Using Qt to Develop for Embedded Linux

Qt/Embedded extends the ease and speed of Qt to embedded application development.
Collisions

At this stage you have a QMainWindow containing a QCanvasView with a canvas that contains items, some of which may be moving. The next step is to make your program more interesting by detecting collisions between the items. You can get information about collisions between QCanvasItems using collidesWith() and collisions(). collidesWith() is used to test if one item will collide with another particular item, and collisions() returns a list of all items with which a specific item will collide. In the Snake game, collisions() is used because the snake can collide with itself, the wall or the target. Listing 2 shows how collisions were handled in the game.

Listing 2. Handling Collisions

The list of QCanvasItems that the head of the snake collides with are assigned to a QCanvasItemList called ``l''. The false argument to collisions() specifies testing for collisions in inexact mode. This will return items that are near the head, but it works much faster than exact mode. If the item is a useful candidate, it is tested with collidesWith().

The ``for'' loop is used to iterate over the list l, assigning each item to a variable called ``item''. Each QCanvasItem on the canvas can have a specified rtti() value, an integer that allows you to identify the items. The target's rtti() value is 1,500, and this information was used in the if statement to test whether the item in the list was the target. If it was the target, the function returns; otherwise it moves on to the next if statement to test whether the item is the wall. Note that this code segment is for illustrative purposes only. In the actual Snake game, there are other if statements in the for loop to handle other situations. The ``do something'' is replaced with code.

Signals and Slots

Another important consideration when developing any program is the design. Qt offers assistance with component programming--otherwise known as object-oriented programming--through its signals and slots mechanism. This is a great feature that saves a lot of time and effort, as it allows easy communication among the different objects in your program. It allows an object to emit a signal() that activates a slot() in another object. Slots can be normal member functions, and parameters can be also be passed into them.

I found this feature particularly useful when developing Snake. An example of the use of signals and slots occurs when the game ends. The snake object emits a dead() signal when it collides with a wall. Then the snake's body, or the edges of the screen, connects to a gameOver() slot in the interface class to end the game and begin a new one. The code for this is in snake.cpp:

//check if snake hit itself
for (uint i = 3; i < snakelist.count(); i++) {
  if (head->collidesWith(snakelist.at(i)) ) {
      emit dead();      // signal to end game
      autoMoveTimer->stop();
      return;
  }
}

And the code from file interface.cpp in the newGame() function is:

// connect the signal to the slot
connect(snake, SIGNAL(dead()), this, SLOT(gameOver()) );

Conclusion

If the test of an application framework is the ability to quickly build professional, powerful and bug-free code, then Qt/Embedded passes with flying colors. As an intern with fairly limited programming experience, I was able to create a 2-D computer game good enough to be included in the suite of applications for the Qt Palmtop Environment. And I did it in under five weeks of actual development time. The tagline for Qt/Embedded is ``Small Enough for the Job''. I think that's pretty accurate. It was powerful, with a rich set of functionalities that made programming very easy, and it took up an amazingly small amount of main memory and Flash. If the other tools I come across in my career are even half this good, I'll be one happy developer.

Natalie Watson (nwatson04@optusnet.com.au) is currently a student at Griffith University, where she is working toward a Bachelor degree in Information Technology. Her programming experience includes Java and C++.

______________________

Comments

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Good Article

Luis Abarca's picture

Hey nice article !!

Muy buen articulo, me despejaste varias dudas que tenia al respecto.

Saludos.

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix