Fix the qscreen manual test for separate X screens

It is fully possible to show a window on all the connected screens
even when the screens are not virtual siblings, i.e. they do not
form one big desktop. When X is configured to use a separate screen
for each physical screen, it becomes essential to do setScreen()
either directly or via QDesktopWidget in case of widgets. The original
code attempting to call QWindow::setScreen() cannot succeed since there
is no QWindow available before the widget is shown. This is easy to
work around.

The app now works identically in all cases.

Change-Id: I519ca0c0109c68aac2f2d4e6972d14b55767b403
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

2 files changed, 14 insertions, 19 deletions

diff --git a/tests/manual/qscreen/README b/tests/manual/qscreen/README
index 5f5da17293..cd1324276d 100644
--- a/tests/manual/qscreen/README
+++ b/tests/manual/qscreen/README
@@ -20,14 +20,10 @@ create two windows, and will center one each screen, by setting the geometry.
 
 Alternatively you can configure xorg.conf to create separate screens for each
 graphics card; then the mouse cursor can move between the screens, but
-application windows cannot: each app needs to be started up on the screen that
-you want to run it on. In either case, ideally this test app ought to create
-two windows, one on each screen; but in fact, it can do that only if the
-screens are virtual siblings. If they are on different Displays, the second
-Display is not accessible to the QXcbConnection instance which was createad on
-the first Display. It can be considered a known bug that the API appears to
-make this possible (you would think QWindow::setScreen might work) but it
-isn't possible.
+application windows cannot: each app needs to be started on the screen that
+you want to run it on (by specifying e.g. DISPLAY=:0.1 for the second screen),
+or the application has to set the desired screen via QWindow::setScreen() before
+showing the window.
 
 The physical size of the screen is considered to be a constant. This can create
 discrepancies in DPI when orientation is changed, or when the screen is
diff --git a/tests/manual/qscreen/main.cpp b/tests/manual/qscreen/main.cpp
index 6f672ee422..1047ffcdfc 100644
--- a/tests/manual/qscreen/main.cpp
+++ b/tests/manual/qscreen/main.cpp
@@ -38,6 +38,7 @@
 #include <QDebug>
 #include <QFormLayout>
 #include <QLineEdit>
+#include <QDesktopWidget>
 
 int i = 0;
 
@@ -66,19 +67,17 @@ void screenAdded(QScreen* screen)
     w->layout()->insertRow(0, "virtualSiblings", siblingsField);
     updateSiblings(w);
 
-    // This doesn't work.  If the multiple screens are part of
-    // a virtual desktop (i.e. they are virtual siblings), then
-    // setScreen has no effect, and we need the code below to
-    // change the window geometry.  If on the other hand the
-    // screens are really separate, so that windows are not
-    // portable between them, XCreateWindow needs to have not just
-    // a different root Window but also a different Display, in order to
-    // put the window on the other screen.  That would require a
-    // different QXcbConnection.  So this setScreen call doesn't seem useful.
-    //w->windowHandle()->setScreen(screen);
+    // Set the screen via QDesktopWidget. This corresponds to setScreen() for the underlying
+    // QWindow. This is essential when having separate X screens since the the positioning below is
+    // not sufficient to get the windows show up on the desired screen.
+    QList<QScreen *> screens = QGuiApplication::screens();
+    int screenNumber = screens.indexOf(screen);
+    Q_ASSERT(screenNumber >= 0);
+    w->setParent(qApp->desktop()->screen(screenNumber));
 
-    // But this works as long as the screens are all virtual siblings
     w->show();
+
+    // Position the windows so that they end up at the center of the corresponding screen.
     QRect geom = w->geometry();
     geom.setSize(w->sizeHint());
     if (geom.height() > screen->geometry().height())