Enable making window-screen associations from QML

Qt Quick provides a Screen attached property to query information
about the screen an item's window belongs to. This is a good start,
but has two problems: it lacks some virtual desktop related info
(e.g. the position in the virtual desktop) and it cannot be used in
combination with the Window element in order to achieve a QML
equivalent of QWindow::setScreen().

Therefore add the missing virtualX and virtualY properties and
introduce Qt.application.screens. The latter is an equivalent to
QGuiApplication::screens() and is a JS array the elements of which
can be set as the value of the new Window.targetScreen property.

This means that a call like
window->setScreen(QGuiApplication::screens()[0]) translates to
Window { targetScreen: Qt.application.screens[0]; ... } when using the
Window type from QML. Screen addition or removal can be acted upon via
onScreensChanged.

QQuickScreenAttached has been split into two in order to allow reusing the
QScreen wrapping queries for other purposes as well.

Task-number: QTBUG-56115
Change-Id: I4b2fbd873315b40d0afe878da2fc50966c00e2e0
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlengine.cpp b/src/qml/qml/qqmlengine.cpp
index 01f1f93b81..daa12fae26 100644
--- a/src/qml/qml/qqmlengine.cpp
+++ b/src/qml/qml/qqmlengine.cpp
@@ -554,6 +554,18 @@ The following functions are also on the Qt object.
     \li This read-only property can be used to determine whether or not the
         platform supports multiple windows. Some embedded platforms do not support
         multiple windows, for example.
+
+    \row
+    \li \c application.screens
+    \li An array containing the descriptions of all connected screens. The
+    elements of the array are objects with the same properties as the
+    \l{Screen} attached object. In practice the array corresponds to the screen
+    list returned by QGuiApplication::screens(). In addition to examining
+    properties like name, width, height, etc., the array elements can also be
+    assigned to the targetScreen property of Window items, thus serving as an
+    alternative to the C++ side's QWindow::setScreen(). This property has been
+    added in Qt 5.9.
+
     \endtable
 
     The object also has one signal, aboutToQuit(), which is the same as \l QCoreApplication::aboutToQuit().
@@ -570,6 +582,8 @@ The following functions are also on the Qt object.
     \li application.layoutDirection
     \li application.font
     \endlist
+
+    \sa Screen, Window, Window.targetScreen
 */
 
 /*!