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Current time:0:00Total duration:2:07

Video transcript

hi i'm haley ivan i'm a software engineer at pixar i worked on the hair simulator for the movie brave hair was a really big deal in brave it was a symbol of freedom that was intrinsic to our main character merida's personality and making hair that feels right meaning messy wild and free is a hard thing to do computationally in our movies hair is a simulated effect that means no one animates its movement by hand the way it moves is defined by physics and programmed into the computer to figure out what hair stimulation should look like we needed to look at real curly hair and see how it worked what we found was this curly hair forms together in locks that reshape themselves when you pull on them kind of like a spring this was great news because springs can be modeled mathematically meaning we can simulate their behavior using a computer program from the computer's perspective merida's hair is just lots and lots of springs that react to forces such as gravity as merida moves the tests we ran using this approach were pretty good but not quite natural enough while stiffer springs held the shape of the curl it didn't bounce like natural curls when we made the springs looser her curls wouldn't unwind when she moved this was even more obvious at high often unrealistic speeds found in animation we realized we needed something to preserve the structure of the curl but not impede the overall motion of the hair kind of like digital hairspray sorry we came up with the idea of connecting the springs that make up merida's on-screen hair to invisible core springs like this the core springs would limit the movement of the on-screen hair when the motion was more extreme this way we could have the best of both worlds our original simulation would create motion that was soft and natural but the core springs would keep the curl from unwinding too much figuring out how to make a hair simulation system that could help us achieve the feeling we wanted from meredith's hair was hard it took a lot of iterations to get it right but it made a big difference merida feels like a real girl messy wild and free