What is New in Qt 5: The QScreen Class

What's New in Qt 5: The QScreen Class

By Jeff Tranter

QScreen is a new class introduced in Qt 5.0.0 that returns information about screen properties, where screen here refers to a display, such as a monitor or LCD panel.

[Update: It was pointed out that Qt 4 has a class named QScreen. However, the QScreenclass in Qt 4 was entirely different from the one in Qt 5 with different APIs and used for a different purpose. So I really consider them to be different classes.]

It can be used to allow your application to handle different screen sizes, multiple screens, or calculate the physical size of items on the screen.

In Qt 4 you could get some of this information from the QX11Info and QDesktopWidgetclasses.

The QScreen class has 20 properties and a number of methods and signals. It is a subclass of QObject.

The QGuiApplication class (new in Qt 5) provides methods that will return the primary screen or a list of all screens as QScreen pointers.

The QWindow class can return the screen it was created on or let you set the screen it appears on using a method or in the constructor.

I'll show here a very simple text-based Qt example program that lists information for the display screens. While it is a non-graphical application, we do need to create aQGuiApplication object since it needs to exist in order to get the information about the screens.

Here is sample output on one system I ran it on:

Number of screens: 2
Primary screen: "VGA-0"
Information for screen: "VGA-0"
  Available geometry: 0 0 1920 x 1165
  Available size: 1920 x 1165
  Available virtual geometry: 0 0 3520 x 1165
  Available virtual size: 3520 x 1165
  Depth: 24 bits
  Geometry: 0 0 1920 x 1200
  Logical DPI: 94.1432
  Logical DPI X: 93.0364
  Logical DPI Y: 95.25
  Orientation: "Landscape"
  Physical DPI: 94.1104
  Physical DPI X: 94.1467
  Physical DPI Y: 94.0741
  Physical size: 518 x 324 mm
  Primary orientation: "Landscape"
  Refresh rate: 72 Hz
  Size: 1920 x 1200
  Virtual geometry: 0 0 3520 x 1200
  Virtual size: 3520 x 1200
Information for screen: "LVDS-0"
  Available geometry: 1920 0 1600 x 900
  Available size: 1600 x 900
  Available virtual geometry: 0 0 3520 x 1165
  Available virtual size: 3520 x 1165
  Depth: 24 bits
  Geometry: 1920 0 1600 x 900
  Logical DPI: 94.1432
  Logical DPI X: 93.0364
  Logical DPI Y: 95.25
  Orientation: "Landscape"
  Physical DPI: 117.987
  Physical DPI X: 118.14
  Physical DPI Y: 117.835
  Physical size: 344 x 194 mm
  Primary orientation: "Landscape"
  Refresh rate: 72 Hz
  Size: 1600 x 900
  Virtual geometry: 0 0 3520 x 1200
  Virtual size: 3520 x 1200

Here is the complete source code for the example:

#include <QGuiApplication>
#include <QScreen>
#include <QDebug>

/*
  Example of using Qt 5 QScreen class.
*/


// Helper function to return display orientation as a string.
QString Orientation(Qt::ScreenOrientation orientation)
{
    switch (orientation) {
        case Qt::PrimaryOrientation           : return "Primary";
        case Qt::LandscapeOrientation         : return "Landscape";
        case Qt::PortraitOrientation          : return "Portrait";
        case Qt::InvertedLandscapeOrientation : return "Inverted landscape";
        case Qt::InvertedPortraitOrientation  : return "Inverted portrait";
        default                               : return "Unknown";
    }
}

int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);

    qDebug() << "Number of screens:" << QGuiApplication::screens().size();

    qDebug() << "Primary screen:" << QGuiApplication::primaryScreen()->name();

    foreach (QScreen *screen, QGuiApplication::screens()) {
        qDebug() << "Information for screen:" << screen->name();
        qDebug() << "  Available geometry:" << screen->availableGeometry().x() << screen->availableGeometry().y() << screen->availableGeometry().width() << "x" << screen->availableGeometry().height();
        qDebug() << "  Available size:" << screen->availableSize().width() << "x" << screen->availableSize().height();
        qDebug() << "  Available virtual geometry:" << screen->availableVirtualGeometry().x() << screen->availableVirtualGeometry().y() << screen->availableVirtualGeometry().width() << "x" << screen->availableVirtualGeometry().height();
        qDebug() << "  Available virtual size:" << screen->availableVirtualSize().width() << "x" << screen->availableVirtualSize().height();
        qDebug() << "  Depth:" << screen->depth() << "bits";
        qDebug() << "  Geometry:" << screen->geometry().x() << screen->geometry().y() << screen->geometry().width() << "x" << screen->geometry().height();
        qDebug() << "  Logical DPI:" << screen->logicalDotsPerInch();
        qDebug() << "  Logical DPI X:" << screen->logicalDotsPerInchX();
        qDebug() << "  Logical DPI Y:" << screen->logicalDotsPerInchY();
        qDebug() << "  Orientation:" << Orientation(screen->orientation());
        qDebug() << "  Physical DPI:" << screen->physicalDotsPerInch();
        qDebug() << "  Physical DPI X:" << screen->physicalDotsPerInchX();
        qDebug() << "  Physical DPI Y:" << screen->physicalDotsPerInchY();
        qDebug() << "  Physical size:" << screen->physicalSize().width() << "x" << screen->physicalSize().height() << "mm";
        qDebug() << "  Primary orientation:" << Orientation(screen->primaryOrientation());
        qDebug() << "  Refresh rate:" << screen->refreshRate() << "Hz";
        qDebug() << "  Size:" << screen->size().width() << "x" << screen->size().height();
        qDebug() << "  Virtual geometry:" << screen->virtualGeometry().x() << screen->virtualGeometry().y() << screen->virtualGeometry().width() << "x" << screen->virtualGeometry().height();
        qDebug() << "  Virtual size:" << screen->virtualSize().width() << "x" << screen->virtualSize().height();
    }
}

In summary, the new QScreen class in Qt 5 in a useful class for getting information about the properties of the display screens on a system in a portable manner. In addition to the properties demonstrated in this example, it also supports a number of methods and can emit signals when the display properties change.

You can download the source code for the example, at least for the next little while, fromhere.

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