What is hair?
Hair is the mass of thin structures on the head of a person, according to the Cambridge dictionary. Of course, everyone knows what hair is, we all have it and it’s part of who we are or who we think we are and it also tells something about ourselves and the moment we are in.
In multiple cultures across the world hair has different meanings and beliefs, like samurai soldiers that would cut the hair if they were defeated or the native american people who believed that hair was sacred and significant to who we are as an individual and if we look at our society, in the present day we can see that hair is still a form of expression. We might not need to cut our hair when we are defeated but a lot of people change their hair as a way to express themselves, about who they are and what they stand for.
What does hair say about you?
It’s not like we can look at someone and know them by their hair style but people take an idea of what you might be like because of some stereotyped definition our society has on a certain hair style. It gives personality to someone and self-esteem, strength even or the opposite, it can make you feel bad about yourself and ashamed. Women rely on hair a lot, it is usually longer than man’s hair so they take more time to take care of it, but for both it is important as it is so close to the face. When someone goes to a mirror to check how they look the first things are face and hair, only then we look at the rest, the head is the first thing someone sees when greeting someone.
Hair in Animation
In movies, we can see that villains usually have crazy, bulky, expressive hair that makes up for their intentions and personality, or an adventurous character has a thick wavy or curly hair, flowy, or an innocent and naïve character has a blonde straight hair very shiny and pretty.
One of the most difficult things to animate is hair, for decades Pixar struggled with it, but it didn’t stop them for sure!
In the animation movie Monsters Inc. (2001) we can see that boo has pigtails, but the director Pete Docter wanted Boo to have long hair, but that would be so hard that they ended up giving her pig tails as it was easier to animate. If we think of Boo with lon hair she stops having that curiosity feel and look that the pigtails give her.
Hair is still a very new thing and still has a long way to go. If we look at history of animation, the first Pixar movies didn’t have a lot of human characters and the ones it had didn’t have much air time, didn’t really show the full body and every human had short hair but, with the evolution of technology things started to change.
The first animated feature entirely populated by humans was Incredibles (2004) where the director Brad Bird insisted on the long hair previously wanted for Boo on Violet, her signature hair is part of her character and took a team fully dedicated to it 6 months to render. Her hair is straight and as it covers part of her face gives her that shy look and the ability to hide with it, but half way to the production of the movie the team didn’t really know if it was possible to fully give life to Violet. In the end they just created different hair styles to be used in different situations and changed it accordingly.
After years improving their methods, the next challenge would be Tangled (2010), to animate more than 20 meters of hair and give it weight, while it could never behave like in real life, such long hair would be a nightmare to walk or move with it. The solution for Rapunzel’s hair was to mix simulation and rigging where animators had a lot of controls to animate but also have the simulation to make it more believable. This was the first time that hair acted like a limb in which animators had controls to blend in animation and simulation.
Brave (2012) came along, Merida’s character key feature is her hair and how wild it is, once again, it is part of her character the red curly hair that refuses to do what the rules want and directly represents Merida’s personality and wild spirit.
This was a whole new level of difficulty, not only long but curly hair, where the hair has to be stiff to maintain the curl but also be soft in it is movement. This process made them create a new technique called “core curve and points”, where the curve is the necklace chain and the points, including the springs, are the beads and allow Merida’s hair to move along her character.
Four years later, the movie Moana (2016) where Moana’s hair is extremely flowy and loose, she has an adventurous and stubborn personality, if no one goes with her she will go alone, she is fearless and her hair says that about her. This time Pixar animators wanted to have Moana touch and play with her hair as she is a teenager and would add a lot to her character so this time artists upgraded the software used for Rapunzel’s hair for an initial groom and developed a new software named quicksilver along with xGen as a new system to control the hair.
All these characters had to be created in a unique way and software was developed specifically just for them – this is how Pixar evolves and continues to exceed our expectations in every movie they make, their tools and team always go beyond what is possible at the moment.
How is hair in animation created?
The human head has around 100.000 hair strands, it would be impossible to animate so many hairs or rig them, so it needs to be simulated and rigged in some situations it is still time
consuming and takes a full team dedicated to it. There are multiple ways to create hair in animation tools like nHair, xGen, shaveandahaircut, ornatrix, among others, these often include both rigging and simulation, as hair is something that cannot be animated by hand.
So, what is a simulation?
A simulation is a mathematical coding, performed by a computer, designed to predict the behaviour and the outcome of a real world or physical system – it basically copies what happens in the real world. With hair it needs physics and maths to programme on a computer and obtain the desired results depending on the type of hair that is being animated.
Long hair was first simulated with violet’s signature hair but the most troubling problem was in Tangled with Rapunzel’s twenty-meter hair, in which the hair was rigged and simulated. Long hair is so hard to animate due to the number of things that have to be put in to consideration as hair needs to react to environment, colliding with the character and with itself. Rapunzel had the need for an extremely long hair so it had to be rigged, as a whole, and animated by hand in shots where the hair had to do unrealistic things such as grabbing a door handle. But simulation always has to help, animating a rig can be time consuming and it is not practical so with simulation it is possible to animate gravity, density, acceleration, velocity and force real life based.

As for curly hair is a bit different as it behaves like a spring so the simulation had to be made through a mathematical algorithm called Hooke’s Law. It states the force needed to extend or compress a spring, sometimes also used in long hair.

F – spring force
k – spring constant
x – spring stretch or compression
This didn’t work at first when Pixar was simulating Merida from Brave as her hair was too loose and would go crazy when the character did sudden movements, so they decided to create a spring core inside the spring as a way to keep the stiffness of curly hair but also it’s natural and loose look.
After long and curly hair comes the grooming and combing the hair, like Elsa’s character from Frozen (2010) and Frozen II (2013) where she has a long braided to which Disney created a software called Tonic that allows artists to model and sculpt the hair as they need through layering systems along with simulation to allow hair to interact with wind and water.

One really important thing are clumps of hair and fur it is needed for a reslistic randon distribution of hair. The Voronoi Diagram, in mathemathics it represents a partition of a plane into regions close to each of a given set of objects. The result of this is something like right side image and creates a patern found in nature, such as the wings of a fly, or a giraffe’s hair patern, leaves, elefant skin. This allows artists to have a real life based mathematical system to distribute hair on a surface or even have it dirty or clumped.
Conclusion
Hair is part of one’s culture and has weight on individual identity, as technology is evolving so fast and each time it looks better and better, hair is becoming a part of storytelling and character “enhancer” due to it’s flexibility to change appearance it can be used to build and give personality to a character as well as reality.
In animation hair is trully a hard thing to do and every time artists encounter more challenges and problems to solve which always ends with them developing a new software to meet their wishes.
The audience needs to connect and be able to relate to the character even through culture or a hair style or even the meaning of that hair style. Teenage years is where we see how important hair is, those are the years when one needs to find himself and hair is, again, a way of expression and change. A good story is the one that actually makes the audience enter it and forget everything else for a moment, the more realistic it is the character the most relatable it can be, now more and more hair is a growing concept that still has a lot to accomplish.
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