React to changing winId?

[almarklein]

This is mostly an issue with Qt, but possibly also other backends. Until now, we've assumed that the window-id does not change after it is obtained.

What we do know:

• The Qt docs say that it can change, but they don't state when.
• Calling winId() on a Qt widget, turns it into a native widget (WA_NativeWindow).
• This has some nasty side-effects, e.g. a known issue is that to move it in a dock, you have to click it before you can drag.
• Other odd behavior has been observed (on Windows) when winId() is called, see [Qt] multiple window/docking support #55

Some questions:

• Under what circumstances can the winow-id change?
• Does this also apply to other gui backends?
• We use the window-id to create a surface object. Does the changed window-id affect that surface object, or can we just keep using it?
• Do the observed issues when winId is called relate to us not updating to new winid?
• Should we react to a changing window-id?