Hacker News Reader

Comment by jchw | Hacker News Reader

FWIW I think a more reasonable goto (than a browser) for a Raspberry Pi dashboard would be something along the lines of Qt QML, maybe with Python Qt bindings if you don’t want to write C++ code. It’s not really lightweight, but it can interface with the bare KMS EGL (no Xorg needed,) is hardware accelerated, and performance was acceptable when I last tried it on, I believe, a Pi 3.

View on HN

I've been monkeying with a Qt/QML app recently on my desktop with an eye towards deploying it on a Pi based thing. One thing really stood out: the Pi support kinda sucks. Specifically, the binary situation is not great and Qt is a bit of a beast to compile (plus I'd have to setup a Linux VM to cross compile in a reasonable amount of time).

Raspbian comes with a fairly outdated version of Qt inherited from Debian, and there are no precompiled EGLFS binaries that I can find. Even the Qt folks don't distribute an installer. I could understand a complex beginners guide[1] if this were lower level stuff. It's not.

1: https://wiki.qt.io/Raspberry_Pi_Beginners_Guide

I had the same experience a couple of months ago. I spent a weekend banging my head against a wall following their documentation to cross-compile for pi3. Turns out it was out of date and there were also a couple of bugs. Since then they did fix one of the issues I reported. The other one already had a long open issue with no resolution (at the time). But I've lost all interest in trying again for the foreseeable future and I wouldn't recommend the experience.

> recently

How recent? Debian's latest stable, Buster, got released a couple of months ago. Raspbian's rebase on Debian Buster is recent, like a good month ago. Raspbian should sport Buster's Qt version.

Right, and Buster has Qt 5.11. Qt 5.14 is nearly out and there've been some fairly significant changes in .12 and .13 (and finally a JS native table model for .14 — Qt Quick 2 is really, really immature).

Of course Debian only bundles X11 versions of Qt so if you're looking for an EGLFS build, you're still stuck rolling your own. If the Qt folks distributed pre-built EGLFS binaries for the Pi this would be a huge usability win IMO.

I was going to suggest the same but with LinuxFB. I don't believe it's hardware accelerated though.

https://doc.qt.io/qt-5/embedded-linux.html#linuxfb

Qt is fairly popular in the embedded space. I'd bet the support and robustness is quite good.

Oh sure, you could go direct to fb. I think the default builds on Raspbian already support the KMS EGL path, though, so in theory it just gives you extra performance at little cost.

I wish someone would implement a bare metal DRM/KMS/GLES backend for https://github.com/AvaloniaUI/Avalonia, e.g. based on NanoVG C library for vector graphics and fonts. .NET core runs way faster than JavaScript in browsers, and C# is much higher level than C++ people use with QT.

FYI: https://github.com/AvaloniaUI/Avalonia/blob/master/src/Linux...

That’s a great news!

I won’t redo the whole embedded GUI from custom NanoVG-based library to Avalonia, started much earlier than 2 months ago. For next embedded Linux project, or major version upgrade of the current one, I’ll definitely evaluate Avalonia.

Does it use GLES to render fonts and 2D graphics? Or they’re rendered on CPU?

Does it support ClearType-like font rendering, like this forked NanoVG? https://github.com/Const-me/nanovg/

Is there something comparable to WPF’s D3DImage to insert custom 3D content? In my custom library, I’ve implemented GlesInterop control which does nothing on the NanoVG render pass, but after the whole GUI is rendered, overlays a custom GLES content on top of the result.

How hard it is to implement custom touchscreen input? I’m currently generating touch events by reading from /dev/input/event0 with a FileStream class.

Is there on-screen keyboard in Avalonia? That’s probably the most complex piece of UI I’ve implemented in that project: input focus, modifier keys switching layouts, and that’s just for US English keyboard.

Qt + Warp 10... Maybe it could be possible !

But the kiss approach was great here. WarpScript includes all you need to render text, vectors, images... The limit is that I cannot use the touchscreen.

Thanks for your replies everyone !

Reply on news.ycombinator.com