Softy

Simulation tools and libraries for animating rigid and soft objects (including cloth) subject to frictional contacts against smooth implicit surfaces.

This repository includes a reference implementations for [1] and [2].

Overview

The included tools and libraries are organized in directories as follows

• implicits --- A Rust crate to generate local and global implicit surfaces.
• implicits-hdk --- A Houdini plugin for the implicits Rust crate.
• cimplicits --- A C wrapper for the implicits crate.
• softy --- A Rust crate for simulating interacting soft (both solid and shell) and rigid objects.
• softy-hdk --- A Houdini plugin for the softy Rust crate.

These tools are mainly written in Rust with C/C++ wrappers.

Installation

There are two installation scripts available: install_min.sh and install_all.sh. Installing HDK plugins written in Rust that use other C++ libraries like MKL or TBB may conflict with Houdini's libraries. For this reasons install_min.sh is there to install only the necessary plugin and command-line tool to create and run simulations. If one wants to only run the included examples, simply install softy-eval and run the included configuration files, see the corresponding README.md for instructions.

Going forward you need the Rust toolchain and Houdini installed.

Most of the code included here is written in Rust, so you will need to have the Rust toolchain installed. Check rust-lang.org for specific instructions. It is typical and recommended to install the rustup tool and then use it to install cargo.

Next, install the cargo-hdk tool with

cargo install cargo-hdk

This tool helps orchestrate building and installing Rust plugins for Houdini's C++ API called the Houdini Development Kit (HDK).

To install Houdini, go to sidefx.com create an account and install Houdini 20.5 (other versions may work, but this one was tested at the time of this writing). Before installing any of the plugins, you must source the Houdini environment variables found in the Houdini installation directory. For details on specific steps needed to build an HDK plugin see the HDK Getting Started Guide. Follow all the steps listed there up until actually compiling the plugin with hcustom and running it.

Finally, run either of the provided install scripts (macOS or Linux only) to install the plugins:

• install_min.sh installs scene-hdk for creating configurations using Houdini and softy-eval for running simulations using the generated configuration files with softy.
• install_all.sh installs all included plugins and command-line tools.

References

• [1] Egor Larionov, Ye Fan, and Dinesh K. Pai. 2021. Frictional Contact on Smooth Elastic Solids.,
• [2] Egor Larionov, Andreas Longva, Uri M. Ascher, Jan Bender, Dinesh K. Pai. 2024. Implicit Frictional Dynamics with Soft Constraints.,

C API conventions

This section outlines the naming conventions for any public C symbols exposed from Rust libraries.

Let pfx be the desired prefix for the library at hand. For instance we may chose hr as the prefix for hdkrs. The following conventions apply to all public facing C API symbols. This includes Rust code with a C public API. Private symbols in Rust code need not be prefixed.

• Function names should be in snake_case and prefixed with pfx_.
• Struct names should be in TitleCase and prefixed with PFX_.
• C Enums should be in TitleCase and prefixed with PFX. Note that some Rust enums will be bound to C structs, in which case their prefix should be PFX_.
• Enum variants should be in SCREAMING_SNAKE_CASE and prefixed with PFX_.

Note that we must set the language for cbindgen to be Cxx or set cpp_compat=true. Otherwise, without proper extern annotations in the generated C headers, the exported function symbols will be mangled by the C++ compiler and effectively lost.

Ideally we would want to wrap any raw C calls in safer C++ wrappers.

License

This repository is licensed under the Mozilla Public License, v. 2.0.

Contributing

See CONTRIBUTING.md for details.