Bullet VS AmnesiaTheDarkDescent

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.

Looks like the source code is publicly available: https://github.com/FrictionalGames/AmnesiaTheDarkDescent and the Sclerosis (this port) developers are preventing the game from being distributed anywhere: https://createam.itch.io/sclerosis " P.S.: Frictional Games prohibited anywhere to distribute my remake, so I'm posting the full version for free without any restrictions on my itch.io in the hope that soon the game will appear on all kinds of forums and sites, after which I will probably hide the game from there. Version v1.7 will remain the final version for Sclerosis: The Dark Descent. "

This curiosity grew even more when I downloaded Amnesia source code and saw in there LOTS of Pointers, but I have no idea what I'm looking at (just yet, I hope).

Here is the source code to amnesia the dark descent https://github.com/FrictionalGames/AmnesiaTheDarkDescent crazy how that exists when you say it can't exist

The game engine that runs Amnesia was written by 2 guys, uses OpenGL (which is a hell to begin with, especially on different hardware) and does use some quite advanced shading stuff for its low complexity. They released the code btw. if anyone is interested.

As for Amnesia it's a similar story; They're using their own in-house engine which does itself use SDL. FrictionalGames recently open sourced Amnesia so you can take a look if you wish: https://github.com/FrictionalGames/AmnesiaTheDarkDescent

Project is seemingly dead with the latest commit being from 2018.

Two major games with code on github I can think of are Amnesia: The Dark Descent (1) and Celeste (2)

(1) https://github.com/FrictionalGames/AmnesiaTheDarkDescent