Pirates of the Caribbean

Flesh Flags and Faux Fashions

Gone are the days when digital actors merely lurked in thebackground, clad in easily animated armor. Now virtual characters areplaced front-and-center, wearing complex costumes that flap believablyin the breeze. At least that's what director Gore Verbinski wanted fora cadre of 24 costumed skeletons in Walt Disney Pictures' Pirates ofthe Caribbean: The Curse of the Black Pearl.

Making those virtual costumes look convincing was the responsibilityof James Tooley, cloth simulation supervisor at Industrial Light +Magic. “Each of the 24 pirates was wearing between five and 11layers of intricate clothing that we had to simulate, which was reallyhard,” he explains. Complicating the assignment was the costumes'tattered condition, which revealed what was underneath when theshredded fabrics moved. “They were like real people wearingclothing,” Tooley says, “but you could see right through totheir rib cages! There were 139 shots of these pirates, and I had closeto 23 people at any given time doing nothing but simulating differentparts of these costumes. It was the biggest simulation team I've everhad to assemble.”

The process began with modeling and animating the characters inAlias' Maya. In addition to doing all the costume supervision, Tooleydesigned the scripts that built the armatures of these characters,which allowed motion capture data to be applied easily. “We usedlots of motion capture as well as keyframing. It was a first for us toput that many creatures through Maya. We built all the animationcontrol systems inside Maya. Then our pipeline took those full-bodyanimations into Cari [ILM's proprietary software] to do facialanimation.

“The model-makers not only had to build skeletal geometry, butalso the skin and muscle tissue that's hanging from those skeletons.Those ‘flesh flags’ had to move dynamically, and we had puttransparency maps on them to make them look raggedy and veiny,”he says. “We also had to model the clothing in all its ripped-upstages. Once that geometry was built, the painters put weave patternson them, and the technical directors lit them. That went on before weeven started our cloth simulation because if we didn't have thegeometry built properly, the cloth sims wouldn't work right.”

ILM's proprietary clothing simulation software has been indevelopment for several years, previously seen most notably when adigital Yoda kicked butt in Star Wars: Episode II. While thevolume of cloth simulation in Pirates was greater than ILM had handledbefore, turbo-charged PCs running the Linux operating system also madethe process go faster. A key challenge was to make this clothing settlebelievably on the characters, avoiding the rubbery appearance thatTooley says “can make characters look like scubadivers.”

The simulation process requires building a mesh “foundationgarment” over which the actual rendered clothing will ride.According to Tooley, having a high-resolution mesh is one of the keysto making clothing look good. It is this layer that actually getsdeformed during the simulation process, and then the geometry of thevisible costume bends along with it. “We'd build a piece ofclothing that didn't necessarily have pockets or buttons orhemlines,” he explains. “In this case, it was somewhatshredded, but it was a fairly continuous surface. It's a grid-likepattern that looks sort of like a weave. At the grid inter-sectionpoints where the lines meet, that's a little dynamic element called apoint mass — it's sort of like a particle system. The grids thatconnect those points together are part of a dynamic coupling that keepsthe particles together. Creating the illusion of cloth is less aboutthe particles themselves and more about the forces that couple themtogether.

“Imagine all the point masses as little BBs from a BBgun,” Tooley says. “We connect every BB to each other witha little tiny spring — an infinitely thin spring. We buildsomething that's akin to chain mail and make a costume out ofthat.” Once the simulation animation starts running, the BBs inthe mesh collide with other BBs. They also collide with the polygonsthat cover other objects, such as other layers of clothing. Thesecollisions create wrinkles in the cloth.

For Pirates, the process was complicated by the fact thatthere were holes in the clothing layers, which could confound thecollision detection software, and having multiple layers meant a hugeamount of data had to be computed. “For sanity's sake, there weretimes that we didn't collide any layers against each other,”Tooley admits. “We'd sim each layer independently, which made thesims go faster because we didn't have all those collisions. We'd launcheach one at the same time on different machines. This technique isn'tas scientifically accurate, but nobody cares as long as it appears towrinkle correctly.”

Further complicating this challenge was that the animation combinedboth cloth (which is part of ILM's Cari system) and rigid objects likemedallions on chains (part of ILM's proprietary Zeno software.)“We're starting to bring them together,” Tooley says,“so we can have rigid things colliding against soft things andmake just about anything become dynamic.”

Over the course of five months, Tooley's team simulated a diverserange of clothes and floppy shoes, hair in dreadlocks, and the ghoulish“flesh flags.” Once the simulations were completed, eachcostumed character was rendered, primarily with Pixar's RenderMansoftware. “The costume and the character is one renderablething,” Tooley says. “We don't composite the layers ofcostume. In practice, it goes along with the character and it getsrendered at the same time.”

Tooley expects that Pirates' well-dressed virtual characterswill be part of a growing trend. “Now that people see you can dodigital doubles with costumes, they'll go nuts and design movies aroundthem. The days of naked dinosaur movies are over!”

Gore Verbinski - Director
John Knoll - Visual Effects Supervisor
Hal Hickel - Animation Supervisor
Geoff Campbell - CG Model Supervisor
James Tooley - Cloth Simulation Supervisor
Juan-Luis Sanchez, Michael Balog - Lead Cloth SimulationArtists
Michael Koperwas, Winnie Hsieh - CG Modelers
Paul Kavanagh - Animator
Dugan Beach, Tim Naylor - Creature Development