It has been a while since my last post!

I am writing this to inform you that I will be attending Qt Developer Days 2010 in Munich, if you happen to be there during the days, feel free to ping me for a conversation.

I proudly announce that we are having a KDE SC 4.4 Release Party in Prishtina, it will be held on 9th of February at 18:00 o’clock at IDI (Information Development Initiative) Academy offices, here is the map to the location and here is the link to the KDE.org release party list, you are free to join us.

Let’s celebrate together this KDE release.

I am a proud Qt Developer now. Yesterday I earned the title Nokia Certified Qt Developer.

At SFK09 (Software Freedom Kosova) Conference held in 29th and 30th of August 2009 in Prishtina, I’ve had a speech on cross platform software development using C++ and Qt.

I was planning to write about my presentation when videos are ready, unfortunately the videos aren’t finished yet and I decided to write about the Qt presentation and publish only the slides, at least for now.

The speech was technical and in Albanian language. I chose Albanian language for my speech because there are several speeches regarding Qt that are in English and everyone has access for watching them, here you can find three recorded videos from Qt engineers at LinuxTAG.

After the room was filled with attendants, I asked two questions, first: “how many programmers are in this room?” and plenty of hands were raised right after my question, second: “how many of you use .NET Framework in your daily basis for solving problems” again, almost all programmers in the room was using it.

During the presentation I was more focused on the advantages of using Qt with open source compilers over .NET with real-world facts.

But I still keep using this motto: Right tool for the right job

Logos for the banner are:

All Qt logos are © 2008 Nokia Corporation and/or its subsidiaries. Nokia, Qt and their respective logos are trademarks of Nokia Corporation in Finland and/or other countries worldwide. Taken from Qt Software website

Heart icon is part of Tango Icon Library and it is taken from their official website

Qt SFK09 Presentation Slides:

There are several cool video players out there with great user experience and one of them is VLC which has an awesome OSD (On Screen Display), for long I wanted this feature on my player.

This blog post is a step by step guide on how to create a rectangular semi-transparent widget that looks similar to VLC’s OSD.

Note: Result in the end is not exactly as seen in VLC screenshot above, but the widget can be adjusted more to look like it, and when a video is playing in full screen, the widget will look prettier as well.

Semi transparent widgets can be created using Qt’s backing store feature introduced in Qt 4.1. For more information on Transparent Backgrounds in Qt read this article.

For implementing a custom widget we start by inheriting QWidget class as shown in Listing 1.

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class CoolWidget : public QWidget
{
public:
    CoolWidget(QWidget *parent = 0);
 
protected:
    void paintEvent(QPaintEvent *pnt);
    void mouseMoveEvent(QMouseEvent *evt);
    void mousePressEvent(QMouseEvent *evt);
 
private:
    QPoint dragging_position;
    QColor current_color;
    QPushButton *cool_wdg_button[5];
 
};

Listing 1.

In CoolWidget class, mouseMoveEvent, mousePressEvent and paintEvent virtual members should be overridden in order to have implementation of specific features of this custom widget, below is the explanation of use for each virtual member:

mouseMoveEvent is used to move the widget.
mousePressEvent is used to get the QPoint where mouse position started dragging the widget.
paintEvent is used to paint the widget in our own way (to achieve our purpose of creating rectangular semi-transparent widget).

In paintEvent, QPainter and QPen classes are instantiated. QPainter and QPen classes are used for painting and drawing rectangular borders around the widget. After instantiating QPen, it’s width and styles are set. In CoolWidget’s case SolidLine pen style is used with RoundJoin as join style and SquareCap as cap style.

After adjusting QPen, alpha value of QColor class instantiated as current_color (See Listing 1) must be set to 100 via QColor::setAlpha method, then use QPainter class’ fillRect method by passing rect() and the current_color as parameters, then CoolWidget will get a semi-transparent background. In the constructor of CoolWidget’s current_color is set to Qt::black. See Listing 5.

We pass QPen to QPainter::setPen() and draw the rectangle using rect() method.

Implementation of paintEvent is shown in Listing 2.

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void CoolWidget::paintEvent(QPaintEvent *pnt)
{
    QPainter painter(this);
 
    QPen pen;
    pen.setWidth(10);
    pen.setStyle(Qt::SolidLine);
    pen.setJoinStyle(Qt::RoundJoin);
    pen.setCapStyle(Qt::SquareCap);
 
    current_color.setAlpha(100);
 
    painter.fillRect(rect(), current_color);
    painter.setPen(pen);
    painter.drawRect(rect());
}

Listing 2.

mousePressEvent is about giving dragging_position a value, which is the subtraction of global position with top left corner of widget’s frame geometry as shown in Listing 3.

