Shape.stagepos does not consider rotation

[ChristerNilsson]

This is what I'm trying to do:
https://christernilsson.github.io/Lab/2018/037-Shortcut-GPS/index.html?radius1=10&nr=6A&level=6&seed=0.1&speed1=0.025&speed2=0.0033

The big circle C is rotating.
The three smaller circles, C1, C2 and C3, are attached to the big circle.
The three smaller circles are also rotating.
The smaller circles are actually two half circles.

To be able to check if a point is contained in a half circle, I guess the half circle and the point must be unrotated and unmoved back to the origin. The other approach would be to transform all points in state.vectors.

I've been developing in p5, but the lack of an object model and problem with translate, rotate and scale together with mouse coordinates, makes me look for a better alternative. rune.js almost fulfills my wish list.