Flutter overflow: hidden analogue

I think it's easier to use clipBehavior: property in container

Container(
clipBehavior: Clip.hardEdge,
height: 400,
width: 400,
child :TheTransformingChild(),)

There is - what you're looking for is a combination of OverflowBox or SizedOverflowBox and ClipRect, or ClipOval, or ClipPath, or ClipRRect etc.

I'd recommend looking through the painting and layout sections of the flutter widget catalog (and the rest of it as well) as it generally does a pretty good job of showcasing the widgets you need.