Vehicular Violence
Issue: Volume: 31 Issue: 2 (Feb. 2008)

Vehicular Violence

The game’s battlefields rumble under the heavy-metal tonnage of hundreds of Necris and Axon (human) assault vehicles; this time, many of them have more curved and animated surfaces to maximize the potential of the Unreal engine. The visual upgrade included the addition of a full-damage system, integrating morph targets, detachable parts, a damage shader, hit-location-specific particles, a location health system, and customizable explosion and vehicle death parameters.

The Leviathan, a powerful five-man mobile assault station with five turrets, was the most complex of the Axon vehicles to create. A vehicle of huge scale and one that is required to hold five players (four turrets and a driver) as well as an integrated super weapon capable of mass destruction, the Leviathan posed quite a challenge from initial concept right to the end. “Its immense size caused levels to be redesigned to accommodate it,” recalls artist Paul Jones. “Ultimately, what makes it all worthwhile is the awesome sight of seeing the articulation and transformation of the vehicle parts as the super weapon deploys.”

The more polished, angular, and insect-like Necris vehicle design emerged from a desire to forge a stark contrast to the mechanical, beaten-up metal of the existing set of Axon vehicles. Early on in production, a smooth, composite shell material was developed for the alien vehicles, setting the style for all new units. Powered by a glowing, moving energy ball and the signature tentacles, the Necris vehicles were born.

“All of them proved a modeling challenge, especially with the frequency of complex, compound curves and intersecting shapes. However, with the organic nature of the Necris vehicles, the normal maps helped immensely in producing the final look of the vehicle,” says Jones.

None of the Necris vehicles proved a greater modeling and rigging challenge than the towering Darkwalkers, which stand on a tripod of Nano-fueled tentacles and dominate the landscape like the giant tripods from HG Wells’ War of the Worlds. Its spider-like legs were animated procedurally in-engine using a form of spline IK.

To get the Darkwalkers’ legs to move, the artists first animated a single-step animation in Autodesk’s Maya. The programmers then used that motion as a reference to move effector nodes that would adjust to the terrain. This way, the nuances of the leg animation could be kept, while the leg would be able to step to any point within a certain range from the body without stepping through the terrain or an object. Finally, in-game physics forced the leg to follow the moving effector nodes. This gave the leg a powerful step that, while remaining true to the source animation, felt fluid and organic as it moved across the landscape.
The vehicles in this version of Unreal Tournament have animated surfaces that take advantage of the new Unreal 3 engine. Damage is shown only in the areas where the vehicles have been hit.

Another spider-like vehicle, more lithe and fast moving than the Darkwalker, is the Scavenger, which scampers across the landscape on three short, spindly legs, occasionally rocketing forward with its legs spinning like razors on all sides. The Scavenger can retract its legs and spin them around the vehicle during an attack, so the physics controllers had to blend on and off to allow the animation to take complete control of the leg.

The new and improved vehicles, with their universal destructibility—featured most prominently in the Ageia PhysX-enhanced PC version—also received a new damage system, one deliberately designed to enable gamers to anticipate when a vehicle was about to disintegrate or explode.

In addition to the textures painted for the damage shader, each vehicle features a wide variety of maps authored at 2048x2048 (though the number usually depends on its physical size). The Leviathan, for instance, which is the game’s largest vehicle, has a total of 12, including diffuse, normal, specular, and damage textures. “Over the course of the project, we decided the visual state of the vehicles should represent their health rather than a traditional bar,” says Jones. The group set up a parent shader through the shader system, along with a child shader, so that if a change was made, it would propagate to all the vehicles in the tree and save time in alterations. A vehicle’s damage is revealed only in the areas corresponding to the locations in which they are hit, thanks to a set of custom masks.  —Martin McEachern