Digital Domain built a rigid body dynamics tools around a core engine called Bullet to create its earthquake mayhem.

"In order to show how massive these disasters are, many of the shots in the Los Angeles airplane escape sequence showed huge office buildings and entire city blocks collapsing and falling into the crack that opens up right under the city," Leo explains. "That meant that these were all large environment shots, and order to make them feel believable and give them scale, there had to be an enormous amount of detail in them.

"To make a collapsing city block feel realistic, you need more than just buildings. You need trees, cars, people, lampposts, traffic lights, fire hydrants and hundreds of other details. Each one of them had to be simulated to shake, break or tumble. And it doesn't end there. Each one of those objects would need secondary effects. A tumbling car needs breaking windows with glass shards, sparks, smoke, dust and debris.

"Another thing was clear from the start: all of this destruction had to be created entirely in CG. There was no off-the-shelf rigid body solver in any software package that could do what we needed to do, so we knew that we had to build our own system. We decided to build our rigid body dynamics tools around a core engine called 'Bullet,' which is an open source project and a very simple but fast and stable engine. Our software team then built a new rigid body simulation system around Bullet, adding our own techniques for shattering objects, creating constraints between the pieces, adding material properties (so some parts could behave like wood, some like glass, others like concrete and so on), and then running the simulations. We called this new rigid dynamics tool 'Drop.'

"Drop also gave the artists intuitive controls to weaken constraints in areas where they wanted major breaks to occur. This allowed them to choreograph simulations, so they could determine where a building should break, how large or small the sections would be, in which direction it should fall, etc. Finally, another huge advantage of drop was that it was extremely fast and stable. It allowed us to run simulations with thousands, sometimes tens of thousands of colliding pieces of geometry in an hour or two, so artists could get several takes out in one day and try variations until they found the best setup."

Double Negative's most complex work (led by Alex Wuttke) involved pyroclastic ash clouds and lava bombs at Yellowstone. The solution was to use pre-simulated libraries of pyroclastic ash-cloud elements, which were then dressed into the shot. The individual simulated elements were generated by Double Negative's fluid dynamics expert, Jason Harris, using Squirt, Dneg's in-house fluids solver. After much testing, he produced the ideal conditions within the simulator under which the team could produce a variety of pyroclastic flows in different shapes and sizes.

Double Negative tackled pyroclastic ash in different shapes and sizes.

Emmerich's brief for the lava bombs was disarmingly simple, that the lava bombs should vary in size from a football to that of a four story house!