[SDL3] Modal Window Issue: Parent Window Remains Interactive on Linux but Not Windows

[larks-x]

Hello, when using SDL_SetWindowParent, SDL_SetWindowModal, and SDL_ShowWindow under SDL3 to set up a modal window, it works perfectly on Windows. However, on Linux, the parent window of the modal window can still be moved, maximized, or minimized. I'm not sure if I missed any configuration settings or if this is a bug specific to Linux.

SDL3 version:3.2.16
Ubuntu version 24.04.2 (Both X and Wayland backends have this issue)

[Kontrabant]

I believe that Ubuntu 24.04 is still on GNOME/Mutter 46, which lacks support for the xdg-dialog-v1 protocol needed to properly set modal status on Wayland windows. GNOME 47 and above blocks the parent window when a modal window is open. My own desktop is on Fedora 42, and it definitely works here.

Beyond that, exactly what a compositor does when making a window modal is very much its own policy. For example, KDE supports the protocol as well and will center the modal dialog on the parent and hide the parent in the window switcher, but doesn't block the parent window from being moved or minimized, and there isn't any particular way to override this behavior.

On XWayland, the _NET_WM_STATE_MODAL atom is set, but, as before, if it is ignored or unsupported, there isn't anything we can do.