Mopping up after the Apprentice

For The Sorcerer’s Apprentice,visual effects supervisor John Nelson oversaw more than 1200 shots featuring plasma ball fights, a Chinese dragon, car chases, magical creatures and the re-creation of the famous Disney Fantasia sequence. We take a look at some of the key work by the two lead facilities, Asylum and Double Negative. (Sorcerer’s Apprentice on DVD Nov 30th)

The film tells the story of sorcerer Balthazar Blake (Nicolas Cage) who recruits unlikely physics student Dave Stutler (Jay Baruchel) as his apprentice. Together they help defend New York against the evil Maxim Horvath (Alfred Molina) who is trying to release other sorcerers from the Grimhold, a magical prison similar to a nesting doll. To conjure up the visual effects for the film, director John Turtletaub looked to John Nelson to consider that both magic and science can sometimes be indistinguishable. “One of the things we wanted to develop is that magic is physics and physics is magic,” said Nelson. “Physics is basically magic that has been quantified and explained specifically, but there’s many things in magic that are waiting to be discovered.” Nelson split the work between Asylum, Double Negative, Method Studios, Rising Sun Pictures, Company 3 and an in-house team.

The Grimhold, the dragon and the confetti

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Early scenes introduce viewers to Balthazar’s antiques store, the Arcana Cabana. A young Dave finds his way into the store and unknowingly releases Horvath from the Grimhold, who appears as hundreds of thousands of streaming cockroaches forming into a human mass. Asylum handled the cockroach transformation as a large behaviour simulation. Other effects included an animated dragon ring, a remote sword fight between Barthazar and Horvath and particle simulation shots of the two being sucked into an urn before Dave escapes the store.

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After escaping the urn ten years later, Horvath unleashes a pack of wolves on Dave at an above ground train station, demanding to know where the now lost Grimhold is. Asylum augmented the wolves to make them more vicious. Balthazar rescues Dave with the help of a mechanical Chrysler Building eagle, a CG creature also by Asylum. For a shot of Balthazar throwing a spell at Horvath and placing him into a watery suspended animation, Asylum created a flexible effect. “Rather than use a stills camera array for your typical bullet-time effect,” noted Asylum visual effects supervisor Phil Brennan, “we shot some plates on the set, then shot Alfred Molina on greenscreen with eight ARRIs at 150 frames per second, and used that to reconstruct him in CG. So we had a CG version of him going into suspended animation and the watery effect over the top.”

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Balthazar convinces Dave to help him search for the lost Grimhold. They start in Chinatown only to encounter a dragon created by another evil sorcerer Sun Lok (Gregory Woo), who initially appears as made from thousands of butterflies. The sequence also included a morph between an elderly lady and Horvath, an acupuncture needle and beaded curtain battle and layers and layers of confetti.


10Oct/app/Asylum_dragon2Lok magically creates the dragon by turning a traditional Chinese parade version on the street into a living, breathing monster, a transition created by Asylum. “We had to turn the parade dragon which was made out of cardboard and cloth into a real dragon over five shots,” explained Brennan. “It was also a story point that the people inside the paper dragon had to be part of the transformation and become the flesh and blood of the real one.”


The transition started first with the head and neck, then body, before cutting to the interior to show the people being absorbed and becoming fleshy material. Asylum modeled the dragon in Maya and used Houdini for the transition shots. “Texture-wise we looked at crocodiles and caimans at a reptile park and shot some high-level reference photos,” said Brennan. “He was a pretty complicated rig and had to have a little bit of personality but not too much. He has horns that were rigid but there were also these tentacles around the head that were more organic and needed to be simulated.”

The creature is puppeteered via a small coiled dragon on Lok’s brass breast plate, necessitating further visual effects work and some skin simulation. To hide the main dragon from the public – to whom good sorcerers are inclined not to reveal their magic – Balthazar multiplies the confetti from the Chinese parade. Asylum created all of the airborne confetti in Houdini and made it flood over the streets in a thick layer, as well as making it interact with the dragon.

