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Posts tagged with ‘opensource’

Contributing to Krita

kinow @ Jan 03, 2017 11:40:03

As I mentioned in the last post, I have been learning Qt and using C and C++ again. Since I used C and C++ more during university (about 10 years ago, phew), decided to read real code.

I used Photoshop, Illustrator, and Fireworks a lot when I was younger and had more time to spend drawing. But some time ago I switched to Inkscape for vector graphics, which I use at work for presentations. So it was only natural to try Krita now.

Since I was going to try Krita, I thought why not check out and build from source, and then in case I found any bugs, contribute back? Or maybe from time to time triage issues, find low hanging ones, and send a patch?

Well, turns out the Krita project has a great community, and it is super easy to send contributions. So far I submitted three patches, some were included in 3.x releases.

While the patches are rather small, they are suggestions on how to fix memory segmentation faults, or strange behaviours in the interface. For these issues, I had to learn more about Qt components, signals and emitting events, and, of course, work with pointers, arrays, Qt data structures, etc. In other words, lots of (geek) fun!

In other words, by contributing to Krita, I am not only helping the project and giving a little back to the community, but also refreshing my memory on C and C++, and slowly learning Qt - which is not very hard if you worked with Swing/AWT, Delphi, Visual Basic, Gtk, etc.

What are you waiting to contribute to Krita? The developers that maintain the project answer tickets and questions posted to reddit in a good time, and are extremely easy to work with.

Read more here how to build from source, and here on how to submit patches.

Happy hacking!

Debugging an application that freezes the X server

kinow @ Jan 02, 2017 00:39:03

Some time ago, I decided to start writing C++ again, and picked Krita for that. Krita is written in C++ and Qt. The bug I was working on involved a memory issue when changing the UI.

The problem was that this UI change would result in, not only Krita, but the whole X server freezing. My set up was basically Ubuntu 16.04.1 LTS, with Eclipse, Qt5, and the latest version of Krita checked out via git.

Initially I spent some time looking at the logs, tracing the binary, even downloaded some Qt utility tools to look at the events and what was happening with the application when it froze.

However, eventually I realized I was going to spend more time on this part of the issue, rather than on the memory bug. So decided to look for a work-around.

Thankfully someone else blogged about a similar issue and saved me a lot of time :-) Here’s how I did it, following the instructions in this blog post.

$ sudo apt-get install xnest -y
$ cd krita_install/
$ Xnest :10
$ twm -display :10
$ export DISPLAY=:10
$ ./krita

That’s it. You should have Krita running in a separate window, with Xnest, and within this window the twm window manager running. So when it freezes, at least you can still debug your application in Eclipse or whatever IDE you prefer.

Happy hacking!

Replacing a HashSet with a BitSet

kinow @ Oct 20, 2012 19:51:39

I always read the messages in the Apache dev mailing lists, including Apache Commons dev mailing list. And you should too. There are always interesting discussions. Sometimes you participate, other times you only watch what’s happening, but in the end you always learn something new.

A few days ago, I found an issue where it was being proposed to replace an unnecessary HashSet in ArrayUtils#removeElements() by a BitSet. Here’s how the code looked like:

HashSet<Integer> toRemove = new HashSet<Integer>();
for (Map.Entry<Character, MutableInt> e : occurrences.entrySet()) {
    Character v = e.getKey();
    int found = 0;
    for (int i = 0, ct = e.getValue().intValue(); i < ct; i++) {
        found = indexOf(array, v.charValue(), found);
        if (found < 0) {
            break;
        }
        toRemove.add(found++);
    }
}
return (char[]) removeAll((Object)array, extractIndices(toRemove));

The HashSet created at line 1, in the code above, was used to store the array index of the elements that should be removed. And at line 13 there is a call to removeAll method, passing the indexes to be removed. And here’s how the new code looks like:

BitSet toRemove = new BitSet();
for (Map.Entry<Character, MutableInt> e : occurrences.entrySet()) {
    Character v = e.getKey();
    int found = 0;
    for (int i = 0, ct = e.getValue().intValue(); i < ct; i++) {
        found = indexOf(array, v.charValue(), found);
        if (found < 0) {
            break;
        }
        toRemove.set(found++);
    }
}
return (char[]) removeAll(array, toRemove);

The first difference is at line 1. Instead of a HashSet, it is now using a BitSet. And at line 10, instead of adding a new element to the HashSet, now it “sets” a bit in the set (the bit at the specified position is now true). But there are important changes at line 13. The method removeAll was changed, and now the array doesn’t require a cast anymore. And the it is not necessary to cast the elements from HashSet anymore, as now the bit in the index position of the set is set to true. So the extractIndices method could be removed.

The code got simpler. But that’s not all. At Apache Software Foundation you can find a lot of talented developers - that’s why I got so excited after joining them. Besides simplifying the code, the developer responsible for these changes (sebb) also pointed out that the new code consumes less memory and is faster. Ah! And he also wrote unit tests

The Developers Conference (TDC) 2011 Botando o Jenkins para rodar seus testes

kinow @ Aug 20, 2011 22:45:03

Botando o Jenkins para rodar seus testes

Event
The Developers Conference 2011
Where ?
Florianópolis
When ?
2011-08-20

Belgium Testing Days (BTD) 2011 How To Automate Tests Using Testlink And Hudson

kinow @ Feb 14, 2011 22:18:03

How To Automate Tests Using Testlink And Hudson

Event
Belgium Testing Days 2011
Where ?
Brussels, Belgium
When ?
2011-02-14