In Cars 3, Disney/Pixar’s third film in the popular series, Director Brian Fee sends Lightening McQueen to training school to recapture his edge, races him in an unexpected demolition derby, and in the film’s climax, wheels him into a dramatic race against his new nemesis, Storm. There is also one major road trip in the film that takes Lightening McQueen back to the past.
But this film is all about the future. The future for racing legend Lightening McQueen, and of lighting and effects at Pixar.
This is the second film at Pixar to use the new path-tracing software RenderMan RIS. Director of Photography for Lighting Kim White led a team in the neighborhood of 45 to 50 lighting artists who lit the fast-moving, colorful film in eight and a half months. Visual Effects Supervisor Jon Reisch led the team of effects artists who applied RIS to volumes of dust and mud.
“Finding Dory was the first film at Pixar to use RIS, and we learned from what the crew on
Dory did,” says White. “We learned from things they didn’t expect. We saw things they had done and standardized them. We learned about things they couldn’t solve and maybe fixed that.
“But, they were underwater,” she adds. “They didn’t have shiny cars.”
The path-tracer gave Cars 3 a different look than the previous
Cars features, which relied on Pixar’s Reyes software.
“In the past, we would have had to cheat the reflections,” White says. “Now, the lights behave like real lights. We had real reflections. There are certain shots I’ve seen a bazillion times where I see Sally and McQueen reflected in each other’s paint, and I still love watching for it. Before, that would have been a big deal, but we didn’t even have to worry about it.”
But, the other side of not having to cheat is that it was difficult to cheat when they wanted to. “The good news is that most of the time the lighting worked fine, but when we needed to cheat something, it was a challenge,” White says. “A different challenge than in the past. We had more hoops to jump.”
For example, reflections sometimes landed in awkward places on the characters’ faces, and the artists wanted to keep the reflections off the characters’ eyes, in particular. Thus, iris and eye highlights were hand placed; they didn’t come from lights on the set.
“If one character is talking to another, it’s cool to see the reflections on the car paint, but on the eyes it’s distracting,” White says.
The crew ran tests before making that decision, one in which McQueen talks to Mater via the Cars 3 version of FaceTime or Skype.
“We saw this weird square reflection on McQueen’s eyes,” White says. “We decided, OK, let’s not do that.”
To manage the overall look, the team set up standards inside shaders to have consistency for the way in which shaders and lights worked together.
“Radiance bouncing off objects would behave the same no matter which object it bounced from,” White says. “We standardized the way lighting would play off a glancing angle… things like that to keep everything feeling like it was in the same world. In shading, they kept the materials predictable; they know how much light energy bounces back from materials, the albedo or reflectivity.”
With RIS, once the lights were set, the artists could see images that looked nearly final even in first renderings. This was so different from working with the earlier renderer that the artists needed to re-think what to do next.
“There was a little learning curve,” White says. “I was used to coming from a place where nothing was for free, so seeing stuff come in that we would have had to toil to get was interesting. We’d see McQueen in the set and he’d look good, but we’d see a reflection we wouldn’t have gotten before. In the old world, we’d cheat that. But now, we might decide to leave it and see if it works. We had to learn when to leave something alone and when to push it.”
If they decided to push the image, they might add a rim light, or brighten an area for shaping, or shift the color. Or, use animation to help.
“The character Storm required a little work,” White says. “That dark snout points down, so we’d lose the line of his mouth and would have to shine more lights to bring in his lips. And sometimes, we’d use animation to get the anisotropic feeling right on the side.”
Some of White’s favorite scenes to light were those that required an interesting artistic touch.
“When Hud is racing against the rookie and flips over him, it’s like a little movie inside the movie, and also it’s a memory, so Bill Cone, the production designer, Jeremy Lasky [DP, camera], and I thought about how to give it its own look and feel. Alfonso Caparrini took those ideas, created the master lighting, and lit all those shots. We looked at old film footage, considered what makes it look like it does, and played with compositing to push the look. And, Jose Ramos did a lot of work on the fog when they first arrive at the ‘ghost track.’ The shaders for the old wood look so good. We pulled in some atmosphere – you can feel the humidity. But, even though it’s very stylized, we still have all the reflections RIS gives us.”
In another scene, the old characters attempt to train McQueen by sending him on a fast race through a forest at night.
“We had to make the forest look like you’d be afraid to drive in it,” White says. “If I felt comfortable, I’d say, ‘Let’s put in a bunch of shadows.’ We’d choreograph light pools that the cars moved in and out of, let the cars be in silhouette, have rim lights, go dark. Getting that to play was fun. It was fun to hack out the rhythm in lighting.”
White also singles out a time in the film after Cruz beats McQueen.
“We have a set of shots that Jose Ramos lit,” White says. “He captured that sense of hope right before McQueen is crushed. I love the contrast. At the end, he’s in shadow and she’s in light.”
The switch to RIS meant that in general, lighters worked with fewer lights on this film than previousCars films. That is, except for the Florida racetrack.
LIGHTING ARTISTS HAD TO AIM MORE LIGHTS AT STORM’S DARK SNOUT TO SEE HIS MOUTH MORE CLEARLY.
“When we got to Florida, we said, ‘Let’s do it. Let’s take advantage of what we’ve got,’ ” White says.
The exciting night race was the perfect opportunity to place tons of lights. Lights in the infield. Lights in pit row.
“At the end of the race, when Cruz jumps over Storm, you can see all those lights reflected in the hoods,” White says. “It was like a celebration.”
Lighting Volumes
Early in production, the effects crew worked closely with RenderMan teams in Seattle and at Pixar in Emeryville, California, to be sure they could create the volumetric effects on the scale needed for the film.
