Caution: does this work when the 3D map is activated - given that that is a QOpenGL widget the behaviour may not be what you expect!

I would also note that setting the map background colour currently does not set it for the 3D map - it should do and I've previously prototyped code that did do it - IIRC you just need to find the place(s) where glClearColor(0.0, 0.0, 0.0, 1.0); is done and convert that to glClearColor(color.redF(), color.greenF(), color.blueF(), color.alphaF()); where color is the QColor that has been set for the map background. I see that is being done in three places but one of them is for the error message - and you might want to change that case to something else like a nice tasteful yellow text on a red background for both the 2D and 3D maps... 😀

Caution: does this work when the 3D map is activated - given that that is a QOpenGL widget the behaviour may not be what you expect!

No this currently only effects the 2D map. Unsurprisingly, as Preferences > Mapper Colors > Background color has no influence on the background of the 3D map before this PR anyway.

I am investigating the 3D map for the potential of tying everything together, but I would argue that even failing that, this PR would be fine in the sense that it adds the functionality to the 2D map without impacting the 3D map.

I would also note that setting the map background colour currently does not set it for the 3D map - it should do and I've previously prototyped code that did do it - IIRC you just need to find the place(s) where glClearColor(0.0, 0.0, 0.0, 1.0); is done and convert that to glClearColor(color.redF(), color.greenF(), color.blueF(), color.alphaF()); where color is the QColor that has been set for the map background. I see that is being done in three places but one of them is for the error message - and you might want to change that case to something else like a nice tasteful yellow text on a red background for both the 2D and 3D maps... 😀

I'm experimenting with this for the 3D map. So far I have the 3D map background color properly setting but am not getting transparency working. Will continue poking it.

... but am not getting transparency working....

Yeah that is the exact sort of weirdness you might get - it is down to the way the OpenGL image is (blitted?) onto the other widgets - and it may also have OS dependent behaviour:

This might be fouling things for you as well:

I've fixed the 3D map background to work with colors as well as alpha values. This works at least for Win11. I haven't tested on other OSes yet and as you've mentioned SlySven, these things can get tricky depending on OS.

It's also possible that setting this flag (setAttribute(Qt::WA_AlwaysStackOnTop);) will create issues. I'll try to test it more, but I'm going to be quite busy for the next two weeks so it'll be a while before I can pick this up again.

I would appreciate some testing! <3

Edit: Tested works with Fedora / Wayland

/create links

works great!