A Crusade
Issue: Volume: 31 Issue: 1 (Jan. 2008)

A Crusade

In the November issue, we kicked off a three-part series on next-gen game titles, starting with a detailed piece on Midway’s Stranglehold, followed last month with a feature on Bungie’s Halo 3. This month, we fi nish with a look at Ubisoft’s Assassin’s Creed.


Ubisoft Montreal, founded as a subsidiary of Ubisoft in 1997, started out developing low-profile projects. A decade later, the company has evolved into one of the largest game developers worldwide, having produced the popular Splinter Cell and Prince of Persia series—both known for their stunning visuals and exciting action. So, it comes as little surprise that this Ubisoft group has once again capitalized on cutting-edge CG technology to take gameplay and game graphics to a new level with its recently released Assassin’s Creed.

By December 13, 2007, the game obliterated Ubisoft’s initial sales expectations by selling more than 2.5 million units in less than four weeks, making it the fastest selling new video game intellectual property and one of the top three best-selling video games in history. On the heels of this record success, Ubisoft raised its sales target for 2007—2008 from 825 million euros to a whopping 975 million euros ($1.4 billion US).

The game, set in the year 1191 as the Third Crusade tears the Holy Land apart, the player assumes the role of Altair, a master assassin who embarks on a quest through three meticulously re-created cities—Jerusalem, Damascus, and Acre—to slay the nine historical figures who are promulgating the Crusades and exploiting the ensuing chaos for their own monetary interests. Along the way, Altair discovers that his targets may be bound by more than a shared interest in personal gain: by membership in a secret society whose true goal leads to a shocking modern-day conspiracy involving genetic memory.

Four years in the making, Assassin’s Creed is set in three fully rendered and historically accurate cities populated by thousands of inhabitants. From the Dome of the Rock, to the Tower of David, to the Church of the Holy Sepulchre in Jerusalem, the game presents a meticulous re-creation of the architecture and culture of the period, where everything and everyone is completely interactive. Altair’s actions always affect how the bystanders respond to him. When passing through a crowd, lightly nudging someone out of the way will not have a significant effect. However, if Altair’s knocks someone to the ground or kills the character, the crowd may mass against him and chase him through the city and across rooftops, attracting the attention of the guards. The player can grab onto and climb a building façade or practically any aspect of the environment; Ubisoft notes that any object that protrudes more than two inches is interactive. To give Altair this level of unlimited interactivity with his world, Ubisoft Montreal created well over 12,000 animations for his character model and modified his control scheme so that buttons correspond to various body parts instead of whole-body actions. For instance, running toward a wall and pressing the “legs” button will make Altair jump the wall, while pressing the “arms without weapons” button will make him vault it like a gymnast.

Motion capture was used extensively for the hero Altair as well as for the 20 main characters and hundreds of secondary characters in the game. However, Altair’s spectacular acrobatics, for the most part, were keyframed.

To create the thousands of animations for the 20 main characters and hundreds of secondary and crowd characters, Ubisoft conducted extensive motion-capture sessions, processing the motion data in Autodesk’s MotionBuilder before importing the cycles into Autodesk’s 3ds Max. Altair’s acrobatic movements depend heavily on extreme accuracy in his interaction with the environment—clasping onto ledges or gaining a precise foothold on a slightly protruding brick, for example. Therefore, using baked, or pre-canned, character animations would have led to constant spatial errors. To create motion on the fly that would be perfectly synchronized with Altair’s environment, Ubisoft used Autodesk’s HumanIK middleware to precisely place a foot or a hand in any frame during gameplay.

During the game, Altair can switch between fighting mode and free running mode, in which he can walk, run, climb, and swing from pole to pole while still retaining the ability to push people aside to move faster and avoid tripping. He can also engage in “social stealth” behaviors, blending in with the crowd by disguising himself among a crowd of monks, for example.

“Since Altair needs to be a ‘blade in the crowd,’ not drawing attention to himself, we needed to create an animation system that would allow total control for the player,” says animation project manager Elspeth Tory. The controls are incredibly responsive to the player’s inputs, from very slow, gentle walking to all-out sprinting. Altair also will automatically turn his upper torso when passing an approaching non-player character (NPC), and the player can use Altair’s hands to gently push the NPC out of his way.”

