animation, graphics, games, and other projects

GDC 2005 Materials: Moving Beyond Ragdolls

This site houses some materials related to my GDC 2005 talk titled:

Moving Beyond Ragdolls: Generating Versatile Human Behaviors by Combining Motion Capture and Controlled Physical Simulation

You can find links to the slides, my thesis materials, and the source code to a simplified version of the demo presented during the talk. The main idea of the talk is to look at techniques to improve the quality of simulated humans by augmenting ragdolls with control systems as well as techniques to interface these simulated behaviors with existing motion data.

Here’s the abstract for the talk:

This talk looks at how developers can create new kinds of animation systems capable of moving from existing motion data to controlled physical simulation and back. Games create compelling characters through imaginative designers combined with skillful artists or a talented actor in a motion capture studio. However, virtual characters often look unrealistic when interacting with living and dynamic environments because the artist’s keyframes or the actor’s movements predetermine the character’s abilities. “Ragdolls” have recently been used to model the physics of the body as it collides with the environment and other characters. Unfortunately, their usefulness is limited because the ragdoll appears lifeless without control systems to produce realistic behavior. Returning character control to prerecorded motion is also difficult because the final pose of the ragdoll is not known beforehand. This lecture discusses how the strengths of motion capture data and physically controlled behaviors can be combined. Hybrid animation systems using this approach can transition from motion data to simulation and back so that each method may be used in the appropriate context. Physical controllers are developed using techniques from biomechanics and robotics literature to infuse life into simulated motion. The proportional derivative controllers may be artist directed and can guide simulated characters to realistic behaviors while retaining their physical realism. These controllers also allow the simulation to move back towards motion data in a natural way. Fast search techniques build a correspondence between simulated postures and large motion databases. This session should provide developers with practical implementation details, proper high-level concepts, and resources to learn more about this emerging approach to animation. Such an approach can drive the future of modern animation systems to empower game developers to deploy characters that can move and respond to the living world of their imaginations.

Idea Takeaway:
Attendees will understand the advantages of combining both simulation and traditional motion data for character animation. The complementary strengths and weaknesses of these approaches motivate the need for an effective hybrid system that can utilize either technique interchangeably. Attendees learn how to move beyond ragdolls to add believable life into simulated character animation with the added ability to move back to motion data. State-of-the-art techniques from the research community are presented in the context of games so developers can understand how to integrate physically simulated behavior into their existing pipelines. Practical implementation tips and references give attendees the resources to get started immediately.

Intended Audience and Prerequisites:

This talk is mostly intended for programmers with at least some high-level familiarity with skeletal animation systems and ragdoll simulation. Each topic covered will review fundamentals so beginners should be able to follow most of the talk and have the resources to begin implementing the presented techniques. In addition, game designers may wish to attend to understand the high-level concepts and how the technology presented can be used to create new gameplay experiences.

This project originated as my Master’s work at Carnegie Mellon University (completed December 2004) under the guidance of Jessica Hodgins. There is more information, movies, screenshots available at my thesis site. You may also be interested in reading my thesis as well…

Presentation Slides
The slides presented at GDC are available in PDF form below:
GDC Slides [PDF]

Controller Demo Source
This is the release of a simplied version of the PD Controller demo shown in my GDC 2005 talk (released under the LGPL). The demo basically sets up a ragdoll character using ODE and demonstrates how a control system can be used to drive the motion of the body. You can download it here.

A description of the demo from the Readme:
An OpenGL implementation of a PD controller based pose controller. The freely available Open Dynamics Engine (ODE) is used to perform the rigid body simulation of the human figure. When the example controller is enabled, the target joint angles are set to 0, pushing the body into the base pose with the arms and legs extended (through joint torques computed by the controller). There is also an option to apply forces to the pelvis to see that the body still responds to the physical world while being controlled.

A more full-featured demo (which was actually shown in my talk) and detailed description of the algorithms used is available in Game Programming Gems 5.

Please feel free to contact me by email with any questions/comments.