PICTURE it will keep trying to focus. The mode has to be on auto but it has to be triggered. So start the trigger here and in your mSessionCaptureCallback 's onCaptureCompleted method should look something like this:

@Override
public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull 
                               CaptureRequest request,
                               @NonNull TotalCaptureResult result) {
    super.onCaptureCompleted(session, request, result);
    mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
                               CaptureRequest.CONTROL_AF_TRIGGER_IDLE);
    mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(),null,null);
   }