Have you tried Allegro? If you can get an environment set up to compile the library and make Allegro projects in C or C++, it has a software renderer for 3D primitives (textured and untextured). It's not an engine in the sense that you can just include it and give it a BSP or some models and it'll run straight away, but it'll give you all the pieces you need to make any engine you want. If you just want to draw some primitives, or do something like the Rise of the Triad rotating menu transitions it'll work. Look at the ex3d example for what's needed (translation/transformation/rendering).

https://liballeg.org/readme.html
https://github.com/msikma/allegro-dos-example
https://www.mrdictionary.net/allegro/
https://github.com/msikma/allegro-4.2.2-xc/bl … examples/ex3d.c

Alternatively, all you need for your task I think is some 3d transformation maths and a triangle or quad rasteriser which are not very difficult to write.

Also don't forget that Rise of the Triad itself is open source so if you're trying to recreate their menu style you can use them as a reference

Also I just found this, maybe Zox3d would be a useful reference as well.
https://bearstrong.net/tekst97/data/programme … /pcgpe10/modex/

graphics engine. It resembles Wolf3D, but has a number of additional features: […]
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graphics engine.
It resembles Wolf3D, but has a number of additional
features:

- texture mapped floor and ceiling (sky, in this demo)
- real, recursive MIRRORS!
- partly TRANSPARENT walls
- input from keyboard, joystick and mouse (at the same
time, too, if you wish)
- controllable camera height - NOT fixed like Wolf3D
- quick resizable window
- online help and fps rating
- advanced collision detection and handling
- supports a variety of tweaked X modes, from 256x256 to 400x300.

The sky and mirrors have to be seen to be beleived!

Zox3D does NOT implement objects, like the guards in
Wolf3D, but that should be a breeze to add.

The complete sources are available. Read ZOX3D.DOC in
the demo archive for information.

Thanks for the help, it's the first time I've heard of Allegro, I'll try to learn one about him, let's see what I can get!