Screen attached property: expose devicePixelRatio property

Change-Id: I08b22766b3e389b7d27ca4c56729f550b0647a08
Reviewed-by: Jens Bache-Wiig <jensbw@gmail.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

examples/quick/window/ScreenInfo.qml

@@ -38,7 +38,7 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.1
+import QtQuick 2.3
 import QtQuick.Window 2.1
 
 Item {
@@ -85,6 +85,9 @@ Item {
         Text { text: "logical pixel density" }
         Text { text: Screen.logicalPixelDensity.toFixed(2) + " dots/mm (" + (Screen.logicalPixelDensity * 25.4).toFixed(2) + " dots/inch)" }
 
+        Text { text: "device pixel ratio" }
+        Text { text: Screen.devicePixelRatio.toFixed(2) }
+
         Text { text: "available virtual desktop" }
         Text { text: Screen.desktopAvailableWidth + "x" + Screen.desktopAvailableHeight }
 

src/quick/items/qquickscreen.cpp

@@ -141,6 +141,15 @@ QT_BEGIN_NAMESPACE
 
     The number of physical pixels per millimeter.
 */
+/*!
+    \qmlattachedproperty real Screen::devicePixelRatio
+    \readonly
+    \since 5.4
+
+    The ratio between physical pixels and device-independent pixels for the screen.
+
+    Common values are 1.0 on normal displays and 2.0 on Apple "retina" displays.
+*/
 /*!
     \qmlattachedproperty Qt::ScreenOrientation Screen::primaryOrientation
     \readonly
@@ -260,6 +269,13 @@ qreal QQuickScreenAttached::pixelDensity() const
     return m_screen->physicalDotsPerInch() / 25.4;
 }
 
+qreal QQuickScreenAttached::devicePixelRatio() const
+{
+    if (!m_screen)
+        return 1.0;
+    return m_screen->devicePixelRatio();
+}
+
 Qt::ScreenOrientation QQuickScreenAttached::primaryOrientation() const
 {
     if (!m_screen)
@@ -340,6 +356,8 @@ void QQuickScreenAttached::screenChanged(QScreen *screen)
             emit logicalPixelDensityChanged();
         if (!oldScreen || screen->physicalDotsPerInch() != oldScreen->physicalDotsPerInch())
             emit pixelDensityChanged();
+        if (!oldScreen || screen->devicePixelRatio() != oldScreen->devicePixelRatio())
+            emit devicePixelRatioChanged();
 
         connect(screen, SIGNAL(geometryChanged(QRect)),
                 this, SIGNAL(widthChanged()));

src/quick/items/qquickscreen_p.h

@@ -57,6 +57,7 @@ class Q_AUTOTEST_EXPORT QQuickScreenAttached : public QObject
     Q_PROPERTY(int desktopAvailableHeight READ desktopAvailableHeight NOTIFY desktopGeometryChanged)
     Q_PROPERTY(qreal logicalPixelDensity READ logicalPixelDensity NOTIFY logicalPixelDensityChanged)
     Q_PROPERTY(qreal pixelDensity READ pixelDensity NOTIFY pixelDensityChanged)
+    Q_PROPERTY(qreal devicePixelRatio READ devicePixelRatio NOTIFY devicePixelRatioChanged)
     // TODO Qt 6 Rename primaryOrientation to orientation
     Q_PROPERTY(Qt::ScreenOrientation primaryOrientation READ primaryOrientation NOTIFY primaryOrientationChanged)
     // TODO Qt 6 Remove this orientation -> incomplete device orientation -> better use OrientationSensor
@@ -74,6 +75,7 @@ public:
     int desktopAvailableHeight() const;
     qreal logicalPixelDensity() const;
     qreal pixelDensity() const;
+    qreal devicePixelRatio() const;
     Qt::ScreenOrientation primaryOrientation() const;
     Qt::ScreenOrientation orientation() const;
     Qt::ScreenOrientations orientationUpdateMask() const;
@@ -91,6 +93,7 @@ Q_SIGNALS:
     void desktopGeometryChanged();
     void logicalPixelDensityChanged();
     void pixelDensityChanged();
+    void devicePixelRatioChanged();
     void primaryOrientationChanged();
     void orientationChanged();
     void orientationUpdateMaskChanged();

tests/auto/quick/qquickscreen/data/screen.qml

@@ -9,6 +9,7 @@ Item {
     property int curOrientation: Window.Screen.orientation
     property int priOrientation: Window.Screen.primaryOrientation
     property int updateMask: Window.Screen.orientationUpdateMask
+    property real devicePixelRatio: Window.Screen.devicePixelRatio
 
     Window.Screen.orientationUpdateMask: Qt.LandscapeOrientation | Qt.InvertedLandscapeOrientation
 }

tests/auto/quick/qquickscreen/tst_qquickscreen.cpp

@@ -63,6 +63,8 @@ void tst_qquickscreen::basicProperties()
     QCOMPARE(int(screen->orientation()), root->property("curOrientation").toInt());
     QCOMPARE(int(screen->primaryOrientation()), root->property("priOrientation").toInt());
     QCOMPARE(int(screen->orientationUpdateMask()), root->property("updateMask").toInt());
+    QCOMPARE(screen->devicePixelRatio(), root->property("devicePixelRatio").toReal());
+    QVERIFY(screen->devicePixelRatio() >= 1.0);
 }
 
 QTEST_MAIN(tst_qquickscreen)