Cool, I'm also writing my own engine.
Java is an interesting choice of language for writing your own game engine, not the fastest.
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Yeah it is not the fastest. The CPU code would run somewhat faster if in C or C++. But the heavy lifting in my code is done by the shaders in the GPU so the game is not affected at all. Congrats on doing the hard work of writing your own engine. At the end it pays back with less bloated software, smaller foot-print distribution and you also have full control.
Could agree more! We also don't need to rely on reporting and waiting for bug fixes from their side (some times takes years for them to get to fix), here we do it ourselves.
I had a past with Java back in 2007, and yes if you do the heavylifting in GLSL you should be good to go, after all minecraft was a hit and originally done java too.
Mine is in C++ with OpenGL and Metal, I'll add DX in future.
Good luck with your engine it already looks very cool!