Pursuing Dave, the dragon crashes through surrounding buildings before pursuing him up a fire escape. “For the smashing scenes, there was a lot of practical stuff there,” said Brennan. “We just had to enhance some shots a little, just to integrate our CG dragon. And other shots we’d do a lot of the destruction and debris in CG.” Eventually, Dave is able to set the small dragon on Lok’s breastplate on fire and this in turn causes the real dragon to burst into flames and fall off the building before turning into butterflies. Production shot a practical explosion which Asylum referenced with other fire elements to create a CG dragon on fire.

Chasing cars and Hungarian mirrors

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A car chase sequence through New York featuring morphing vehicles and a magical Hungarian mirror was also handled by Asylum. After a small accident on the first night of location shooting, production could only drive the cars up to 25 miles per hour. Along with constant rain, this meant Asylum had to add more CG shots and create speed ramps for the chase.


The sequence begins with Balthazar and Dave in a Rolls Royce Phantom – a car actually owned by Nicolas Cage – in pursuit of Horvath. Horvath turns a corner and changes his car into a yellow cab along with all the other cars around him. Production shot multiple passes of the cabs which Asylum assembled along with some CG versions for the shot. Horvath then turns his taxi into a Ferrari, with the transition realised as a liquidy-melting effect. “The actual source and destination cars were quite a bit different,” noted John Nelson. “So instead of making everything go rubbery, we tried to have this water motif of water pouring over the car. The wheels wouldn’t change shape too much, while water flowed over the car and made one shape change over the other.”

Later, the Rolls Royce Phantom morphs into a Mercedes-Benz SLR McLaren and continues the pursuit through the Park Avenue tunnel, which Horvath fills with smoke, a simulation created by Asylum. As Balthazar’s car nears Horzath’s, the McLaren is forced, airborne, into a giant ‘Hungarian mirror’ and enters an empty world where everything is in reverse. The only way back into the real world is by driving through another mirrored surface. “Cutting back between worlds was a challenge editorially and a lot of the shots didn’t exist,” said Brennan. “So we had to build many of the streets in CG.”

Asylum re-created whole blocks of 7th Avenue all the way down to Times Square, adding cars and background environments. Horvarth keeps Balthazar and Dave from re-entering the real world by destroying all the reflections until they are able drive though a falling 10 foot shard of glass. Finally, Horvath is able to change his Ferrari into a garbage truck, while Dave only manages to transform the McLaren into an old Pinto, again achieved as a watery morph. The Pinto is smashed by the garbage truck, a mostly practical effect.

Fantasia re-created

In one of the film’s signature sequences, Dave attempts to clean his underground lab before the imminent arrival of a girl he likes, Becky (Teresa Palmer), with rudimentary sorcerer’s skills. He brings alive mops, broomsticks and sponges until it all goes horribly wrong. The sequence is based on The Sorcerer’s Apprentice segment of Disney’s 1940 Fantasia. In the present film, Double Negative created the effects for the clean-up scenes under visual effects supervisor Adrian De Wet.

For the shoot, production based the filming on previs led by Dneg animation supervisor James Lewis. The special effects team created a rig that allowed the set to be flooded in ankle deep water and then drained and re-flooded. “We also employed a whole bunch of puppeteers who wore green suits for a second unit shoot directed by John Nelson to carry the mops and brushes around the place as if they were going to be in the scene,” said De Wet. “We painted out the green guys in some shots and then added our CG mops and things which we had more control over.”

Double Negative needed to have precise control over the animation of the mops and other cleaning characters, but still provide a realistic movement. The rig that we eventually came up with,” said Dneg CG supervisor Graham Jack, “had several ‘legs’ that the tendrils could be gathered into. We could then control how dynamic the tendrils were along the length of the leg and also from the centre of the leg to the outside.”

