Computer Graphics World

June 2009 40 n n n n Digital Sets•VFX originally built for Batman that automati- cally stitches the bracketed exposures and tiles that we shot with long lenses into pan- oramas. When we didn't have enough detail for the baroque architecture and statues, we relied on our texture painters and sculptors." e bigger problem was lighting the square for day and night. At night, lights point up to the top of the colonnade, flood- lights point down, and numerous lights illu- minate the basilica façade. "It was the most complex lighting we've done," says Jack. DNeg uses Pixar's RenderMan, and to help optimize the shadow generation for the hundreds of light sources, the team ren- dered multiple passes using RenderMan's point-cloud occlusion. "We rendered the floor, the colonnade, and the basilica into different point clouds," Cook explains. "And then to calculate the ambient oc- clusion and color bleeding, we combined all the point clouds into one using a little command-line tool that read in the mul- tiple passes after we baked them. So, if the lights had to change in one area, we needed to re-calculate only that layer." To create the crowds in the square, the team applied two techniques. Particle-based sprites created with Maya and RenderMan put extras, shot on a greenscreen stage, into the background. Artists placed these sprite-based crowds by painting areas on the ground plane. When people needed to move in particular ways—especially when the shock wave from the explosions hits the crowd—the crew used a solution built around Side Effects Houdini's particle sys- tem and its channel operators (CHOPs). "Every particle has a metaball associ- ated with it," Cook says. "ey move based mainly on how crowded the area is around a particle; the system can find the nearest particle and plot a course to avoid other particles. Because the system knows the position of all the particles, it works out, based on velocity, how to blend motions and trigger ac- tions. It matches the size of a step to the distance traveled, and blends be- tween walk speeds." Motion capture provided the animation clips, and a RenderMan skinning tool provided bodies for people. e explosion is a combination of practical effects and a fluid-dy- namics simulation created at dNeg. "We wanted a believable explosion in a style that echoes things people have seen, but something that no one has ever seen before," Bickerton says. At first, the dNeg team created nuclear explosions using Squirt, the studio's in- house fluid-dynamics solver, but Howard felt that was too cataclysmic. "We changed gears to develop something more astro- nomical and bathed in light," Jack says. e resulting explosion starts with pyro footage, then becomes a fluid-dynamics simulation that contracts to a point and expands back out. "To do the final effect, we used a combi- nation of fluids rendered in our volume ren- derer, procedural effects, and matte-painting elements, all composited together in (Apple's) Shake," Cook says. "Our fluid solver allows you to compress or expand, so we could suck the explosion back to a point." Path of Illumination Except at the very beginning, the entire movie takes place one night in Rome, with Langdon trying to deduce where the Il- luminati would execute four kidnapped cardinals, one after another. Each loca- tion represented a primordial element, and CIS-Vancouver helped create the interiors of two: e Chigi Chapel in the church of Santa Maria del Popolo, where Langdon arrived too late to save a cardinal branded with an Earth symbol from death, and the church of Santa Maria della Vittoria, where he arrived too late to save another cardi- nal from immolation. Actors were filmed inside detailed sets for both these church scenes. CIS extended the sets and created the fire that burned the second cardinal, using a mix of practical and CG elements. e majority of CIS's work, though, cen- tered on the enormous St. Peter's Basilica. CIS used NewTek's LightWave to ex- tend the Santa Maria del Popolo set, but built everything else, including St. Peter's, with Maya. ey rendered the models with Mental Images' Mental Ray, and compos- ited the shots with Shake. Visual effects su- pervisor Mark Breakspear led that studio's work, as he had for e Da Vinci Code. To prepare for the studio's work, Break- Double Negative extended the set built for St. Peter's Square (top) using 3D models and projected textures. Artists then filled the set with crowds they created and animated using two particle-based techniques for the shots in the final sequences (bottom). The cataclysmic and climactic explosion starts with pyro footage, changes to a fluid-dynamics simulation that contracts to a point and then, still using fluid dynamics, expands back out.

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