Bullet VS Torque3D

For typical game physics engines... not that much. Math libraries like Eigen or Blaze use lots of template metaprogramming techniques under the hood that can help when you're doing large batched matrix multiplications (since it can remove temporary allocations at compile-time and can also fuse operations efficiently, as well as applying various SIMD optimizations), but it doesn't really help when you need lots of small operations (with mat3 / mat4 / vec3 / quat / etc.). Typical game physics engines tend to use iterative algorithms for their solvers (Gauss-Seidel, PBD, etc...) instead of batched "matrix"-oriented ones, so you'll get less benefits out of Eigen / Blaze compared to what you typically see in deep learning / scientific computing workloads.

The codebases I've seen in many game physics engines seem to all roll their own math libraries for these stuff, or even just use SIMD (SSE / AVX) intrinsics directly. Examples: PhysX (https://github.com/NVIDIA-Omniverse/PhysX), Box2D (https://github.com/erincatto/box2d), Bullet (https://github.com/bulletphysics/bullet3)...

I suspect most C++ physics libraries like Box2D (https://github.com/erincatto/box2d) or Bullet3 (https://github.com/bulletphysics/bullet3) could really benefit a lot from SIMD.

No, they replaced Bullet with Jolt. That is considerably more than "some adjustment", regardless of what you think of the result.

Vulkan graphics via Intel GVK, and physics via Bullet

The first two have a bunch of great examples, and I’m tying them together by refactoring some of the THREE examples to fit the ECS paradigm defined in AFrame. then upping the ante by adding physics using AMMO, which is more challenging since it’s only a partial implementation of Bullet, and already poorly documented (yet popular) physics engine.

Plus, SM uses a system called bullet physics, I imagine this would be rather complex to rework into a modern engine such as Unreal or Unity (after all, the majority of performance issues come from the physics engine rather than the graphics engine)

The physics in HDT-SMP are actually being calculated outside of Skyrim's engine with Bullet, an open-source physics engine. So this isn't some limitation of Skyrim's engine.

On a similar note, released games with open sourced code: https://osgameclones.com/?tag=official

https://torque3d.org was used on Airship Dragoon, Marble Blast Gold, Penny Arcade Adventures, Legions: Overdrive and descends from the original Tribes engine.

Hellbreaker, Bit Champs with https://u3d.io

And plenty of successful games with Ogre, including Torchlight: https://www.ogre3d.org/showcase

Torque 2D/3D: Didn't do too much digging around on this one, but both versions are MIT licensed like Godot, but it seems like the project is a little more mature, with built-in multiplayer support. Could be worth looking into as an alternative to Godot if you really want something with MIT licensing.

But from now on, I think I will abandon that, and continue with Torque3D engine : https://torque3d.org/

Torque3D- This one seems great for beginners, as it's free and open-source. The downside is, I'm not sure if it has enough features for complex projects or how secure it is.

Torque3D (the engine used to make Tribes 2, now open-source)

No lie, that overall looks a lot like a game done for a senior design project 15+ years ago using Garage Games' (now https://torque3d.org/) RTS kit.

Torque