fix(snapping): fix bug when the map contains a multi-geometry features (MultiPolygon / MultiLine)

[smeijer]

MultiPolygon layers trigger a bug in the snapping algorithm. This PR fixes this by breaking the MultiPolygon layers up before adding to the _snapList.

Fixes #257. More details explained in this comment: #257 (comment)

[smeijer]

Related PR: #279

I haven't tested, but I don't expect that both are needed. The scope of #279 looks larger by adding MultiPolygon support, whereas this PR exists to "just fix the snapping bug #257".

My first idea of fixing the snapping bug was also to loop over the rings in the _calcLayerDistances method. But I decided to take the more simple approach of pre-fixing it in the _snapList for performance purpose. (create a couple of extra layers upon init vs an extra loop on every mouse-move).

That being said, maybe it's needed to add support for MultiPoint or MultiLine the same way. But again, haven't tested those. Adding support for them in the same way should be an easy job though.

[smeijer]

Turned out, MultiPoint works as expected. Not causing any troubles.

MultiLine lacks the same support. I'll push an update in a few minutes.

[smeijer]

Any chance this one can get merged? I'm currently using my own fork. Would be nice if I could use the main branch again.

[smeijer]

Rebased on develop

[codeofsumit]

@smeijer thank you for your work on this.
Just to clarify: if we had proper multi polygon/line support, this would still be needed (as it's part of the solution) - do you agree?

[codeofsumit]

I've noticed some bugs in this PR.

Currently, you can't snap a hole to it's outer polygon ring, in this PR that is now possible but not to all sides.
Also: a vertex of a polygon can now be snapped to it's original position which should not be possible.

But this PR really helps me in getting my head back into this issue 👍 - I'm looking at multi polygons today and hope to make some progress