Bird of Prey
At the outset of the design phase, Ubisoft tailored both Altair’s model and all of his movements to bear a metaphorical resemblance to a well-known bird of prey: the eagle. In fact, this overarching aquiline aesthetic even extended to the gameplay design, whereby Altair executes each assassination by stalking from above, alighting on his prey, and going in for the kill. “Our hero, like an eagle, will hunt down his target, observe his every move, and then strike with a single killing blow. He is always in control, analyzing his environment so he can choose the best possible course of action, all the while keeping an incredibly low profile,” says technical director of animation Francois Levesque.

Altair’s aesthetic and movements resemble those of an eagle, an analogy that is carried throughout the game.

Moreover, Altair’s clothing is designed to give him the form of an eagle: the tip of his hood is shaped like a beak, while during flight and swift acrobatic maneuvers, his cape spreads like eagle’s wings to give him a sense of weightlessness.

For modeling and texturing all the characters, the artists used 3ds Max, Pixologic’s ZBrush, and Adobe’s Photoshop. Because he is always close to the camera, Altair exists in one level of detail that ranges from 7000 to 9000 triangles, depending on his rank in the assassin’s order and the equipment he acquires throughout the game (such as better boots and climbing gloves). Crowd characters come in three levels of detail, peaking at 3500 triangles at the high end.

Cloth & Crowd
With their complex folds, wrinkles and texturing, the long, flowing robes, hooded garments, chain mail, and armor of the period costumes was critical to the title’s realism. Artists sculpted the folds in ZBrush and baked them into Altair’s normal map. To accentuate some of the details, they blended a displacement map based on the sculpted folds into Altair’s diffuse map. Finally, Ubisoft developed an in-game cloth simulation for Altair’s skirt that can create larger folds dynamically.

Tory describes the in-game cloth simulation system: “We used dynamic bones whose movement is calculated in real time, with physics constraints based on such properties as leg rotations, gravity, inertia, and wind. (There are also approximately 20 other optional rigs available to dynamically animate all the in-game accessories, such as hair, long sleeves, hoods, arrow casing, and bags.) For Altair, we added a second layer that deforms the cloth by vertex and then uses his ragdoll for collision. And since the physics setup isn’t always perfect, we also have the option of hand-animating the dynamic bones to correct areas in which the real-time simulation lacks precision.”

The artists used 3ds Max to model the characters, and Zbrush and Photoshop to texture them.

To individualize the thousands of citizens roaming the cities, Ubisoft’s artists hand-modeled 150 characters, each built to stringent specifications with 120 bones apiece, so their heads and bodies could be combined and differentiated using a randomization system. “Our focus was on creating citizens with a lot of personality, not merely with slightly altered body shapes or facial structures,” says Levesque. “Each of the 140 high-res characters (ranging from 3000 to 750 polygons) were modeled in a week and baked to low res in a day. Our randomization system then changes accessories, head, colors, dirt, height, voice, hair, beard, and skin tone. Our artists can quite literally randomize anything they want without involving programmers; it’s very efficient.”

Each character sports between 3mb and 1.5mb of textures, which include a diffuse, normal, and specular map. In addition, artists added some rim light to give the heavy cloth an Oren-Nayar-Blinn shader feel. They also use a diffuse curve, similar to ZBrush’s, to describe how the light interacts with a material depending on the angle of contact. The most complex shaders are used by crowd characters for randomizing cloth color, dirt patterns, and skin tone. The shader editor, says Levesque, is similar to that of Unreal 3 and Maya: “basically, a schematic view with a lot of texture operators.”

While texturing hard surfaces, such as the whitewashed limestone facades of the buildings, was easier compared to the cloth, the metallic chain mail was a constant challenge. “Even a small amount of distortion makes [the chain mail] look terrible, so it’s hard to rig. Moreover, their rings are so tiny that texture compressions tend to destroy them. Chain mail also tends to look like goo when viewed from a distance, unless you edit the texture’s mip maps manually,” explains Levesque. “Interestingly, medieval knights didn’t wear shiny plate armor until the late 13th century, so there aren’t many reflecting surfaces in Assassin’s Creed; hence, we used simple environment maps for our swords and helmets.”

Character Rigging
Driving the 12,000 mocapped animation cycles that create the incredible realism and fluidity of Altair’s movement is a base skeleton comprising 77 bones in his body and 27 in his face. While this skeleton is also shared by a large percentage of the game’s NPCs, Altair has an additional six bones for his robe and its flaps, one for the hidden blade, four to five bones for his accessories, a few additional roll bones for his shoulders, and four bones for his hood, resulting in a total of 136 bones.

