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The development of SlideViewer A QML-based presentation program


At Qt developer Days in Berlin 2013 I had an Aha! moment. I saw a presentation written in QML rather than the usual Powerpoint/LibreOffice/Keynote. It wasn’t that I did not imagine this was possible, rather the contrary, after all in KDAB we have more than 3000 slides on Qt-related topics, all written in …. LaTeX. It was nevertheless an Aha! moment for me, as it showed me a way out of a corner I had painted myself into.

Over the years I’ve insisted on us staying with LaTeX rather than going to LibreOffice, as that allowed me to apply numerous tools that we all knew from development, most importantly the capability to store a whole slide deck in git and have multiple people working on it at once, possibly on different branches. Just imagine you were developing a Qt application, and you were forced to store all of the application’s source files in one binary blob that could not easily be merged.

The downside with LaTeX was, however, that only a few of us knew how to operate its corner cases – It isn’t really efficient that you only have one person, the training director, who is capable of writing a macro that puts a rounded blue box around text. (And trust me that macro took me a whole day to get right).

Unfortunately the system I saw at Qt Developer Days lacked numerous key features I needed, so I decided to give it a shot myself, to implement a system that would do exactly what I needed.

Today we have such a system, and I have to admit that there were quite a few people who helped me out with the effort. Over the following four blog posts you will meet them, each telling their story about a specific piece they composed.

One person you will, however, not meet is Michel Giroday, who nonetheless deserves to be mentioned. He single-handedly rewrote most of the 3000 slides from LaTeX to the new QML-based system.

In this blog I will tell you a bit about what SlideViewer is and some of the design decisions made, but I won’t dive too deep into the technical bit. Stay tuned for the remaining four blogs for that.

Let me introduce to you: SlideViewer

So SlideViewer was born. The beauty of it is that all our Qt developers can help to add features and fix bugs, and even more importantly, we no longer have to stare at incomprehensible error messages from LaTeX, or hunt down a book that will tell us how to get page numbers in the table of contents.

SlideViewer in action looks something like this: Slide

The above slide was written with this QML code:

Slide {
    slideId: 1902
    title: "QCoreApplication, QGuiApplication & QApplication"

    topRight: SVImage { source: "images/QApplication.png" }

    text: "* In addition to QCoreApplication
           * QGuiApplication
           ** Window management
           ** Mouse cursor handling
           ** Clipboard interaction
           ** Keep track of system properties
           *** Palette
           *** Fonts
           *** Style Hints

           * Non-Widget(Qt Quick) applications"

    QtDoc {
        link: "qtgui/qguiapplication.html"
        text: "QGuiApplication"

As you can see the QML snippet is straight forward, and it displays QML’s power to be extended to a domain-specific language very well. A few notes to the above slide:

  • The first and foremost design goal was that it should be as easy as possible to write slides. I would under no circumstances accept any complexity in implementation that made it harder.
  • As an example of this design decision, the Slide element, for example, has an implicit row layout which means that elements added will automatically be stacked. The simple case must be simple.
  • Slide, SVImage, and QtDoc are all elements we’ve created in regular QML/C++.
  • A SVText element also exists which can be used like this:
    SVText {
        text: "* bullet 1
               * bullet 2
               * ..." 

    The Slide element has such an element implicit already, to which the text property links. (The simple case must be simple).

  • The only unexpected thing above is the slideId property which we enforce on all slides. This is simply for internal tooling, such as checking that the slide deck does not contain the same slide twice, and to allow us to jump directly from a slide displayed in SlideViewer to the slide itself in Qt Creator.

What other features does it have?

My goal from the very beginning was that it should not be more restrictive than what we already had in LaTeX. A rather ambitious goal, given that the LaTeX slides represented almost 15 years of development, and as mentioned we had more than 3000 of them!  At the same time, I wanted to avoid the problems that WYSIWYG tools have, resulting in each slide looking vastly different from the others. I believe we succeeded with those two goals, and here are just a few of the features SlideViewer offers:

  • Code blocks are highlighted for any of the possible languages included in the slides, including QML, C++, XML, Python, and shell commands. A code block simply looks like this:
    QMLCode {
       code: "NumberAnimation on x {
                from: 0; to: 150
                duration: 1000

    The highlighting happens in C++ with the help of Python for QML code and a JavaScript engine for other code snippets. This part will be discussed in detail in one of the coming blog posts. Here is another example of a slide with a code example on it:

    Slide {
        slideId: 2009
        title: "Using Identities"
        topRight: EmbeddedQml { codeItem: exIdentity }
        QMLCode {
            id: exIdentity
            fileName: "../../addon/qml-intro/ex-identity/ex-identity.qml"

    In this example the code is read directly from a file, so we don’t have diverging slides and examples, and furthermore the example is instantiated directly on the slide. This is nice for two reasons: 1) No more diverging slides/code examples and images 2) If the example is interactive the trainer can show it in action directly on the slide.

  • Arbitrary depth of sections, subsections, sub-subsections… are possible. These levels are introduced with a simple SlideSet element:
    SlideSet {
       title: "Introduction to Qt"
       Slide { ... }
       Slide { ... }
       SlideSet {
           title: "..."

    And of course the slide deck can be split over multiple files.TOC The table of contents is generated with a simple element:

    TOCSlide {
      section: "part-intro-to-qq"
      depth: 2
      verticalCompression: 0.6

    The above results in a table of contents for the slide set with the label part-intro-to-qq to a max depth of two levels (sub-subsections) and compresses the bulleted points a bit. Each point is a link to the actual section.

