2D Skeletal Animation Transformations
- by Brad Zeis
I have been trying to build a 2D skeletal animation system for a while, and I believe that I'm fairly close to finishing. Currently, I have the following data structures:
struct Bone {
Bone *parent;
int child_count;
Bone **children;
double x, y;
};
struct Vertex {
double x, y;
int bone_count;
Bone **bones;
double *weights;
};
struct Mesh {
int vertex_count;
Vertex **vertices;
Vertex **tex_coords;
}
Bone->x and Bone->y are the coordinates of the end point of the Bone. The starting point is given by (bone->parent->x, bone->parent->y) or (0, 0). Each entity in the game has a Mesh, and Mesh->vertices is used as the bounding area for the entity. Mesh->tex_coords are texture coordinates. In the entity's update function, the position of the Bone is used to change the coordinates of the Vertices that are bound to it. Currently what I have is:
void Mesh_update(Mesh *mesh) {
int i, j;
double sx, sy;
for (i = 0; i < vertex_count; i++) {
if (mesh->vertices[i]->bone_count == 0) {
continue;
}
sx, sy = 0;
for (j = 0; j < mesh->vertices[i]->bone_count; j++) {
sx += (/* ??? */) * mesh->vertices[i]->weights[j];
sy += (/* ??? */) * mesh->vertices[i]->weights[j];
}
mesh->vertices[i]->x = sx;
mesh->vertices[i]->y = sy;
}
}
I think I have everything I need, I just don't know how to apply the transformations to the final mesh coordinates. What tranformations do I need here? Or is my approach just completely wrong?
