AFAIK, turning off GC in D is not feasible whenever using large portions of the standard library, but there were efforts underway to change that. Do you know if there's been much progress?

Lots of progress, but there's still work to do. If the GC is unacceptable for your application, slap `@nogc` on your `main` function and you're guaranteed to not use it.

I'm writing OpenGL code. I know lots of languages claim support for OpenGL, but in my opinion dealing with gpu stuff is something best written in C or C++. All the guides, all the answers to questions, all the popular books, everything out there assumes you're using C or C++ when you're working with GPU code. It's fine. I like using C++ for this. OpenGL in any other language and you're a second class citizen at best.

Have you tried https://github.com/tomaka/glium?

D much like C++ interfaces to C see:

https://dlang.org/spec/interfaceToC.html

D was at one point a C++ compiler but Walter Bright decided to break backward compatibility with C syntactically to allow the language to evolve in ways that C restricts, while still allowing it to interface with C. Sorry if I worded this poorly, but you may want to reconsider D and see for yourself if it feels like a second class citizen or what? There are sample projects interfacing to C projects (LuaD comes to mind).

I first heard about D from Gamedev.net, so you can certainly do OpenGL with it. I believe there have even been commercial games written in D.

Kenta Cho's shooter _Torus Trooper_ is written in D and might make a good example. (It's a damn good game, too.)

https://www.youtube.com/watch?v=PJMTQmqxBqg

http://www.asahi-net.or.jp/~cs8k-cyu/windows/tt_e.html

Also, ported to Linux: http://www.emhsoft.com/ttrooper/

What is the tooling and library ecosystem like for D compared to Java?

D programs can make direct (=zero overhead) calls to C functions (like we do in C++). Which basically means you have access to any C library.

The D standard library is very dense (it makes C++14 standard library look ridiculously incomplete), so most things are available out of the box (threads, processes, filesystem, network, random, algorithms) ... in a portable way.

There's a Visual Studio plugin available, and I know VS Code has a nice plugin as well ( you need to install certain tools yourself in that case ), as well as other editors with their own feature set. There is also Dub[0] which is a build tool for D and gives you access to all sorts of D packages. I'm still a beginner to D so forgive me if my answer doesn't suffice.

[0]: https://code.dlang.org/getting_started