Subflows with MRTREE algorithm - incorrect position and width calculation

[belamajoros]

Hi, when using the mrtree algorithm with subflows, the position of the nodes inside of the subflow is incorrectly calculated. Also in case of a subflow inside a subflow, the width of the parent subflow is also incorrectly calculated and part of the child subflow gets placed outside of its parent subflow.

example for elklive:
{
id: "root",
layoutOptions: {
'algorithm': 'mrtree',
'elk.direction': 'DOWN',
'elk.spacing.nodeNode': '50',
},
children: [
{ id: "n1", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP'} },
{ id: "n2", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP'} },
{ id: "n3", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP', 'elk.algorithm': 'mrtree', 'elk.direction': 'DOWN'}, children: [
{ id: "n7", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP' }},
{ id: "n8", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP'}}
]},
{ id: "n4", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP'} },
{ id: "n6", width: 30, height: 30, layoutOptions: { 'elk.alignment': 'TOP'} }
],
edges: [
{ id: "e1", sources: [ "n1" ], targets: [ "n2" ] },
{ id: "e4", sources: [ "n1" ], targets: [ "n3" ] },
{ id: "e3", sources: [ "n2" ], targets: [ "n4" ] },
{ id: "e5", sources: [ "n1" ], targets: [ "n6" ] },
]
}

Screenshots

This in itself would not be a huge problem as I am able to correctly position the nodes inside the subflow after calling elk.layout().

Regarding the incorrect parent subflow width:

Screenshots
If the subflow is on the right side of the branch (incorrect):

If the subflow is on the left side of the branch (correct):

ELK Version
0.9.3
algorithm: mrtree

[Eddykasp]

This is indeed a bug, minimally reproduced in this example. The problem seems to be in the position and size calculation of the graph after layout.

[seloElo]

Thanks for the issue raising on github you saved me an headache on my graphs...
Was this fixed on elk 0.10 but not packaged in the js package?

[Eddykasp]

It should also be fixed in elkjs 0.10.0. If it's not I'll have to look into whether there is a separate issue or whether something went wrong during transpilation. Do you have an example that is broken?

[seloElo]

Used the example of react-flow let me know if this not okay.

https://stackblitz.com/edit/xfsrw92e?file=App.tsx

Same example if I use layered, we can see that the weird padding is not there:

[Eddykasp]

There is definitely something wrong somewhere, I'm investigating this and will keep you updated

[Eddykasp]

I can now confirm that it is broken in elkjs 0.10.0, but the behaviour is different to the bug in 0.9.3. I need to reconfirm that Java ELK 0.10.0 behaves correctly and then hopefully I can figure out what is causing the discrepancy.

[Eddykasp]

I've created a PR (eclipse-elk/elk#1142) that should fix this issue. It was caused by separated components i.e. multiple tree layouts. They are layouted individually and then put back together. In this step, the bounds of the packed graph was not recomputed but rather the bounds of the components were merged, causing the described issue in the result.