Game Development Reference
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get transformed according to their assigned bone. The position of a vertex is a
weighted sum of these transformed weight positions. The Internet provides a lot
of detailed documentation on this format.
Geometry produced from this specification works well as a kinematic basis
for the secondary deformations presented here.
The vertices in the MD5 format are given implicitly as a sum of weights:
struct ModelVertex { int start; int count; } ;
Here, start defines the first weight and count the number of weights after the
starting weights that belong to this vertex:
struct ModelWeight
{
int joint; float bias; Vector3 pos;
}
;
The weight contains the information of how to construct the final vertex po-
sitions; pos defines the position of the weight, and bias states how much the
weight contributes to the vertex. Using the weight, we can access the bone model
information, since joint assigns each weight a joint:
struct ModelJoint
{
char name[64];
int parent;
Vector3 pos;
Quat4 orient;
} ;
This is basically the same definition of a joint that was used before. List-
ings 14.2 and 14.3 show the application of the surface-detail preservation and the
bone-distance preservation forces to an actual MD5 model. Since an MD5 model
can consist of several independent meshes, we have to specify which one we want
to deform. The supplementary material includes an application that demonstrates
the interactive deformation of the animated Stanford armadillo model (see Fig-
ure 14.12 ) .
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