Direct3D engine in C

While a D3D engine in C would be possible the code would certainly look horrible since C++ is better suited for D3D. I'm not sure if there actually is a D3D engine in C. Why does it have to be in C anyway?

I want to convert an old game (with 2D graphics) written in C and make it 3D. I don't think that mixing C and C++ is possible for me to achieve, as well as I don't want to bother with low level Direct3D drawing.

You can mix C and C++ in the same project perfectly fine. If the engine uses C++ you'll need a wrapper layer around it to be able to call it from C code though.

Why does it have to be D3D in this case? OpenGL would be ok too and that has a native C interface. Also mixing C and C++ is no problem at all. Generally you can compile your C sources as C++ without any modifications.

It's possible, yes, but not pleasant. You're better off trying to link C with C++, as suggested above.

If OpenGL is OK, perhaps you could use the Quake 3 engine. It is written in C and open source. It may be older than what you were hoping for though.

Actually, a more modern C game engine would be pretty cool because it would allow many languages to use it through their foreign function interfaces.