“With such a realistic setting and historical context, one of our biggest challenges was creating a character who looked and felt real, but whose movements were still spectacular,” says Tory. By creating contextual animations for each possible situation, Altair’s movements are smooth and realistic. Although the engine occasionally does some of the blending, most of it is done with these transition animations, resulting in smooth, fluid movement. While it resulted in a large number of animations, Tory believes the end result was worth the effort.

How bystanders react to Altair depends on his actions; for instance, if he knocks a character to the ground, the crowd is likely to rise against him.

Animators created all the cycles in 3ds Max using Autodesk’s Character Studio. “Whenever motion-capture files were in­volved, we would do initial touch-ups of the animations in MotionBuilder before transferring the files to Max, to finalize the movements,” explains Tory. Motion capture was a key part of the animation pipeline, though a great deal of keyframe animation was done, as well. For some of Altair’s more spectacular moves, keyframing with reference footage proved to be the best option, while at times motion capture provided the ideal solution, Tory notes. However, even with motion capture, the animators always reworked the posing and timing to ensure Altair maintained a consistent look and feel.

“You can never replace the work of a talented animator on a production, even if you’re dealing uniquely with motion capture,” Tory says.

Sword Fighting
Rather than glamorize the sword fighting or follow predefined styles of combat such as martial arts, Alex Drouin, artistic director for animation, sought to capture the raw violence and chaos of medieval warfare. “He wanted to convey the sheer weight of sword fighting: the heavy weapons, the armor, the brutal impact of a hit, and the desperation in the movement. I think this is why we’d often get some of our best mocap shots near the end of a day, when exhaustion and adrenaline were starting to kick in,” Tory says. In an unusual twist, the animators themselves, including fight animators Kristjan Zadziuk and Hugues Richer, wore the mocap suits to capture the combat animations, which helped produce a more rugged, untrained style. “[Drouin] wanted to make the player feel like he’s fighting a group of guys while desperately trying to survive,” Tory adds.

The bird-of-prey motif is also reflected in Altair’s movements, especially in his silhouettes and posing, which Tory says are essential in animation. “If you look closely at Altair when he’s perched on a beam or when he’s doing a ‘leap of faith’ dive, you’ll often see the outline of an eagle,” says Tory. “The symbolism is deeply woven in the character and his behavior. He circles slowly, gathering information about his target before making his move. He has one goal—taking out his target—and he swoops in for the kill with raw beauty and spectacular grace.”

The environments in Assassin’s Creed areawash in a hazy white atmosphere, a lookthat was produced by hand and by using anumber of procedural tools.

Using IK, Altair can plant his hands or gain a foothold on any surface protruding more than 10 cm, an ability that demanded close coordination among the animators, level designers, and programmers. “We needed to create a climbing and jumping system that looked smooth but was also fun to play. HumanIK allowed us to get results quickly. We then needed to coordinate very closely with the level design and level art teams to ensure that all the buildings allowed for efficient and smooth climbing,” says Tory. This enabled the artist to develop a totally different type of level design because they could create a path over anything in the scene using this system.

Essentially, anytime Altair needed to keep his feet on the ground or to climb or to push through the crowd, the group used the HumanIK setup, which was directly integrated by the programmers into the engine. The IK was essential for hands, feet, the horse’s feet, and more. After the artists set up their animations, they flagged them as needing IK, and the IK automatically would be interpreted in the engine.

“It allowed us to see spectacular animation right off the bat. We didn’t have to develop our own animation systems for many of these complex actions,” says Tory. “HumanIK helped us make the game look real, and enabled us to accomplish our goal of allowing our main character to have total freedom to move anywhere within the game’s environments.”

For both the cut-scene and in-game facial animation, the characters use a bone-based system comprising 44 poses for phonemes and facial expressions. The facial animation track contains the percentage of these poses rather than their specific bone positions, which saves animation time and enables the team to individually modify facial animations for any character. Ubisoft captured all the performances for the cut-scenes using professional actors, and then used OC3 Entertainment’s FaceFX for the facial animation and for processing in-game dialog.

Pallid Light
With the omnipresent dust and the white stone buildings, the cities are suffused in grey, pallid, ashen lighting. According to graphic technical director Danny Oros, the haze and diffusion demanded a sophisticated real-time lighting system that could sustain the rendering of large numbers of varied characters and crowd elements, and yet still remain flexible from an artistic point of view. “The system is simple and clean, and is as visually enticing as it is performance-friendly on our target console platforms,” he says. The lighting is fully dynamic, from the omnipresent sunlight to the directionals, omnidirectionals, and projectors. Scenes are lit using these simple direct-lighting types and, consequently, cast shadows and perform bump and specular calculations on a per-pixel level.

