Wētā Digital showcased the tools and solutions they used to create Avatar: The Way of Water's photorealistic water.
Digital visual effects company Wētā Digital – now part of the Unity family – has recently shared a comprehensive blog post showcasing the tools and solutions they developed for James Cameron's Academy Award-winning Avatar: The Way of Water.
Breaking down the production process behind the movie's photorealistic water, the team discussed the formation of the Water Taskforce, a team of experts that included Unity and Wētā’s water simulation VFX specialists, and the award-winning water toolset with a number of distinct solvers they developed to produce both large- and small-scale water simulation.
According to the developers, most of the tools they created are powered by Loki – Wētā’s proprietary simulation framework that includes solvers for multiple water states, such as procedural water waves, bulk water, spray, mist, hero bubbles, diffuse bubbles, foam, capillary surface waves, and more.
Furthermore, the team spoke at length about the Loki state machine – an airborne spray system that most of the aforementioned solvers use describing how it allows multiple solvers to run in tandem and explaining how it helped them "keep large-scale water simulations efficient while still capturing the very fine droplet interactions required by spray and mist."
Moreover, the team showed how a practical approach for modeling close-up water interaction with characters, first unveiled during SIGGRAPH 2019, was leveraged to handle any sequence that involved characters emerging from the water.
As for when the characters are pictured underwater, Wētā also highlighted the method they used to simulate underwater bubbles, which involved an incompressible two-phase Navier-Stokes solve on an Eulerian grid and FLIP/APIC particles.
On top of that, the team presented a neat method of post-processing that took a simulation as input and increased its apparent resolution by simulating detailed Lagrangian water waves on top of it.
And finally, Wētā showed how The Way of Water's whitewater particles were made, breaking down the method they came up with, which allowed for the realistic movement of underwater bubbles.
"One key aspect of our whitewater method is the interaction of two solvers: a grid-based fluid solver coupled with bubbles, and an SPH solver for foam constrained to the water surface. The declarative solver framework in Loki is what makes building and supporting these complex systems possible in production without having to develop new solvers from scratch," commented Joel Wretborn, senior research engineer at Unity and Wētā Digital.