dartanbeck.com - Dynamic Hair

Like any physics simulation, dynamic hair takes patience and practice. I am by no means an expert in any field of physics sims of any kind, including this - just letting you know that up front.

After seeing the Alita Battle Angel movie, I really wanted to up my game for my two main characters.

I've practiced Carrara's dynamic hair before, but was largely unsuccessful at getting it to not flutter wildly - and I think that's because I wanted it to be very long and curly. The curls (unless we want really stiff curls) are controlled by the hair shader, and I think that also plays into difficulties with having hair really long AND curly.

It was even more difficult because it was a time when my main Carrara computer was toast and I was trying to do this on a laptop that could barely run Carrara, let alone a decent hair sim!

Still, I was pleased that I was making headway of some sort.

When evilproducer and Garstor visited me for another of our Three Carrarateers conventions (even though Gars Man's a total LightWave junkie now! LOL) I was having difficulty sending the demonstration video I made for them to my Google ChromeCast, so I reluctantly uploaded it to my YouTube channel. Oh well... it's fun to go back through my older work and see how awful I can be as I grow in all of this!

I started experimenting with many different ways to get this working. I knew that I still needed it to be long and curly, but maybe I could sacrifice a bit of one or the other - perhaps even both?

In my decision to pick this back up, my first stop was the amazing video tutorial series done by Carrara Discussion Forum member: JonStark. Back when he first released them, I liked them so much I asked if I could sort them in order into a single playlist, and he granted me permission.

JonStark's Carrara Dynamic Hair Course

To get to this stage, I really must insist that you check out JonStark's video course above. I wouldn't want to take anything away from his hard work and excellent presentation of his findings, but also don't feel a need to repeat him either. He does such an amazing job!

Now that you've seen JonStark's videos, let's have a look at what I've been experimenting with.

A word of Note

As I'm sure you've noticed, Rosie's hair isn't perfect in the "Introducing Rosie 5" video. Try not to be put off by that. Rosie's hair is quite a difficult and time-consuming endeavor. Most hairstyles will work just fine and even simply! See JonStark's videos for examples of what I mean.

Also, I was purposely making really long animated renders simply for that video, so that she could stand there being dynamic as I spoke about her. Most of the time we're just doing really short clips of a scene. Mostly not longer than three seconds. These normal animation renders are much easier to work with.

Tip - I prefer to add a bit more to the animation before the time I want to start rendering, and some more at the end as well, so that the dynamics are in effect by the first rendered frame.

Carrara's Dynamic Hair has a lot of flexibility regarding the quality of Simulation and quality of Render. In these tests, I'm using settings that are very close to the Lowest quality settings available simply for testing purposes. It's quite amazing how much we can change the overall look of the hair by increasing these quality settings!

For starters, I don't want to grow the hair directly onto the figure. Sometimes we want to start a fresh version of our character, and I don't want to have to redesign the hair because of something like that. So I use a hair cap. Daz 3d provides us with a conforming hair cap for Genesis for use with Carrara hair, but I didn't want a conforming item. So I am using the cap figure that came with Aery Soul's Liltsure Hair.

The cap is a conforming object, but instead of conforming it I used Edit > Fenric > Unlock Figure with "model" selected and then Animation > Remove Skeleton to remove the mesh from the skeleton rig. Now I'm free to drag "model" out of the hierarchy, delete the no-longer-in-use hierarchy, and use the cap as a prop.

Of course, this meant that I had to work with the mesh to get it to take the shape of Rosie's head.

I did the same unlock and detach process on the hair band that also came with Liltsure Hair. I'm using this differently than its original design or I could have left that conform. I wanted to completely reposition it to fit with my vision.

I then created some simple shapes for the hair to collide against. There are so many tiny polygons in the human figure (Rosie 5, in this case) that really don't need to be interacting with our hair during simulations - not simply to save time and resources, but these sorts of collisions can also make the end result look pretty funky, as the hair is getting hung up on something that it really shouldn't - like eyelashes, etc.

I repeat this process for the neck, collars, shoulders, forearms, chest, each pectoral, abdomens 1 and 2 and the hip. I've also made some for the thighs but don't keep them on the figure - I saved each of these collision objects for each of the body parts to my browser in case I need to add them for some reason. Really came in handy when I did a fresh new version of the character!

I also made these simple shapes for the hands, although I usually only turn collision on for those when I feel the need.

A Word About Collision

When working with Dynamic Hair, it's ever so important that we set Everything in the scene to Not collide with hairs in the Effects tab. This goes for lights, cameras... anything that we don't want hair to collide with. In fact, when I do want the hair to collide with other objects, I still set them to Not collide with hair, and then make a simple proxy shape where I want the hair to collide.

