Game Development Reference
In-Depth Information
struct Ve r t ex
{
Vector3 pos; Vector3 vel; Vector3 goalPos;
Vector3 force;
// force coefficients
real factorRest;
real factorDetail ;
real factorNeighbors;
real factorDamping;
// one of the edges to retrieve neighborhood
DirectedEdge edge;
real mass;
} ;
Listing 14.1. The complete vertex class.
for the model in question. A suitable parameter-fitting algorithm is presented
in [Shi et al. 08]. We have to keep in mind that there are limits within which the
parameters have to be set for a stable simulation. A complete vertex structure
that accumulates the per-vertex information about everything discussed until now
could look like Listing 14.1.
We accumulate the forces discussed so far with
+ α neigh
i
f neigh
i
f total
i
= α rest
i
f rest
i
+ α detail
i
f detail
i
·
·
·
and check whether the calculations work as intended. A block of 16 vertices
connected in a simple geometry is defined to test the implementation (see Fig-
ure 14.7) . The red spheres are the rest positions of the mesh while the white
spheres are the goal positions of the shape-matching algorithm. The actual po-
sitions are the yellow spheres. First, we can displace every vertex just a bit and
watch it go back into its original shape. If we apply a driving force to our block
on the right, even the vertices on the other end of the body start to wiggle about.
In the demo, we can also switch on a gravitational force (and set factorRest
to zero) and watch the body hit the ground. The body stays in shape just by means
of the shape-matching algorithm (see Figure 14.8 ) . A demo is included with the
supplemental materials.
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