Inertial mouse pointing

Basically just want a trackball mode for the trackpad.
I already have a trackball. It will never glide as smoothly as software.
Apologies if this is a duplicate; I couldn't find the original, nor the feature if it was added.

sorry, I don’t think this is something I will add. I evaluated this ~10 years ago but came to the conclusion that it’s too much effort for me.