Practical water on the set served well for interaction reference, with artists adding hundreds of passes of sprays, splashes and ripples in CG. Eventually, Balthazar arrives and clears all the water away, an effect achieved as a huge water simulation starting with the studio’s proprietary Squirt fluid simulation software. The look of the water as it disappears went through a number of iterations at Double Negative. “We tried Maya’s fields, created our own in Houdini and played with all kinds of attractors and negative divergence to create ‘black holes’ which would eat away the water,” recalled lead FX TD Georg Kaltenbrunner. “The final brief was to create a few areas were you get the feeling of a helicopter flying above the water, pushing it down and displacing it outwards at the same time.”

Once artists were content with the main simulation, they meshed the particles and brought them into Houdini. The various elements like foam, bubbles, floating debris and spray were simulated and everything was brought back into Maya, rendered through RenderMan and comped in Shake. “Additionally we had the water flow out of screen and into invisible holes in the walls which we animated to open like a dam,” continued Kaltenbrunner. “The helicopter effect was mostly achieved with the use of Maya fields. Here we used the mesh to birth new particles in various areas and drive those with the velocities of the fluid simulation. That way we were able to simulate different types of foam, bubbles and white wash, as well as spray. We also simulated floating debris which was a particle instancing technique were we sampled the velocities in the surrounding water to achieve proper rotations.”

In the first of the dispersal shots, the mops, brooms and sponges freeze in mid-air until Balthazar releases them. Double Negative orchestrated a rigid-body-dynamics simulation, making the objects fall into the water where they are washed away. For the many individual splash elements in the other shots, artists brought the animated characters into Houdini, sampled their motion against the water and created an emitter which was then used to emit into a fluid simulation in Maya. “The resulting data was brought back into Houdini and filtered to achieve the desired look,” said Kaltenbrunner. “Handing the data back and fourth between Houdini and Maya was achieved with scripts that would build the scenes procedurally based on minimal user input. Multiple matte passes – age, density, speed – were rendered to help the integration of the elements in 2D.”

The Fantasia sequence also allowed Double Negative to test a new piece of software called Bambi, a generalised task dependency system that let artists create simple modules representing particular tasks and connect them together. “It would then work out the order that the tasks needed to be processed in and execute them on the render farm,” explained Jack. “This was essential for the Fantasia sequence where we had lots of different types of props coming to life like mops and brooms. All of them had their own slightly different pipeline for cloth or fur and Bambi allowed us to chain these all together correctly.”

Plasma balls

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Earlier, Dave’s lab is the scene of a training session with Balthazar on the creation and use of plasma balls, energy that a sorcerer can conjure in their hand and fire as a weapon. “We had to design the look of the plasma balls and so we went straight to plasma itself which is essentially a super-heated gas,” said De Wet. “You can create it at home, but you shouldn’t, because it’s dangerous. How you do it is you get a flame like a candle and you put it in a microwave with a jar over the top. You turn the microwave on and what happens is the stuff called plasma appears in the jar – basically ionised gas.”


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On set, actors sometimes interacted with a blue quartz-like light on a stick that would be flown over by a stuntsman and stopped directly in front of their face, or they would hold lights in the palms of their hands when creating one the plasma balls. To replicate that look of a white hot volume of gas, Double Negative started with the look of plasma and added more detail in 3D with smoke, charged dust and particulate elements being kicked about. Further detail came from mini bolts of lightning connected from the hands to the plasma ball. “In 2D, they made the ball flicker and fluctuate in size and brightness between flames,” said De Wet. “The glow that would come off the ball would flicker from frame to frame as well in a stichato fashion.”


Musical Tesla coils

For a scene in which Dave plays music to Becky via large Tesla coils in his lab, Double Negative created the necessary lightning effects. “We designed a system where you could choose particular frames where the bolts connected and that would be the hero frame,” said De Wet. “At first it wasn’t super obvious that it was playing along with the beats of the music, so we had to heighten the contrast between an on and off frame to make it look like it was playing along in time with the music.”

