Add the ability to re-run layout for compound node children.

[aindlq]

I'm trying to do some ad-hock collapse/expand feature for compound nodes.

Collapse is done with changing position of all compound node children to one point:
elem.descendants().positions(elem.position());

And then, on expand, I'm trying to re-run layout over all node children:
elem.descendants().layout({name: 'cose-bilkent'});

Reading the http://js.cytoscape.org/#eles.layout it seems that it should be possible to layout only some collection of nodes. But it seems this doesn't work for compound node children.

See http://jsbin.com/didunafota/1/edit?html,output

[maxkfranz]

Not an issue with Cytoscape. If you try with a different layout like circle, you'll notice your demo works fine.

See cytoscape/cytoscape.js-cose-bilkent#14

[maxkfranz]

@aindlq In the meantime, I suspect you could just run the random layout before cose-bilkent and it would work OK as a workaround. You can use the boundingBox to constrain the layout bounds.

[maxkfranz]

@aindlq Or rather than running a layout to expand, you could save the relative positions of each child before collapsing. Then you can restore that relative position on the expand action.