This month in rustsim #8 (August − September - October 2019)

Welcome to the eighth edition of This month in rustsim! This monthly newsletter will provide you with a summary of important update that occurred within the rustsim community. This includes in particular updates about the nphysics (physics engine), salva (fluid simulation), ncollide (for collision-detection), nalgebra (for linear algebra), and alga (for abstract algebra) crates. This eighth edition will actually contain updates for the past three months (I got sick between the second and third month so I did not get the time to write a new post then. Sorry!)

Join us on discord and on our user forum!

Progress of current developments

Two new crates for fluid simulation: salva2d and salva3d!

[![salva logo](](

We are thrilled to announce that the release of two new crates: salva2d and salva3d! Check out their website:

Salva is our new project dedicated to fluid simulation. The goal of salva is to provide CPU-based, particle-based, 2D and 3D, fluid simulation libraries that can be used for interactive and offline application like animation. It could be used, to some extents, for video games (especially the 2D version), as long as the number of particles is kept small. Right know, salva is still very new and lacks a lot of features. We don't consider it to be ready for public use, though we feel like it's a good time to share our progress so far. Right now, the following features are supported:

  • Pressure resolution based on the Position-Based-Fluids (PBF) method.
  • Viscosity based on the XSPH method.
  • Multi-phase fluids with different densities and viscosity coefficient.
  • Two-way coupling with nphysics: fluids can interact with nphysics' rigid bodies, multibodies, and deformable bodies. Large density ratios are not well handled yet.

This last point is the one that took us the most time to get right from a design point of view. At first, we wanted to implement fluid simulation directly as part of nphysics. This proved very difficult considering particle-based fluids use their very own type of force computation methods and even have their own ways of detecting contacts. Moreover, it turns out most of the literature on two-way coupling already assume that rigid-bodies are handled in a separate engine. Hence, it was both more easier, more efficient, and cleaner, to design salva2d and salva3d as crates of their owns.

The name of the project, salva, is inspired from the famous artist Salvador Dalì. The logo of Salva is inspired from its renown painting The Persistence of Memory featuring melting clocks. You can salva it in action (including two-way coupling) in the following video:

You can also play with it in the 2D WASM version and the 3D WASM version.

Improvements on nphysics 0.13

Some support of breakable joint constraints

It is now possible to define a maximum break force for joints constraints on nphysics 0.13. Simply call the .set_break_force or .set_break_torque method from any joint constraint and it will automatically break as soon as the joint would be required to deliver more than this break force/torque.

More improvements on the integration with ECS

The version 0.12 of nphysics introduces a massive change on ways bodies, colliders, and joints, were stored. However it was still not quite enough to allow custom ECS-compliant storages to be used as storages for nphysics entities. This is now much simplified with the amazing contribution made by @distansient from the Amethyst community. You may want to take a look at specs-physics which is a work-in-progress crate for integrating nphysics with specs.

New sponsorship platform: GitHub sponsor

I (the main developer of all the current rustsim projects) have been added to the GitHub sponsor beta. This means that besides patreon, it is now possible to make a financial contribution through GitHub sponsor there. Also note that GitHub will match your donations during the first year! So for each $ donated, GitHub will itself donate the same amount as a bonus!

Your continued help allows me to dedicate more time to those Rust crates. Thank you all!

Next steps

The next two months will be dedicated to making salva ready for public use. In particular the priority will be to:

  • Allow the removal of fluid and boundary objects from the world. Right now you can only add them.
  • Allow the removal of a coupling with a collider from nphysics. Right now you can only add them.
  • Implement another pressure resolution method: DFSPH. The user will be able to choose between the PBF and DFSPH solvers. This will also allow us to improve the design of salva to define the traits required to allow users to define their own solvers.
  • Implement surface tension.
  • Implement (optional) adaptive timestepping.


We would like to thank the whole community and contributors. In particular, thanks to the contributors from the past three months1:

Finally, thanks to all the former, current and new patrons supporting me, sebcrozet, the lead developer of the current crates part of this organization on patreon or GitHub sponsors! This help is greatly appreciated and allows me do spend a significant amount of time developing those crates.

  1. The list of contributors is automatically generated from the past two months' github commit history. Don't hesitate to let us know if your name should have been mentioned here.