[flohofwoe]

Nuklear returns a bunch of vertices, vertex-indices and draw commands, so it plugs best into a 3D API (like GL, D3D, Metal, Vulkan...). To render into a frame buffer you'd need to implement a simple software rasterizer with texturing support.

[0x0203]

One of their demos already has a software rasterizer. I've used it to draw directly to a frame buffer for a custom OS that didn't support accelerated graphics. It's in the demo directory under x11_rawfb. I made some tweaks to that (getting rid of all X11 stuff) and wrote my own fb/tty/mouse/keyboard driver and got it working great without any graphics API layer between it and the pixels that get drawn directly to video memory and the screen.