• 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.
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    “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.


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    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.

    Animation Tapestry

    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.

    Kilts

    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.

    Angus

    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.

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  • Lights

    Danielle Feinberg has an amazing history with PIXAR. As concured in Sharon Calahan’s story on CGSociety in February, techniques in lighting of course have changed in some ways and in others it has stayed the course. "Relatively speaking, CG is a young field and tools and the technology have changed pretty quickly," Feinberg explains. "Obviously if you compare A Bug's Life to Brave, it has changed vastly. The amount of illumination able to be put onto the scenes and the amount of control of color these days, makes it seem like we are light years ahead of how things were, but the fundamentals of lighting are all still there. We can all get better images with the tools we have at our disposal in some ways but how lighting can help tell the story, give emotion to things, bring depth and beauty, guiding the audience's eyes, all of these things are all the same as they were back in the days of The Bugs Life.”

    Some of the earlier films from Pixar lighting-wise, look a little bit 'glowy', where the light would be placed on a surface and the rest would be on shadows. "Block light, if you will," Feinberg continues. "There was less bounce values being used back then. It’s much easier now to generate more contrast and depth than we used to. There’s now more control of color. Instead of being one color, the light can incorporate many hues in the one shaft of light. With every movie, the creative appetite gets bigger, we are advancing our tools to deal with that.”

     


    Over the years, Pixar has developed a couple different ways of introducing some elements of real-time lighting renders into their workflow. But to get the playback closer to ‘real-time’, they have to drop out certain things. Only rendering out the elements that are influenced by the light, will show the effect of that light, as you decide on the angle, color and intensity. “A lot of it is management of the assets, along with the tools,” says Feinberg. “We’re not a real-time lighting just yet, but we have solutions to fill that gap.”
     

    The Wind

    Olivier Soares was another computer scientist kept busy on the Pixar crew, developing a new wind model for Brave. This was based on a technique that had begun testing while working on the Aslan character in the second Narnia movie a few years ago and improved on Brave. “We wanted to create something giving us more details that a simple moving noise pattern,” explains Soares. “The idea behind this new wind model was to calculate the wind occlusion while it's traversing a big mass of hairs like in Merida's mass. If you have Merida's hair with some wind, the hairs on the outer shell will get more wind that the hairs which are deeply inside the volume as the wind intensity decreases while it's traversing the volume.”

    Using a similar technique, the Pixar team also simulated the occlusion that the body and other objects around the character are creating. For example, if the character is close to a big rock on its left and the wind is coming from the left as well, the big rock will occlude, partially or totally, the wind and reduce the intensity it would have if the big rock was not there. This new wind model also simulates the wind gust to look more natural.

     

    Forests

    Creating the Scottish highlands for the movie was definitely a challenge for the Pixar team. The complexities of the lighting, and colors of the rocks, moss patches and foliage were a major hurdle which was wrangled headlong by the team early on in the production with the concept team taking a valuable trip across to Scotland. Inigo Quilez is credited with developing the procedural vegetation system for the forest scenes.. Another challenge was how to use the weather and lighting in Scotland to best serve the look of Brave. The look of mist and rain and quickly changing weather patterns was used in multiple sequences. The depth of shadows was utilized to help the mood in several instances.

    “What I hit upon early on was; there was an accident of the computer barfing on me, sort of,” explains Danielle Feinberg, “it dropped out all my lights and all I was left with was the mist, and it gave me just these incredible silohuettes of the vegetation and the mist.” Feinberg and the team tried to hold onto that, as, “this was the perfect look for this forest. We forced everything back into the darkness outside of the action in the forest.” Since this was a mystical forest, the Pixar team wanted to go with this because it would mean that it is totally unknown what is beyond where you currently are.”

    The research team of Olivier Soares, Samantha Raja, Rich Hurrey and Hayley Iben have a SIGGRAPH Paper to be presented this year in LA, called 'Curls on Fire: Hair Simulation in Brave'. Claudia Chung, Danielle Feinberg, Tia Kratter and Colin Thompson also have an extensive Production Session, 'Pencils to Pixels' about the hair and the clothing created for the Brave movie.


     

     


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