Expose any Qt5 program via VNC

5 min read
fairly easy
Article URL: https://raymii.org/s/articles/Expose_any_QT_program_via_VNC.html Comments URL: https://news.ycombinator.com/item?id=28597870 Points: 1 # Comments: 0
Published: 20-09-2021 | Author: Remy van Elst | Text only version of this article

Remote Coffee Machine Qt GUI via VNC

A few months ago I wrote about Microsoft Teams running on a coffee machine. That was a fun work experiment where I got a VNC client running on the linux-based coffee machines that we produce at work. In the comments on hackernews Jean-Michaël Celerier pointed me to the reverse, a way to expose any Qt application over VNC. This article shows you how I use this feature to work on our Qt 5 based coffee machine frontend as well as how you can use this on your machine, for example, to expose Dolphin, the KDE file manager, over VNC.

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Our Qt frontend for the coffee machines can run as a local application just fine, it's nothing more than a client towards an HTTP API. One other such client is our touchless feature, that exposes a part of the machine over MQtT to a website.

One issue with running the Qt application on my workstation is that remote media is not loaded. The coffee machine can display images and video (and show a QR code), but those images are dynamically loaded in QML, via a filesystem path that my machine does not have. I could setup an sshfs mount, but that would require fiddling with permissions. In the instances that I have to work on that part of the code I run the UI via VNC directly on a coffee machine, all the filesystem paths are available then.

Qt 5 applications via VNC

You can append a command line flag to any Qt application or set an environment variable to expose the application over VNC. The command line flag is -platform vnc and the environment variable is Qt_QPA_PLATFORM="vnc" . Here is how to run Dolphin via VNC on port 5900:

Qt_QPA_PLATFORM="vnc" dolphin # or dolphin -platform…
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