Cinesite’s work revolved around a proprietary tool that the crew has built inside Houdini, called csSmoke. The tool had to be developed further than ever to execute the effects for Dawn Treader. As 3D supervisor Stephane Paris explains, the challenge was to place the mist in that middle ground between reality and the imagination.

“The filmmakers wanted something not physical, but not too ghostly at the same time,” Paris says. “The mist is an idea. It’s temptation. It’s evil. You never know what its intention is. They wanted something you can fear. So it was all about attitude and animation. It was difficult and really exciting to find a way to make that happen.

Cinesite’s approach to the animation evolved through a back-and-forth with the film’s VFX supervisor, Angus Bickerton. First, Cinesite delivered 2D concept images helping establish the basic look of the smoke – it would glow from the inside, with different aspects of shadow and light visible in its mass.

To set it in motion, Cinesite started by animating a cylinder and having it drive the particle simulations. “That was not enough,” Paris recalls. “It needed more character.” So instead of plain-vanilla cylinders, animators used eel characters to give the mist’s movements a more nuanced quality.

But since that animation was driving the complex fluid simulations that would create the smoky mist effect, it was important that the team kept a close eye on how each animation decision affected the look of the particles. “It was tricky to create a nice animation with accelerations and decelerations,” Paris says. “Normally, when you slow down the movement of something like that, you have an accumulation of particles, and then when you accelerate you suddenly have nothing. The main problem was achieving regularity in the particle emissions, and making sure we weren’t breaking the simulation at the same time. We were refining the rig on a shot-by-shot basis.” The mist was roto’d into scenes on the deck of the Dawn Treader, where Cinesite had to make sure it integrated smoothly with the live-action blue-screen footage.

At one point, Cinesite was called upon to embellish the on-screen appearance of Tilda Swinton, who reprised her role as the White Witch. But this time she wasn’t really the White Witch. “In the story, Edmund had a relationship with the White Witch, and here the mist is taking her shape in order to manipulate him,” Paris says. “Edmund knew the character, so she had to be recognizable, and we had to make sure we didn’t kill Swinton’s performance.”

A digital double was created for every aspect of Swinton’s performance, including lip-sync. That model was used to drive fluid simulations off her body in the final shots, recreating her as a smoky, ill-intentioned version of herself. On set, Swinton’s hair was covered, and Cinesite created a floating hair simulation, as though she were underwater, and emitted some fluids from that hair to create more smoke. “The most complicated thing was putting all of that together in the comp to make her look beautiful but scary at the same time,” Paris says. “It took a huge number of passes, but it gave us the freedom to create the character in that way.”

The project represents a significant first for Cinesite – the facility has never before completed an entire project in Nuke. Staying in a single compositing package can make working on elaborate composites more straightforward. “When you look at the Dawn Treader boat in the mist near the end of the film, they’re surrounded by a huge amount of fog,” Paris says. “That’s at least seven layers of 3D smoke to make sure all the light interactions are working properly, and three or four layers of 2D fog on top of that. Because we were using only Nuke, we were able to share a lot of assets and geometry in the composite.

“Our environment for that sequence was just geometry with matte paintings projected and animated directly in Nuke. I think that was the first time we did it that way here.”