Helix Toolkit VS Win2D

About ditching WPF and using Unity: it should be possible without any problems, maybe outside of the license but that of course depends on the use case. You could also probably use helix, it's whole thing is supporting 3D in WPF.

For Windows only, Win2D!

You're looking for Win2D: https://github.com/microsoft/Win2D. It's the official D2D WinRT wrapper, supports UWP and WinUI, has seamless interior with XAML, it's very easy to use and has extensive interop APIs (even more so once we ship the next release) that give you maximum control if needed. I recommend checking it out 🙂

Your easiest bet is likely to use Win2D within UWP or WinUI 3, then you could just throw a CanvasControl as the root of your UI and draw whatever you want on it, including setting individual pixels. Alternatively an easy way to do that could be to use a WriteableBitmap in WPF/UWP/WinUI 3 just drawn into a root Border or something, and then you can easily manipulate pixels there. Of course, that'd be slower and not CPU accelerated, but still viable depending on your exact use case.

Alternatively you can also try Win2D, which is an official wrapper for D2D available for UWP and WinUI. You could use its CanvasAnimatedControl panel and then do your drawing from there, and just manually draw all your particles. The actual drawing would still be GPU accelerated, so it'd be relatively efficient (though less than using a custom shader, as you'd be queueing each particle from the CPU side).

To make a long story short, it's a UWP app since I've used DirectX 11 for drawing on the screen. I use C#, and I needed win2d (https://github.com/microsoft/Win2D)

Universal Windows Platform was introduced as the new hotness, but in my personal experience lacks a number of features from WPF I couldn't part with. It seems to have flopped a bit outside of applications developed by Microsoft. Projects that I though would bring features I really wanted (like win2d: GitHub - microsoft/Win2D) seem to have lost support. I'd hold off on this.