Rhythm & Hues and Cinesite Artists Apply Houdini Talent and Pipeline Efficiencies to Create Film's Imaginative Mutant and Seamless Environmental Effects

May 6, 2003 - Santa Monica, CA - Side Effects Software™, developer of the award-winning Houdini® family of 3D software, announced that two major production facilities, Rhythm & Hues and Cinesite Hollywood, have used Houdini extensively to create the imaginative mutant and seamless fire, smoke, water and atmospheric effects seen in X2: X-Men United. Cinesite and Rhythm & Hues both relied on the powerful, procedural nature of Houdini to develop flexible pipelines and render final elements. Cinesite's Houdini work included CG pyrotechnics, explosions, Cyclops' laser beams and Nightcrawler's super-cool "BAMF" teleportation effect, while Rhythm & Hues used Houdini to tackle the film's attack tornadoes sequence, X-Jet and other effects. The next adventure in the X-Men saga, X2: X-Men United, directed by Bryan Singer, with Michael Fink supervising visual effects, opened May 2, 2003, to the biggest worldwide weekend boxoffice in history.

Rhythm & Hues Effects Using Houdini

Houdini was the primary commercial software package used by Rhythm & Hues for the company's X2 effects, which spanned from natural elements like snow, water and wind to more human-bound phenomena, such as bullets, blood, and breaking glass. Whether for controlling individual droplets or a lake unleashed, the result called for a modeling, animation and effects rendering workflow that would allow particles and volumetrics to be easily set up and then adapted.

In one example, when the X-Men X-Jet speeds into a wintry, wooded landscape, Rhythm & Hues used Houdini and Houdini Mantra to animate and render chunks of snow and tree debris flying up, over, around or on top of the aircraft. In another, particles were generated in Houdini and rendered in Mantra for a sequence that required both controlled water sources and turbulent current effects. A third scene saw Rhythm & Hues artists maximizing the power of Houdini to shatter glass with a higher degree of choreography over the falling shards. And, when Magneto finds a creative way to make bullets in the movie, Houdini was used to model and animate how this unusual ammunition gets formed.

Throughout the film, Houdini was used to add engine thrusts, heat distortion and dust to the X-Jet material, all of which was done by Rhythm & Hues. The facility also created Storm's signature effects, including clouds and tornadoes.

"The tornadoes were animated using our in-house Voodoo application and then imported into Houdini, where particles basically drove the volumetric elements," said Richard Hollander, Senior Visual Effects Supervisor, Rhythm & Hues. "Here, Houdini became the control surface from which all of the characteristics -- from the way the constructions were lit to the direction they were moving -- could be varied infinitely before sending out for rendering. Working this way, we were actually able to design some 93 differently tweaked tornadoes for a single sequence.

Cinesite Effects Using Houdini

Of the more than 100 shots created by Cinesite using Houdini, half of these showcase the capabilities of Nightcrawler, a mutant who dematerializes into trails of smoke as a means of transport. Bringing this "BAMF" effect imaginatively from the static comic book page to the screen was one of the team's key challenges.

"For Nightcrawler, we needed an effects and rendering pipeline that we could easily control and change on the fly to produce approval and final versions for approximately 50 "BAMF" shots," said Vijoy Gaddipati, Lead FX TD, Cinesite. "In contrast to having the character disappear in a puff of smoke, the idea here was more sophisticated: to stream out tendrils of black and colored smoke whenever he 'BAMF's in and out of a scene. The extensibility of Houdini, which always gives us the possibility of hooking in our in-house tools to take things a step further, was crucial to achieving the uniqueness and impact of this effect."

After researching possible approaches, Cinesite set up a workflow with Houdini serving as an API interface to drive the facility's turbulence noise generator. The live-action Nightcrawler stunt performance was brought as a match-framed CG model to Houdini, where this rough geometry was used as a surface from which to build effects and emit particles. The process enabled fluidic smoke-like behavior to be instilled on particles so that they took on the characteristics of the actor's real motion and clothing before collapsing on themselves. All of the "BAMF" scenes, including a dramatic 17-layer CG shot where Nightcrawler spins and flips his way past numerous foes, were completed in this fashion and rendered volumetrically in Houdini Mantra.

Cinesite also used Houdini to enhance the familiar powers of other X-Men mutants to fit the action of X2. Cyclops' beam is back in several forms, built at its core as a Houdini particle system with geometries animated to spring from his visor at varying directions, speeds and intensities. The effects were rendered entirely in Houdini Mantra, using Houdini's VEX shaders to layer in different types of noise. Shield effects used by Dr. Jean Grey were designed as mapped, animating geometries with VEX shaders, and a similar technique was used for generator explosion. Artists working on Pyro created CG fireballs based on Houdini particles, deforming spheres and VEX shaders that blend seamlessly with live-action practical pyrotechnics and look realistic even when lobbed 30 to 50 feet. Additionally, Houdini was used to light and render elements for a lake shot, lending realistic sun glints and other atmosphere effects to the scene.

Houdini's flexible, powerful and scalable architecture allowed the many different Cinesite teams working on this movie -- "BAMF", Cyclops Beam, fire effects, explosions and energy effects -- to creatively and efficiently build components, animate geometry, get buy-off and render their work with all of the benefits of Houdini proceduralism, said Serge Sretschinsky, Cinesite's digital effects supervisor. Houdini also provided a front end to which many custom shaders and in-house applications could be authored and attached, even by non-technical artists.

Rhythm & Hues' and Cinesite's X2 effects will be explained in further detail at the May 20, 2003, Los Angeles Chapter SIGGRAPH meeting, sponsored by Side Effects Software.