Fix Embedded Game disappear when not focused on KDE 5

[Hilderin]

• Fixes Embedded Game window stops rendering when editing other nodes in the editor #102043

This PR resolves the issue where the Embedded Game Window disappears when the Floating Game Window is not focused on Xorg/Kubuntu.

On Ubuntu 24.04 Gnome and Fedora 40 KDE Plasma 6.1.5, a window of type _NET_WM_WINDOW_TYPE_UTILITY remains visible even when the parent window is not focused. However, on Kubuntu/KDE (tested on Kubuntu 22.04 and KDE Plasma 5.24.7), this type of window is hidden when the parent window loses focus, causing the Embedded Game Window to disappear.

To address this, this PR changes the window type to _NET_WM_WINDOW_TYPE_NORMAL. A side effect of this change is that the Embedded Game Window now appears in the alt-tab window list. I tested several window types, but none could simultaneously prevent the window from disappearing when the parent is not focused and exclude it from the alt-tab list. Although the _set_window_taskbar_pager_enabled method was designed for this purpose, it does not seem to work on Kubuntu/KDE. Given the circumstances, I believe this trade-off is acceptable.

[akien-mga]

A side effect of this change is that the Embedded Game Window now appears in the alt-tab window list. I tested several window types, but none could simultaneously prevent the window from disappearing when the parent is not focused and exclude it from the alt-tab list. Although the _set_window_taskbar_pager_enabled method was designed for this purpose, it does not seem to work on Kubuntu/KDE. Given the circumstances, I believe this trade-off is acceptable.

I'll try to test too in coming days, but if the problem is specific to KDE 5, maybe we can test if we're running it on startup, and use this workaround only then.

It can be checked (possibly not reliably) with the environment variables XDG_CURRENT_DESKTOP and KDE_SESSION_VERSION. On my Fedora 41 KDE Wayland:

$ echo $XDG_CURRENT_DESKTOP
KDE
$ echo $DESKTOP_SESSION
plasma
$ echo $KDE_SESSION_VERSION
6

But I'll also test this PR on KDE 6 and see if the tradeoff for the workaround is indeed acceptable, so we don't need to make the logic too complex.

[Hilderin]

I'll try to test too in coming days, but if the problem is specific to KDE 5, maybe we can test if we're running it on startup, and use this workaround only then.

I don't have enough installed systems to be 100% sure that the issue is really KDE 5 specefic. Right now, it's the only system where the issue was reported. But if you can test it on your side, it could give us more information, thanks. I have no problem to add a check on a desktop version.

[akien-mga]

I tested this on KDE Plasma 6.2.5 on Fedora 41, and indeed the change seems to be a bit of a downgrade. Having the embedded game appear when alt-tabbing isn't too bad, but there are fade in/fade out animations when switching between Game and 2D/3D/Script tabs, which might bother users and break the "magic" of having the window embedded.

4.4 beta 2:

2025-02-04.23-42-24.mp4

This PR:

2025-02-04.23-43-44.mp4

So I think a surgical change only for KDE 5 might be better to start with, and we can re-evaluate if we get other bug reports for other desktop environments.

I tested this, which restores the previous behavior for me on KDE 6. I don't have a system with KDE 5 to test with.

diff --git a/platform/linuxbsd/x11/display_server_x11.cpp b/platform/linuxbsd/x11/display_server_x11.cpp
index 8244e48c5a..95181a1c81 100644
--- a/platform/linuxbsd/x11/display_server_x11.cpp
+++ b/platform/linuxbsd/x11/display_server_x11.cpp
@@ -6276,7 +6276,7 @@ DisplayServerX11::WindowID DisplayServerX11::_create_window(WindowMode p_mode, V
 			}
 		}
 
-		if (wd.is_popup || wd.no_focus) {
+		if (wd.is_popup || wd.no_focus || (wd.embed_parent && !kde5_embed_workaround)) {
 			// Set Utility type to disable fade animations.
 			Atom type_atom = XInternAtom(x11_display, "_NET_WM_WINDOW_TYPE_UTILITY", False);
 			Atom wt_atom = XInternAtom(x11_display, "_NET_WM_WINDOW_TYPE", False);
@@ -6422,6 +6422,7 @@ DisplayServerX11::DisplayServerX11(const String &p_rendering_driver, WindowMode
 	KeyMappingX11::initialize();
 
 	xwayland = OS::get_singleton()->get_environment("XDG_SESSION_TYPE").to_lower() == "wayland";
+	kde5_embed_workaround = OS::get_singleton()->get_environment("XDG_CURRENT_DESKTOP").to_lower() == "kde" && OS::get_singleton()->get_environment("KDE_SESSION_VERSION") == "5";
 
 	native_menu = memnew(NativeMenu);
 	context = p_context;
diff --git a/platform/linuxbsd/x11/display_server_x11.h b/platform/linuxbsd/x11/display_server_x11.h
index 166b2cb57b..edd70d454d 100644
--- a/platform/linuxbsd/x11/display_server_x11.h
+++ b/platform/linuxbsd/x11/display_server_x11.h
@@ -338,6 +338,7 @@ class DisplayServerX11 : public DisplayServer {
 	bool xinerama_ext_ok = true;
 	bool xshaped_ext_ok = true;
 	bool xwayland = false;
+	bool kde5_embed_workaround = false; // Workaround embedded game visibility on KDE 5 (GH-102043).
 
 	struct Property {
 		unsigned char *data;

[Hilderin]

Indeed, the fade in/fade out animations seems a bad downgrade. I don't have access anymore to a KDE 6 Desktop right now, can you confirm that the original issue when using the Floating Window does not occur on KDE 6 on your side? Because if we can only reproduce the issue on KDE 5, I think your suggestion is good.

[akien-mga]

Yeah I can't reproduce the linked issue on KDE 6.

[akien-mga]

I went ahead and included my diff to make it specific to KDE 5. Let's keep an eye out for similar bug reports for other desktop environments to see if we need to extend the heuristics.

[Repiteo]

Thanks!

[Hilderin]

Thanks @akien-mga to test and finish this PR.