2D Vector Drawing Challenge / options

Godot Version

4.2.2

Question

The challenge is to draw something like a specialized border line along a polygon.

The border line which i strive for is:
expected

so the areas i am facing look like:
circle_area_2

They are crafted line2d’s from supposed polygons.

If we look at the overall points, we see that they are not really symmetrical or nice to work with:

circle_area

These are made from draw_multiline() ( basically a Dashed line )

If we would use _Draw() then it means that we have to recalculate every line and cut these, and then also add the second center line.

i can only imagine this would cause a lot of lagg due to gdscript calculations and calls.

What other alternatives do we have to efficiently create such special designed lines ?

Perhaps with shaders ?