[Interest] DPI

igor.mironchik at gmail.com igor.mironchik at gmail.com
Sun Feb 23 14:03:06 CET 2014

I’m absolutely sure that Qt determines DPI wrong.

I’ve received from Qt that my screen has 72 DpiY, where actually it has 130.

So my question is what can I use else then QDesktopIWidget::physicalDpiY()?

I need cross-platform solution of finding average finger size (it’s somewhere 10 mm)...

From: Andre Somers 
Sent: Sunday, February 23, 2014 1:30 PM
To: interest at qt-project.org 
Subject: Re: [Interest] DPI

igor.mironchik at gmail.com schreef op 23-2-2014 13:24:


  I want to determine how much pixels in 10 mm.

  I use the next calculations:

  static const qreal fingerSize = 0.0393700787 * 10;

  static const qreal h = (qreal) QApplication::desktop()->physicalDpiY() * fingerSize; 

  And this calculations return to me 28 that on my desktop is 5 mm only.

  0.0393700787 is how  much inches in millimeter...

  What am I doing wrong?

Are you sure that the right physicalDpi is returned? That is not a value you can absolutely rely on.


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