Introduce QWidget::setScreen

Follows the QWindow semantics, and is a replacement for creating
a QWidget with a QDesktopScreenWidget as the parent.

We can now remove much of the special handling of QDesktopWidget and
the Qt::Desktop window type, and get rid of QDesktopScreenWidget.

Add a manual test that allows local testing. Our CI environments
only have a single screen, and no multi-head display server setup
which is the primary case where QWidget::setScreen is interesting.
For the more common case of a virtual desktop, QWidget::setScreen
has no real impact (just as QWindow::setScreen doesn't).

Change-Id: Id0099e069d316741bacd8c795c396ccad37be297
Fixes: QTBUG-85483
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

5 files changed, 179 insertions, 1 deletions

diff --git a/tests/manual/widgets/kernel/CMakeLists.txt b/tests/manual/widgets/kernel/CMakeLists.txt
index 9be003391d..b4443fa3e2 100644
--- a/tests/manual/widgets/kernel/CMakeLists.txt
+++ b/tests/manual/widgets/kernel/CMakeLists.txt
@@ -3,3 +3,4 @@
 # add_subdirectory(qtooltip) # special case broken in dev
 add_subdirectory(sizeonhide)
 add_subdirectory(layoutreplace)
+add_subdirectory(setscreen)
diff --git a/tests/manual/widgets/kernel/kernel.pro b/tests/manual/widgets/kernel/kernel.pro
index 5dbd25f8bd..236c9ff9d6 100644
--- a/tests/manual/widgets/kernel/kernel.pro
+++ b/tests/manual/widgets/kernel/kernel.pro
@@ -1,2 +1,2 @@
 TEMPLATE = subdirs
-SUBDIRS = qtooltip sizeonhide layoutreplace
+SUBDIRS = qtooltip sizeonhide layoutreplace setscreen
diff --git a/tests/manual/widgets/kernel/setscreen/CMakeLists.txt b/tests/manual/widgets/kernel/setscreen/CMakeLists.txt
new file mode 100644
index 0000000000..cf31341d7c
--- /dev/null
+++ b/tests/manual/widgets/kernel/setscreen/CMakeLists.txt
@@ -0,0 +1,18 @@
+# Generated from setscreen.pro.
+
+#####################################################################
+## setscreen Binary:
+#####################################################################
+
+qt_add_manual_test(setscreen
+    GUI
+    SOURCES
+        main.cpp
+    PUBLIC_LIBRARIES
+        Qt::CorePrivate
+        Qt::Gui
+        Qt::Widgets
+)
+
+#### Keys ignored in scope 1:.:.:setscreen.pro:<TRUE>:
+# TEMPLATE = "app"
diff --git a/tests/manual/widgets/kernel/setscreen/main.cpp b/tests/manual/widgets/kernel/setscreen/main.cpp
new file mode 100644
index 0000000000..70ec067d3d
--- /dev/null
+++ b/tests/manual/widgets/kernel/setscreen/main.cpp
@@ -0,0 +1,156 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtWidgets>
+
+class ScreenWidget : public QWidget
+{
+public:
+    ScreenWidget(QWidget *parent)
+    : QWidget(parent, Qt::Window)
+    {
+        textEdit = new QTextEdit;
+        textEdit->setReadOnly(true);
+
+        QHBoxLayout *layout = new QHBoxLayout;
+        layout->addWidget(textEdit);
+        setLayout(layout);
+    }
+
+    void updateText()
+    {
+        QString text = "<html><body>";
+        text += QString("<p>Screen: %1\n</p>").arg(screen()->name());
+        text += QString("<p>DPR: %1\n</p>").arg(screen()->devicePixelRatio());
+        text += QString("</body></html>");
+
+        textEdit->setText(text);
+    }
+
+private:
+    QTextEdit *textEdit;
+};
+
+class Controller : public QDialog
+{
+    Q_OBJECT
+
+public:
+    Controller()
+    {
+        QPushButton *screenButton = new QPushButton;
+        screenButton->setText("Show on Screen");
+        screenButton->setEnabled(false);
+        connect(screenButton, &QAbstractButton::clicked, this, &Controller::setScreen);
+
+        QPushButton *desktopButton = new QPushButton;
+        desktopButton->setText("Show on Desktop");
+        desktopButton->setEnabled(false);
+        connect(desktopButton, &QAbstractButton::clicked, this, &Controller::setDesktop);
+
+        QPushButton *exitButton = new QPushButton;
+        exitButton->setText("E&xit");
+        connect(exitButton, &QAbstractButton::clicked, QApplication::instance(), &QCoreApplication::quit);
+
+        QHBoxLayout *actionLayout = new QHBoxLayout;
+        actionLayout->addWidget(screenButton);
+        actionLayout->addWidget(desktopButton);
+        actionLayout->addWidget(exitButton);
+
+        QGroupBox *radioGroup = new QGroupBox;
+        radioGroup->setTitle(QLatin1String("Select target screen"));
+
+        QVBoxLayout *groupLayout = new QVBoxLayout;
+        const auto screens = QGuiApplication::screens();
+        int count = 0;
+        for (const auto &screen : screens) {
+            QRadioButton *choice = new QRadioButton;
+            choice->setText(QString(QLatin1String("%1: %2")).arg(count).arg(screen->name()));
+            connect(choice, &QAbstractButton::toggled, this, [=](bool on){
+                if (on)
+                    targetScreen = count;
+                screenButton->setEnabled(targetScreen != -1);
+                desktopButton->setEnabled(targetScreen != -1);
+            });
+            groupLayout->addWidget(choice);
+            ++count;
+        }
+        radioGroup->setLayout(groupLayout);
+
+        QVBoxLayout *layout = new QVBoxLayout;
+        layout->addWidget(radioGroup);
+        layout->addLayout(actionLayout);
+        setLayout(layout);
+    }
+
+private slots:
+    void setScreen()
+    {
+        QScreen *screen = QGuiApplication::screens().at(targetScreen);
+        if (!widget) {
+            widget = new ScreenWidget(this);
+            widget->setAttribute(Qt::WA_DeleteOnClose);
+            widget->setWindowTitle("Normal Window");
+        }
+        widget->setScreen(screen);
+        widget->show();
+        widget->updateText();
+    }
+
+    void setDesktop()
+    {
+        QScreen *screen = QGuiApplication::screens().at(targetScreen);
+        QWidget *desktop = QApplication::desktop(screen);
+        if (!desktopChild) {
+            desktopChild = new ScreenWidget(desktop);
+            desktopChild->setAttribute(Qt::WA_DeleteOnClose);
+            desktopChild->setWindowTitle("Child of a Desktop");
+        } else {
+            desktopChild->setParent(desktop);
+        }
+        desktopChild->show();
+        desktopChild->updateText();
+    }
+
+private:
+    QPointer<ScreenWidget> widget = nullptr;
+    QPointer<ScreenWidget> desktopChild = nullptr;
+    int targetScreen = -1;
+};
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+
+    Controller controller;
+    controller.show();
+
+    return app.exec();
+}
+
+#include "main.moc"
diff --git a/tests/manual/widgets/kernel/setscreen/setscreen.pro b/tests/manual/widgets/kernel/setscreen/setscreen.pro
new file mode 100644
index 0000000000..f06006ea3a
--- /dev/null
+++ b/tests/manual/widgets/kernel/setscreen/setscreen.pro
@@ -0,0 +1,3 @@
+TEMPLATE = app
+SOURCES = main.cpp
+QT += widgets