Enable transparent background for GUI tooltips

[kleonc]

Fixes #76071.

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.2.

[tropical32]

Would this also need to be applied to MenuButton and OptionButton?

[kleonc]

Would this also need to be applied to MenuButton and OptionButton?

For their PopupMenus (obtainable with MenuButton.get_popup()/OptionButton.get_popup()), yes.

In general any Viewport (Popup extends Viewport) can have such issue.

When such Nodes are user-created then the relevant Viewport's background transparency can be enabled manually though, see: #81669 (comment). So for runtime things it should already be solvable by the user. In case of nodes using a Viewport themselves (like MenuButton, OptionButton or ColorPickerButton) the background transparency can be still enabled easily as long as there's a method like get_popup allowing to obtain such Viewport. Tooltips aren't directly created by the user so this was kinda a different case (default tooltip Popup is not easily obtainable AFAICT).

But in-editor created nodes don't have transparency enabled (at least in most cases), meaning e.g. a custom editor Theme with transparent parts for Popups currently have the same issue:

So this editor part probably needs addressing.

The simplest solution (for both editor and user projects) would be to change Viewport background transparency to be enabled by default in some cases (like for Popups drawing StyleBoxes). I guess the question is whether doing so could hurt the performance in general case. If yes, then it probably shouldn't be done (then the question would be whether editor stuff should enable backgroud transparency by default).