[q_andrew]

Hey! Congrats on the launch, the touted performance increases are mind blowing.

I think physics engines are difficult for a few reasons:

- They don't mesh with a lot of features that modelers take for granted (non-uniform scaling, concave meshes, lax model scaling)

- It's hard know intuitively what values to use for things like acceleration, density, velocity, damping, friction. Especially because they are very inter-dependent.

- Interaction with moving kinematic or non-physics objects is an undefined behavior that has to be tested pretty rigorously.

- In gamedev, rigidbody physics are basically a trojan horse for gameplay bugs like clipping through the map and sudden bursts of high speeds (Which is both magical and frustrating). It's a non-trivial task to sandbox those behaviors completely.

- Projectiles. There's no catch-all solution for small fast-moving objects, it's always a tradeoff. But that's mostly because big O dictates it to be so.

[looklookatme]

Thanks for those insights! I think some of the things you mention (non-uniform scaling, concave meshes) are getting easier these days, thanks to tooling around things like convex decomposition and relaxed memory requirements, although, even without considering physics, it seems scaling causes huge problems for _everyone_ - feels like every Blender tutorial out there will say "remember to apply scale" to sidestep those scale issues. The other things you talk about feel very second-nature to me at this stage, so it's interesting to hear that kind of perspective. I think physics engines in general could certainly be doing a better job at documenting how the exposed physical parameters map unto use-cases.

[throwaway17_17]

Do you think the problems with scaling (particularly non-uniform) primarily arise because most physics, animation, etc., are biased towards uniform normalized scale? Or is there some other issue I am unaware of that causes the issues?