  • We have a large Config file where the individual trainer can specify which sections he wants included and which he doesn’t. That way changing a single property in that Config file (which of course also is a QML file), he can exclude entire sections of the material, or simply individual elements:
    SlideSet {
        title: "Network Programming"
        include: config.includeNetworkProgramming
        Slide {
            title: "Error Handling"
            text: "..."
            Text {
                visible: config.includeSSL
                text: "* ..." 

The road ahead

When I started this mission I had two goals: 1) Get us away from LaTeX 2) Create a foundation we could use to make our trainings more interactive, more fun, and a greater learning experience. We’ve now migrated all the material, so we are on par with what we had in LaTeX.  Ahead are all the fun parts.

Further, we can make any kind of interactive improvements, say a remote controller running on an Android device, where the presenter can see the next slide and/or instructor notes that will remind him of a key point on a given slide.

Another cool idea would be a test where students use their own computers to answer say a Q/A section, the statistics being shown directly in the slides as they answer.

Controlling the tools also makes it much easier for us to ensure quality in all the slides. Today, We for example already have a unit test suite that extracts single slides as PNG files for comparison against a baseline. I dare to declare that we are the first people in history to have continuous integration tests of our slide deck!

Another tool I’d like to see would enable the recording of which slides are used in which trainings, so we can improve precisely those slides used more often than others, or split out slides that most trainers spend a lot of time presenting.

In the coming blogs

This blog sets out the stage for four blogs to come which will go into details with specific technical issues we had when implementing SlideViewer, and which we believe many of you may also have in your projects. Stay tuned.

41 thoughts on “The development of SlideViewer”

  1. This is AWESOME. This is ABSOLUTELY where slides/presentations should go! I’m very much looking forward to the technical details in the following blog entries, and especially the dynamic-loading/refreshing of QML code examples to support (make easier) interactive “editing/creation” of the presentation. — GREAT stuff!

  2. Hmm, interesting project!

    This got me thinking what a music editor in QML would look like instead of LaTeX like in the lilyput project…

    You can say that this post was Inspiring, at least to me. 🙂

  3. Where can we get SlideViewer? Or is it not ready for public consumption yet?

    As a lover of LaTeX for writing papers, I’d love something similar for slides.

    1. Jesper K. Pedersen

      We haven’t decided if we want to make SlideViewer available to the public yet. Anyone interested in us doing so, please raise your voice, so we at least have an idea about the public demand for it.

      1. +1 Applications like this will raise the profile of QML as a powerful alternative to existing languages. Its definitely more than just a GUI programming tool!

        1. +1
          I’ve seen this presentation system at KDAB training sessions several times now. Great software! I’m still waiting for this to be released to the public.

  4. Is there any collaboration with the KDE Calligra guys planned?
    What you have there sounds like a cool foundation for a next-generation Calligra Stage

      1. +1 for collaboration.

        Since libreoffice sucks for slides. HTML5 libraries are awesome but have XML overheads, QML is the best of all worlds.

        Having a GUI to work when i’m having lazy days is always good 🙂

  5. Currently, all my presentations are done in LaTeX too. Would be nice to have an alternative too.

    Please consider releasing the tool, I think it will be useful for more people too.

  6. I’m a bit surprised that you didn’t work on the existing open source project that Gunnar started in 2011 and that has seen quite some improvements since then.
    And I don’t think that the marked for qml based presentation software is big enough to make a financially viable product out of it 🙂

    Here are the sources to Digias solution that is open source and has been used in many dev days presentations:

    1. Jesper K. Pedersen


      I did indeed consider basing my work on top of that, and indeed Gunnar’s tool was what I saw at DevDays. My need for a tool for 1000+ slides are, however, rather different than a tool for regular presentations, which meant that I already back then imagined that there was several features I needed that I would have to “fight” hard to get integrated into Gunnars work.

  7. Good, I wonder is that, it could be opensourced.. so that Qt would have it’s own truly Qt’iest office streamline Software stack, rather than bloated KDE things..

  8. Public demand?? This is fantastic (but not if other people can’t use it, utilize it or enhance it with supplementary tools). I think it could be the ultimate standard.

  9. Can it export to pdf? Having a pdf as backup is always a good thing: If suddenly your notebook does not work for whatever reason, a pdf will save you since there is always someone else with a pdf viewer.

    Oh, and LaTeX masters math formulas perfectly well. What about that? 🙂

    1. Jesper K. Pedersen

      Yes it does support PDF export using a rather cool mechanism where we paint the items using QPainter. Stay tuned for Thomas telling us all much more about that.
      No, we never had a huge need for math, but as someone else suggested MathML or similar could be an extension vector.

  10. Looks interesting. Very clean code. Will it support math typesetting? E.g. through MathML or MathJax?

    1. Jesper K. Pedersen

      Currently it doesn’t support math, no. This is not due to insurmountable problems, but more an issue of lack of need.

  11. Hmm, interresting. But you don’t plan to share your slides? Or how would other open these files, is there a pdf export?

    1. Jesper K. Pedersen

      Yes it supports a PDF export. This will be covered in one of the upcoming blogs. That part was anything by trivial 🙂

  12. I would really like to see this go public too. I have been using Gunnar’s implementation a few times and found QML to be a great language to write slides in.

    Have you by any chance considered math typesetting support with LaTeX/MathJax in the slides? I tried extending Gunnar’s system with math support a while ago, but only ended up with a hacky solution that called PDFLaTeX and returned the image file name for QML to use.

    1. Jesper K. Pedersen

      Thanks for your feedback.
      As mentioned, we’ve not really looked into typesetting math (yet).

  13. Sounds like an extremely cool thing. As someone who has always used LaTeX, I am very interested in having the sources of this available.

  14. Interesting stuff. I’d like to see how you’re going to support printing all these slides to PDF handouts or paper…

    We’ve just build a QML/Quick1 based reporting engine, relying on Quick1 partly because it is all QPainter based.

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