Detecting points on the edges of a polygon

[JvandenAssum]

Would it be possible to alter the visibile_vertices function to detect points on the edge of a polygon as well?

For example in the following example:

p1 = vg.Point(0.20,0.1)
p2 = vg.Point(0.50,0.5)
p3 = vg.Point(0.49,0.5)

polys = [[(0,0),(1,0),(0,1)]]
G = vg.Graph(polys)

vg.visible_vertices.visible_vertices(p1,G1,destination= p2) will return [Point(0.00, 1.00), Point(0.00, 0.00), Point(1.00, 0.00)]
vg.visible_vertices.visible_vertices(p1,G1,destination= p3) will return [Point(0.49, 0.50), Point(0.00, 1.00), Point(0.00, 0.00), Point(1.00, 0.00)]

Would it be possible to maybe alter the visibile_vertices function to get [Point(0.00, 1.00), Point(0.00, 0.00), Point(1.00, 0.00), Point(0.50, 0.50)] from vg.visible_vertices.visible_vertices(p1,G1,destination= p2) as well? Or is there another way to achieve this result?