If you think you've done everything correctly, but even a simple draping of the hair causes the hair to do unexpected things, chances are that something in the scene is colliding with the hair that shouldn't be. One time I discovered that it was a sky dome that was hundreds of feet away that was causing issues!

Working with/in scenes

If you need to render the hair into a scene, that's fine. Go through each and every little thing in the scene and set it to Not Collide with the hair (effects tab) and simply drop in an invisible proxy primitive if the hair needs to interact.

Some scenes are not so easy to set up like this. So many things to turn collision off on! In these cases, run the hair simulation first with nothing in the scene but the figure, then drag the scene in from your browser after the sim has calculated. If you need the scene to assist with animation (we often do), go ahead and do that. Set everything up before the sim. If the hair needs to interact with the scene, make proxies for those areas and keep them out of the scene's group.

When the scene and animation are complete, stow the scene away in the browser and then delete it.

Next remember to Edit > Remove Unused Masters > Remove Unused Objects and then the same for Shaders. Now run the hair simulation and bring the scene back in when you're done.

In reading that last bit, it probably sounds like a real pain in the tush. Don't worry. The more you work with the hair simulations the more you get used to setting everything up to work with it.

Layers, Forces and Physical Properties

For the version of hair I was using in "Introducing Rosie 5" I had four separate hair objects. Three of them had at least three (one had four) different hair layers: Base, Longer and Back Long. The main one also had some shorter hairs on the top: Fly Away, I called it.

In early tests, I only used the one main hair object with the four layers and I set the Air Dampening field slightly higher as each layer got longer so that the shorter hair had more movement than the long.

It was during these tests when I was also reading through the 3dXtract e-zines and found the articles on Physics and Forces to be most interesting. When I'd try the hair simulation on a walking character the hair would just slide over the shoulder and float back behind the character. Probably not too unreasonable, but I didn't want the hair always just sliding around like that.

My first move was to increase the Friction and lower the Bounce in the collision settings of both the hair and the collision proxies (Effects tab). This helps.

After reading the articles on Forces, I decided to try a Point Force parented to the hip to see if that would help. That's where I was when I did the video above. The difference between that and the results I got before were outstanding. At that time, instead of using point forces to help shape the hair, I had made more proxies and increased the collision distance in order to push the hair outward.

Adding more point forces to the rig has been another amazing feat.

I started with one parented to the neck and positioned where I want the hair to be biggest. I give it a negative value to push outward rather than pull in, and give it a short distance falloff of two and a half feet. That worked really well but I was still seeing the hair fly back more than I'd expect to see in real life. Not that I want something real-life, but I would really like to see some of that long hair remain in front of the shoulders!

So that's where the next point force came in - I put another positive force (pulling inward) in the chest to try and keep the hair sort of clung to the body. This made it necessary to increase the power of the hair shaping force in the neck. I also added two negative (pushing outward) point forces in front of the face - one in front of each eye that are fairly mild in strength and are meant to try and help keep the hair from resting upon the face shield.

After many tests with this setup, it became clear that the single point force in the hip was causing too much of a singularity for the longest hair. So I dropped the strength and added two more on each thigh. Much Better!

Although I'm not focussing on the actual hair simulations themselves, you may be interested in seeing my actual workflow around Animating, then Simulating the clothes, then Simulating hair before working on the Scene and finally Compositing the whole works together.

Just keep in mind that, in the video when I mention that I'm speeding up the screen capture video 300, 500 or 700 times, those numbers are actually the percentages, not the number of times the speed has been multiplied!

For example, when I say "300 times", it's actually three times or 300% the normal speed. I was working for over 38 hours without sleep when I recorded the dialog for that video! LOL

I'm going to continue writing in this article as time permits. I'd like to add more details and illustrations, etc., and even some tutorial videos. Keep an eye on this space for more

A word of Note - Again

Tip - I prefer to add a bit more to the animation before the time I want to start rendering, and some more at the end as well, so that the dynamics are in effect by the first rendered frame.

Have a Question? Just Ask!

I love to help others as best I can. This is a rather broad topic: CG Filmmaking, so my articles on any particular topic may not answer your specific question.

Most of the questions directed to me are regarding Carrara or How did I do this?

For these sorts of things, post your question at the Carrara Discussion Forum (or another appropriate category) at Daz 3D.com forums, and if I don't see it right away, someone else might. They are such a friendly and helpful bunch! I've learned so much from that forum over the years!

For a more immediate question directed to me, log into those forums and Send me a PM!

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