Cinefex Weekly Update | Issue 22

Rhythm & Hues' 140 shots primarily served two sequences, including an introductory one on 'Planet UV' -- where Riddick is chased by bounty-hunting mercenaries -- for which the company generated 3D and 2D landscapes. But the majority of Rhythm & Hues' work is featured in sequences on the scorching hot, and aptly named planet Crematoria, the site of a subterranean prison where Riddick is incarcerated. Among the Crematoria effects is a planet-wide storm -- caused by temperature extremes -- that follows the movement of the sun. "David Twohy asked for something that didn't look like a sandstorm," said Rhythm & Hues visual effects supervisor Mike Wassel, "because it isn't supposed to be dust -- it is supposed to be a 'visible thermal front.'"

To create the VTF storm, Rhythm & Hues essentially 'poured' a fluid simulation over CG landscapes modeled in 3D. "That gave us the basic movement of the storm over geometry," Wassel explained, "but the real look of it was derived in compositing, where they manipulated many layers of particle animation. Compositors also created a white-hot leading edge to the storm, which lights up the landscape as it moves across the surface."

Rhythm & Hues also executed composites featuring New Deal Studios miniatures for wide shots of the underground prison, designed as a vertically-oriented, 200-foot-deep structure with a control room -- dubbed the 'cork' -- that extended from the ground surface to 60 feet into the subterranean cavity. New Deal built prison miniatures in two scales: a 1/16th-scale prison interior and a 1/8th-scale control room. The 1/16th-scale miniature was featured in a composite shot of Riddick's initial descent into the prison. "The camera does a 180-degree move," said Wassel, "first looking up at Riddick as he is lowered. Riddick then passes camera, and the camera tilts down to reveal the full depth of the prison." Rhythm & Hues photographed Diesel motion control against greenscreen on stage in Vancouver -- where the entire show was filmed -- then scanned the selected take, tracked it, and output the motion control data files for New Deal crew members to run when they shot their motion control move on the prison interior miniature.

In the story, prison authorities cull the convict population by releasing vicious hellhounds, rendered in 3D by Rhythm & Hues. The design for the massive, scale-covered dog came down from the production art department, which also sculpted a full-size foam maquette -- measuring seven feet long, without the tail -- that was used on set for purposes of staging and framing. Back at Rhythm & Hues, digital modelers used geometry from a scan of the maquette to build the CG hellhound, which featured 9000 modeled scales. Though canine in appearance, the hellhound was animated to suggest the behaviors and body language of a big cat. "The movements of a cat are inherently scarier than those of a dog," Wassel commented. "Cat-like movement helped us to make the hellhound more terrifying." Although the movie's PG-13 rating mandated that the bloodshed be played largely offscreen, the hellhounds are seen taking down numerous prisoners. Live extras pantomimed being attacked on set, then Rhythm & Hues animated the hellhound to tie it to those live-action performances.

The most challenging shot was one in which a hellhound pushes his head through a waterfall, finding -- and ultimately befriending -- Riddick. On the set, the visual effects team had pushed a lifesize model of the hellhound head through a practical waterfall and shot it on video to provide reference. "That was a good guideline for developing the fluid simulation so that we could match the on-set waterfall," Wassel stated. A plate was then shot clean, sans water, to allow for the addition of a simulated waterfall and the CG hellhound. Rhythm & Hues effects animators worked for a year to develop fluid simulation tools specifically for this shot. "The simulated waterfall was made up of three separate entities -- the laminar flow, the water sheet and the particle spray coming off of it -- which we balanced in the composite. The main issue was making it really look as if the dog was interacting with the water, splitting the flow apart and pushing its head through. And that led to the next problem, which was that now we had a wet dog. To create an undulating surface of water sheeting off the dog, we photographed real water and used it as a texture map to displace the skin texture."