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Building Brawl-Handling Interacting Characters in EA Sport's MMA

By Kelly L. Murdock | Published Nov 29 2010 11:00 PM in Visual Arts

fighter team fighters game mma system sweat animation texture
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Setting the Ambiance


The fight audience was pulled from the Fight Night crowd and retrofitted for this game. It consists of 10 basic animations that are offset and spaced apart. Simon says, "The key is avoiding large repetitive motions that would pull the eye away from the fighters and/or animations."

The venue lighting is supplied using light maps that are stored as 8-bit RGBE textures and all specular surfaces had environment maps applied with normal maps to break up the highlights.

Lighting the fighters was accomplished using a relatively dim directional light coupled with the surrounding ambient light that is emulated through the environment maps. For subtle lighting across the fighter's face, Volga said, "we also used a novel SSAO (Screen Space Ambient Occlusion) technique as well as SSS (Sub-Surface Scattering in UV space) that is specifically tuned to work for all of the different skin tones we have in the game. As for specular highlights, we used the Kelemen-Szirmay-Kalos model for the directional light as well as using reflection cube maps to capture the subtle breakup of the reflections over the skin during the sweat buildup."

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Figure 4: Several lighting techniques were used to light the venue and the fighters.

To animate the ring ropes, collision discs are placed along the length of the ropes whose extents are compared to the skinned limits of the fighter mesh and the results are fed to the ring ropes vertex shader.

The sound effects were created by an Academy award-winning sound designer. Rob Hyder describes how some of the Foley sounds were obtained, "I believe that one of the most successful was a large beef roast that he purchased and then proceeded to punch and hit with various implements until he got the sounds he wanted."


Landing a Punch--Creating Fighter Interactions


Regardless of how realistic the fighters look, it is the interaction between the fighters that has a greater impact on the realism of the fight. The team made heavy use of motion blends for procedural animation tuning to create the fighter interactions. Simon describes this system, "We have a system that allows us to layer, override, and subtract or add animation to any part of the body at any time (similar to Photoshop layers). We also have several tools for controlling the visuals of blending animations and make heavy use of those tools on MMA."

Contact between the fighters was created using a non-uniform player scaling system, a relative IK system and a series of what the team called "touch tags." These touch tags used the HumanIK feature included in MotionBuilder to adjust the animation in and out of a specified target.

The HumanIK feature in MotionBuilder was also used to define foot positions and prevented the foot from slipping as the body moved. It was also used to retarget animations to various skeletons and to maintain contact with opponents. Finally, the feature was used to track the fighter's head, which the team referred to as "head tracking with attitude."

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Figure 5: Autodesk's HumanIK feature was used to maintain contact between fighters.

The MMA team tried to avoid the use of any physics-based system when animating the interactions between the fighters. Simon mentioned, "we felt that it was important to maintain that visual ideal of “intention” in our actors on screen, so we use Fight Night physics to clean up interpenetrations, but we use other procedural animations systems, which are very often "informed" and driven but not posed by physics simulation. The idea was to give the artists control over the characters’ posing while allowing physical simulation to often drive the animation decision tree."

To create the effect of an impact on a fighter's face during the slow-motion replays, a cloth simulation was used. This worked by having the artists paint a mask over the face vertices that indicates which vertices to include in the cloth simulation. During the simulation, the direction and force of the punch was fed into the simulation as an extra force.

Particle systems were used to trigger blood spray, sweat cloud spray, spit spray, dripping blood from gaping wounds, and ambient sweat dripping. The blood, sweat and spit used a high perparticle cohesion value to create a "stringy" effect as they travel through the air.

The MMA team spent a lot of time researching skin rendering. This is apparent in the damage model that was developed for MMA including how cuts break and develop further by bleeding and running. The face also becomes deformed to accommodate swelling.

Another trick that added to the realism of the fight was to allow the blood to transfer to the opponent's body and to the canvas. To get blood on the mat, the team simply renders a special pass of the particle system into a texture that is only sampled at runtime. After a few seconds, the blood particle starts to fade out, but its position is rendered onto the mat's blood texture where it persists throughout the match.

Concerning the game's AI system, Rob Williams describes the team's four AI goals, "First, don’t be a sap. The computer does not take any action taken by the opponent as a cue to do a negatively predictable behavior. Second, be yourself. A certain level of predictable behavior must be built-in, at least enough so a fighter performs in a way that agrees with their real-life counterparts. One fighter may prefer or be more skilled at stand-up striking, while another may prefer or be more skilled in the ground game. Third, mix it up. Within the constraints of behaving as the real-life fighter, unpredictability can be done by collecting the preferred actions of the fighter and choosing one at random, with actions more greatly preferred by the particular fighter given greater likelihood of being selected. Finally, live and learn. In all situations the computer observes which fight tactics yield positive results for the computer, and which behaviors yield negative results, just as a human fighter does in a real match."


Conclusion


EA Sports new MMA game has been called "the most-realistic fighting game ever." With advanced tools and skilled artists, the results are dramatic. The effort put forth by this team has added realism not only to the character's look, but also to how they interact with other fighters and with the environment. Certainly the team has pushed the envelope. For MMA fans and gamers that enjoy realistic fighting games, this is definitely one to check out.

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About the Author(s)


[i]Kelly L. Murdock works as a freelance consultant and author. He has written extensively on 3D graphics including the 3ds Max Bible and many other titles. [/i]






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