Computer Graphics World

face, and the interface was what we called RenderMan. How did the interface come about? Pat Hanrahan was an employee of Pixar at the time, and he took the lead. ere were 19 companies involved in this, fi ve very active. But, we didn't have a design by committee. e way we set this up, and I felt very strongly about this, was that Pat had the fi nal call about what went in. He was the architect. And to this day, that's how we make our movies. We have the leading conceptual designer on a movie or, in that case, the interface, and nobody can override that person. But Pat listened to every body, which is what made him good. I'm going to get a bit technical here. With rendering, like with raytracing, you have to have all the information before you can start to do anything. You don't actually care about the order of things because you can't start until everything's there. But with a real-time machine, you have to be able to process information as soon as it shows up, so you care about the order. Basically, the original interface was designed so that the order mattered. If you were doing real time, you could process it when it arrived, but if you were doing sophisticated render- ing, you could wait until it all got there so you could do raytracing. e trick was, if you thought about both, you could get the order right. If you only thought about one, then you would screw up the other one. So getting that right was part of the trick of the original interface. So it would work either way? at's right. If you pay attention to the order to begin with, you can have it both ways. If you don't pay attention, then you make mistakes. I believe the late Jeff Mock said we could do all this in software, and someone, I forget who, suggested calling it RenderMan. (In the forward to Steve Upstill's e RenderMan Companion, published May 1989, Catmull credits Pat Hanrahan. David A. Price, in his book e Pixar Touch, quotes Hanrahan sharing the credit with Jaron Lanier.] e shading language started with Rob Cook's shade trees, which generalized the shading formulas, and then Pat and Jim Lawson generalized this—with everybody thinking about it—into the shading lan- guage that is part of RenderMan. Do you remember which fi lms outside Pixar fi rst used RenderMan? I'd say the milestone picture was e Abyss. Well, it was more like a stepping- stone. e fi rst milestone, when people fi rst noticed it, was Terminator. And the big milestone, when the rest of the indus- try [other than ILM] switched over was in 1993 with Jurassic Park. Does Pixar use exactly the same com- mercial version of RenderMan as every- one else? At one time, the Pixar version was dif- ferent from the industry version because Pixar's needs drove the development in a diff erent direction. But, after a while, we realized it was a big pain in the neck for everybody. So it evolved into one version that Tony Apodaca's group controlled. One time, we delayed a release of impor- tant technology, the hair stuff , and we realized that was a mistake. We've never done that since. at was deep shadows? Yes. at was when we deviated from the pattern. But the studio believes now—very, very fi rmly—that we always want it to be the same for everybody. When I say the studio, I include all the technical people. It's easier to think about it as a product; it's clearer, and, from a reliability point of view, it's a better place to be. Why did you move the RenderMan group to Seattle? Tony went into production, and Dana Batali took over the group. He's so good that when he had to move back to Seattle for family reasons, we moved the group with him. It's better because the group doesn't get sucked into production crises. Is the RenderMan group a profi table unit? Oh yes. A lot of people, you know, would like rendering to be free, but I think the industry now gets that the free renderers don't advance as much. If the companies don't make money on them, they don't want to invest in them. We have a price structure that everybody knows supports the RenderMan group, and the group uses all its resources to make the product better for the fi lm in- dustry. So while the industry has to pay for it, its not getting something targeted at CAD/CAM or games. Pixar rendered Cars using raytracing in PRMan, the studio's commercial version of RenderMan. It was Pixar's fi rst use of raytracing throughout a fi lm; the cars demanded it for the refl ections. Cars received an Oscar nomination in 2007 for Best Animated Feature. February 2009 39 Trends & Technology ■ ■ ■ ■

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