Issue link: http://digital.copcomm.com/i/259450
SHORT FILM 34 ■ CGW Ja n u a r y / Fe b ru a r y 2 014 an artificial intelligence-based simulation. They only walked, stopped, or stood. For the cars, the crew modified models created for the film Cars 2. "We removed the eyes and mouths, and stretched their chunky, thick proportions into more normal cars," Burrows says. "We also removed most of the undercarriage." Similarly, they used a simplified version of the Cars 2 driving system. "Animators could have a car travel on the road, and the system would automatically lock the tires to the ground," Burrows says. "So, we modeled potholes into the street sur face. All the animators had to do was keyframe the car from one end of the street to the other, and the car would bounce a little up and down. We laid out an animation cycle for three city blocks that lasted for 2,000 frames, and re-used it. You couldn't tell." Although it sometimes seems the city, the crowds, and the cars extend for miles, the crew managed that illusion using the complex but smaller six-block set they started with. "We had a few long, looking-down-the-avenue camera scenes," Burrows says. "We found that once we added atmosphere, six blocks with some matte-paint extensions were enough. Facing the Rain For those long shots of the city, lighting artists added depth-based fog, and for shots of Blue flying through the air, effects artists cre- ated fluid simulations and rendered volumetric clouds. But always, there was rain. Once the first raindrop hits Lisa at the beginning of the film and the music begins, it never stops raining. The rain sets the mood. "I come from Hamburg [Germany], where it rains a lot, so I feel closely attached to rain," Unseld says. "The rain, to a certain extent, is the third main character." In fact, as with the mailbox, the electrical outlet cover, and other faces in the city, Unseld named the rain. Not with anthropomorphic names, but with words that describe emotions. "Saschka had really clear ideas about what he wanted the rain to look like," Burrows says. "So, we needed to get the rain right from a storytelling standpoint. He had a chart listing very specific looks." The rain might heighten a love scene, create mystery, or be as fierce as a gladiator. Unseld's rain-driven moods ranged from boring to stormy. "When they [Blue and Red] meet, I wanted soft, hazy, ro- mantic rain," Unseld says. "When the [blue] umbrella falls into traffic, I wanted the rain to be brutal, harsh, uncomfortable. We did a lot of work on the rain." To create the rain, the effects artists used Side Effects Software's Houdini's particle and fluid simulations. "For the hero shots, like when the rain hits the mailbox, we'd run high- resolution fluid simulations to get a splash element," Burrows says. "But for a majority of the rain shots, 75 to 80 percent, we had a library of rain and splashes on the ground they could just run. One thing we did that was neat was to have splashes that don't correspond to any rain hitting. When you put the shots together, you can't tell." For the falling rain, rather than replacing particles from the simulation with curves at render time, the artists did the replacement before rendering and saved the simulations to a cached file format. "We cached animated curves, not animated particles," Burrows says. "By doing this further upstream, we could modify attributes on the curves in Katana." For example, Unseld described one type of rain as "gladia- tor" rain, referencing the slow shutter speeds used for the film Gladiator. To create that look, artists working in Katana reduced the number of points on the curves to shorten them and make the rain sharper. For another look, they might rotate the curves to be at 45-degree angles. "For some of the emotional transitions, we did hero rain box simulations," Burrows says. "For example, to time the rain with the action when Blue struggles to not go into the subway sta- tion, we created a hero rain sim and put the rain through it. But for the most part, we're running curves through the air." The artists changed the look of the rain in other ways, as well. To heighten a romantic scene, for example, the artists toyed with motion blur. "We played a lot with motion blur," Unseld says. "Sometimes, we faked the length of motion blur to create a softer, smoother, more romantic feel." Burrows explains the process. "We used a shader trick," he says. "We rendered the curve as a ribbon and faded in trans- parency at the top and bottom. Then, to make the rain look softer, we made that transparent region longer." On screen, the artists working in Katana would see what Bur- rows describes as "lots of little lines." "What you eventually see depends on the render, so the effects artists would adjust the lines in Katana and then poke the render. They might tweak the ■ THE EFFECTS ARTISTS CREATED and rendered specific types of rain to heighten the mood: (top left) sharp rain for a brutal scene and (top right) softer, more mysterious rain.