Gameplay is always king, Gresko emphasizes. In planning this approach to a film-to-game adaptation, Stormfront began with a diagram of the core themes of the film “license,” and then identified the gameplay elements that captured and expanded on those themes. For example, during the story, Eragon is accompanied by Brom, an ally who aids him in his quest. To support this theme, the team developed a rich, cooperative element that provides a full-featured AI ally in single-player mode, and also allows another player to jump in and take over the ally at any time.
“We have the appropriate companion around to help capture key story moments and also to add tons of depth to the experience,” says Gresko. It’s not only great fun, but the gameplay is directly tied into the license.”
During the film’s production, Stormfront received character and location concept art, detailed set-design plans—including blueprints of the extensive Varden set—various drafts of the script, and some of the early animation tests for Saphira. The art director and concept team also visited the set locations in Budapest, Hungary, capturing images of the weapons, props, and actors in full costume.
The team visited the Carvahall set and a little of the Daret location, and got early glimpses of Gil’ead and the Varden encampment, which were both midway through production. Artists referenced the photos while creating the many digital matte paintings that captured the grand, sweeping vistas seen in the film. The photos served as style guides and construction reference for the general design of the digital sets, which artists had to modify for the sake of better gameplay. Most of the texture maps were also derived from the photos, though artists also digitally painted textures in Adobe’s Photoshop to replicate the feel of each location.
“In Hungary, we also were able to speak directly with the stunt coordinator and learn about the various fighting styles each character would use, which was extremely important information for the animators and subsequently fed directly into our combat system designs,” says Gresko.
Using photographic references, the artists built the principal actors in Autodesk’s Maya, with approximately 4000 to 5000 triangles. To make the facial animation and lip sync more expressive, they also sculpted high-resolution models of each actor’s head. Since the screen teems with hordes of enemies, the group was limited to roughly 2000 triangles. Saphira, the dragon, presented the greatest modeling challenge, mostly because she wasn’t fully realized by the effects house until later in the production schedule, meaning the game artists had to do a lot of guesswork and make adjustments late in development.
“Most of the film captures given to Stormfront showed actor Ed Speleers (Eragon) conversing with a dragon-head-shaped piece of cardboard stuck to a pole. There were many questions in the beginning; we didn’t know what size she would be, if her wingspan would be realistically proportioned to support her in flight, and so forth,” says Gresko.
Underlying all the characters is the same base skeletal rig consisting of 70 to 100 bones, which allowed a lot of flexibility in transferring animation from one character to another. The rigs use FK/IK switching for arm animation, IK for the legs, and Set Driven Keys to control such actions as finger bends. More complicated characters use spline IK to control challenging body parts, such as Saphira’s tail. “With Saphira, our goal was to make her look believable and to keep the joint count as low as possible. Too many joints would affect performance,
but too few would make the animation look unnatural,” explains Gresko.
While watching footage of each actor, Stormfront developed its facial animation system using a combination of roughly 25 blendshapes for core emotions and lip sync, with additional bones for brow movement and tongue control. With so many actors providing voice work to film-based games, hand-keying lip sync and facial animation using the performances as a guide is mandatory. Almost all of the film’s stars contributed vocal performances, including Speleers, Sienna Guillory, Garrett Hedlund, Djimon Hounsou, and Robert Carlyle.
“Lip-synching was always hand-keyed. We feel the results of hand animation are far superior to the mechanical look seen in programmatically driven algorithms used for lip sync. Moreover, handcrafting the lip sync allows us to personalize the way words are spoken and match the unique way each character speaks,” says Gresko. “Having film actors involved in a game brings many advantages to the mix. First, it gives the fans a cohesive experience with the film, bringing the movie and interactive game experience closer together. Also, having top acting talent brings richness and believability to the acting performances in the game.”
Moreover, for Stormfront’s animators, hand-keyed animation is the only way to capture the many nuances and emotional beats of a dramatic scene. Motion capture was reserved for hit reactions and traversals, which were recorded using Vicon’s 4MP system at Mova’s 4000-square-foot motion-capture stage in San Francisco. Autodesk’s MotionBuilder was used for animation transfer, and Autodesk’s Maya for final cleanup.
In addition to the standard walk and run cycles, animators created a variety of “mood modifier” cycles. These cycles convey the character’s emotional or physical reaction to the adverse conditions of a scene. For example, characters will shiver or cower in fear as they creep along through the current of rushing streams deep in the Beor Mountains, fearful of an Urgal ambush.
The art director and concept artists visited the film set to get
an accurate vision for the weapons and clothing, which they re-created for the game.
