Qt Quick development process

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Revision as of 13:22, 5 April 2014 by Bruno (talk | contribs) (minor)
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Learning Qt Quick

Some pointers to discover Qt Quick:

A step by step exercise to dig into Qt Quick with the QtCreator development environment:

Coding Style

We follow this coding style.

Source code

Here is the official repository for the source code. Alternatively you can also get the code on GitHub.


  • Get the source code
  • Download and Install the lastest stable version of QtCreator for Android
  • Start QtCreator and open the project file GCompris.pro at the root of the source code
  • Compile and run it.

To make it run on Android you need first to follow these instructions.

Adding a new activity


Let's say you want to port the algebra_by activity.

cd src/activities
./createit.sh algebra_by

And you're done, you can run GCompris in QtCreator and your actvitity should appear on the list.


You must create a directory for your activity in src/activities. In it, create an ActivityInfo.qml, algebra_by.pri and your qml entry point Algebra_by.qml.

  • in src/activities/activities.txt add the directory name of your activity (keep the file sorted).
  • add an include for your .pri in the top level GCompris.pro (to be correct it should be kept sorted with the others): include(src/activities/algebra_by/algebra_by.pri)
  • check algebra_by/ActivityInfo.qml that the name references you Qml activity entry point and that the icon point to your icon name.

Getting old menus

If your activity is an existing one, you can copy its ported ActivityInfo

  • git mv menus/algebra_by.qml algebra_by/Algebra_by.qml

the svg icon is not under git so you have to pick the old GCompris's icon named algebra_by.svg and copy it in algebra_by. You can get it from the GCompris-gtk GitHub: https://github.com/bdoin/GCompris/tree/master/src

Extending another activity

If the activity is just an extension of an existing one you have to create it either manually or automatically and then change you .qml file to extend another one. The 'erase_clic' activity is a good example.

In your .qml file:

  • just import the activity you want to extend with for example: import "qrc:/gcompris/src/activities/erase"
  • instead of have your root item being an 'ActivityBase' you just create an object of the base type you want to extend like Erase.
  • Use a property to pass parameters to your base item and customize it

Speeding startup

When you work on an activity you will run GCompris many time and the final stage that combines the qrc in the binary is long. To speed your development process, just comment the include of the activities you don't need in the top level GCompris.pro

Coding guidelines

Keep only small javascript in the QML code, all the game logic must be in your javascript file. This makes it easier to read the activity logic. It is possible to have several javascript files if needed. The QML files must be seen as the graphical interface description and the javascript the logic of the game.

Resolution independence

Your activity must look nice on tablets and desktops. The resolution and dpi value may differ a lot. On mobile with high dpi the size of your images will look smaller. You must set an initial size related to ApplicationInfo.ratio like this:

Image {
    id: ball
    source: "qrc:/gcompris/src/activities/ballcatch/resource/ball.svgz"
    sourceSize.height: 100 * ApplicationInfo.ratio

Window resize

Your activity must adapt its content properly when the window is resized.

Screen rotation

Your activity must support screen rotation. If you use a layout or you specify an item coordinated related to the window width you are safe. If you create absolute coordinate items, you may need to reset them when the screen is changed. To detect a rotation you can add a code like this in your ActivityBase:

    onWidthChanged: Activity.withChanged()


Creating Audio items is rather slow. If you have a lot of items on the screen, do not create an Audio item for each. Instead create a single Audio and pass it to all your items.

Adding resources

  • For the media, you have to put them in the qrc file and then reference it by qrc: in the source. The path is defined in the qrc file.
  • You can see the qrc in qtcreator, it is Ressources/gcompris.qrc it is auto generated at build time
  • To add new images, create a resource directory in your activity folder and in you .pri file add:
	  $$PWD/resource/myCuteImage.jpg \
  • And in your source use : qrc:/gcompris/src/activities/algebra_by/resource/myCuteImage.jpg

Background image

You must not use a background image to bring useful informations. It is not possible to keep the background aligned with items when the resolution is changed.