Game Development Reference
chapter take much less computation time than the collision-handling routines that
are needed to have different models and geometry applying forces on each other.
The collision handling of deformable bodies has to be more sophisticated than
that of rigid bodies, since there is always a certain penetration depth when two de-
formable objects collide and deform each other, and there is always the possibility
of self-penetration (see [Teschner et al. 05] for detailed information).
For simulating the effect of surface connectivity, a technique called “shape
matching” [Muller et al. 05] is used, which takes care of maintaining surface
details during the simulation.
Several approaches to addressing volumetric effects of a solid material and its
applicability are discussed, and the best-fitting technique is used.
If the lack of realism of these techniques is not acceptable, the method pre-
sented in Chapter 10 is a much better approach to simulating deformable objects,
since it is completely based on a physically correct description.
Throughout this chapter, we are seeking for drop-in solutions that can easily
be integrated into an existing simulation.
Objects in current computer games are surface mesh, so our deformable simu-
lation should be surface based while still being able to naturally simulate volumet-
ric behavior. This way, the deformation model can efficiently be integrated into
the rendering pipeline, and the computations can even be done on the graphics
Because of the simplifications made, the simulation will rely on material prop-
erties that need to be tuned by a designer during content creation to become real-
In this chapter, all the background necessary to understand what is going on in
principle is covered, while always focusing on practicability. We will work on an
implementation of a deformable mesh simulation that will gradually be extended
and can be modified to suit any special purpose in a game.
Section 14.2 will introduce the force model used for the simulation and points
out potential pitfalls. Section 14.3 incorporates the effect of surface connectivity
in a polygonal mesh in an economical way. The shape-matching algorithm is
described. The following section, Section 14.4, accounts for the influences of the
volumetric effects on a solid material without an accurate physical simulation of
the interior of the mesh.
14.2 The Interaction Model
The starting point of the simulation is a triangle mesh of vertices with positions
x i . It can be animated in time (e.g., using keyframes), but it does not have to,