For ILM, the water work was the most challenging part of Evan Almighty. The CG ante was upped because this was the first time the studio created water shots that occurred mid-day. All images © 2007 Universal Studios. Photo credit: ILM.

It's an act of God that propels the story in Universal's Evan Almighty, the sequel to 2003's Bruce Almighty, but it was a far-less-mysterious force called Industrial Light & Magic that created and controls the forces of nature in this updated version of Noah's Ark.

Director Tom Shadyac returns behind the camera, with Steve Carell reprising his role as newscaster turned Congressman Evan Baxter and Morgan Freeman recast as God. In this Almighty continuation, Baxter's desire to be closer to his family prompts God to inspire him to build an ark.

ILM and Rhythm & Hues split the lion's share of the vfx work. While R&H handled the animal work, ILM tackled the climactic sequence of the flood sweeping through Evan's suburban development and carrying the ark through Washington, D.C., to the steps of the Capitol.

ILM associate vfx supervisor Lindy De Quattro says the water work was the most challenging part of the film. "We've done water before, mostly in night sort of disaster-type situations, so it is glimpses of things happening in the water, a shot here and a shot there," she elaborates. "This is the first time where we had to do a whole series of shots that were happening mid-day, where you were going to get a really long look at the water and what it was doing."

New tools were required that would allow the water's movements to be choreographed. As a result, a shape-targeting system was developed, which was added to the PhysBam engine ILM used on last year's Poseidon.

Water on the Move
The water also had to behave as though it was being controlled, requiring new tools that allowed ILM to choreograph its movements. "We had to develop what we call a shape-targeting system to do that, which essentially means we could sculpt certain shapes and then describe how tightly the water needed to hit that shape at a certain frame," De Quattro suggests.

ILM added those tools to the PhysBam engine it developed in conjunction with scientists at Stanford University and used on last year's Oscar-nominated movie, Poseidon. Shape targeting combined PhysBam's simulation ability with the need to control the water as though it were a character, she explains. "It needs to move like water and act like water but it also needs to act like a character. That was the first time we really needed to control water to the extent that we had to."

The extent of the water's "acting" changed throughout production, getting toned down from some very active early animatics and controlled in ways that obeyed the needs of the story instead of the laws of nature. "Tom was very sort of nature conscious and he didn't want to damage the trees or make it look like the trees were getting harmed so we had to be very careful with what exactly the water took out," adds De Quattro.

ILM's Lindy De Quattro says one of the studio's goals was to automate the process of simulating water and its tricky transitions from solid shape to the blobby particles of splash to mist as much as possible.

Automating the Right Look
Getting the right look of the water had its challenges as well. De Quattro maintains that one of ILM's goals was to automate the process of simulating water and its tricky transitions from solid shape to the blobby particles of splash to mist as much as possible.

"It needs to be seamless, but they're treated in the computer using very different techniques and they're each rendered as separate elements so getting that transition has always been something that's required a lot of sort of manipulation in the compositing," continues De Quattro.

"We did get to a point where we could run the computer simulation and it would create particles which would be both above and below the water surface -- particles below the water surface would render basically as bubbles that would give kind of an aerated look to the water, and particles above the surface would be rendered as kind of the blobby bits that came off the water," she says. "We would run a secondary particle simulation to get the finer spray off of that and then again another simulation to get the mist off the spray."

The ark posed a number of unexpected problems too. Lighting was a major issue, as most of the shots of people on the ark were shot on a greenscreen stage and had to match an outdoor setting full of water that reflected light around the environment. There also was a partial ark about a quarter the size of the full size built on location in Virginia for shooting scenes of animals and people boarding that required set extensions.