Make greeter window fullscreen

[aleasto]

Only fullscreen clients can decide the output display on wayland

Fixes #1672

[aleixpol]

This fix is wrong though. We are not using xdg shell so the premise of "only fullscreen windows choose output" doesn't apply. It should either be using layer shell or xdg fullscreen, on either this change shouldn't make a difference (at best) or it broke for other use cases.

I'd suggest reverting this and taking some time to understand what you are seeing.

[aleasto]

This change fixes it for QT_WAYLAND_SHELL_INTEGRATION=layer-shell

[Vogtinator]

This fix is wrong though. We are not using xdg shell so the premise of "only fullscreen windows choose output" doesn't apply. It should either be using layer shell or xdg fullscreen, on either this change shouldn't make a difference (at best) or it broke for other use cases.

IMO this fix is not wrong in any case, as we want the greeter to be fullscreen (except maybe for test mode? Debatable). According to the QWindow::show doc:

This is equivalent to calling showFullScreen(), showMaximized(), or showNormal(), depending on the platform's default behavior for the window type and flags.

Currently this defaults to showNormal() on the wayland platform.

[aleasto]

This change fixes it for QT_WAYLAND_SHELL_INTEGRATION=layer-shell

Well, I went to double check and it doesn't. I must have been trying with QT_WAYLAND_SHELL_INTEGRATION=xdg-shell which I can confirm double-checked is fixed by this

[Vogtinator]

To clarify, it's still broken with QT_WAYLAND_SHELL_INTEGRATION=layer-shell but works with xdg-shell now?

[aleasto]

Yea. Previously both showed the behaviour of spawning both windows in the same screen, as per my screenrecording in #1672

[Vogtinator]

Can be reproduced easily by using dbus-run-session kwin_wayland --wayland-display $WAYLAND_DISPLAY and then WAYLAND_DISPLAY=wayland-1 QT_WAYLAND_SHELL_INTEGRATION=layer-shell ./src/greeter/sddm-greeter --test-mode.

With WAYLAND_DEBUG=1, it shows that it does not specify an output on layer creation:

zwlr_layer_shell_v1@24.get_layer_surface(new id zwlr_layer_surface_v1@38, wl_surface@43, nil, 2, "window")

[Vogtinator]

Works with this patch to layer-shell-qt:

diff --git a/src/qwaylandlayersurface.cpp b/src/qwaylandlayersurface.cpp
index dd17aa0..e172b52 100644
--- a/src/qwaylandlayersurface.cpp
+++ b/src/qwaylandlayersurface.cpp
@@ -25,6 +25,10 @@ QWaylandLayerSurface::QWaylandLayerSurface(QWaylandLayerShell *shell, QtWaylandC
 
     wl_output *output = nullptr;
     QScreen *screen = interface->desiredOutput();
+    if (!screen) {
+        screen = window->window()->screen();
+    }
+
     if (screen) {
         auto waylandScreen = dynamic_cast<QtWaylandClient::QWaylandScreen *>(screen->handle());
         // Qt will always assign a screen to a window, but if the compositor has no screens available a dummy QScreen object is created

That would be a rather big oversight though, so I wonder whether that was intentionally not done.

[aleasto]

Yes that works on my test set up.

[Vogtinator]

I opened https://invent.kde.org/plasma/layer-shell-qt/-/merge_requests/26 for discussion