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void CoolWidget::mousePressEvent(QMouseEvent *evt)
{
    if(evt->button() == Qt::LeftButton)
    {
        dragging_position = evt->globalPos() - frameGeometry().topLeft();
        evt->accept();
    }
}

Listing 3.

mouseMoveEvent is about moving the widget. Widget movement is done using move() method, by passing global position QPoint subtracted by dragging_position QPoint as shown in Listing 4.

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void CoolWidget::mouseMoveEvent(QMouseEvent *evt)
{
    if(evt->buttons() == Qt::LeftButton)
    {
        move(evt->globalPos() - dragging_position);
        evt->accept();
    }
}

Listing 4.

In constructor the widget is resized to 300×300, current_color is set to black and 5 QPushButtons are created as shown in Listing 5.

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CoolWidget::CoolWidget(QWidget *parent)
        : QWidget(parent)
{
    current_color = Qt::black;
 
    resize(300, 300);
 
    for(int i = 0; i < 5; i++){
        cool_wdg_button[i] = new QPushButton(QString("Cool Button %1").arg(i), this);
        cool_wdg_button[i]->move(10, i * 40);
    }
 
}

Widget is used with the following snippet:

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CoolWidget *coolwdg = new CoolWidget(this);

And CoolWidget in action:

If you find this post useful or have questions regarding the topic, don’t hesitate to either to leave a comment or write me an email at: milot.shala [at] gmail [dot] com

First international free software conference in Prishtina, Republic of Kosova is on 29th and 30th of August. Conference  is organized by the local open source community called FLOSSK (Free Libre Open Source Software KOSOVA)  and University of Prishtina, people from two sides were working together to bring the conference to the masses.

In 24 August 2004 a local linux users group called AlbaLINUX (www.albalinux.org) organized a small conference for software freedom day, in which I was one of the helpers and speakers at the conference, but we had very small place for the presentation and it was very modest one, at that time we gave Linux CDs and software freedom day t-shirts for free. So in other hands this was just a start of activities from the local open source software users.

In August 2008 I was in contact with James Mike DuPont and he informed me that he started to work for a bigger conference and that is where all begun. After one year after I started helping I am happy that finally we made it with both help of FLOSSK and University of Prishtina and other young hacker volunteers.

I will be speaking for the conference on the topic of programming in C++ using Qt framework, for which I am very happy because I want to spread Qt programming in Kosova and see more and more local developers using such a powerful framework. I will be publishing slides online and I will try to record the whole speech and publish that online too under the creative commons license.

For this conference we have a great keynotes which are listed below:

Giuseppe Maxia is the MySQL Community Manager.
Daniel Carchidi is Publication Director at MIT OpenCourseWare.
Flavia Marzano is a Computer scientist. She is a member of the Italian Open Source committee.
Brian King is President of the Mozdev Community Organization.

More information about schedule, other speakers and registration you can find more at the conference website at http://www.kosovasoftwarefreedom.org/

I am inviting all of you that are reading this post to come and join us to mark this special weekend.

Recently I have seen an arstechnica article describing how to shorten URLs using PyGTK+ with http://is.gd/ service.

I really liked the post and here I will explain how to do something like that but instead of using PyGTK+ I will be using Qt and C++ and instead of http://is.gd/ I will be using my favorite service for shortening URLs, tinyurl.com.

First of all we will start by creating slots in which we will connect to the corresponding signals to. In our case we will be creating two slots, one to connect with the QPushButton clicked signal, and second to connect with the QHttp’s done(bool) signal to handle the response, then we declare a private QHttp member which will be sending post requests to the tinyurl’s service:

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private slots:
    void responseFromTinyUrl();
    void shortenUrlClicked();
private:
    QHttp http;

In the above code snippet I’ve written the main parts of a header that I will handle in this blog post.

Now back to our source file, in the constructor I will set the host of the QHttp instance to www.tinyurl.com, which is very simple, just have to call the setHost(QString) function,

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http.setHost("www.tinyurl.com");

after setting the host on the constructor we connect our slots with corresponding signals, suppose that I already have a QPushButton object instance called buttonShorten,

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connect(buttonShorten, SIGNAL(clicked()), this, SLOT(shortenUrlClicked()));
connect(&http, SIGNAL(done(bool)), this, SLOT(responseFromTinyUrl()));

the implementation of the shortenUrlClicked slot is done by calling a post(QString, QByteArray) function to send a post request to the server,

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void ShortenURLDialog::shortenUrlClicked()
{
     http.post(QString("api-create.php?url=%1").arg("very long url here"), QByteArray());
}

then we will handle the response that is the actual shortened URL from tinyurl.com service on the responseFromTinyUrl() function, in which we call the readAll() function to read the whole response because there will be only the shortened url string which we will display it on a simple QMessageBox,

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void ShortURLDialog::responseFromTinyUrl()
{
    QMessageBox::information(this, "Shortened URL", http.readAll());
}

Conclusion
You can use any other service like tinyurl.com (for example is.gd), just replace the host and post functions to the service’s API. You can see an example of how to update the Twitter status using the same method explained in my earlier post.

