Getting intersected faces by area


I have implemented the rough lasso selection.
I would like to make the area selected with different color.
I can’t be sure how to call that. But seems “multiple intersected faces”.

Please help me with this.

I think for this you would need a spatial index for the geometry, that you can intersect the lasso shape with. You would also need to generate a proper representation of the lasso geometry. It’s not trivial.