MPC developed two software components, Emily and Alice, that were used to create the digital soldiers. Here, Agamemnon's army marches outside the city of Troy.

The process started with three weeks of motion capture covering 90 different moves. The actors randomly performed these moves for two minutes at a time. The data was then broken by Emily into eight-frame segments, which created a motion library of some 1,000 clips. Once the database was completed, the program analyzed each individual clip and referenced all the other clips that it could be blended with. In the end, the 1,000 clips were able to produce 100,000 different combinations, thus giving the effects team a virtually unlimited variety of movements.

“The idea was that any single motion, such as walking or running, would be the result of, say, 100 different moves combined together,” comments Jarrett. “Our A.I. program would say: ‘I want this individual to walk from A to B,’ and Emily would answer: ‘Here is what I have. Select the walk clips that you need.’ It meant that you could never have two characters walking or running the same way since the clips combination would always be different.”

CG soldiers were sometimes placed next to real soldiers in group battle scenes, such as this one where Greek warriors meet face to face against the Trojan soldiers outside the walls of Troy.

Making it Look Good
Although Alice was designed to handle thousands of CG extras, the animators could isolate groups of soldiers, or even individuals, and modify or delete specific action. During the animation process, the characters were represented as mere squeletons, even as cube piles some times. The actual geometry was added in the shader, a task handled by CG supervisor Gary Brozenich and his team. Depending on the nature of the scene, the number of CG soldiers would vary from shot to shot. “In theory, there were 50,000 Greeks against 25,000 Trojans,” notes Jarrett. “However, there were shots in which it looked like there was much less than 75,000 soldiers on screen. So, we decided to handle it on a shot per shot basis, adding as many soldiers in the frame as needed to make it look good. With this approach, we ended up with shots featuring 150,000 soldiers!”

The A.I. program produced realistic crowd animations, but was not suited for complex combat simulation. Individual fights were handled separately, with stuntmen performing complicated routines on a MoCap stage. The resulting animation was composited in the foreground of the battle scenes by digital effects supervisor Rudi Holzapfel’s team. As often is the case, CG soldiers ended up much closer to camera that what had originally been planned. “The CG extras had been developped for long shots, but eventually, we had to use them in closeups too…” adds Jarrett. ”There are some shots in which CG soldiers are composited right next to the principal actors.”

As if the massive shots on the battling armies were not enough, MPC also created many effects involving the main characters in action. Brad Pitt, Orlando Bloom and company didn’t exactly shout it out in the media, but many of their action shots were filmed without an actual weapon in sight… To start with, Bloom never fired one single arrow on the set, although his character Paris is a gifted archer in the film. “He made the move of firing, empty-handed, and we added the arrows in CG,” reveals Jarrett. “The same was done on the swords. It was too dangerous for the principals to swing their weapon on the set. So, they only had the handle and the blade was added in CG. In some shots, we also had to replace their hand, or even the whole arm, with a digital replica in order to animate a more natural move — it’s difficult to simulate the action of hitting something when you actually don’t hit anything.”

Besides the battle scenes, MPC also tackled the creation of the city itself. For a while, Jarrett considered using a large miniature but eventually opted for a complete CG approach after watching a test in which a virtual building proved to be as realistic as its model counterpart. 30 buildings were modeled in CG, each side featuring different details in order to multiply the possibilities. Another layer of variety was added with color patterns and some 25GB of textures.