Hi there. I wanted a smooth animation for my pie charts, where I wanted to be able to use any d3.easing. The problem is that once you have more than one element in the pie I didn't know how to give the whole pie an animated feeling (similar to what one can do with a single arc), so I wrote some code to test out my ideas. You can see it working on https://observablehq.com/@carlos-vazquez/stacking-transitions. It also works for stacked bar charts ()