Computer Graphics World

JANUARY/FEBRUARY 2011

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CG Water n n n n their quest. “In adapting the story to film, they created a sort of entity, an evil cloud if you will, which wasn’t in the book,” Valdez says. When the ship, which is under oar power at this point, rows into this dark cloud, the sea serpent attacks. Many of the subsequent shots are all-CG: CG boat, digital doubles, the characters Reepicheep, dragon, and serpent, and water. To help the audience understand how far the boat must travel inside the cloud, and, therefore, how dangerous the journey, MPC built towering columns from particle simu- lations created with Maya and Flowline ren- dered from various angles and lighting posi- tions. Te layout department established a travel path for the boat and camera position for every shot. And then compositors work- ing within Te Foundry’s Nuke placed the columns in the environment to establish the look of the place. “Once we had animation and layout un- der way, we worked with the fluid-simulation team to create an escalating series of oceans us- ing four levels of choppy water,” Valdez says. “It all came together in Nuke: the enormous pillars, a sky dome with layers of mist, and the ocean surfaces. Te sky dome was one big ren- dered environment that we could tweak per shot in Nuke, but we rendered the monster, the boat—or boat extensions—and the water on a per-shot basis.” At one point during the battle taking place in the dark cloud, the dragon claws at and lands on the serpent’s skin. To connect the dragon’s talons to the serpent’s soft skin, the riggers provided specific tools for the anima- tors, and the technical animators used deform- ing techniques and cloth simulation to add realism to the skin grab. Similarly, when the serpent bites off the prow of the wooden boat, a special bolt-on rig gave the animators the tools they needed to connect the two and give the serpent’s mouth more detailed controls. “When I first saw the post-vis, I thought the work would be pretty intense,” says Ben Jones, MPC character lead. “But, it was great to see the shots come together.” The Wave Te problem with creating a standing wave, Framestore’s Jonathan Fawkner points out, is that we know what a wave looks like: forward movement drives its inherent mo- tion. But, what does a wave look like when it stands still? Te wave appears during the final sequence in the film. Te children walk into a hole MPC artists often worked with live-action elements to create wide expanses of ocean, such as this, on which to place their CG boat. in the wave, look back, and then float back into the bedroom from which they had come. Tey had entered Narnia early in the film through an oil painting of a seascape that Framestore had animated with a roll- ing sea. “We took one frame of footage from the film Master and Commander, which Fox owned, a horizon with a stormy sea, and used Corel Painter algorithms to turn it into a nice effective painting,” says Fawkner, VFX supervisor. “Ten we drove the painting with motion vectors from the real footage. When that broke at 10 frames, we painted a new painting and drove the motion vec- tors backward and forward, and blended between. We ended up with paint that sort of fol- lowed where the waves moved in the painting.” To extract the motion vectors from the live- action plates, the crew used Nuke’s optical- flow plug-in. Halfway through production, though, the producers decided that the film would be projected in stereo 3D, so rather than a flat painting with water spewing off it, it became a window into Narnia through which water would flow. “Tat was a good decision, but we then needed a CG ocean and a CG boat,” Faw- kner says. “So, we used the same technique, but the motion vectors from the ocean were free because it was CG. MPC provided the boat and gave us the camera move. We en- gineered a system that allowed the stereo cameras to track forward while still creating a flat image. Ten we diverged the eyes and increased the interocular distance to give the audience the feeling that the depth grew right in front of them. Te depth opened up as we flew through the painting.” When it was time for the children to return, water needed to carry them back into the bed- room, as well. Framestore used a geometric surface that the modelers distorted around an offset nodal point to create the shape of a standing but curling wave. To create the move- ment within, they used five different scales of Tessendorf noise patterns. “Tat gave it a fluid-like feeling,” Fawkner says. “We mapped them onto various areas of the wave. Ten we shaded it in RenderMan doing multiple ray- traced passes, using the canopy of white water that blows over the top of a wave like a big area light to simulate the translucency from a backlit spray. Te biggest challenge was that in 30 shots, every time you looked, there it was in broad daylight.” To spin the children back into the real world, the crew sent a corkscrew of water into the wall using a beta version of Exotic Matter’s Naiad software. Framestore’s Fluidity man- aged the rendering. Te water crashes into the bedroom, and the final sequence with the chil- dren swimming in the bedroom and finding their familiar objects is a compositing trick. Te director shot the children in one set that could descend into a water tank, and then in another dry set in exactly the same positions doing the same performances. “Our job was to marry the two,” Fawkner says. For this and other shots, the compositors worked in Nuke. “Everyone approached this show with a sense of trepidation,” Fawkner says. “On paper, it’s a sequel, but people always want to push the en- velope and do something different. And, it was a different client and a different studio. But, it was a joy. We had the right amount of time to do the work, and we had really nice clients. We all really enjoyed it.” n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net. January/February 2011 39

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