How to apply ELK layout config to nested nodes and edges

[jwzaden]

I have a diagram with nested nodes, where the nested nodes have edges connecting them. The ELK layout that I have configured works well for nodes and edges that are not nested, but the same config is not being applied correctly to nested nodes. Interestingly, some of the config is applied, like the layout algorithm and direction, but other options like "elk.layered.spacing.nodeNodeBetweenLayers" are not applied.

I have searched through the documentation and issues but haven't found a clear solution. Is there a limitation on nested nodes/edges having the ELK layout applied, and is there something I can do to apply the layout to them?

[martin-fleck-at]

Hi @jwzaden, that is a very interesting question! So I assume you have automatic layout enabled or you trigger the layout explicitly while creating your Elk layout module on the server side through configureELKLayoutModule, is that right?

So the two pieces that are really involved when applying the Elk layout are the Elk Layout Engine that transforms the GModel into an Elk graph and then applies the layout information back to the GModel and the LayoutConfigurator which decides which Elk options are applied when doing the transformation from GModel to Elk graph element. By default, only options on the graph level are applied but maybe some of the options you require also need to applied on a different level (node, edge). Currently, there is no special consideration for nested nodes when performing the transformation to the Elk graph, maybe we are missing something here. It would be great to get your perspective on that.

Please note that we very recently updated the layouting on the client-side and the server-side by updating our Elk.js version to 0.10.1 and allowing the layout engine to take the triggering LayoutOperation as an optional parameter in case of a direct Layout call in order to provide client-side information (viewport size, zoom level etc.).