How to get rounded corner for given MagicImage

[pchandoria]

There is no clear information available on how to get rounded corner for given image.
Somewhere on the internet I found this suggestion but I have to idea how to map it equally to .NET. Besides that it should be really simple API similar to css border-radius

magick thumbnail.gif
( +clone -alpha extract
-draw 'fill black polygon 0,0 0,15 15,0 fill white circle 15,15 15,0'
( +clone -flip ) -compose Multiply -composite
( +clone -flop ) -compose Multiply -composite
) -alpha off -compose CopyOpacity -composite rounded_corners.png

I also tried this
new Drawables().RoundRectangle(0, 0, width, height, 10, 10).Draw(magicImage);
but it actually rendered rounded corner black image with corners showing actual image. I guess we just need to flip it and set corner transparent.
Please help.

[pchandoria]

We are in 2025 and still there is no simple working solution to get rounded corner using MagicImage. Shouldn't it be a simple API using drawable?

I tested solution discussed in #253, unfortunately it does nothing actually.
The only thing works incorrectly is
new Drawables().RoundRectangle(0, 0, finalSize.Width, finalSize.Height, 25, 25).Draw(magicImage);
but it generates output in unexpected way

for the original image something like this