Total immersion: Wētā Digital’s VFX toolset on Avatar: The Way of Water

Talking about Tulkuns

Every once in a while, something on the screen needed to happen that would break physical laws. “There would be a call for a very special looking water splash, or a creature that has never been seen before does something and you need to figure out what’s going on with it,” says Stomakhin. “Whenever that came up, we would always start running our solvers to experiment and see what we get out of it. But then we’d get some artistic feedback, some artistic notes from VFX supervisors or directors saying it looks good, but it’s not exactly conveying the message that the movie is supposed to be conveying at this story point. So we would have to essentially modify our tools, tweak the parameters, and have to break the laws of physics that we have introduced just slightly, so that we can achieve that specific effect.”

Lo’ak (Britain Dalton) and a Tulkun in 20th Century Studios’ AVATAR: THE WAY OF WATER. Photo courtesy of 20th Century Studios. © 2022 20th Century Studios. All Rights Reserved.

When asked if there were any sequences or shots in Avatar: The Way of Water that James Cameron or the VFX supervisors asked for that really pushed skills and technology to the limit, Stomakhin replies “all of them”, but then goes on to focus on specific challenges.
One of these was the whale-like tulkun creatures that have a special bond with the Na’vi.
“James Cameron was very particular about the tulkun,” says Stomakhin. “Those were quite challenging because they really wanted to make sure we got the splashes, the whitewater and the spray and air interaction all correct and matching real-world whale references.
“The Loki state machine that creates those transitions between different states of water was the big push towards ensuring that a tulkun breach would look realistic,” he adds.
However for some of Pandora’s creatures, applying such recognisable physics was not as appropriate at times.
“Take the skimwings, those big crocodile creatures with wings, where in the final battle they’re in the water and quite aggressively swimming the tails back and forth quite a lot. When we applied that motion straight inside of a physics solver, we were getting all sorts of different splashes that the director didn’t like.
He was very particular about the curve that the tail of the creature was supposed to leave on the water as they propel themselves forward and how the splashes look. So we really had to tune that look, not necessarily making all physically based decisions. It definitely was a challenge.”

Stomakhin also revealed why Cameron chose to film the characters in the water “instead of just cheating and filming it all in the air”.
“An actor can move in the air in a way that would not be appropriate for the water just because the water has so much resistance. And if a person does one of those really fast motions during motion capture and we try to run a physically based simulation with those. It may not result in the effect that we would expect the solver to produce. Maybe the water will get disturbed more, generate more bubbles and stuff like that. Because we’re dealing with physically based tools, we expect the input motion to be somewhat physically plausible. So that’s why actually immersing actors in the water was critical to get those more realistic inputs for the later stages of production.”

“We also knew in advance that there was going to be a lot of characters getting in and out of water constantly and we really wanted to capture that that roll off of water off of the skin. We had to pay a really high price for that solution.
One of the most challenging shots was where kids fight in the sand and shallow water, and we had to simulate that water layer on all of them and we had to use such a high resolution. It wasn’t that much water, but it was a lot of particles to simulate, and that turned out to be one of the most expensive simulations in the entire movie. It took something like eight days to complete. An artist would just send the sim to the Render Wall and have to forget about it for a week before they could see any kind of results.

Example frame of a thin film simulation on a skin surface following [Stomakhin et al. 2019]. ©Wetã FX.

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