To address the long render time, a custom lighting pipeline was built by lead td Philippe LePrince. "We avoided ray-tracing whenever possible," Franklin notes. "The desired glassy look was created through the use of an in-house reflection card tools that placed reflection maps on 3D coordinate systems. Rather than reflecting each other, the shelves and spheres reflected pre-rendered HDRI maps of the surrounding geometry. Rather than use geometric level of detail, we structured the scenes to use regular geometry close to the camera and shelves baked into PrMan's brickmaps in the background. Tds would choose how to partition their scene with user-friendly selection-based tools. Whenever we could, we used point-based occlusion and indirect illumination. The shelf assets contained baked occlusion and indirect lighting. The last destruction shots used dynamic point-based indirect illumination to allow falling prophecies to light their surroundings as they fell. New advances in PrMan allowed us to simulate area lighting in large dynamic scenes at a reasonable cost."

After 19 months of intense work, the team of 250 artists, developers and technicians, delivered Double Negative’s final shot. All agreed that the visual effects work hugely benefited from the uncommonly long schedule. 

Climax in the Veil Room
Having managed to vanquish the Death Eaters, the children discover a strange amphitheatre-like room containing a huge arch holding a magical veil. The plates were shot on a partial set built on a stage. Due to height limitations, the walls and arch topped off at approximately 20 feet, which necessitated digital set extensions on most of the shots. The Veil itself was created using a combination the Syflex cloth simulation plug-in for Maya, and a set of custom shaders that produced a subtle combination of highlights and refractions.

Soon though, the Death Eaters are back to set upon the helpless children. The final battle is about to begin… Once keyframed on digital stunt doubles, the Death Eaters animation was baked out from the rig onto the surface geometry, which could then be exported to other systems for procedural animation. The trailing ribbons of cloth and tendril-like vapor plumes were animated in Houdini, whilst the billowing clouds of smoke were created in Maya fluids. All elements were then rendered in with a combination of PrMan and DNB, Double Negative's proprietary volumetric renderer.

"Custom tools developed by R&D lead Trina Roy and lead td Eugenie von Tunzelmann enabled the geometry to pick up the underlying shape of the voxelized fluid simulation," Franklin explains. "Basic A-over-B comps would show us how the animations in the different layers were working together. Once we were happy with the elements, they would be sent for integration by senior compositor Bridget Taylor. The final look of any of the Death Eater shots was a combination of 2D and 3D work."

It's a particularly intense battle for Sirius: a collaboration between 2D, 3D and practical effects. On set, Gary Oldman was carried up on a flying rig through the Arch. "We matchmoved the shot in 3D, rotoscoping Gary's action onto a 3D stunt double," Franklin continues. "This was then used by 3D sequence supervisor Phil Johnson and lead td Alison Wortman as a guide to animate layers of sweeping cloth simulations that wrapped themselves in a series of waves around Gary. 3D passes for lighting, displacement and normals were rendered out. 2D was then used to distort the image of Gary whilst progressively dissolving selected areas of his body away. In addition, we sucked out the color from Gary's face and added a subtle cataract dullness to his eyes."

First Class Operation
After 19 months of intense work, the team of 250 artists, developers and technicians, delivered Double Negative's final shot. All agreed that the visual effects work hugely benefited from the uncommonly long schedule. "By joining the show at such an early stage, we were able to develop unique and complex R&D-lead solutions to a wide range of challenges," Franklin concludes. "In the current climate of increasingly pressured post schedules, that was a luxury and a privilege. The time that we were given undoubtedly made a major contribution to a first class result from all the companies involved. The Harry Potter machine -- certainly from a vfx point of view -- is a first class, `Rolls Royce' operation to work for!"

Alain Bielik is the founder and editor of renowned effects magazine S.F.X, published in France since 1991. He also contributes to various French publications, both print and online, and occasionally to Cinefex. In 2004, he organized a major special effects exhibition at the Musée International de la Miniature in Lyon, France.