A Dynamic Motion Control Middleware for Computer Games
Masaki Oshita and Akifumi Makinouchi
Kyushu University, Japan1Introduction

In this sketch, we present a middleware for computer games that has
the ability to realize dynamic motion control of characters. The specific novelty of the middleware is to produce dynamically changing
motions in response to physical interaction between the characterand environments such as collision impulses and external forces asshown in Figure 1.
In many three-dimensional computer games, it is required to produce continuous and realistic character motions on the fly. Currently most games generate such motions by combining short motion clips that are created and stored in advance. Although thisapproach basically works well, in this framework, characters cando nothing but just repeat prepared motion data. This limitation
leaves players with a monotonous impression. The most serious
problem is dynamic reactions caused by physical interaction withother characters and environments. These kinds of reactive motions
should change in response to the timing, direction, and amount of
the physical interaction. However, because current computer games
just play a fixed motion in this kind of situation, unnatural results
are sometimes generated. For example, characters fall down in thesame way however it received the impact. To handle this kind ofmotions, the resulting motions should be generated dynamicallyconsidering the physics of the characters.

Figure 1: The middleware provides dynamic motion control in response to physical interaction between the character and environments.
Game Application
ActionDatabase

Middleware
Controller

Motion Synthesiser

2

Reactive Action

Synthesized motion

Proposed Middleware

Reaction Generator

Motion Controller

The proposed middleware is linked and cooperates with game application. The system structure is shown in Figure 2. The application program gives an appropriate action data that is selected fromthe stored action data collection based on player control in context.
The middleware controls the angular accelerations of the character
joints based on the input action. The input action is normally executed as it is given and only when unexpected physical interaction
happens, dynamically changed motions are produced. Because ofthis approach, the middleware makes use of existing motion clips
and it is easy for the developers to use our system.
The controller in the middleware consists of three components;
motion synthesizer, dynamic controller, and reaction generator. The
motion synthesizer realizes smooth transition from one action to
the following action considering the constraints of the end-effectors
even when the character posture is slightly changed by external interaction. The dynamic controller then computes output angularaccelerations for all joints based on the synthesized motion. It realizes human-like dynamic control in response to its balance andjoint stresses of the character. For example, it moves the pelvis tokeep its balance or swings the arms to reduce the stresses on theback or legs. Our dynamic control method is specified to humanlike articulated figures and it controls each body part through aminimum number of degrees-of-freedom. The reaction generator
produces dynamic reactions such as protective step for balancing,falling down and recovery motion. The reaction generator works
when the dynamic controller cannot handle too large external influence. More details about the dynamic control techniques are foundin [Oshita and Makinouchi 2001].

Output acceleration for all joints
Simulator
Update state
Character's StateAnimation

Figure 2: System structure of the middleware and application.

3 Application
We have developed a prototype of the proposed middleware and weare also developing a demo application which works on the prototype. The demo application is a kind of action game in which acharacter controlled by the user fights with other characters. Compared with existing games of similar type, it generates more appropriate dynamic motions. For example, when a character hits
another, dynamic motions are generated in response to the positionand power of the collisions. The developed demo application isgoing to be available soon on our web site: www.e-motion.ne.jp.

References
O SHITA , M., AND M AKINOUCHI , A. 2001. A dynamic motion
control technique for human-like articulated figures. Computer
Graphics Forum (EUROGRAPHICS 2001) 20, 3, 192–202.

 moshita@db.is.kyushu-u.ac.jp

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