When nodes are connected across multiple layers, draw edges once per layer, with appropriate color coding

[albertocottica]

Sometimes we want to visualize two projects simultaneously; other times a single project has a natural partition (like POPREBEL and its fora in different languages). It may happen that two nodes are connected across more than one layer. It is natural to represent layers by color-coding edges.

In this case, we want to:

1. Draw one edge per layer.
2. Each edge should be appropriately color-coded.

Layout algos like FMˆ3 in Tulip make sure that parallel edges are not superimposed on each other, so 1 should be covered. At the moment, 2 is not working. Try:

1. Impose the layout on the root, before stacking (!)
2. Color-code the root
3. Create the various stacked graphs, making the new edges inherit the color of the unstacked
4. Create the subgraphs by level of K on the separate layers, and compare the visualizations there.

The resulting hierarchy is:

• root
  • layer 1 (for example a project)
    • stacked
      • k= 2
      • k = 3