Computer Graphics World

May 2009 23 Lights•Shaders n n n n "Usually, in the past, even on Iron Man, we had to rejiggle materials to make that possible," Snow says. Interestingly, though, the realism was too much for a sequence of shots that take place in a dark factory lit only by sparks and explosions. "e terminator looked too busy," Conran says. "We had to dial it back." To do so, the lighting TDs used broader lights and fewer of them. With all the new shaders came a differ- ent way of working. Although the shaders reduced the number of pre-passes necessary to set the lighting, it took longer to com- pute each rendering pass. "What you want is quick feedback so you can do as many iterations as you want," Rebours says. To make that possible, Conran wrote a GL preview that they named Layer Cake. "We could position a light, see how it moves with the creature, and even render the entire shot frame by frame to see how it looks in motion," Rebours says. e GL render didn't reproduce the final Render- Man result exactly, but it was close enough for lighting design. e tight schedule for this project made the Layer Cake tools especially impor- tant—the crew had from October to May to create the effects. "In the life of a sequence, you first create creatures, viewpaint them, texture them, put in the animation, and then go into lighting," Rebours says. "You discover the character of different creatures in anima- tion. And, it's the same on the TD side. You discover how the creature takes light and learn how to beautify the creature. Usually, you do that on three or five shots in pro- duction, but our schedule was so tight we did lighting on creatures in layout. We did this discover process very quickly." Art-Directing Fluid Sims In addition to new lighting technology and techniques, the crew also used the studio's Zeno tools and Maya to create rigid-body and soft-body simulations, explosions, debris, dust, and smoke, and developed new tech- niques for working with fluid simulations. "We have five fluid-simulation shots," Conran says, "Our fluid artist, Lee Uren, was looking at all the knowledge from previous shows. en, halfway through production, our R&D department came up with a new smooth-particle Hydro- dynamics (SPH) system, which is a particle system where all the particles are connected to one another, and Ian Sachs came up with a great lava-simulation technique." With this technique, a CG artist could place particle emitters set to initial tem- peratures that streamed down a trough. As the particles cooled, they became stickier, more viscous. By judiciously placing the emitters, the artists could cause particles to cool at the edges more than in the center. "It was a stunning visual effect," Conran says, "and so easy from an artist's point of view. We'd get the shape from a fluid simulation, layer this liq- uid-metal particle sim on top, set the initial temperature, and it would give us rich colors and cooling. We'd get a beautiful simulation with black-body radi- ation—blacks with oranges and reds running in the middle." Long Shots ose shots of molten metal were among the final shots that ILM finished. "We also had some that didn't look so hard, with planes flying in a canyon sequence," Conran says. "It looks like a traditional shot, but the whole can- yon is digimatte." Although the various terminators are the most obvious effects in the film, among the 20 minutes of footage with digital effects that ILM created are long chase sequences for which the artists blended CG terminators, digital vehicles, digital doubles, and digimattes, that is, digital environments, with an astounding mixture of location photography and mo- tion-control and miniature shots. In one such blended sequence, for ex- ample, the harvester emerges from a gas station explosion, the Moto-Terminators scream out of its legs, and the vicious bikes chase after humans in cars and trucks on the road. Snow details the visual effects work as the sequence plays on screen in an ILM view- ing room: "e practical guys built a driv- ing screen, a scaffolding thing with pots of gasoline that created a wall of fire." Snow continues: "We shot it with mul- tiple cameras and cloned it to get an even bigger wall of fire. en, as the CG har- vester emerges, we added CG fire elements to help with the transition as it smashes through the gas station canopy, which we fully replaced with CG. You can see the flame breaking around him. e Moto-Ter- minators that come out are fully CG, but we inserted some over stunt riders that we had to paint out, so we had to reconstruct the road. e tow truck bouncing around is real, but we replaced the ball hanging down. e cars are real, and we shot a car being launched, but it went straight up in the air. So, we replaced it with a CG car that hits a truck and rolls over it. As the camera whips around, the CG bike throws itself on its side to dodge the rolling car, gets back up, and speeds off." For another sequence, ILM built a digital bridge and an 800-foot canyon beneath to blend and extend shots filmed in three loca- ILM matched the Stan Winston mechanical puppet of the T-800, which starred in some close-up shots, and turned its CG fighting machine loose. Stan Winston and his studio created the first terminator for the 1984 film.

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