Flutter - How to make a center blur-focused screen on the QR code reading screen?

Question

I have to make a QR code screen, I need to work on this screen with the focus of Qr reading in the middle and its surroundings blurred.

I want to make a focus point in the middle of the background blur on the QR code reading screen, I wrote paint for this, but I could not reach a healthy result. The only thing missing from ShapeBorder is that the background is blurred. How can I add this?

    class QrScannerOverlayShape extends ShapeBorder {
      QrScannerOverlayShape({
        this.borderColor = Colors.red,
        this.borderWidth = 3.0,
        this.overlayColor = const Color.fromRGBO(0, 0, 0, 80),
        this.borderRadius = 0,
        this.borderLength = 40,
        double? cutOutSize,
        double? cutOutWidth,
        double? cutOutHeight,
        this.cutOutBottomOffset = 0,
      })  : cutOutWidth = cutOutWidth ?? cutOutSize ?? 250,
            cutOutHeight = cutOutHeight ?? cutOutSize ?? 250 {
        assert(
          borderLength <=
              min(this.cutOutWidth, this.cutOutHeight) / 2 + borderWidth * 2,
          "Border can't be larger than ${min(this.cutOutWidth, this.cutOutHeight) / 2 +         borderWidth * 2}",
    );
    assert(
        (cutOutWidth == null && cutOutHeight == null) ||
            (cutOutSize == null && cutOutWidth != null && cutOutHeight != null),
        'Use only cutOutWidth and cutOutHeight or only cutOutSize');
  }

  final Color borderColor;
  final double borderWidth;
  final Color overlayColor;
  final double borderRadius;
  final double borderLength;
  final double cutOutWidth;
  final double cutOutHeight;
  final double cutOutBottomOffset;

  @override
  EdgeInsetsGeometry get dimensions => const EdgeInsets.all(10);

  @override
  Path getInnerPath(Rect rect, {TextDirection? textDirection}) {
    return Path()
      ..fillType = PathFillType.evenOdd
      ..addPath(getOuterPath(rect), Offset.zero);
  }

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    Path getLeftTopPath(Rect rect) {
      return Path()
        ..moveTo(rect.left, rect.bottom)
        ..lineTo(rect.left, rect.top)
        ..lineTo(rect.right, rect.top);
    }

    return getLeftTopPath(rect)
      ..lineTo(
        rect.right,
        rect.bottom,
      )
      ..lineTo(
        rect.left,
        rect.bottom,
      )
      ..lineTo(
        rect.left,
        rect.top,
      );
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection? textDirection}) {
    final width = rect.width;
    final borderWidthSize = width / 2;
    final height = rect.height;
    final borderOffset = borderWidth / 2;
    final mBorderLength =
        borderLength > min(cutOutHeight, cutOutHeight) / 2 + borderWidth * 2
            ? borderWidthSize / 2
            : borderLength;
    final mCutOutWidth =
        cutOutWidth < width ? cutOutWidth : width - borderOffset;
    final mCutOutHeight =
        cutOutHeight < height ? cutOutHeight : height - borderOffset;

    final backgroundPaint = Paint()
      ..color = overlayColor
      ..style = PaintingStyle.fill;

    final borderPaint = Paint()
      ..color = borderColor
      ..style = PaintingStyle.stroke
      ..strokeWidth = borderWidth;

    final boxPaint = Paint()
      ..color = borderColor
      ..style = PaintingStyle.fill
      ..blendMode = BlendMode.dstOut;

    final cutOutRect = Rect.fromLTWH(
      rect.left + width / 2 - mCutOutWidth / 2 + borderOffset,
      -cutOutBottomOffset +
          rect.top +
          height / 2 -
          mCutOutHeight / 2 +
          borderOffset,
      mCutOutWidth - borderOffset * 2,
      mCutOutHeight - borderOffset * 2,
    );

    canvas
      ..saveLayer(rect, backgroundPaint)
      ..drawRect(rect, backgroundPaint)
      // Draw top right corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.right - mBorderLength,
          cutOutRect.top,
          cutOutRect.right,
          cutOutRect.top + mBorderLength,
          topRight: Radius.circular(borderRadius),
        ),
        borderPaint,
      )

      // Draw top left corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.left,
          cutOutRect.top,
          cutOutRect.left + mBorderLength,
          cutOutRect.top + mBorderLength,
          topLeft: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      // Draw bottom right corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.right - mBorderLength,
          cutOutRect.bottom - mBorderLength,
          cutOutRect.right,
          cutOutRect.bottom,
          bottomRight: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      // Draw bottom left corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.left,
          cutOutRect.bottom - mBorderLength,
          cutOutRect.left + mBorderLength,
          cutOutRect.bottom,
          bottomLeft: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      ..drawRRect(
        RRect.fromRectAndRadius(
          cutOutRect,
          Radius.circular(borderRadius),
        ),
        boxPaint,
      )
      ..restore();
  }

  @override
  ShapeBorder scale(double t) {
    return QrScannerOverlayShape(
      borderColor: borderColor,
      borderWidth: borderWidth,
      overlayColor: overlayColor,
    );
  }
}