Playing with Qt Quick; Imago

In learning Qt, I of course needed to get some experience with the newest and shiniest bits of Qt: Qt Quick.

One of the things I’ve done with that is to make a simple application, an image viewer called Imago. The code can be found at Gitorious. It is a bit different from typical Qt Quick applications as it is not a mobile application but rather targets the desktop. Thus I’m using standard desktop UI concepts like drop-down menues, and ordinary file-chosers.

Imago - single image view

Imago - single image view

Imago - "traditional" view

Imago - "traditional" view

Imago - grid view

Imago - grid view

The lists can be “flicked” through using the pointer, or using the scroll wheel. Moving between the views that show multiple images and the single-image view has a small animation.

Implementation

In a Qt Quick application two languages and runtimes are involved; C++ and the declarative language that forms the basis of Qt Quick, QML. Qt supports bi-directional communication between the two using a number of metods.
In my case I chose to make a QObject class that  maintains all of the central state in the application. This includes things like what folder is currenty open, the images in that folder, which image is currently focused/selected. All these attributes are implemented as QObject properties, and are notifyiable (meaning they have an attached signal that you guarantee to emit each time the value changes). Exporting this object to QML then allows these properties to be used in property bindings, or for one to connect to the notification signals.
So in Imago QML is basically used as a “stupid” UI layer for the image view. Other things, like window title and drop-down menues are handed by the C++ side, but by using the signals and properties of the same object.

Writing a desktop application means that one cannot assume a fixed window size like people tend to do for mobile device applications. With setting the resize property of the QDeclarativeView (the widget that displays the QML stuff) to QDeclarativeView::SizeRootObjectToView and using anchor layouts throughout this is possible, but it took me a good while to get working properly. Mostly because the concepts are new, and most (all?) the examples in the documentation seem to neglect this aspect.

The grid and traditional view are actually implemented in different QML files (though the delegate for the images in the list is shared). I did this to test how having several UIs would be like, and for a simple application like this it works out just fine.

Where to now?

Imago right now is very simple,  and could benefit from some added features and some designer love. I also just found a bug in the traditional view that needs to be fixed. I have documented these things in the README file in case someone is interested. As I have moved my focus over to other projects, I probably wont be taking this application much further, at least not at this time.

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Back from Qt Dev Days, first Qt projects

I’ve actually been back close to a week now, but never mind that…

In the per-conference day with training sessions I attended the Qt Essentials track, which was more or less as expected. Glad I read a full Qt book beforehand, it would have been challenging to keep up with the shear amount of information without it.
The keynotes I attended on the second day were not particularly exciting: no major announcements nor insights were given. The technical talks on the other hand were filled with goodies. The talks by Jens Bache-Wiig and Roberto Raggi on Qt Quick were especially good.*

The talks definitely made me want to try Qt Quick for doing user interfaces for small-form factor devices, especially because it allows for very rapid prototyping and iterations when developing. The current lack of widgets and traditional layouts probably limits its usefulness for typical desktop application with more complex user interfaces though. There is nothing that helps you achieve a native look and feel either, but the Qt Components project is aiming to bridge those gaps.
I also suspect that the declarative and dynamic nature of QML poses several new challenges for developers, especially for those that are mostly used to traditional Qt programming with C++. I’m especially concerned that there was no way to visualize or do static checking on the property-bindings that are so central in QML. Very curious as to how that plays out in practice.

*I’m told the talks will be online after the Qt Developer Days event in San Fransisco is over.

Qt projects you said?

Going forward I’ll be doing some projects with Qt, in the same way I have done with GTK. My first project has already started: implementing viewer-class OpenRaster support for Qt. This means that applications using Qt and QImage will soon be able to display fully-rendered OpenRaster images!
Development of the Qt integration happens in the repository on gitorious, and the libora modifications currently lives in my personal clone. It will be pushed to mainline as soon as I have more-or-less settled on the API, and done a basic implementation. Using libora for all the OpenRaster specific stuff is being a bit more painful than expected, but it is the right thing to do as it means that other consumers benefits as well. Like a potential GdkPixbuf plugin or applications not using Qt or GTK. I’ll write more once it reaches a useful state.

After that is done I will probably do something with more UI, like a proper application. Hopefully I will get to toss Qt Quick into the mix as well. I’ve got an idea that I think would be a nice fit, so we’ll see.

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