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Digital Acrobatics

May 30, 2007 10:28 AM, By Michael Goldman

Inside Imageworks, Spider-Man effects veterans discuss the franchise’s visual effects evolution.

Sand Issues

That theme of mixing and matching also applied to characters in other ways—particularly where two other important characters, the villains Sandman and Venom, were concerned. Both of them required rare combinations of character animation with CG effects to sell their illusions. Sandman, as his name implies, is a character made out of, and able to control, sand; while Venom is an alien “goo creature,” able to take recognizable shapes, but inherently not like anything remotely human. Thus, in his natural state, Venom had to move in ways that were both believable and not recognizable as human or animal-like.

In both cases, Imageworks had to take new steps forward in the art and science of effects—particles for Sandman and liquid for Venom—and then incorporate those effects into the character work.

Digital Effects Supervisor Ken Hahn, who joined the production following a stint developing believable fire for Ghost Rider, explains that the sand challenge, in particular, vexed artists because the character had to be subtly believable, yet not totally realistic, at a far greater volume than what the facility was used to doing with particles.

Part of the solution came as a new rigid body solver called "SphereSim," created by Jonathan D. Cohen, for certain scenes (particularly for the crucial birth of Sandman sequence) as well as custom fluid solvers for scenes where Sandman simply dissipates and floats away in the wind. But the best conceptual method for animating a naturally occurring substance still required extensive debate inside Imageworks.

“Our problem with any natural phenomenon-type effects—whether water, fire, or moving sand—is that it is computationally very expensive, and yet not very art-directable,” Hahn explains. “By the time I came onto the show, we had a couple people who had already put in well over a year’s worth of work in developing some impressive tools—very good rigid body solvers, gas and fluid solvers—and they had volume rendering worked out nicely, and other clever things like getting RenderMan curves into stuff that looked like geometry or RenderMan points that would shade looking like multi-faceted surfaces. So, they had this nice framework and foundation for all these tools ready when I came in.

“But we needed to be able to apply those within the context of the actual shot work. When the animators got hold of Sandman, they were animating him as though he was just a regular, articulated, skeleton-enveloped creature, and they weren’t thinking so much in terms of moving sand for the character himself. We realized there was a disconnect there, and on the big birth-of-Sandman sequence, I sat down with all the animators and all the effects [technical directors], and we worked hard to get the animation guys to think more like effects people, and the effects guys to understand why animation was doing certain things. And also to make sure they understood that their data sets had to be done in a way that the color and lighting and shading guys would be able to render them out so that it didn’t look like we were just getting tons of sparkly types of things.

“The birth of Sandman was particularly challenging because it was three minutes of film time, where all you were seeing was a digital image of a big pile of sand in a big bowl. And yet [Sam Raimi] put this entire story arc and emotional content into the sequence. So it was a fair revelation, because it became pretty clear from those initial meetings that animation wasn’t considering all these factors, and that moving sand should not be so rigid and well articulated, and that the effects guys had to understand that animation had certain constraints because of what Sam Raimi was asking for. At that point, it became an artistic-driven thing where we had the natural phenomenon of sand obey the laws of physics, based on the tons of reference and study we did of sand, but not so much that we couldn’t contradict it for creative reasons if Sam needed us to.”

Cook says the response to giving sand the kind of character movement that Raimi was seeking required a combination of realism and artistry. “[It largely involved] finding that balance between adding what is fantastic, exciting, or dramatic about how the sand moved, and maintaining what is familiar about sand,” he says. “We’d have it move on its own in trails and streams, in ways sand would not normally move on its own, and yet, we’d also have it spending much of its time falling or spilling exactly as you are used to seeing sand.”

The whole thing was so complicated that Hahn says, “We had five people work on tool development for Sandman for roughly two years—that’s about 10 man-years' worth of effort. We needed about 1,000 to 1,500 dual-processor [rendering machines] just to render all the sand from that opening shot of [the birth of Sandman]—about 2,700 frames in the actual movie. There were maybe 40 or 50 people who touched that shot in one form or another, so even with the fast tools we have today, it’s still a complex problem to do a character like that.”

One of the central weapons in Imageworks’ battle to handle the massive sand shots and to render many of the virtual buildings throughout New York was the company’s new, node-based lighting tool, dubbed "Katana." Katana was central to speeding up the production’s pipeline as various visual effects shots were added, subtracted, or frequently altered based on Raimi’s desires.

The risk in using it, however, was the fact that, when the production got underway, Katana was brand-new. In fact, Spider-Man 3 and Surf’s Up were the first two movies to take advantage of the tool at Imageworks simultaneously.

“We decided at the beginning of Spider-Man 3 that our previous tool was no longer going to cut it—it was too slow and cumbersome, and artists took too long to turn changes around with it,” says Peter Nofz, the project’s other digital effects supervisor, alongside Hahn. “We really needed something that was more intuitive and node-based, much like what happened earlier with compositing tools—when they became node-based, everything got faster. And that’s certainly true here, especially since all of the compositing people already understood the logic of node-based systems—anyone who worked on Maya or Houdini, for instance. It was a big step forward for a show like this. If artist ‘A’ came up with a great lighting setup for buildings and characters, artist ‘B’ could immediately copy that and start working.”

This approach was particularly useful for the New York setting. “[The movie] got really close to the buildings this time, especially in the alley-chase scene with Spider-Man and the Goblin—what I call the ‘never-ending alley,’" Nofz says. "We also went higher, up near the tops of skyscrapers.”

© 2008 Penton Media, Inc.