Artists produced the hazy white atmosphere through hand tinkering and a host of procedural tools for adjusting fog, 3D ambient properties, ambient occlusion scalability, light blooming, and particle effects. “Much of what you see in Assassin’s Creed has been done by hand to obtain the desired look, around which the development tools were then designed. Unfortunately, there was no time to implement more advanced features such as light scattering for a richer atmospheric perspective,” says Oros.

Indirect lighting on all surfaces is calculated per pixel from the bumped surface using a three-dimensional lookup. “This technique allowed us to fine-tune the amount of simulated indirect lighting from the sky, bounce light from the lit street pavements, and so forth, from an artist’s perspective,” Oros says. The artists also calculated an ambient occlusion term from the visual meshes using their own algorithms. Because each instance’s ambient occlusion data is unique, based on neighboring occluders, the artists were able to encode this data (per vertex, for memory consumption and performance considerations) into the instanced mesh data.

Both the direct and indirect lighting systems can be tweaked independently for both the environment elements and characters. “This gave us greater artistic control over the delicate balance in lighting between our subjects and their backdrops—in both cinematic scenes and game­play environments—thus increasing gameplay readability,” Oros adds. Meanwhile, shadows are rendered in real time for every frame at 30 frames per second using a Cascading Shadow Map system, which casts multiple concentric, cascading shadow maps from near to far, meaning the maps cover a larger area the farther the point of interest is from the camera.

The action unfolds in three historically accurate cities. Artists began constructing the locales using a Lego block approach,eventually adding painstaking details.

The team wanted the whitest stone surfaces to reflect the blinding, arid sunlight as much as possible. To that end, the artists made sure their sun intensity/brightness was above the range of local light sources (such as torches), in order to simulate what the human eye might perceive in real life in contrast to the darker, shaded areas.

At dawn, Jerusalem is known as the City of Gold, because of the local limestone buildings that cast a golden light. Ubisoft experimented successfully with capturing this lighting effect using complex rendering methods such as BSSRDFs (Bidirectional Surface Scattering Reflection Distribution Function); however, the performance cost of such a technique precluded it from being included in the final game.

Holy Set Creation
To construct the three, fully traversable cities, Ubisoft’s level artists began with small, instanceable template modules. Level designers and level artists placed these template modules into the environments, progressively refining each module using Ubisoft’s content editing tools as they built up the cities like Lego blocks. “A city that initially looked like a grey mass of angular blocks with no detail eventually turned into an immense interactive piece of art,” says Oros.

Each module contains embedded surfaces for climbing, grasping, and anchoring, such as short protruding beams, window ledges, and cracks. Using these  “graspable” surfaces, the game engine automatically generates navigational information for Altair’s climbing, free running, pole balancing, and other maneuvers.

Residing within these core architectural modules are many smaller modules that can be instanced to refine the coarse layout of the larger buildings. “These included poles, signs, arches, ladders, additional detail windows, bails of hay, mountable crates and barrel—all of which helped in breaking up the grossly large elements, [infusing them] with immersive detail while creating that flexible gameplay-rich sandbox experience,” says Oros.

The environments and the all-encompassing staccato stone surfaces make liberal use of diffuse maps, normal maps, and specular maps. Most buildings and ground surfaces comprise as many as three sets of these textures (three diffuse maps, three normal maps, and three specular maps), which are vertex weighted and blended by the artists to create complex textured surfaces.

The common texture resolution for the diffuse and normal maps is 512x512, while specular maps appear at a slightly lower resolution. “We rendered the maps with non-anisotropic filtering [which reduces aliasing and blurring of texture maps] instead of non-anisotropic filtering to increase detail levels,” adds Oros.

A New Level
Assassin’s Creed is setting a new standard in gaming, delivering a compelling interactive story, complete with stunning visuals and exciting gameplay. Yet, this end result was four years in the making. Thus, creating Assassin’s Creed—whose story is set in the Third Crusade—required the artists to embark on a long, exhausting crusade of their own.

Unquestionably, this journey has ended in victory, catapulting Ubisoft’s profitability to record highs as the game becomes a harbinger for the dominance the company is likely to achieve with such future releases as Tom Clancy’s End War, Brothers in Arms, Far Cry 2, and the video game adaptation of James Cameron’s Avatar.  

Martin McEachern is an award-winning writer and contributing editor for Computer Graphics World. He can be reached at martin@globility.com.