2019.2.5f1: No UI buttons, no gizmos, unusable

[JillCrungus]

SabreCSG is completely unusable in Unity 2019.2.5f1, the UI does not show and nor do any gizmos show on CSGModels.

The console warns that SceneView.onSceneGUIDelegate is obsolete.

[pjbaron]

Same in 2019.2.10f1

I'm looking at the errors and they're mostly trivial to fix but some parts like this:
if (!EditorHelper.SceneViewHasDelegate(OnSceneGUI)) (CSGModel.cs:1345)
inspect the list of delegates for the SceneView. That doesn't appear to be possible any more (the new 'SceneView.duringSceneGui' can only be used on the left of a += or -= instruction)

This was always a bit hacky, the comment explains:

// Make sure the events we need to listen for are all bound (recompilation removes listeners, so it is
// necessary to rebind dynamically)

So maybe someone can answer the question: in Unity 2019 does recompilation still remove listeners?
If not then we can just add the delegate once in a constructor or init function.

If that won't work then (unless SceneView contains a way to check if a delegate has already been assigned - I flicked through the docs but didn't see one) we will need to maintain a list of which delegates were added, and reset it when compilation occurs.

[Henry00IS]

That's just been fixed! It was really a puzzle, but I found a simple workaround (see PR). Have fun in 2019! 😁