A Code for the Code: Simulations Obey Laws of Physics With USD

Universal Scene Description now sports an extension so objects can be simulated to act just like they would in the real world thanks to the collaboration of Apple, NVIDIA and Pixar Animation Studios.
by Richard Kerris

Life in the metaverse is getting more real. 

Starting today, developers can create and share realistic simulations in a standard way. Apple, NVIDIA and Pixar Animation Studios have defined a common approach for expressing physically accurate models in Universal Scene Description (USD), the common language of virtual 3D worlds. 

Pixar released USD and described it in 2016 at SIGGRAPH. It was originally designed so artists could work together, creating virtual characters and environments in a movie with the tools of their choice. 

Fast forward, and USD is now pervasive in animation and special effects. USD is spreading to other professions like architects who can benefit from their tools to design and test everything from skyscrapers to sports cars and smart cities. 

Playing on the Big Screen 

To serve the needs of this expanding community, USD needs to stretch in many directions. The good news is Pixar designed USD to be open and flexible. 

So, it’s fitting the SIGGRAPH 2021 keynote provides a stage to describe USD’s latest extension. In technical terms, it’s a new schema for rigid-body physics, the math that describes how solids behave in the real world.  

For example, when you’re simulating a game where marbles roll down ramps, you want them to respond just as you would expect when they hit each other. To do that, developers need physical details like the weight of the marbles and the smoothness of the ramp. That’s what this new extension supplies. 

USD Keeps Getting Better

The initial HTML 1.0 standard, circa 1993, defined how web pages used text and graphics. Fifteen years later HTML5 extended the definition to include video so any user on any device could watch videos and movies. 

Apple and NVIDIA were both independently working on ways to describe physics in simulations. As members of the SIGGRAPH community, we came together with Pixar to define a single approach as a new addition to USD. 

In the spirit of flexibility, the extension lets developers choose whatever solvers they prefer as they can all be driven from the same set of USD-data. This presents a unified set of data suitable for off-line simulation for film, to games, to augmented reality. 

That’s important because solvers for real-time uses like gaming prioritize speed over accuracy, while architects, for example, want solvers that put accuracy ahead of speed. 

An Advance That Benefits All 

Together the three companies wrote a white paper describing their combined proposal and shared it with the USD community. The reviews are in and it’s a hit. Now the extension is part of the standard USD distribution, freely available for all developers. 

The list of companies that stand to benefit reads like credits for an epic movie. It includes architects, building managers, product designers and manufacturers of all sorts, companies that design games — even cellular providers optimizing layouts of next-generation networks. And, of course, all the vendors that provide the digital tools to do the work. 

“USD is a major force in our industry because it allows for a powerful and consistent representation of complex, 3D scene data across workflows,” said Steve May, Chief Technology Officer at Pixar. 

“Working with NVIDIA and Apple, we have developed a new physics extension that makes USD even more expressive and will have major implications for entertainment and other industries,” he added. 

Making a Metaverse Together 

It’s a big community we aim to serve with NVIDIA Omniverse, a collaboration environment that’s been described as an operating system for creatives or “like Google Docs for 3D graphics.” 

We want to make it easy for any company to create lifelike simulations with the tools of their choice. It’s a goal shared by dozens of organizations now evaluating Omniverse Enterprise, and close to 400 companies and tens of thousands of individual creators who have downloaded Omniverse open beta since its release in December 2020.  

We envision a world of interconnected virtual worlds — a metaverse — where someday anyone can share their life’s work.  

Making that virtual universe real will take a lot of hard work. USD will need to be extended in many dimensions to accommodate the community’s diverse needs. 

A Virtual Invitation 

To get a taste of what’s possible, watch a panel discussion from GTC (free with registration), where 3D experts from nine companies including Pixar, BMW Group, Bentley Systems, Adobe and Foster + Partners talked about the opportunities and challenges ahead.   

We’re happy we could collaborate with engineers and designers at Apple and Pixar on this latest USD extension. We’re already thinking about a sequel for soft-body physics and so much more.  

Together we can build a metaverse where every tool is available for every job. 

For more details, watch a talk on the USD physics extension from NVIDIA’s Adam Moravanszky and attend a USD birds-of-a-feather session hosted by Pixar.