Game Development Reference
Figure 13-1. Network of particles and springs
Each line in the wireframe flag shown in Figure 13-1 represents a spring-damper ele‐
ment, while the nodes where these springs intersect represent the particles. We modeled
the springs using the spring-damper formulas that we showed you back in Chapter 3 .
The (initially) horizontal and vertical springs provide the basic structure for the flag,
while the diagonal springs are there to resist shear forces and lend further strength to
the cloth. Without these shear springs, the cloth would be quite stretchy. Note that there
are no particles located at the intersection of the diagonal springs.
In this chapter, we'll show you how to use those same techniques to simulate something
like a hanging rope or vine. You can use these techniques to simulate all sorts of things
besides cloth and rope or vines. For example, you can model the swing of a golf club if
you can imagine one rigid body representing the arm and another representing the golf
club. We'll get to that example in Chapter 19 , but for now let's see how to model a hanging
rope or vine and some other springy objects.