// intersection of lines p1..p2 and p3..p4
function line_intersection_2d(p1,p2,p3,p4) = [
// from https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line
// intersection of lines p1..p2 and p3..p4
function line_intersection_2d(p1,p2,p3,p4) = [
// from https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line