CARS 3: Pixar Embraces New Renderer with Stunning Detail

For Cars 3, Pixar took advantage of its new rendering architecture, RIS in RenderMan to tell the latest adventures of race car Lightning McQueen. (All photos copyright 2017 Disney/Pixar. All Rights Reserved.)

By IAN FAILES

The first Cars film from Pixar Animation Studios was released in 2006. Cars 2 followed in 2011. This summer, the third installment of the franchise featuring race legend Lightning McQueen will be in the spotlight. And with each new feature, Pixar has upped the ante on the compelling stories they tell and the technology used to help tell them.

That’s particularly the case with the upcoming Cars 3, directed by Brian Fee, since Pixar has now completely adopted its new physically-based, path-tracing rendering architecture known as RIS inside of its renderer, RenderMan.

On the previous Cars films, the studio’s REYES (Render Everything You’ve Ever Seen) algorithm, mixed with some ray-tracing techniques, had been used to deal with shiny car surfaces. But, after implementing RIS on Finding Dory, Pixar also embraced the new renderer for Cars 3.

The third installment in the franchise sees race car Lightning McQueen (voiced by Owen Wilson) deal with the impact of a major crash, aided by race technician Cruz Ramirez (Cristela Alonzo), as they also take on a new foe in Jackson Storm (Armie Hammer).

The results look to be stunning, but getting there was not without some major challenges – ranging from the particular needs of highly reflective cars, to audacious effects involving mud and volumetrics.

A NEW RENDERING PARADIGM

Although just about every film Pixar makes throws up a series of tough rendering assignments, the Cars films tend to have very specific ones such as metal-fleck paint, high specular reflections, gloss coats and generally lots of reflections. These are rendering challenges that ray tracing lives for, but prior to RIS, Pixar was using ‘the tricks of the trade’ to simulate the required look.

Concept art for the film shows a dynamic beach race.

“The problem was that metal-fleck paint has all these tiny little specks which are reflecting specular highlights at all random times and that kind of looks like noise. So we ran the risk of, if we used too much de-noising, we’d get rid of all the beauty of the metal-fleck paint.”
—Michael Fong

“Now with RIS that all comes automatically,” outlines Pixar supervising technical director Michael Fong. “We did a lot of cheating in the past and now we try to figure out how materials would really respond in different lighting conditions. And we try to model those materials more correctly.”

Interestingly, the ability to model and render those materials, such as car surfaces, in more detail and more realistically also required a new way of thinking about the things themselves. “Before,” notes Fong, “we approached it like this: well, it kind of looks like car paint to us. Now, it’s: well, exactly what would car paint be? It would have these various layers, and the metal-fleck would do this, and the gloss coat would do that.”

One challenge came simply from all the ‘free’ detail Pixar received in the renders. Now, lights placed along a race track were inherently featured as reflections of light shooting across the surface of the cars. While this looked exciting, and realistic, occasionally they had to have it art-directed.

“You have to remember that we’re an animation company,” states Fong, “so we want to make sure that you can read the character’s faces. We need this to be a character who’s emoting and is talking to the audience.”

Another challenge of the new RIS approach emerged with Pixar’s use of de-noising – a process used to speed up rendering times. “The problem was that metal-fleck paint has all these tiny little specks which are reflecting specular highlights at all random times and that kind of looks like noise,” says Fong. “So we ran the risk of, if we used too much de-noising, we’d get rid of all the beauty of the metal-fleck paint.”

LIKE A CAR IN MUD

Top to bottom:
Michael Fong,
Jon Reisch, Bill Cone,
Jason Hudak,
June Brownbill

One particular effect that was made easier with Pixar’s new renderer, while also offering up a wave of new challenges, was mud. In one action sequence, the race cars run through mud, have mud flicked up onto their faces and fenders, and generally stir up a whole concentration of the substance.

Pixar therefore had to create many different types of mud; the kind sitting on the ground in a puddle, the kind that sprays when the cars run through, and the kind that stuck to car bodies and tires. That involved devising, notes Pixar Visual Effects Supervisor Jon Reisch, the “dynamics of a viscous fluid like mud,” as well making sure it “felt natural and blended in with the great shading work that had already been done.”

“A big part of it too,” adds Reisch, “was making sure we got that sense of this being a really kinda raucous sequence without covering up all the great acting the animation team had done with all of our mud.”

Mud was particularly challenging because of its solid and liquid qualities (often at the same time). “We needed to see some sense of detail that’s still left behind and kind of infected through this sloppy mess,” says Reisch, “and then add additional detail by putting in chunks and pieces of ‘aggregate’ to give a break-up of texture and something that the light could play off of on the surface.”

Because there were so many types and layers of mud, artists split out the mud simulations, done in SideFX Software’s Houdini, into smaller ones. “The mud that gets kicked up from the tires would be a separate simulation,” describes Reisch. “The mud that hits and cakes up in the wheels and gets layered up on the character bodies would be some combination of detecting where the collisions of our splash sim would hit, and then passing that data over to either our character shading folks or trying to put an additional set of meshed mud on top of it.”

A VAST VOLUME OF VOLUMETRICS AND EFFECTS

In addition to mud, Cars 3’s various racing sequences involve not only a wealth of ray-traced vehicles but also accompanying dust, dirt, sand, tire smoke, burnouts, debris and even fire.

“The big thing was making sure that we could get a clustered simulation set up,” says Reisch. “We had lots of independently sim’d volumes which we could run in parallel on the farm for a shot. For example, if McQueen is burning down a straightway of a dirt track, he’d be kicking up a tremendous amount of dust behind him and it may be a quarter mile in length, we wanted to get a certain amount of detail in there. So we’d break that sim up into smaller components.”

Among the other effects challenges on Cars 3 were crowds, again realized in Houdini. Here, animators would create clips of animation to populate stands. “We then selectively chose the ones that really needed to stand out,” outlines Fong, “and we have animators come in and actually hand-animate key members of the crowd.”

Crowds could be particularly expensive to render, so Pixar also optimized them, as Fong explains. “The crowd models are actually variations on our normal models, and we’re just always trying to hide that transition from real model to crowd model. We do tricks like we might switch from subdiv to polys, we might remove pieces, we might cheapen the shading, and all we’re doing is just to hopefully make it more efficient.”

KEEPING IT REAL, IN THE CARS WORLD

Pixar’s new RenderMan RIS architecture has already been used for the visual effects in several live-action feature films to help provide stunning photorealistic sequences. That’s always something within Pixar’s reach, too, but of course their work on this latest animated feature had to stay in the already-established Cars realm.

“I think with the new renderer it’s a lot easier to hit photorealism,” suggests Fong, “and I think we definitely have examples where we can push it to that level. But that’s not the level, or the look, we’re going for in this particular movie. We’re not doing things like introducing film grain and that sort of thing to make it feel like it’s a filmed piece. We want people to know it’s still a Cars movie, but we also want to make sure people are aware of, hey, this is a different type of Cars movie.”

Cars 3 from Disney and Pixar is scheduled to be released in the U.S. on June 16, 2017.

Read about the development of Pixar’s other 2017 film in The Journey of Coco