brokenprogrammer/Mass — reverse-engineered prompt

Build me a small 3D first person shooter project called Mass in Java, made from scratch as a learning style game engine project. I want it to open into a simple playable 3D scene where you can move with keyboard and mouse, look around with an FPS camera, and have basic shooting so it feels like a real prototype instead of just a tech demo.

Please include the core pieces you’d expect in something like this, a game loop, rendering, player movement, simple level geometry, collision or physics, and a clean way to organize the code so it is easy to study and extend later. It does not need to be a full game with lots of content, but it should feel polished enough to run and show the basics of a homemade 3D FPS.

Keep it faithful to a from scratch Java project and use the usual Java libraries for low level graphics and physics if that makes sense. If anything is unclear, look up current docs online and make sensible choices.