Creating image masks in flutter

Question

Flutter provides several ways for masks based on paths i.e. clip paths. I am trying to figure out a way where one could take an image with transparency layer like example below and use that image to mask another image / view or as a general mask.

My first instinct was to look at CustomPaint class, but I can't figure it out past this initial idea.

Answer 1

Flutter has BoxDecoration class that takes in BlendMode enum. By utilising these you can achieve various mask effects using images, for my particular case above dstIn was a solution.

Answer 2

I have posted an answer to my own same problem here, using a custom painter class with a squircle mask and image.

  @override
  void paint(Canvas canvas, Size size) {
    if (image != null && mask != null) {
      var rect = Rect.fromLTRB(0, 0, 200, 200);
      Size outputSize = rect.size;
      Paint paint = new Paint();

      //Mask
      Size maskInputSize = Size(mask.width.toDouble(), mask.height.toDouble());
      final FittedSizes maskFittedSizes =
          applyBoxFit(BoxFit.cover, maskInputSize, outputSize);
      final Size maskSourceSize = maskFittedSizes.source;

      final Rect maskSourceRect = Alignment.center
          .inscribe(maskSourceSize, Offset.zero & maskInputSize);

      canvas.saveLayer(rect, paint);
      canvas.drawImageRect(mask, maskSourceRect, rect, paint);

      //Image
      Size inputSize = Size(image.width.toDouble(), image.height.toDouble());
      final FittedSizes fittedSizes =
          applyBoxFit(BoxFit.cover, inputSize, outputSize);
      final Size sourceSize = fittedSizes.source;
      final Rect sourceRect =
          Alignment.center.inscribe(sourceSize, Offset.zero & inputSize);

      canvas.drawImageRect(
          image, sourceRect, rect, paint..blendMode = BlendMode.srcIn);
      canvas.restore();
    }
  }

Result: