Computer Graphics World

September 2009 27 CG Creatures n n n n sect jitters," Nichols says, "fast, razor-sharp, hyper-real movements. e aliens have the physicality of humans but with extra twitches and fast motions that humans couldn't do." Only a Mother Could Love Initially, Image Engine scanned a maquette created by Weta Workshop, and created the 3D hero alien model from that. But during postproduction, Blomkamp asked the modelers to make the characters more insect-like, particularly the faces, and the aliens evolved into the grotesque grasshop- per/lobster creatures that the humans in the film called "Prawns." "e original concept was a prosthetic outfit an actor would use on set," Kaufman explains. "But the costume was bulky, and Neill wanted thin limbs, like an insect, skin-like cartilage, and so forth. But the biggest change, and one of the last things we did was make the face more insect-like yet capable of showing emotions and ex- pressions we could recognize." James Stewart, creature supervisor, sculpted the new alien face to have small, interlocking plates that move to form ex- pressions, and he led a modeling team that worked in Maya and Pixologic's ZBrush to create the creatures in 3D. "I tried to have people focus on the construction, the lines of the polygons, to make sure they would deform correctly," Stewart relays. "In mod- eling today, people sometimes create turn- tables without considering that the things have to move, articulate, talk, emote." Take, for example, laugh lines. For the face, modelers created what Stewart calls "subtle linear shapes." "We animate faces muscle by muscle using linear shapes that can combine, but the root is simple," he says. "For a laugh line, if you don't build a shape with a crease down the middle, you can't blend that shape into a realistic fold. On the other hand, if you make it too com- plicated, as you increase the deformation, it becomes tough to figure out which fold is what. So, we add shapes in an almost road map way—this area is that polygon." In addition, a proprietary tool called Mayhem handled the constantly moving tentacles and mandibles on the front of the aliens' faces. "It does rigid-body dynam- ics," says Shawn Walsh, executive producer. "But we used it to simulate these soft-body tentacles, so we could tailor the simulation and have control over close-up shots. We use this idea of jangling rigid-body objects against each other to drive a simulation in a number of ways." Image Engine also used Side Effects' Houdini for volume rendering, footfalls, and dust hits, Next Limit's RealFlow for fluids—spittle, vomiting, urine, and so forth—that helped make the aliens believ- able, and Maya's nCloth, Houdini, and the rigid-body simulation for clothing and other soft bodies. A new project manage- ment tracking system, called Jabuka and developed by Image Engine's R&D de- partment, managed the hundreds of as- sets needed to create aliens with individual looks for the secondary characters, and provided shot continuity. "We tried to create a diverse textural palette of aliens living in a Soweto-like place," Walsh says, referring to Johan- nesburg's infamous shanty-town. "Neill [Blomkamp] asked what we could do to bring them into the environment, and we started riffing on that idea." ey gave some aliens torn T-shirts and wrapped stuff around others' arms; they imagined each alien would choose stuff it liked or needed. Some chose garbage bags. Some had splashes of paint and graffiti on their bodies. Others pasted skateboard stickers on their shells and wore hats. "We had a number of hats in the asset management system and 12 different stick- ers," Walsh says. "We could publish a set of assets with each character; it was literally like building a wardrobe that we could save on a shot-by-shot basis. is alien dressed like this exists in these three shots." On the Surface Painted texture maps created in Adobe's Pho- toshop and Maxon's BodyPaint 3D com- bined to create varying patterns of color and displacement, as well as to provide lighting information for 3Delight, a RenderMan- compatible renderer from DNA Research. A "behemoth" shader provided controls for specular, wet specular, and so forth. "[e aliens'] necks had a wet, slug-like feel," Stew- art says. "To get that feeling and at the same time have the aliens look dirty without kill- ing render times was a challenge." Animators at Image Engine gave the alien Christopher Johnson emotional facial expressions by moving the plates that make up his face. Procedural animation helped move the tentacles.

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