particle rotational movement tracking

Hello!

I would like to track the rotational movement of a circular particle 2D, by for example, highlighting a radius shaped line of the particle, from the center to the boundary.

How do I achieve this with my code? Because I find myself losing the information of the highlighted line when it rotates…

Do i have to draw a line of to pinpoint all of the nodes that have to be highlighted??

Regards

Puigar