A lighting technique used on Cars was radiance, which is primarily the color light spill from one object onto another. An example is seen in the reddish puddle of light mixed into McQueen’s shadow.  

One of the biggest tasks was being able to accomplish all of the expanded lighting techniques while cutting down on the render time, which, early on, approached 17 hours per frame. “We instrumented a lot of what we did with statistics so we could glance at the numbers and figure out if we were doing what we should be doing and to catch our mistakes,” Ostby adds. “Say we had an object that was using ray tracing for shadows. If we knew that the whole world was looking to the car for shadows, it could be expensive. But if you could limit that to just one road, you could simplify things dramatically, particularly when you have the vegetation that we had, which contains a lot of detail. So we wanted to make sure that the part of the ground that was checking for information from plants was doing so only from plants in its neighborhood.

“We reengineered our lighting pipeline in a couple of ways. The primary thing was we wrote a new tool for ourselves for the setting up lights, which made it possible to deal with the complexity of light sources and all the things doing ray tracing. We put those controls in the hands of the lighting team. We also reengineered the way we construct low level lighting so we could hook together different parts of a light and make it more powerful and modular, so a light could do both shadowing and occlusion. One of the highlights with a lot of eye candy value is the neon sequence. There we had to do a lot to make it look lovely, primarily to get the sense of light emanating from all along the neon tubes. For that we needed light sources that weren’t just point sources but were areas all along the tube casting spill along the buildings and along the ground. Of course, the tubes themselves had to glow and there were dirt and dust on the tubes. Plus for all the characters that were reflecting those neon lights, we wanted the neon to reflect off a particular body panel. So there was a lot of cheating of light source location so it would read just right and tell the story that we wanted to tell.”

Pixar created the tool Ground Locking just for Cars. It allowed the animators to lock the wheels to the ground but give the car real suspension and bounce.  

Besides lighting, Pixar created a whole new set of other tools for Cars. One was Ground Locking. “We wanted to help the animators concentrate on the expressions of the cars,” Ostby continues. “Shoulder motion, head motion. So we made the cars automatically stick to the ground. This was new to us. We could make the wheels lock to the ground and roll, and then make the body position dependent on that as if there were springs and a real suspension in there. As a result, the cars were already where they needed to be and all we needed to do was add something special. The car would react to bumps in a realistic way. Certain cars had a bouncier suspension than others.

“The Kingpin system allowed cars to behave in a realistic way, including all the secondary motion involving wheels, suspension, springs and antenna.

Universal Rig was the technology behind the character rigging setup. That was a single character that the animators liked to work with, and we found a way of applying those central controls to other characters. So all the characters worked essentially the same way. This made it easier to build them.

“The animators did a lot of tests and dialed in how bendable the car should be without throwing you out of the movie. You don’t want rubbery looking cars or have them be too hard looking so you lose expression. After a short while, you realize it’s like a person’s face where it’s not too elastic and there’s a sense of structure there.”

Sweetland, meanwhile, says Cars is all about creating fantasies within a believable, naturalistic world — it’s why the movie lends itself so well to the computer animation medium.

Bill Desowitz is editor of VFXWorld.