This week we fixed a lot more deprecated code. We are now very close to try building digiKam with Qt6 for the first time.

Last week’s QSet warnings merge request was merged.

Improving Random Number Generation in digiKam

Many image filters in digiKam rely on random number generation. Some require high-quality non-deterministic random numbers while the others can work with pseudo random number generators seeded with system time.

There were two ways in digiKam :-

  • Using qsrand() and qrand() from Qt often seeded with system time for common use. Now deprecated.
  • Using the RandomNumberGenerator class that uses boost::random generators and distributions. This class was written before 2011 and at that time there was no std::random. That is why the code had to rely on boost.


The first option with qsrand()/qrand() pair was especially ugly, hard to read. For example, in this file the code generates a random number in range [0, 15] and checks if it is less than 6.

if ((qrand() & 15) < 6)

At the first glance, it is hardly readable and takes a few seconds to understand what it does.

Since Qt 5.10, we now have the option to use QRandomGenerator. It is a very simple API and much more readable. It also has the ability to securely seed itself. To use it for common purposes, it provides a thread-safe global object QRandomGenerator::global() and it was perfect to replace deprecated qrand() and qsrand(). The code snippet above can be simplied as:

int num = QRandomGenerator::global()->bounded(0, 16);
if (num < 6)

Readble, with no bit manipulation and clearly defined range.

These merge requests do exactly this:

Porting RandomNumberGenerator class

We don’t need to rely on boost to generate random numbers anymore. The task involved replacing boost::mt19937 generator with QRandomGenerator and replace distributions like boost::bernoulli_distribution with std::bernoulli_distribution since QRandomGenerator is compatible with std generators. The merge request. We have dropped one more boost dependency.

Removing Qt X11 Extras module

The ICC color profile settings for X Window System in digiKam relies on this module which was removed in Qt 6.0. It had to be replaced with something else. The best solution we could find was to import code of QX11Info class from Qt source tree. This class will land in Qt 6.2.0 again in September this year as a private API but for now we needed to find solution so we can build digiKam with Qt6 without removing this feature. This is currently under review.

Replacing QMutex with QRecursiveMutex

This is one of the few remaining class which is partially deprecated in Qt6 and is used in digiKam. So we just replace QMutex with QRecursiveMutex wherever needed with some Qt version checking since QRecursiveMutex was introduced in Qt 5.14. The merge request under review.


A lot happened this week. Almost all major deprecation warnings have been resolved. The master branch build log is 6693 lines long because of all the warnings. The fix-QMutex branch has just 886 lines now. That is almost 87% less than master. Very few deprecated warnings remain and most of them are not related to Qt.

So, in coming weeks I will try for the first time to build digiKam with Qt6 :)

Thanks for reading! Cheers!