How can I limit the travel range of an icon?

I'm trying to repurpose the circular slider as a temperature thermostat. Is there a way I can limit the travel of one icon to only traveling along a half circle? Or better yet that only a half of a `bgCircle` gets rendered?

Start by reading the circular slider entry point and the handling of the icon and `bgCircle` mentioned in the issue. Determine whether limiting one icon to a half circle or rendering only half of `bgCircle` is the intended feature, then verify the resulting thermostat-style behavior against the existing slider behavior.

Written by the indexing model from the issue text.