Bring the greeter on primary screen to the front

[liangjs]

When there are multiple monitors connected, sddm-greeter creates new views for each screen, and activates the primary one to focus on its password field. However, if the monitors are initially setup to display the same content, different views will overlap with each other. The views created by non-primary screens may be placed on top of the primary view. In such cases, the primary view will be focused but not visible to the user.

This is fixed by calling view->raise for the primary screen. The primary view should be raised whenever a new screen is added, in order to avoid being covered by the newly created view.

Fixes: #612 #514

[arrowd]

How does one configure X server to reproduce this problem?

[liangjs]

How does one configure X server to reproduce this problem?

It can be reproduced by connecting two monitors (for example, one builtin and one external) and then start sddm.

[arrowd]

I wonder if it is SDDM's own responsibility to start X server either in duplicated or Xinerama mode? Or maybe even a theme may request that from the daemon?

Some themes might be prepared for the Xinerama scenario, for example by drawring only the background on the second screen.

[liangjs]

I wonder if it is SDDM's own responsibility to start X server either in duplicated or Xinerama mode? Or maybe even a theme may request that from the daemon?

Some themes might be prepared for the Xinerama scenario, for example by drawring only the background on the second screen.

The SDDM greeter creates views for each screen, and then each view is managed by the theme separately.

sddm/src/greeter/GreeterApp.cpp

Lines 277 to 283 in 50409a3

	// Create views
	const QList<QScreen *> screens = qGuiApp->primaryScreen()->virtualSiblings();
	for (QScreen *screen : screens)
	addViewForScreen(screen);
	// Handle screens
	connect(qGuiApp, &QGuiApplication::screenAdded, this, &GreeterApp::addViewForScreen);

I don't know much about Xinerama. If it configures X server in a way that only one screen will be detected by SDDM, a single view will be created.

[Vogtinator]

The primary view should be raised whenever a new screen is added, in order to avoid being covered by the newly created view.

Not sure I agree with this - effectively this means whenever a screen is plugged in, the primary screen (essentially random) gets focus. Ideally focus shouldn't change, unless the new screen is the primary one, which is what the code does.

However, if the monitors are initially setup to display the same content, different views will overlap with each other. The views created by non-primary screens may be placed on top of the primary view.

This sounds like the root cause. What about detecting whether a view overlaps anonther one (completely) and then ignoring it?
Can we assume that after a view appears, its position will not change?

[lianghwe]

Why do we create multiple views when two monitors showing the same content? I think that is the problem.

[Vogtinator]

Why do we create multiple views when two monitors showing the same content? I think that is the problem.

In the case that all monitors have the same geometry, sharing would be possible, but in any other case it's not. To make it consistent, it's never shared.