CGSociety :: Production Focus
27 June 2012, by Paul Hellard
Pixar Animation Studios started toying with their hair simulation about 12 years ago, within the throes of creating Monsters Inc. Then in 2009, with the beginning of BRAVE the 13th animated production at the studios, a research project was begun to work out how to depict curly hair. The following year, this digital shampoo was brought into production for Merida’s hair in BRAVE.
“Hair is often very shading and lighting dependent,” adds Claudia Chung, Tailoring Cloth Supervisor at Pixar. “In terms of simulation, the core simulator we used on BRAVE
for cloth is exactly the same one we used all the way back to Monsters Inc.
, even Geri’s Game
.” Of course over the years, through Ratatouille
and The Incredibles
, a modeling suite was written for the simulator to create the costumes for Toy Story 3
and the same system was used to create the assets on BRAVE
. The idea of hair-to-hair interaction was important for BRAVE
, because the bounce and free flow of the hair was particularly important for the Merida character to be accepted. She had to have hairs out of place. So, in terms of hair, it was a completely new simulator.
Figuring out how the hair would move was also a huge challenge for Claudia and the team. “The main character Merida had some ideas of how life was, which are challenged during the movie,” Chung says. “Life is more complicated than she thought.” Claudia Chung found that 3D CG hair had a life of it’s own as well and sometimes things didn’t go that way she thought they should either. It was a great adventure for both Merida and Claudia.
There is no change to the philosophy, there’s still the Points and Springs. The curves are all still the same. But in order to create such immensely complex, the Pixar crew knew they needed to make this much faster to deal with Merida’s hair. With cloth models and hair models, they’re all network points and springs. The simulation artist decides how strong that spring is. “If you look at curly hair, its a bit of a paradox,” explains Chung. “The coils never unwind. They will stretch out, but they will snap back into place. This is a physical property that is inherent to its design. That means that the spring system we had to design for the hair was quite rigid. But the way curly hair sits, its pliable and soft. So we had to create a new spring system that ran through every curl of hair.” The Pixar team had to create an entirely new spring system which ran through each coil and that would give it the softness and the springiness that curly hair had.
All the models are simulated in normal Earth gravity, other than the hair. The soft flow of hair movement for Merida was created after the mass of the hair was calculated. The simulation system measurements for the hair curls was wound back to half the gravity of Earth, and more akin to that of the Moon. “It was the only way we could get the effect we required for the hair to flow and bounce,” adds Chung. A major in Computer Science, Claudia learned a lot about animation on Brave
, and because of it’s flow, color and bounce, the hair became its own animated character. She says she is now able to go from core computer science discussion through to knowing where the pleat should fall.
The reach of different looking extras, especially at the Highland Games, where Merida was 'playing for her own hand', is special for more than the foreground action and drama. Animator Austin Madison tells of the intricate detailing of the bit-part characters that can pull the eyes comically around the screen as the foreground action carries. This is not a distraction though, but weaves many stories through the film as it rolls on. Watch. "When we are given productions such as this, we want to 'walk a mile in the character's moccasins', if you will," says Madison.
"Every Friday at Pixar was Kilt-Friday. We'd have sword-fights, throw hammers, shoot arrows and generally get into the characters," Madison continues. "Animator Paul Mendoza was in charge of Crowds and he took pride in not just giving them stuff to do, but not just action, but specific story outlines and that is what lends itself to a second viewing where you can keep discovering new things about the characters, that didn't even get a name or any lines." This was devised thru research into the culture back then when everything was hard to get done. "All these sub plots are sprinkled about in the background and the foreground is just one of the many stories happening in the film," he says.
When Claudia Chung first saw the reels for BRAVE
, she’d seen character sketches and noted at Fergus the king was set to be this boisterous, fun-loving king who’s jumping all over the place, instead of being a heavier guy, a slower, older kind of ruler. Getting the kilt right was one of the biggest challenges for the simulations team. “At first, we had him looking like it was a cheerleading skirt. Too short and the pleats were too sharp,” exclaims Chung. “Others just looked like a toga. Kilts really have to be nine yards of material wrapped around the person in a particular way.” Understanding how all the threads and folds worked was instrumental in the creation and correct lighting of the Kilt. A Pixar Shading TD on the character team Philip Child came up with a technology that he studied the way tartans are weaved. Child came up with a shader that would weave the individual threads and fibres of the cloth so they looked like a real tartan. Zooming in super close, you can see the individual threads, cos the fibres themselves are incredibly complex. The mesh has to be created at that detailed level in order to look that real. “You can’t have cloth without understanding what the material is,” explains Chung.
Another character in the movie that we spent a lot of time on was Angus, Merida's horse. While not having curly hairs, he was almost as difficult as Merida to get right. I worked a lot with some animators to get the correct behavior of his hair, mainly the mane, tail and fetlocks. The new hair simulator that was developed for Brave is called Taz (like the Looney Tunes character). It began as a research project by Andy Witkin then later Hayley Iben.