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class Child
{
public:
  Child();
  void printGreetingMessage();
};
 
Child::Child()
{
}
 
void Child::printGreetingMessage()
{
   std::cout << "Greetings from a Child class\n";
}

To achieve the goal you must have a Factory class which has two methods one for creating a Child object and second for destroying it, the function for creating the object returns a pointer to Child class.

Before continuing to the Factory class implementation, suppose that you have some header file included in this source file that has a function named Child():

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inline void Child()
{
  std::cout << "Greetings from a function with the same name\n";
}

While you are designing your Factory class you run into compile-time errors telling you that you must be more careful with this one, this is because if try to declare a class in the standard way the compiler cannot identify a class and a function that possess the same name, you must be more specific to the compiler in this situation telling compiler that the following Child class is a class by specifying class keyword in front of the class type:

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// when creating a Child object
class Child _child;
 
// when calling Child function
Child();

and here is complete code for a Factory class using elaborated type specifier:

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class Factory
{
public:
  Factory();
  ~Factory();
  class Child* createChild(); // return pointer to Child object
  void destroyChild();  // destroy created object
 
private:
  class Child *_child; // declare pointer to child object
};
 
Factory::Factory()
{
}
 
Factory::~Factory()
{
  destroyChild();
}
 
class Child *Factory::createChild()
{
  _child = new class Child(); // create instance of a Child class and return it's pointer
  return _child;
}
 
void Factory::destroyChild()
{
  delete _child; // free the mallocs!
}

Main function using elaborated type specifier for Child class:

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int main()
{
 
  Factory f;
  // still using elaborated type specifier
  class Child *real_child = f.createChild();
  real_child->printGreetingMessage();
  Child();
 
  return 0;
}

After compilation output:

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milot@lambda:~/Desktop$ ./elaborate
Greetings from a class
Greetings from a function with the same name
milot@lambda:~/Desktop$

After you received this information, don’t try this in a real project, it may cause headaches and is not recommended to use such construct but you can use it if necessary, as for me, I barely use this construct, but sometimes I find it useful.

For this kind of problem, we will be using QHttp class which provides the HTTP Request functionality, and we will be using Twitter API to send an http request via POST method.

Now we need to create an instance of QHttp class:

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QHttp *twitter_http_updater = new QHttp();

QHttp class provides methods for sending http request to the server, but first we need to tell in which host to send the message, we will need to tell the username and password for the message because the Twitter system is not that intelligent to know that you are sending a message without knowing your credentials and in the end as I mentioned above we need to use twitter api to send the message.

Code means a thousands words

Signatures of the functions that we will be using are:

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// for setting the hostname
QHttp::setHost ( const QString & hostName, quint16 port = 80 )
 
// for setting the username and password
QHttp::setUser ( const QString & userName, const QString & password = QString() )
 
// for sending the request to the server
QHttp::post ( const QString & path, const QByteArray & data, QIODevice * to = 0 )

As seen in the code above QIODevice optional value of the parameter is set to 0 and if we don’t use that parameter it will be 0, but in the other hand QByteArray reference variable need to be passed and we pass the empty QByteArray() because we are using only path parameter to send the data with the request as seen in the code below:

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twitter_http_updater->setHost("www.twitter.com");
twitter_http_updater->setUser("yourusername", "yourpassword");
twitter_http_updater->post("/statuses/update.xml?status=mybeautifulmessage", QByteArray());

One more thing for the end, in Twithor I am handling done signal by a slot. Done signal is emitted when the request was sent and the response is received in other words when the communication is finished between the host and your client, done signal has the following signature:

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QHttp::done ( bool error )   [signal]

I connected this signal to a slot nicely:

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connect(twitter_http_updater, SIGNAL(done(bool)), this, SLOT(updateTwitterStatusFinish()));

And this slot will be fired when the signal is emitted and I’ve implemented the the slot to tell the user that his or her status is updated, you can see more features by reading the docs here.

I named it Twithor (after Marvel’s Fictional Character THOR) and it opens in a small window which doesn’t bother you while working and you can place it on your desktop, but since it is in the early stage of development I am not posting the source code yet because before releasing the source code I must do some code refactoring to avoid WTFs. I will also port it to Windows and of course it will be translated in to my native Albanian language.

Below is screenshot (taken under Linux) that I made and here is the message posted to twitter.

Update: Ported Twithor to Windows, thanks to Qt framework!