I made this with the Metal APIs in VisionOS 2.0. It now gives access to low-level mesh features and buffers directly, meaning lots more particles are possible (around 5-10x)! The hand-tracking also seems much, much smoother.
The fluid sim is a version of SPH running on the GPU, with the particles drawn with billboarding orientated to the headset position.
Would love to hear any feedback - for anyone with a AVP, it's available to try for free here:
https://apps.apple.com/app/id6470201263
With more information about Lungy here (https://www.lungy.app).