HiDPI devices are very common today. Users need to scale up UI to make them looks like normal size. Common scale factors are: 1.25, 1.5, 1.75, 2, 3. This means UI dimensions are not integers anymore. Qt provides classes and functions that accept and return qreal instead of int. They usually end with F.

  • QRect --> QRectF
  • QPoint --> QPointF
  • QWidget::devicePixelRatio() --> QWidget::devicePixelRatioF()

KDE and Qt applications may render blur icons and graphics. This guide shows how to make everything sharp and clear in HiDPI devices. Both Qt 5 Widgets and Qt 5 Quick applications are supported.

Migrate to Qt 5 and KF5

Qt 4 doesn't support HiDPI rendering. Please migrate your application to Qt 5 and KF5.


You don't need to do anything special. Text rendering should support HiDPI out of box.


In your application's main function, add the following lines at the very beginning:

int main(int argc, char *argv[])
    QApplication app(argc, argv);
    QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps, true);

Then all icons in your application should look sharp.


Change all QPixmap from

pixmap = QPixmap( width, height );


pixmap = QPixmap( width * dpr, height * dpr );

So where is the dpr variable from? You can get it from any QWidget objects with function devicePixelRatioF(). F means the function return a float number (qreal). If you are not in a QWidget class context, you can get the value via:

const qreal dpr = qApp->devicePixelRatio();

And don't forget to change width and height from int to qreal.


QPainter has various drawing functions. You need to change parameters of those functions from integer types:

  • QRect
  • QPolygon
  • QPoint
  • int

to floating types:

  • QRectF
  • QPolygonF
  • QPointF
  • qreal

For example, you need to change this code:

QPainter p;
p->drawText(0, 0, 12, 50, Qt::AlignLeft | Qt::AlignTop, text);


QPainter p;
p->drawText(QRectF(0, 0, 12, 50), Qt::AlignLeft | Qt::AlignTop, text);

After all these changes, your QPainter object should be able to render HiDPI graphics.

Qt Quick Controls 1

If the QML contains Qt Quick Controls 1, all text components will be blur and small in HiDPI display. This is likely a Qt bug.

To solve this, we suggest you to migrate to Qt Quick Controls 2.

This page was last edited on 1 March 2020, at 07:41. Content is available under Creative Commons License SA 4.0 unless otherwise noted.