Cutting through Alagaesia’s mountain ranges are many rivers and streams requiring realistic effects for crashing waves, foam, and sea spray. For water simulation, Stormfront continues to use a complex shader developed for the PS2. It combines procedural shader effects, animated textures, specular maps, and particle effects for the foam and the spray.
“Our fast-moving stream water is particularly convincing after using this method, but it also works well for still water. We also used vertex painting to place scum and foam around still objects in the water,” notes Gresko. “In areas such as Daret’s waterfront docks, we created animated reflections using geometry to add the look of movement to the water.” Artists handled transitions between dry and wet surfaces through alpha blends between each shader.
The most difficult levels to create were those set in Gil’ead, due to their size and open-ended gameplay. “Durza’s looming tower is such a complex maze of interconnecting floors and vertigo-inspiring views that the environment team wanted to make up T-shirts saying ‘I survived Durza’s Tower,’ ” says Gresko. In the Xbox 360 version of the game, normal maps adorn many surfaces, especially rock formations—although with greater subtlety than you’d see in other games, he points out.
“We’ve observed that some next-gen games have gone overboard with the use of normal maps and specular effects, making everything look plastic and fake just for the sake of showing off the technology. In our implementation, we hit a nice balance of increased detail, but not at the expense of the scene as a whole,” adds Gresko. “One of the best places to see the effect of dynamic lighting on a normal map is in one of the new Xbox 360-only levels: The Ruins of Orthíad. Using his magic, Eragon illuminates some gems set within a great hall of stone carvings, and the effect of the light spreading across the surface is fantastic.”
No fantasy game would be complete without a shroud of fog and a veil of mist to cloak the land in a mystical atmosphere. Stormfront used z-buffer fog for adding depth to a scene, and particle effects for creating localized fog patches, smoke, airborne soot, light beams, and so forth. Dancing perpetually across all the environments are the ubiquitous dynamic light sources, from the sun and the moon to the torches, burning arrows, and eerie light from Eragon and Saphira’s magic. Stormfront used vertex lighting, light maps and, in the Xbox 360 version, dynamic lights. According to Gresko, the dynamic lighting accentuated the detail in the normal maps, but also made it harder to maintain the carefully honed atmosphere established by the light maps and baked-in vertex lighting.
The principal characters were built in Maya, using 4000 to 5000 triangles,
while the enemy models were limited to approximately 2000 triangles.
Magically Assured Destruction
With Eragon wielding his magic powers over his enemies and Saphira unleashing fire-breathing mayhem on hordes of Urgals, you’d be correct to expect that the world of Alagaesia is primed for massive destructibility. Orchestrating the medieval carnage is Stormfront’s internal physics engine, code-named The Storm Engine.
“During the game, you’ll direct Saphira to smash large structures to bits, whip enemies into the air with her tail during dragonflight sequences, make your way across a bridge that’s literally falling apart as you traverse it, and pull down rocks to smash your enemies with Eragon’s magic,” notes Gresko. “We also capitalize on the simple fun of ‘cliffing’ enemies by throwing them off perilous ledges or propelling them with Eragon’s magic.”
The Storm Engine’s AI technology is tailored specifically to support the gameplay mechanics of Eragon. Besides providing autonomous behavior in the enemies and the AI-controlled allies (such as Brom or Saphira), designers can also create specific “brains” that characters can use to fit a situation. For example, in some sequences, Saphira will focus on aiding the player in battle by swooping down, snatching up Urgals, and dropping them to their deaths. In other scenarios, she will respond to Eragon summoning her to target a specific threat, usually smashing it to bits or burning it to ash.
“The game’s combat system offers tons of ways to approach a combat situation, presenting a challenge that couldn’t be addressed with a simplistic AI solution,” explains Gresko. “Our AI-controlled allies are able to perform moves as unique and dynamic as Eragon’s, and will select attacks that fit specific situations in an intelligent way.” For example, when an AI Brom grapples with an enemy, he’ll look for nearby cliffs to toss him over. If Eragon knocks down an enemy with magic, Murtagh will finish him with a coup de grace, providing some dynamic cooperative gameplay.
“Some of the best focus-test feedback we’ve received was centered on the ‘alive’ and helpful ally AI,” Gresko says. “Having a second human join in the fun is where Eragon really shines. A friend can just plug in a second controller to start playing (even in the middle of a level), and the AI will adapt seamlessly.”
Just like the film, the interactive version of Eragon proved a hit with audiences, immersing them further into the rich fantasy world—one of gaming’s most valued features.
Martin McEachern is an award-winning writer and a contributing editor for Computer Graphics World. He can be reached at firstname.lastname@example.org