Tensegrity and Clothing Simulation

In the 1960s Buckminster Fuller coined the word tensegrity as a combination of tension and integrity, to describe a structure which holds its form through the balance of tension between its parts. It’s a great metaphor when thinking about how energy is distributed in a visual effects simulation at rest and I’ll misuse it as a shorthand for just that.

Let’s take clothing dynamics for example. Look at the clothes you’re wearing. Every fold and wrinkle is an expression or the outcome, of a complex set of interconnected forces – friction, tensile strength, elasticity, etc. The shape exists as it does, solely because of the physical forces of the pieces of fabric, how they’re attached to each other, and the mutual exertion between the cloth and its environment. This is its tensegrity, and the folds of a shirt are a system of balanced tensions, momentarily stabilized.

So what use is this to simulating clothing in animation? Well, because it explains why it’s such a pain in the ass. The cloth’s tensegrity is essentially a lot of forces to keep in check with one another. Let’s look at it backwards.

When a fold is modeled into a shirt for instance, to get an approvable geometric model, and that model is then used as the basis of a simulation – what’s modeled is not actually a fold, but a complex interconnected web of physical tensions and exertions, held together in a sate by, and according to, its tensegrity. When the forces to that matrix of physical interplays change, the system must rebalance, and since the original balance was not based on anything resembling the physics of cloth, it’s efforts to rebalance are not very cloth-like.

Traditional clothes start out as really weird flat shapes. What materials these shapes are made of and how these shapes are attached to one another establish their tensegrity. That results in specific shapes, folds, draping and motion in response to environmental forces – shape is motion and motion is shape. Most CG modeled clothing could never be “unstitched” to lie flat – it would have odd warping, buckling and distortions. The simulated forces act on those structural malformations as input, and the simulation math tries to make sense of it all, as if the warpings were intentional distributions of mass in space.

The visual results are weird, “bubbly”, oozing, and overreactive motions that fold unexpectedly, and keep crawling after the character stops. Those are the simulation engine’s efforts to reestablish balance in the energy of the clothing mesh. It’s just the simulation version of a computer never does anything you don’t tell it to do.

for an actual, more scholarly explanation of tensegrity start here (please) http://en.wikipedia.org/wiki/Tensegrity

an interesting example of a 3D printed dress that uses modeled forms rather that flat patterns (and moves more like a sim)

take a peek at pattern making
http://craftsy.me/1Fc0sAi

#simulation #clothsim #cfx #tensegrity #moviephysics #patterndrafting #3dprinting

#Siggraph2013 #effectsOmelet

The “Effects Omelet” presentation at SIGGRAPH is always a great source for inspired creativity on the ground by VFX artists and TDs.  David Lipton, Head of Effects at Dreamworks Animation, gave a particularly interesting talk about he achieved the Jack Frost frost effect in DWA’s “Rise of the Guardians”.

Interesting use of old school approaches to get more controllable artistic results in the expressive effect of Jack Frost’s frost in DWA’s Rise of the Guardians.  The frost needed to be a highly stylized, very art directable and expressive effect, where Jack’s staff would freeze objects by propagating elegant, icy arabesques that skated across surfaces, covering them in stylized frost patterns.

Lipton said that they were helped immensely by the copious notes, reference images and concept art prepared by the Art Department.  This gave him and his team a very distinct target to aim for, and helped to narrow the problem at hand.

The first approaches were simulation based, but proved to be hard to control, espescially because the effect itself needed to be an expressive actor in the film, with its performance often leading directing the eye through key story moments.  The winning approach was to look far back into the history of computer graphics to an old standby of cellular automata.  These are systems in which cells of a grid, like pieces on checker board, follow simple rules that determine how each cell becomes filled by its neighbors.  In this case the rules would determine how ice would grow from square to square as time progresses. The speed at which the squares were filled defined paths, like roadways, along which the delicate and stylized crystal patterns would be constructed.  Because the automata exist in a grid, the rules could be “painted” in like pixels in a digital photo providing a high degree of control.  The end result was a controllable, yet very organic looking crystal propagation that added a sense of magic and expressiveness to the scenes.

Siggraph 2013 emerging tech Girish Balakrishnan

#Sigraph2013 Emerging technology
Girish Balakrishnan, a masters candidate from Drexel University was demonstrating his performance capture camera rig made entirely of commodity consumer components. It’s centered around an iPad and attached Playstation3 controllers that provide the rig’s spatial tracking as well as the user interface components.

The virtual world which the camera operator navigates is provided as a Unity game engine scene runing on the iPad. As the the operator moves through space the iPad displays that motion through a virtual camera in the game scene – like Avatar on a beer budget. The iPad integrates data from the playstation with its own, storing it as a file that can be imported into Maya or Motion Builder.

Balakrishnan has been interested in performance capture for years and feels that the current crop of tools leaves users too tethered to the mouse and keyboard. He wants to change that using tablets, commodity cameras, and game technology. His enthusiasm for the project might just make it a reality.

In its current configuration it can serve as a low budget indy game production tool or a very inexpensive previs tool for independent film and video production. Girish is looking into how to incorporate new HD cameras like the Black Magic to build a more robust camera performance capture system that could expand the creative palette of independent film makers. Performance in the venue was hampered by the huge amount of wireless interference in the Emerging Technologies hall, but it would be interesting to see how it performs in its intended environment – the mocap green screen stage in your garage.