Shape Shifting in <em>The Sorcerer's Apprentice</em>

Check out The Sorcerer's Apprentice trailers and clips at AWNtv! [1]

There's a lot more to The Sorcerer's Apprentice [2] than electrifying vfx -- there's also a lot of shape shifting courtesy of Asylum FX's 500 noteworthy shots: Horvath (Alfred Molina) forming out of cockroaches, a parade dragon turning into a real dragon and cars morphing into other cars.

Indeed, Asylum (under the supervision of Phil Brennan) worked on most of the vfx in the first half of the film (up to the end of the Chinatown sequence) and a few later sequences such as the Car Chase and the Mirror/Bathroom scene. Asylum also created many of the CG characters in the film such as the Chrysler Eagle, Merlin's dragon ring, Sun Lok's belt dragon and the Chinatown dragon.

Nearly all of the vfx were extremely complex and involved some sort of CG. In addition, the nature of the film meant that there were a huge number of one-off effects, all completely different, and every one had to be intricately researched, designed and developed.

"The roach sequence featured hundreds of thousands of roaches scurrying to form a vertical mass, which would resolve into Horvath," Brennan explains. "The major challenge here was to reconcile the director's artistic vision [Jon Turteltaub] with the set of physical limitations, which were implied. Individual roaches needed to be clearly climbing over each other (interacting with each other) at a believable speed and yet quickly resolve into a human form. Since all bugs would potentially influence all others, this meant that a small change to the motion of a few bugs could dramatically alter the look of the simulation as a whole. So, much work went into designing a system which allowed specific changes to be made while guiding the subsequent interactions toward a desired result."

Care was taken to choreograph the motion such that the desired actions would be highlighted in visible areas while allowing maximum throughput in others. Tools were developed to influence the motion of each bug based on its proximity to types of features, density of structure beneath it, physical speed limits (based on reference), proximity to the "surface" of the evolving mass, among other factors, and to control the extent to which any of these factors would affect each bug individually or regionally.

 Once the roaches knew where to go, they needed to know what to become. Each roach, based upon its final position within Horvath was assigned a texture and a material. Furthermore, the surface of each bug would deform to match the surface into which it would merge. There were flesh bugs, bone bugs, cloth bugs and fur bugs. The closer the bugs crept toward their destinations, the more their textures, materials and topologies would change until they literally became parts of Horvath. This required a system by which textures and geometric information could be passed from the model of Horvath to the individual bugs based on this unique final position (and frame).

The dragon in the Chinatown sequence was needed to relate closely to the parade dragon yet still be extremely threatening. Numerous designs and styles of animation were explored. "At times, it looked more like a dinosaur, a snake, a komodo dragon and a crocodile," Brennan continues. "The final design was a very complex eight-legged creature animated to walk down the street, climb buildings, spray fire and smash through walls using a combination of practical and CG elements."

Asylum's most difficult challenge, arguably, was to transform the parade dragon into the real one. "The parade dragon was modeled and carefully matchmoved," Brennan notes. "Cloth simulations were then used to build a CG version, which could slowly transform into the real dragon. Each shot had to be treated as a separate one-off effect with its own rigs and blend shapes. Asylum's pipeline allows data to be moved very easily between Maya [3] and Houdini [4], which proved invaluable."

The car chase was another challenging sequence. Once again it is filled with very complex one-off effects: morphing/melting cars, numerous other CG cars, a smoke filled tunnel, morphing people, magical mirrors, exploding glass windows and several fully CG blocks of 50^th street and 7^th Ave. "While filming, the production had absolutely the worst luck possible -- car accidents and the subsequent speed restrictions as well as weeks of torrential rain made it almost impossible to shoot all the elements required," Brennan concedes.

For the transitions, reference plates were shot of each car, but the actual transition was built over the clean plate using fully CG cars. Both cars were scanned and modeled in very high detail and a third model was constructed that performed the blend animation between the two vehicles. This model was used to drive the shapes of the high-resolution geometry in Houdini and create the waves of transforming metal. Several layers of CG water spray were then added to tie the whole effect together.

Once inside mirror world, Balthazar (Nicolas Cage) has to escape back through another mirror to return to the real world, but Horvath is ahead of him, shattering his chances of escape. Asylum used extensive Lidar data to build several full blocks of 7^th Ave. approaching Times Square. Since the windows couldn't really be shattered, the plan was to replace the store fronts of the building in CG.

"This way we could control reflections on the windows to best convey the story of mirror world," Brennan continues. "Ultimately 10 of the shots were fully CG: everything (cars, buildings, road surfaces, sidewalks, street signs, etc.) had to be created from scratch. To pull this off, we combined fully textured, lit and rendered geometry with texture projections built from the extensive photographic reference gathered on set. All reflections had to be removed from the photographic textures and the correct ones properly calculated and added back in the shader. The distant environment was built using Nuke [5](by projecting additional photographic reference and animated signs) then passed back to the lighting team to be properly reflected into the streets and foreground buildings. The effects team created dozens of elements per shot including fog, drizzle, atmosphere, shattering glass, tire spray, man-hole steam and plasma balls.

"At the end of the day, those 500 effects shots felt like 1,500!

Bill Desowitz is senior editor of AWN & VFXWorld.