Computer Graphics World

July 2009 24 n n n n CG Characters scale comes a demand for detail at our level. We killed ourselves putting this thing to- gether, and when we showed it to Michael [Bay], he said, 'Huh. It almost looks like a toy.' " Bay's comment forced the crew to add even more detail, and they continued adding detail to it during the entire post- production process. Devastator builds itself by smashing into one mining-construction robot after anoth- er; six in all, each as complicated as Optimus Prime. Its head is a cement mixer. A crane becomes one arm, and a scoop loader the other. One dump truck becomes the torso, and it attaches another as a leg. A second leg is a bulldozer. "And, these aren't normal construction scoops," Smith says. "ey're for mining. e scoop isn't a normal back- hoe scoop; it's eight feet tall, and we get close with the camera, so we needed to have the rivets, and the dirt, and dents, and scratches, and shiny metal—and that's just the scoop. You start working your way up the arm, and pretty soon you have a heart attack." So, having the parts library helped. By the time the modelers needed to build Devasta- tor, they had already built the construction vehicles and the robots they transform into, and could use library parts from those mod- els to assemble the giant, adding new parts as needed to get the form right. "I think maybe 40 percent of Devastator painted itself," Fo- gler says, referring to the library parts with material and paint assignments that the sys- tem automatically applied at render time. "So now we have the heaviest asset we've ever built," White says. "ere are guns on Devastator's arms. He has cranes and ca- bles—a phenomenal amount of detail and geometry. And on top of that, we had to work at IMAX resolution, which is eight times the resolution of normal 35mm film. And, every time we thought we were done, we'd get a shot like this." White pulls up a scene on the computer screen. Devastator fills the screen. Crawl- ing up the monstrous robot's back are two other robots. "ey're twins, new characters that move and climb all over him," Smith says. Created from small cars, the twin Au- tobots are approximately 11 feet tall. "We had so much visual complexity in the frame, our challenge was to separate the ro- bots so you can actually see the small ones," Smith says. To do so, they used such tech- niques as putting smoke behind a character to provide visual separation. Sucking Sand And then, on top of that, during a sequence that takes place in the desert, the Devasta- tor opens its huge cement-mixer mouth and sucks in everything in its path, creat- ing a huge vortex of sandy dust, trucks, and debris. e vortex is a particle simulation, but rather than running that simulation re- peatedly for approval, the technical directors shaped a cone that connects to the creature's "mouth" and to the ground. ey blocked in movement for the particle simulation by running a cloth simulation on the cone. "at gave us the fluttering and motion we wanted to integrate into the dust," White explains. "e particle sim would have taken overnight to run. We could run the cloth sim in under an hour, and get a buy- off on the overall flow." e team then streamed the particle sim- ulation over the surface. Because this was an IMAX shot, which would project at 4k on a multi-story screen, ILM used grid render- ing and wavelet technology to add details. "In the past, we'd instance clouds of sprites or other particles to add dust, and you sometimes see little dust bunnies popping on and off," says Smith. "For this show, we used volumetric rendering that treats the density as values in a 3D volume, a grid." First, the TDs ran a low-resolution fluid simulation in a 3D grid. en, they emit- ted dust material into the grid and added "octaves of noise." Smith explains: "Imag- ine that each cell might say, 'I'm zero per- cent dust,' or 'I'm 50 percent dust.' When we add velocity, the cell would say, 'I've got 50 percent dust moving east,' and the grid to the east would say, 'let me take that dust from you.' We call that density." To add complexity, they increased the resolution of the fluid grid by dividing each cell into eight, sometimes even 64 cells. en, the team added noise. "We inter- polate the directions and velocities in the fluid sim along these new tiny cells, and at The Autobot leader Optimus Prime delivers more dialog than in the first Transformers and fights with additional brutality. Fun Facts from ILM: Optimus Prime will be life-size on IMAX screens in many forest-fight shots. All the robot parts laid out end to end would stretch from one side of California to the other, about 180 miles. If all the texture maps on the show were printed on one- square-yard sheets, they would cover 13 football fields.

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