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- So far we've been exploring what a software engineer does at Pixar, which is creating the tools used in the filmmaking process, such as a hair simulator and all the parameters artists can't control. The person actually using these tools in each film is known at Pixar as the Technical Director. To better understand this kind of work, we've invited Jacob Brooks, a technical director who has used hair simulation in our films. Hey Jacob. - Hey, how are you? - Pretty good, so you worked on Spot for The Good Dinosaur, - I did, I did, yeah. - So were the artisticals for Spot's hair? - Well Spot was one of those characters that you knew we wanted to fall in love with right away. So he had a lot of appeal in him, but he also kind of straddles that world of being in the wilderness so he's gotta wild and a little unkempt. So with his hair we were able to kind of bridge those two worlds so that you can still get that feeling of kind of a matted tangled, kind of wild animal feel to him but also get that appeal of like, just a child that wakes up in the morning and has adorable bed head. So it's just super familiar to us. So for the hair, as far as the texture goes, we knew we were gonna have to have strands that were intertwining and felt like they hadn't been washed in a while, not going towards that gross factor but something that definitely feels entangled and unkempt, but also just kind of hit those shapes that we knew that we'd want to just frame his face nicely and be appealing, so that he does have that genuine appeal in the film. - So how did you model the hair to meet these artisticals? - Well before we can actually simulate the hair on a character that's moving, like Spot as he's running around in the film, we actually have to groom the hair, we have to model that shape, and for Spot, it was an interesting challenge because his hair is so tangled it becomes a very important thing to make sure those hairs aren't intersecting in weird ways and that you can feel that the hairs are actually twisting around one another, in order to do that, we ended up using a technique that was developed at Disney Animation where we're using geometric tubes to shape gross shapes in his hair, so that you can really get the appeal of individual clumps of hair, and see how it tapers along towards the end of the hair, so with those tubes, once they're shaped in a certain way, we fill those tubes with curves, and those are the curves that we end up simulating as we go forward. - Now that you had the shape that you wanted, how did you set up the hair simulation to get the look that you wanted? - The sim of the hair for him is obviously a little bit different as well because you've got this mangled mass of hair, it needs to hold that shape, and it doesn't move like even your hair would or someone with straighter hair, so it doesn't hang with gravity like you would think, as a whole for Spot, his hair is a little tighter than most of our hair, the springs are a little bit tighter so that you don't get quite as much sag and it really does feel like it's been teased and frazzled and kind of holds up and defies gravity a little bit more than natural like longer hair would be. - [Interviewer] So Spot had variation for his hair. Like when he was wet, so how were you able to do that? - Because he was in the wilderness and we knew there was a bunch of weather changes where sometimes it's starting to rain, sometimes it's in the middle of the rain where it's getting heavier, and sometimes he's soaking wet 'cause he gets in the river, my colleague David Liley and I worked on something to where we started thinking hey, wouldn't it be cool if we just changed simulation parameters to get the hair that he started with to be the hair as it changes. And so he started on the soaked version of the groom, and by changing things like the stiffness of the springs we could lose that groomed shape that was all spirally, it would make it kind of flattened out, we would turn up the gravity so that it hanged a little bit tighter to his face. So what that allowed us to do was change the simulation parameters a little bit at a time, so maybe gravity would get a little bit stronger or the springs would get a little bit looser, so that you can get a variation of that transition from dry to wet, but you had various stages in the middle that you could get which normally if we were just doing independent grooms, we would have more of this kind of on and off switch, of like, it's dry, it's wet, now we can get a nice blend through that range. - That's pretty cool, thanks Jacob for coming by. And now onto lesson two.