“We knew that about 70 percent of our work would involve volumetrics in some way,” Reisch says. “Mud, dust, fireballs, even white water. We would have a quarter mile of dirt track with tire smoke and cars kicking up dust. With the first release of RIS, the focus was on modeling the light paths, on getting all those multiple bounce refractions. But after Finding Dory, we needed to improve volumes because there is so much data. Terabytes of data. And, overlapping volumes. We needed to be sure RIS could handle all this efficiently.”
With the Reyes renderer, effects artists diced the volumes into micro-voxels, which represented volumes. With the path-tracing RIS, the team devised a more probabilistic solution.
“With the path-tracer, we calculate that a certain amount of a volume along a ray has a certain percentage of likelihood of getting absorbed or reflected,” Reisch explains. “And for thin volumes like dust, we focused on de-noising our volume renderer as well. We don’t get a lot of samples when the volume is thinnest and darkest, so we needed to be sure they were noise-free.”
In the past, effects artists would have overcranked the density to make dust feel thicker and more detailed, or they might have disconnected it from the lights.
“But, that was always a cheat,” Reisch says. “We stepped back to approach dust the right way, to get detail without having to overcrank it. We are really pleased with the way light scatters within a volume now. We get a beautiful glow and backlight.”
Reisch, along with Julian Fong, a senior software engineer, and Magnus Wrennige, a principal software engineer on the RenderMan team, will reveal some of their techniques during a Production Session at SIGGRAPH.
“Mud was the biggest challenge on the show,” Reisch says. “Mud is such a difficult thing to do. It’s between a solid and a liquid. And in the Thunder Hollow Crazy 8 sequence [the demolition derby], mud was front and center. We used Houdini’s fluid simulation, but a lot of thought went into how we set it up with varying viscosity to create a clumpy feel.”
PIXAR HAD TO PREVENT RIS FROM ADDING DISTRACTING REFLECTIONS TO EYES.
After spending time with reference material, the crew decided they needed multiple components to give a CG volume a muddy feel. “There are areas that are almost like dirty water, other areas with a chunky flow along the surface that has wrinkly detail, and another area with sharp aggregate-like pieces of rock that track along with the fluid surface,” Reisch says.
With that in mind, Effects Artist Stephen Marshall worked on making mud for six months before mud oozed into any shots.
“We’d take a two-pass approach,” Reisch says. “We’d have a top layer, very liquidy, that would fill back in after a car ran though and created a tread mark. A lower-resolution base simulation of the puddle would cover the ground and any trenching as the cars went through it and pushed the mud aside. On top of that, we’d have some high-resolution clustered splash simulations. We put the detail and computational resources on those simulations, on the stuff that hit against the cars. That way we could make adjustments on only one cluster of a splash simulation. By not approaching this as a monolithic solution, we could make sure the audience could read the action in a sequence like Crazy 8.”
ARTISTS IMPROVED HOW RIS HANDLES VOLUMES TO RENDER MUD, DIRT, SMOKE, WHITE WATER, AND SO ON EFFICIENTLY.
The idea of simulation clusters came from techniques the crew had developed for the rivers in The Good Dinosaur, which had relied on the previous, Reyes-based incarnation of RenderMan.
“We came up with optimizations and a new acceleration structure for RIS so we could break up simulations into independent clusters like we did for the white water on The Good Dinosaur,” Reisch says. “The clusters don’t know about each other, but by breaking the problem into component pieces, we could get the detail we needed for all those cars across lengths of track.”
The mud, dust, fireballs in the Crazy 8 sequence, the tire smoke… all these natural phenomena effects help make the world seem real, help the audience believe that real characters are interacting in a real world. Done well, the effects establish or heighten emotion.
In one scene, McQueen crashes. He tumbles end over end, kicking up debris. There’s roiling engine smoke. He hits the ground in slow motion with quick cuts, scraping along the track.
“That level of realism helps make the audience care for the character,” Reisch says.
Some new technology helped the artists achieve that realism.
“During that beautiful slow-motion shot where McQueen turns over in mid-air, we simulated the air flow around the car,” Reisch says. “We do that for all the cars, but that shot shows it off. We do it as a pre-pass and then feed it into our high-resolution simulator.”
THE EFFECTS ARTISTS SIMULATED AIRFLOW AROUND THE CARS.
The technique has another application, as well. “The clusters of dust and smoke don’t know about each other,” Reisch says, “but the velocity pre-pass gives a perception of these sims being tied together so they don’t look completely independent from each other. It makes so much sense to break the simulations into clusters in space because of the amount of details. On The Good Dinosaur, it didn’t matter if there was a piece of volume a quarter mile away. But we needed that feeling of velocity trailing right behind McQueen that we saw in our racing reference all the time.”
Mentoring
Cars 3 is about mentoring. Hud and the old-timers mentor McQueen. McQueen mentors Cruz. For White and Reisch, mentor-ing extended beyond the story.
White, for example, took on a co-DP for the show, Mike Sparber.
“I picked him because he wanted to be the DP, but he was new, so I mentored him on the show,” she says, “which is cool.”
Similarly, Reisch sees his role as supervisor including a responsibility to find artists and help them along the way. And, he appreciated the film’s message. During the film, it becomes clear that McQueen’s trainer, Cruz, had secretly wanted to be a racer, but people had not taken her seriously. After McQueen becomes her mentor, Cruz shakes off the debilitating judgment of others and wheels herself onto the racetrack.
“My daughter was born a couple days before A Good Dinosaur released,” Reisch says. “Seeing the message that [Cruz] can do anything she sets her mind to touched me deeply. She belongs on that track.”
As do we all.
Barbara Robertson (BarbaraRR@comcast.net) is an award-winning writer and a contributing editor for CGW.