Automatic rescaling of an application on high-dpi Windows platform?

windows qt hdpi rescale highdpi
Robin Lobel picture Robin Lobel · Jun 23, 2014 · Viewed 19.9k times · Source

I'm writing a Qt application that needs to run on high-dpi Windows (192dpi instead of 96dpi).

Unfortunately the Qt framework does not have support for high-dpi yet (at least on Windows), so my application and all its elements looks half the size it should.

Is there any way to force/simulate automatic upscaling of such apps by Windows?

Answer

Nejat picture Nejat · Feb 19, 2015

Applications that use fixed coordinates and sizes will look small on high-DPI resolutions. Although even if using layouts there are some issues regarding element and font sizes and margins. Fortunately there is support for high-DPI displays since Qt 5.4 as there has been many high-DPI issue fixes.

An application on Windows can assume one of the following levels of "DPI Awareness" (From the Qt documentation) :

  • DPI Unaware: This level has been introduced in Windows-Vista. Windows will pretend to the application that it is running on a standard display of 96 DPI of 1920x1080 and scale the application accordingly. It is intended to accommodate older applications designed for low DPI displays. Some artifacts may result from this type of scaling.
  • System-DPI Aware: This level has been introduced in Windows-Vista. It differs from Per-Monitor DPI Aware only when multiple monitors are connected. Windows will calculate a scaling suitable for all connected monitors.
  • Per-Monitor DPI Aware: This level has been introduced in Windows 8.1. Windows does not perform any scaling at all.

Also it states that :

Qt applications by default are Per-Monitor DPI Aware on Windows 8.1 or System-DPI Aware on older versions of Windows. As of Qt 5.4, the level can be specified by passing a parameter to the platform plugin (see Using qt.conf):

<application> -platform windows:dpiawareness=0,1,2

You can read more information here.

In general to have a good UI on high-DPI displays, consider the following :

  • Use the latest version of Qt
  • Use layouts and avoid fixed sizes (unless you calculate scaling ratios on your own)
  • Make appropriate DPI-related settings depending on your application needs, for example set Qt::AA_UseHighDpiPixmaps attribute if you work with QPainter and pixmaps, or calculate a scaling ratio for adjusting certain element sizes in special situations.

Related questions

Qt 5.1.1: Application failed to start because platform plugin "windows" is missing

Edit: Some people started to mark my question as a duplicate. Do not forget that many similar questions existed when I asked this one (see e.g. the list below). However, none of these answers solved my problem. After a …

Read More
How to install PyQt5 on Windows?

When I try installing the PyQt5 on Windows using the command python configure.py I get this error: Error: Make sure you have a working Qt qmake on your PATH. I got the pyQt5 from PyQt5 Download. How can I …

Read More
Console output in a Qt GUI app?

I have a Qt GUI application running on Windows that allows command-line options to be passed and under some circumstances I want to output a message to the console and then quit, for example: int main(int argc, char *argv[]) { …

Read More