Sponsored Feature: Multi-Core Simulation of Soft-Body Characters Using Cloth 2

Author: by Staff

In the latest Intel-sponsored feature, part of the Gamasutra Visual Computing microsite, Intel senior software engineer Brad Werth explains how multicore CPUs can be leveraged for an efficient method of representing soft-body characters by way of cloth simulation. Because of CPUs constrained with limited computational power, most character animation is done today with a bones-and-skin method, which uses a small number of invisible control points, linked together as bones, to control the a figure. To "skin" the character, the visual portions of the figure are then bound to specific bones. While this method provides a relatively fast way to animate characters given CPU constraints, the advent of two-core and fore-core processors is allowing for more sophisticated character animation techniques: "With additional processing power, the bones-and-skin method can be extended for more detailed animation. More bones can be added for additional degrees of freedom. But there is no need to create additional bones unless a new joint is being modeled. Improvements are also possible by focusing on more complicated movement of the bones. Instead of just blending between canned animations, animations can be blended with physics to create dynamic motion in the bones. This is already implemented in games that use "rag doll" corpses, and has been implemented in some middleware products also. Bones-and-skin is one method for character animation, but it is not the only viable choice assuming that increased computational power is available. Since the skin is the only visible part of the character, an alternative is to ignore bones and calculate the shape and movement of the skin directly. If the skin is disengaged from bones, then only local forces and constraints maintain the character's form. The resulting skin can be manipulated equally well from internal and external forces. A character built this way is sometimes called a "soft-body" character. In a soft-body character, simulated cloth can be used as a skin. Forces applied to the cloth create the form of the soft-body character. Sock puppets are a simple example of this technique. The cloth provides local constraints to maintain the form of the sock, and the hand provides the forces to give the character volume. When simulating cloth computationally, the hand becomes an invisible mathematical construct and the sock is attached to that construct at key points. By expanding on this concept, a variety of soft-body characters can be created." You can now read the full feature, which includes specific technical details and visual aids.