One of the great things about a superhero movie is the chance to watch talented visual effects artists have some fun. In this summer’s blockbuster X-Men: The Last Stand, audiences will be amazed as Magneto redirects the Golden Gate Bridge and Juggernaut smashes through thick concrete block walls. These kinds of shots present a technical challenge that studios such as Framestore CFC and CIS Hollywood enjoy meeting head on. To help hit their deadlines without sacrificing creative freedom, both studios chose to build their effects around Houdini’s new dynamics architecture.

The Golden Gate Challenge

One of the shots that Framestore CFC was charged with was the important and complex one of Magneto uprooting the Golden Gate Bridge and reattaching it to Alcatraz. Sean Lewkiw, Ben Schrijvers and Joe Thornley, Senior FX Artists at Framestore CFC, knew that they would have to rely on dynamic simulations to give this and the other shots a more natural feel.

“To achieve the large-scale destruction, we relied on Houdini’s dynamics to perform simulations that would be impossible using any other software package,” says Schrijvers. “We ended up doing many more dynamic simulations than originally planned because of the success and speed of being able to provide iterations.”

When Lewkiw, Schrijvers and Thornley first started these shots, the new dynamics architecture in Houdini 8 had just been released. Every shot brought with it a learning opportunity and the chance to keep pushing boundaries. Schrijvers points out that they ended up with different and better methods for every shot. VFX Supervisor, Craig Lyn, adds that he was very happy with the quality as well as the complexity of the shots being run through Houdini's RBD simulations. “Many of the simulations were being approved on the first pass through, which just goes to show, something must be working well," he adds.

Another major benefit using Houdini was the ability to save time by testing shots using low resolution geometry. “Houdini allowed us to run a simulation using proxy geometry and then substitute high resolution geometry at render time,” says Lewkiw. “This gave us major productivity benefits we wouldn’t otherwise have had”.

As the 1.7 mile long, 887,000 ton bridge is uprooted, moved and reattached, the resulting dynamics simulations would need to raise some dust and smoke. The team at Framestore CFC relied on Houdini and Mantra to pull off this particularly dirty job. For the smoke volume rendering, they used a Houdini Digital Asset that encapsulated the whole rendering setup, including details such as shadow maps and pipeline tasks like sending the shot to the render farm.

For Framestore CFC, Houdini’s tools and techniques provide a creative freedom necessary to create high-quality shots. “Our Houdini pipeline allowed us to experiment freely with ideas because it’s so easy to swap data into an operator chain,” says Schrijvers. “Maya requires so much more setup and has much less reusability, so you’re less likely to try something because of the hassle.”

Juggernaut Crashing Through Walls

CIS Hollywood was called upon to create the important and effects-intensive laboratory scene in which the mutant Kitty Pryde is chased through successive walls by the villain Juggernaut. As Juggernaut bursts through each wall, a hole is created and pieces of concrete fly out in all different directions. John Cassella, Lead FX Artist at CIS, relied on Houdini’s Rigid Body Dynamics to achieve these dramatic effects.

Geometry was imported as OBJ files then converted to an implicit surface/volume representation within the dynamics environment. It was then run through several different levels of simulations. The set was built with pre-made holes in the walls and floor, big enough for the actors to run through, and the CIS team traced these holes and built pre-scored geometry for each chunk or rock or floor. These were then used as rigid body objects to be smashed by a match-moved proxy model of Juggernaut.

“There are really no other rigid body packages that I’ve tried that have enough control to do interlocking geometry well,” says Cassella. “Cracking walls and floors usually have interpenetration issues galore, but with Houdini, the implicit surface volume type of interpenetration checking makes it so much easier

From Maya to Houdini and Back Again

When it came to employing Houdini Digital Assets, Cassella used them to increase interactivity and the sharing of toolsets. Digital assets were used for the import/export of objects and animation data to and from Maya. On either end of the pipeline, Cassella created “conduit” GUI’s scripts and nodes which transferred data into a format that the other package could understand.

“On the Maya side, we would place wall and floor chunks in tracked/animated plates, and through some scripts export the scene tree that would get imported into Houdini,” says Cassella. “We also took the match-moved Juggernaut animation and transferred it into Houdini using this pipeline, which gave us a moving RBD Juggernaut that we slammed through the wall RBD objects for the proper effect.”

On the Houdini side, the “Maya Conduit” digital asset would read the scene data and animation curves, and build all the proper networks needed to recreate the scene. Then all that had to be done was hook up some fields and a solver to the rigid body objects and run the simulation. “This system of export/import allowed us to teach a new animator the whole pipeline, including tweaking simulations, in less than a day,” adds Cassella.

After a good simulation was approved, channel data could be written out for all of the rigid body objects; sometimes there were over 500 simulated objects. This channel data was then brought back into Maya using another “Houdini Conduit” script and applied to the original geometry.

“For people unfamiliar with Houdini, this pipeline made the transition pretty simple,” says Cassella. “There was little hand wiring of networks, the conduits on either end took care of most of the low level connectivity, and the ability to wrap GUIs and buttons around the scripting on either end allowed even higher level controls to simplify things.”

Productivity Leads to Creativity

For both Framestore CFC and CIS Hollywood, the productivity gains achieved with a Houdini pipeline gave them more time to focus on the creative process. The procedural nature of Houdini allowed the artists to prototype an effect in one shot and/or by one artist, and then share those techniques across other shots by exchanging digital assets, procedural networks or scripts. Being able to quickly publish and share data gave them freedom to explore a variety of ideas.

For CIS Hollywood, being able to make changes quickly was a pleasant surprise. “More often than not, the words ‘creative’ and ‘simulation’ don’t jive well together,” says Cassella. “Being able to revamp a simulation quickly and with little pain definitely helped us be more creative and achieve these great results.”