Game Development Reference
In-Depth Information
Soft Bodies Using Finite Elements
Cesar Mendoza and Marcos Garcia
Much of the physics in three-dimensional game engines is still based on rigid-
body dynamics. Effects such as cloth or soft bodies are rarely used, and only
some basic precalculated approaches are usually applied. However, the increas-
ing demand for realism in the video game industry has started to change this, and a
different approach is required for the underlying real-time algorithms to simulate
deformable bodies. With this trend, the latest video games and real-time graph-
ics applications have started to simulate soft bodies based on their real physical
behavior. Including physically based soft bodies into a computer game enhances
the realism, but it also poses a great challenge to the game developers since the
algorithms are more complex, slower, and less controllable.
Nowadays, many of the techniques used to simulate physically based soft bod-
ies rely on mass-spring systems. They are the simplest, the easiest to implement,
and the most computationally efficient if used together with an explicit integra-
tion scheme. The general idea is to represent the vertices of the mesh as mass
points, governed by Newton's second law, and the edges as elastic massless links
(springs). Hence, the object is deformed when the lengths of the elastic links (rel-
ative to the resting length) change. This happens when the relative position of the
mass points changes due to external forces, such as friction, gravity, and object
collisions. However, these models have some important drawbacks. In the first
place, the motion of the mass points depends on the direction of their connect-
ing links, i.e., they are topology dependant, which in most cases is not the best
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