Join simple polygons and draw the resulting contours in Eyeshot

Question

What is the simplest way to join a collection of polygons and draw the resulting contour using Eyeshot? So far I was able only to get filled regions but I am interested in the merging of the contours.

Answer 1

I came up to this solution. To display the polygons simply iterate through the joined regions, iterate through the ContourList and create the LinearPaths.

private List<PolyRegion2D> Joiner(IEnumerable<Polygon2D> polygons) {
        // The resulting polygons are unconnected
        List<PolyRegion2D> res = new List<PolyRegion2D>();

        // Put every polygon in a region to do the unions.
        LinkedList<PolyRegion2D> polygonRegions = new LinkedList<PolyRegion2D>();
        foreach (Polygon2D polygon in polygons) {
            polygonRegions.AddLast(new PolyRegion2D(new Polygon2D[]{polygon}));
        }

        while (polygonRegions.Count > 0) {
            PolyRegion2D first = polygonRegions.First.Value;
            polygonRegions.RemoveFirst();
            PolyRegion2D union;
            LinkedListNode<PolyRegion2D> connected = FindConnected(first, polygonRegions, out union);
            if (connected == null) {
                // Unconnected polygon
                res.Add(first);
            } else {
                // Intersection found
                polygonRegions.Remove(connected);
                polygonRegions.AddFirst(union);
            }
        }

        return res;
    }

    private LinkedListNode<PolyRegion2D> FindConnected(PolyRegion2D poly, LinkedList<PolyRegion2D> polys, out PolyRegion2D union) {
        LinkedListNode<PolyRegion2D> node = polys.First;
        while(node != null){
            PolyRegion2D[] union_ = PolyRegion2D.Union(poly, node.Value);
            if (union_.Length == 1) {
                union = union_[0];
                return node;
            }
            node = node.Next;
        }
        union = null;
        return null;
    }