How to Use DPAPI with Qt Framework to Encrypt and Decrypt Data

When dealing with data encryption and decryption in Windows operating systems, probably one of the best choices is to use the Data Protection API. In this post I’ll be sharing two simple functions that can be used to encrypt and decrypt data (such as passwords, recovery keys and so on) that you want to store in an easy, quick and highly protected manner. Needless to say, these functions can be used with C++ and Qt Framework.

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Cascade Classifier Training – FAQ, Known Issues and Workarounds

After receiving almost the same questions about Cascade Trainer GUI application all over again from many different users, I realized that it will be much more useful for anyone with a similar question, and much more efficient for me to actually compile a list of frequently asked questions, all the known issues and error and warning messages and try to answer them all in one place. Here is the result.

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Download Prebuilt OpenCV Libraries for MinGW

This is something that is very commonly searched but not easily found. So, as a reference for myself and anyone who might need it, I have shared the prebuilt OpenCV libraries for MinGW in this post, namely OpenCV 4.1.0 for MinGW 7.3.0 32-bit.

Note: I’ve assumed that you already know how OpenCV is built but you’re just looking for OpenCV prebuilt libraries instead of building them yourself. However, if you want to build OpenCV for MinGW by yourself, you can search my website for plenty of tutorials and information to get you started.

You might be wondering what sort of CMake parameters (or changes) I used to prepare these libraries, so to answer it very briefly, here they are:

  • WITH_OPENCV_D3D11_NV = OFF
  • BUILD_opencv_world = ON
  • BUILD_opencv_python3 = OFF
  • BUILD_opencv_python_bindings_generator = OFF
  • BUILD_opencv_java_bindings_generator = OFF

You can use this link to directly download the libraries, and post your questions below in the comment box.


How to Build OpenCV 4.X for Native Android Development

For a number of different reasons, you might want/need to build OpenCV from scratch instead of using the pre-built and official libraries provided by OpenCV. Since you’ve ended up reading this post, there’s a good chance that you already know why you might need to do this, but if you don’t, you can check out my similar post from a couple of years ago for some answers on this. That post was based on OpenCV 3.3 which is considered out-of-date these days, especially with OpenCV 4 out in the market (OpenCV 4.0.1 at the time of writing this article), so I decided to write a new tutorial to address some of the differences. So without without further ado, here we go.

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A Simple Script to Build OpenCV 3.4.3 for Windows

Over the years I have written quite a few guides and tutorials that describe building OpenCV from sources for Windows, however they were mostly done using the GUI. It means you’d have to be using CMake GUI to set some parameters and then a few other actions and you’d end up building OpenCV using Visual Studio like any other VS solution. Even though it’s quite simple to build OpenCV like this, you can’t automate it and you need to perform all the required actions manually. In this post though, I’ll be sharing a few simple commands that can be put inside a batch script that will allow you to build OpenCV for any platform you like, simply by executing (or double clicking) that script!

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Adding External Libraries to Qt Projects

As simple as it sounds, most of the time it’s a hassle to add the required libraries to your Qt projects. You have to add the include path, the libraries and if you are aiming to have a cross-platform project, you need to account for Windows, macOS and Linux operating systems separately. Well, there are a couple a methods to simplify this a bit which I’ll describe in this tutorial.


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How to Convert Videos Using Qt and FFmpeg

In this post I’m going to describe how you can use FFmpeg library to convert videos in your Qt applications, or even write a Video Conversion program that uses FFmpeg as its underlying powerful conversion engine.

Unfortunately you can’t use Qt Framework out-of-the-box to convert video files and formats to each other (at least that is the case until the time this post was published, or in other words until Qt5.10.1). One of the most practical workarounds for this missing capability is using 3rd party video conversion libraries and tools such as FFmpeg.

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How to Make a Qt Widget Transparent to Mouse Events

Before I come up with the current title of this post, I thought of many other titles including:

  • How to send mouse clicks and events to a Qt widget behind another widget
  • How to make a Qt widget ignore mouse events
  • and so on …

Although the answer was very straightforward and easy, I struggled a lot with it since I wasn’t asking the right question.


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