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Artificial Intelligence: Animation Control


Navigating detailed worlds with a complex, physically driven locomotion: NPC Skateboarder AI in EA’s skate

Mark Wesley (Electronic Arts Black Box)
PDF link, Artificial Intelligence and Interactive Digital Entertainment (AIIDE), 2008.
Abstract: This talk describes the motivation, design and implementation behind the AI for the NPC Skateboarders in skate. The complexity of the physically driven locomotion used in skate means that, at any given point, there is an extremely large number of degrees of freedom in potential motion. In addition to this, the rules governing whether it is possible to navigate from any given point A to a secondary point B are entirely dependent on the skateboarder’s state at point A. The state required at point A involves a large number of variables, as well as a complex set of previously executed maneuvers to have reached it.

Simplified Animation Selection

Chris Hargrove (Gas Powered Games)
AI Game Programming Wisdom 2, 2003.
Abstract: This article describes an animation selection mechanism for determining the active animations of an arbitrary number of animation channels, based on a narrow set of discrete inputs and events, in a manner that's easy to manipulate for both artists and AI programmers. The system allows for just a few simple inputs (such as a character's cardinal movement direction, posture, weapon type, etc) and isolated triggered events (such as waves or taunts) to determine the entire animation state of a character at a given time, even in the presence of hundreds of animations.

The animation channels, input names and values, and control-flow "actions" are all configurable via a simple artist-friendly scripting language, allowing the artist to take nearly full control over the animation selection pipeline. In addition, the AI programmer's job is made easier due to the simplified conduit between a character's abstract behavior and its animation inputs. The result is an animation selection scheme that gives the artist a level of control usually only available to programmers, without losing the simplicity and flexibility of other data-driven approaches.

Pluggable Animations

Chris Hargrove (Gas Powered Games)
AI Game Programming Wisdom 2, 2003.
Abstract: This article discusses an extensible plug-in based animation pipeline that combines the handling of pre-built and dynamically-generated animation facilities into a single unified mechanism. This allows artists and AI programmers to take advantage of procedural animation effects in the same manner as regular animations, adding an additional level of flexibility and control to the look of your characters.

Animations are created based on a set of "abilities" that activate and deactivate at different points in time within the animation's length. These abilities can perform any number of effects on the character, from a simple application of pre-built animation frame data, to a complex on-the-fly Inverse Kinematics operation using external "satellite" points in space provided by an external source, to esoteric visual effects like bone attachment manipulation and vertex deformation. The abilities themselves are provided as plug-ins, and new abilities can be added during the development process (or in some cases even afterward, by "mod" authors) without changing the core of the animation pipeline. The process of creating of these kinds of animations can be made friendly to artists without much effort, via a simple GUI dialog box based primarily around a single list view control.

Intelligent Movement Animation for NPCs

Greg Alt (Surreal Software), Kristin King
AI Game Programming Wisdom 2, 2003.
Abstract: This article describes an intelligent movement animation system for non-player characters (NPCs). This system is used in the PC and PS2 versions of Fellowship of the Ring and two upcoming games from Surreal Software. First, the article briefly explains steering behaviors and animation systems. Next, it describes the middle layer between them. This layer includes a system for NPC movement, a movement animation behavior, and an animation controller. The movement animation behavior ensures that the animation being played and the way it is being played are appropriate, given the NPC's current movement. The animation controller provides a simple high-level interface to the underlying animation system. Finally, the article also gives some tips on gotchas that can come up during implementation of the middle layer and some ideas for further enhancements.

A Data-Driven Architecture for Animation Selection

Jeff Orkin (Monolith Productions)
AI Game Programming Wisdom, 2002.
Abstract: Animation selection is a common task for AI systems. Due to advances in animation technology, it is now common to provide a much wider range of animations for characters, including specific animations for specific situations. Rather than simply playing a "Run" animation, characters may play a specific "RunWithSword", "AngryRun", or "InjuredRun" animation. The Action Table is a simple data-driven approach to animation selection. This article describes the implementation of the Action Table, and goes on to describe how this technique can be extended to handle randomization and dynamic animation lists.

Realistic Character Behavior with Prioritized, Categorized Animation

Jeff Orkin (Monolith Productions)
AI Game Programming Wisdom, 2002.
Abstract: Skeletal animation systems allow AI programmers to creates realistic behavior for characters by playing multiple, layered animations simultaneously. The challenge comes in trying to manage these independent layers of animation. This article describes the implementation of a system in which layers of animation are prioritized, and categorized by the region of the body they affect. This data-driven approach moves the management of the layers out of the code. The article and companion CD provide code for this layering system. Handling of blended transitions between animations is discussed using a bone caching technique.

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