Cinesite's Simon Stanley-Clamp explains that the extreme speed of the sleigh implied that a lot of physical ground was being covered, so a huge 3D environment in Houdini was constructed for the underlying cityscapes.

"David wanted to make the rides straddle the real and fantastical worlds," Bicknell says. "To explain how Santa could deliver the presents in one night, we developed a kind of warp speed that required moving the sleigh so fast through the environments that it ends up being just a streak in the sky. I initially found the visual hard to grasp as the sleigh was so un-aerodynamic and the wind interaction on the characters a relative breeze compared to the 1,000 miles plus an hour speeds. Eventually, the juxtaposition of these two elements created a sort of cocoon inside the sleigh that actually helped sell the concept that they were traveling in our world, but somehow within the fabric of it."

Cinesite created most of the sleigh ride scenes, with in-house Visual Effects Supervisor Simon Stanley-Clamp overseeing the effort with VFX Producers Angie Wills and Catherine Duncan. "The extreme speed of the sleigh implied that a lot of physical ground was being covered," Stanley-Clamp notes. "3D Supervisor Jon Neill, with Zoran Arizanovic, constructed a huge 3D environment in Houdini for the underlying cityscapes. For the cloud work, we modeled a series of organic cloud shapes in Houdini. From this, we set up an automated grid, which could cover an area from as little as a foreground element to a vast panorama.

We were able to paint clouds and gaps where we wanted. Then, from the resultant geometry, points were derived from the surface and from the interior of the shapes using our proprietary software to create a volumetric point cloud. Then, again, using in-house tools, a sprite was assigned to each point. We attached a shader that had subsurface scatter and lighting direction attributes, which was rendered out as RGBA passes for integration and regarding in compositing. All this enabled us to create huge layers of 3D clouds to pass through at high speed and place them to match the angle and direction of the gimbal sleigh. For wider shots featuring the actors and practical sleigh, a 3D track was generated from the live-action plate and our reindeers added into the shot. This involved attaching the hitching gear of our CG to the practical sleigh at the linkage, and hand animating our CG reins from the reindeers to line up with the actors' hands."

During principal photography, each live reindeer was shot and extensively photographed under flat controlled lighting conditions to provide the backbone for the fur textures and details of the antlers.

During principal photography, each live reindeer was shot and extensively photographed under flat controlled lighting conditions to provide the backbone for the fur textures and details of the antlers. Modeler Erik Ellefsen took precise measurements and notes before embarking on the 3D model build in Maya. Meanwhile, Head of Animation Quentin Miles filmed the reindeers to capture reference for walk, trot and run cycles, jumps, leaps, etc. A lot of thought went into the design of the hitching gear, the mechanism by which reindeers are attached to a sleigh for the actual pulling.

When the initial ride becomes an actual gift delivery, Rainmaker UK used a wide variety of packages to create the shots.

"David Dobkin's main concern was that the sleigh in flight should not look like it was on a roller coaster -- i.e., too controlled and predetermined," Stanley-Clamp observes. "Peter Clayton and Jason Ivimey blocked out initial animation flight paths, building in secondary animation once trajectories were signed off -- to "rough up" the flight paths for air pockets, etc. Peter also modified the sleigh animation rig so that the leaf springs of the sleigh runners would squash-and- squeeze and move independently from the main body of the sleigh. It was subtle, but added a lot to the landing shots." The shots were then composited with Shake or Inferno.

The Delivery Ride When the initial ride becomes actual gift delivery, Rainmaker UK was called in to create the shots. VFX Supervisor Adam Gascoyne oversaw the project, with VFX Producer Laurel Schneider and Head of CG Sean Lewkiw. The team used a wide variety of packages, including Houdini, Maya, LightWave, modo and ZBrush for modeling, Houdini for volume lighting, RenderMan, Mantra and LightWave for rendering, and Photoshop, Shake and Stitcher for compositing.