Per-element values, specified by functions

[maxkfranz]

Some of the layout options should be able to be specified on a per-element basis, rather than a graph-wide basis. For example, the edge length should be able to be specified as a function(edge) : double in order to create an edge-weighted result (i.e. the edge length varies by score).

I think that this feature may have existed before in COSE, but it may have been lost during the refactoring into layout-base and cose-base.

The following options should allow for functions:

• nodeRepulsion : function(node) : double
• idealEdgeLength : function(edge) : double
• edgeElasticity : function(edge) : double

What are your thoughts, @ugurdogrusoz?

I assume that making the change within this project would enable the function options within any of the COSE family of layouts, which is why I'm filing the issue here.

I'm tagging @chrtannus, as he's interested in this topic.

[maxkfranz]

For reference, the built-in version of COSE allows for functions on the above options, although it is generally not as sophisticated as the later versions: https://js.cytoscape.org/#layouts/cose

It would be great to have the ability to use these function options. I think that's the only thing missing from the later COSE versions that the built-in version has. I'm in the process of evaluating the removal/replacement of the old COSE in Cytoscape.js v4, and not supporting functions would be a blocker.

[ugurdogrusoz]

@maxkfranz @chrtannus We never had this in cose-bilkent but we had request for it (cytoscape/cytoscape.js-cose-bilkent#1). Anyway we could implement this. Is there a strict timeline for v4 release?

[maxkfranz]

No, there isn't a strict timeline for v4. However, @chrtannus and I would like to use some of your latest layouts in some of the new Cytoscape cloud projects (e.g. Cytoscape Explore, which is like Google Docs for graphs). For the new cloud projects, having the function options is necessary. We'd really like to use FCoSE, for example, but we need to be able to have edge-weighted results.

The experimentation of layouts like FCoSE in Cytoscape Explore will help to inform how we move forward with Cytoscape v4 w.r.t. FD layouts -- like a case study.

[hasanbalci]

Progress update:

• I added per-element value functionality for nodeRepulsion, idealEdgeLength and edgeElasticity in layout-base.
• I also integrated this functionality into fCoSE, CoSE-Bilkent and CoSEP layouts. fCoSE v2.0.0 is released with this functionality as well as support for user-specified placement constraints.
• Per-element value functionality is currently only available in the unstable branches of CoSE-Bilkent and CoSEP layouts.
• I will also integrate this functionality to CiSE layout.