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Thanks to VEX technology, Stan Lee's X-Men comic became a full-length motion picture. Will Strauss dicusses how Digital Domain and Sony Pictures Imageworks used the latest side effects technology to bring Wolverine, Storm and friends to the big screen. Humans beware.

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By  Will Strauss Published  September 21, 2000

Thanks to VEX technology, Stan Lee's X-Men comic became a full-length motion picture. Will Strauss dicusses how Digital Domain and Sony Pictures Imageworks used the latest side effects technology to bring Wolverine, Storm and friends to the big screen. Humans beware.

You might think that a feature movie based on a comic book strip that once had a circulation of over eight million readers wouldn’t need much help to make it a success. But when a filmmaker needs to recreate cartoon mutant super heroes in a realistic modern US world, and make them appeal to a world cinema audience, it sometimes isn’t enough to rely on past popularity alone.

Success can sometimes need that one percent of computer-animated inspiration to aid the 99 percent perspiration of filmmaking. The case in point is X-Men. A supremely popular comic book that this year has been transferred to the silver screen via the magic hands of Sony Pictures Imageworks and Digital Domain.

An eagerly awaited release, the movie is yet another special effects laden blockbuster that relies more on action and “candy for the eyes” images than it does on story, characterisation or plot. And the creation of the mutants’ special powers, so much easier to draw in a cartoon than to import into life like action, plays a major part in the proceedings.

Pedantic Fans

One of the many problems with recreating a cartoon hero, or heroes, is satisfying the pedantic needs of the obsessive fan base. X-Men fans will be expecting Storms weather powers to mirror exactly the strength she has in the comic.

Wolverine fans will expect his hair to be a specified spikiness. So not only did the special effects people have to keep a director, producer and film company happy he also had to appease several generations of X-Men fans.

One application used to create some of the more specific effects for X-Men was VEX technology found in side effects software’s Houdini version 4.0. The technical directors at Digital Domain and Sony Pictures Imageworks used VEX (Vector Expressions), an expression-based expression-based programming language, to write not only custom shaders but also, geometry, compositing and particle functions. By applying code written for shaders to geometry, the technical directors found they were able to realise their effects, not just faster, but also with a higher degree of realism.

"I believe that VEX has the potential to integrate the process of rendering with the processes of modelling and animation, to an unprecedented extent,” explained Side Effects Software, Senior Mathematician and creator of VEX, Mark Elendt: I'm very pleased that our users have so quickly begun to apply the power of VEX."

Digital Domain was brought onto the X-Men project in October 1999 at which time they were requested to create 95 effects shots. In June this year they delivered 149 shots.

"X Men has definitely been a fast track production for us," said CG Supervisor, David Prescott. "The work primarily involved a huge sequence at the beginning of the movie creating Magneto's light effects, and the same effect later around the Statue of Liberty.

Finally, there was Senator Kelly's death sequence, a key scene in the movie comprised of an extremely challenging series of shots."

With tight deadlines to adhere to and high standards for quality set before them, Digital Domain turned to Houdini to realise a number of their 3D effects, including Kelly's death sequence which according to Technical Director, Sean Cunningham was the most challenging shot he had ever worked on.

"We knew we could achieve a level of realism that the audience would accept through scan line methods, but we wanted to go a step beyond in terms of realism. We did a test with VEX and V Mantra [Houdini native renderer] and the results spoke for themselves. So, we took the leap of faith and switched over to the newly released Houdini 4.0 [from version 3.0] and VEX."

Notable Moment

In one of the X-Men's most notable moments Senator Kelly is transformed from a man lying on a table into a sack of water which bursts open and spills onto the floor. This shot would prove very difficult to create due to various factors: Kelly would be 50 to 80% of the frame, he would be completely digital, and the shot would last for ten seconds.

An animated model of Kelly was created in Houdini 4.0 and fitted with animated textures based on photographs of the actor after one of his makeup sessions.

From a technical point of view the shot would require DD to render with displacement: a time consuming and imperfect process if one is trying to have an object contact the displacement surface at render time.

"With VEX and Vmantra we were able to create water displacement on Kelly's surface and get the low frequency undulations flowing through his body," explained Prescott. "Then we were able to attach his heart probes to his body by using that displacement shader as a SOP to deform our remaining geometry. Using VEX and Vmantra saved us a huge amount of time: it was a quick, eloquent solution."

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