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“In Houdini we created a selection of possible paths for the lightning and based on a set of rules one or more of these paths was selected,” explained Graham Jack. “There were various levels of noise warping the path of the lightning that could be controlled as required.”


In the sequence, Dave firstly plays Stevie Wonder’s ‘Superstition’ and then OneReplublic’s ‘Secrets’. The songs were only finalised three or four weeks before delivery. On set, the rhythm of the music, although not the final piece, was tapped out when photographing the plates. When the final music was decided, Double Negative removed and re-timed the interactive lights. “We had a full CG build of the set and used PRman’s point cloud based indirect diffuse lighting tools,” said Jack, “writing points from the lightning curves and using them to cast light onto the points generated from the set. This lighting had no textural information but it was used as an element in the composite to grade the scan.”

The final battle

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Evil sorcerer Morgana le Fay (Alice Krige) is released by Horvath at Bowling Green park, taking the form of sorceress Veronica Gorloisen (Monica Belluci). She attempts ‘The Rising’, a spell that will summon sorcerers from the dead. Double Negative created whooshes of fiery energy mimicking earlier shots of a Merlin Circle created by Bathazar in Dave’s lab, but on a massive and catastrophic level. The energy raises above the buildings of Manhattan into a huge pentagram that triggers dark energy, a black cloud of evil darkness. “The circle was made up of a Houdini particle sim which made up the trail of embers left as the energy travels through Manhattan,” said Jack. “The head of the energy stream was a fire sim created using Squirt. There was another Houdini particle sim that used velocities from a fluid sim to push the particles to get a more realistic motion to the embers. There were also a bunch of other data passes like motion vectors and distortion passes which were used in comp to build the final effect.”


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Meanwhile, Horvath re-animates the bronze Wall Street Bull to attack Balthazar. Using the actual bronze bull as reference, Double Negative obtained a 3D scan and built a model using Zbrush, Mudbox and Maya. “Initially, we were trying to match it exactly to the real statue,” noted Jack, “but ultimately we made a few changes to make it a bit more intimidating, like sharpening the horns. There was a balance to be struck between having realistic muscles and skin sliding, and trying to give it a more rigid feel to reflect the metallic nature of the bull. The lighting was primarily image based. We had great access on set to acquire HDRI light probe images and the bronze material of the bull leant itself to this kind of lighting. We were also re-projecting the scans onto rough geometry of the location and ray-tracing against that to get realistic ground reflections.”


In a final battle between Morgana and Dave, she is revealed to be a spectral spirit demon. “We thought she could be made of thousands of dots in a particle sense,” said De Wet, “which meant she could move around not just as a two-legged humanoid but could also shape-shift more like a shoal of fish. John Turteltaub really latched onto the idea that the creature would move like that. Originally it was like a shoal of lampreys which are parasitic fish and a bit like leeches. Over that there was a layer of particles and they swim about a bit like fish. Also, there was energy inside her like a layer of lightning and a storm of particles over the top. Through all that you can still see her face and it still has to have expression.”


Artists relied on a Houdini setup for Morgana, starting with a a geometry cache based on the body track of the actress which was scaled or tweaked where necessary. “This was turned into a level set and filled with particles,” added Graham Jack. “The level set was used to generate a force which would push the particles in when they were outside her volume and out when they were inside. There were curves that the artists could edit to fine tune these forces. To generate the overall swirling motion there were a couple of different options in the setup, a curl noise force to get some general swirling motion or a fluid sim where something broader was required. The scan of the actress was projected onto the particles based on their birth position. There were also loads of lighting and data passes which could be used in comp to tweak the look, such as age and the levelset value.”

The Sorcerer’s Apprentice is on DVD and Blu-Ray Nov 30th
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