lastSubStrokeCIImage = CIImage(mtlTexture: self.currentDrawable!.texture, options: nil)!.oriented(CGImagePropertyOrientation.downMirrored)
subStrokeUIView.image = UIImage(ciImage: lastSubStrokeCIImage)

lazy var ciSubCurveAccumulator: CIImageAccumulator =
    {
      [unowned self] in
      return CIImageAccumulator(extent: CGRect(x: 0, y: 0, width: self.frame.width * self.contentScaleFactor, height: self.frame.height * self.window!.screen.scale ) , format: kCIFormatBGRA8)
      }()!
ciSubCurveAccumulator.setImage(lastSubStrokeCIImage)
strokeUIView.image = UIImage(ciImage: ciSubCurveAccumulator.image())