Simple initial implementation of angular bending springs.
These are much better suited for creating stiff hair. The previous bending springs are based on "push" type spring along the hypothenuse of 3 hair vertices. This sort of spring requires a very large force in the direction of the spring for any angular effect, and is still unstable in the equilibrium. The new bending spring model is based on "target" vectors defined in a local hair frame, which generates a force perpendicular to the hair segment. For further details see "Artistic Simulation of Curly Hair" (Pixar technical memo #12-03a) or "A Mass Spring Model for Hair Simulation" (Selle, Lentine, Fedkiw 2008) Currently the implementation uses a single root frame that is not yet propagated along the hair, so the resulting rest shape is not very natural. Also damping and derivatives are still missing.
This commit is contained in:
parent
86a4da1c54
commit
7a7778d003
|
@ -124,6 +124,7 @@ ClothVertex;
|
|||
typedef struct ClothSpring {
|
||||
int ij; /* Pij from the paper, one end of the spring. */
|
||||
int kl; /* Pkl from the paper, one end of the spring. */
|
||||
int mn;
|
||||
float restlen; /* The original length of the spring. */
|
||||
int matrix_index; /* needed for implicit solver (fast lookup) */
|
||||
int type; /* types defined in BKE_cloth.h ("springType") */
|
||||
|
@ -175,7 +176,8 @@ typedef enum {
|
|||
CLOTH_SPRING_TYPE_SHEAR = (1 << 2),
|
||||
CLOTH_SPRING_TYPE_BENDING = (1 << 3),
|
||||
CLOTH_SPRING_TYPE_GOAL = (1 << 4),
|
||||
CLOTH_SPRING_TYPE_SEWING = (1 << 5)
|
||||
CLOTH_SPRING_TYPE_SEWING = (1 << 5),
|
||||
CLOTH_SPRING_TYPE_BENDING_ANG = (1 << 6),
|
||||
} CLOTH_SPRING_TYPES;
|
||||
|
||||
/* SPRING FLAGS */
|
||||
|
|
|
@ -1287,39 +1287,71 @@ static int cloth_build_springs ( ClothModifierData *clmd, DerivedMesh *dm )
|
|||
}
|
||||
}
|
||||
else if (struct_springs > 2) {
|
||||
/* bending springs for hair strands */
|
||||
/* The current algorightm only goes through the edges in order of the mesh edges list */
|
||||
/* and makes springs between the outer vert of edges sharing a vertice. This works just */
|
||||
/* fine for hair, but not for user generated string meshes. This could/should be later */
|
||||
/* extended to work with non-ordered edges so that it can be used for general "rope */
|
||||
/* dynamics" without the need for the vertices or edges to be ordered through the length*/
|
||||
/* of the strands. -jahka */
|
||||
search = cloth->springs;
|
||||
search2 = search->next;
|
||||
while (search && search2) {
|
||||
tspring = search->link;
|
||||
tspring2 = search2->link;
|
||||
|
||||
if (tspring->ij == tspring2->kl) {
|
||||
spring = (ClothSpring *)MEM_callocN ( sizeof ( ClothSpring ), "cloth spring" );
|
||||
if (G.debug_value != 1112) {
|
||||
search = cloth->springs;
|
||||
search2 = search->next;
|
||||
while (search && search2) {
|
||||
tspring = search->link;
|
||||
tspring2 = search2->link;
|
||||
|
||||
if (!spring) {
|
||||
cloth_free_errorsprings(cloth, edgelist);
|
||||
return 0;
|
||||
if (tspring->ij == tspring2->kl) {
|
||||
spring = (ClothSpring *)MEM_callocN ( sizeof ( ClothSpring ), "cloth spring" );
|
||||
|
||||
if (!spring) {
|
||||
cloth_free_errorsprings(cloth, edgelist);
|
||||
return 0;
|
||||
}
|
||||
|
||||
spring->ij = tspring->kl;
|
||||
spring->kl = tspring->ij;
|
||||
spring->mn = tspring2->ij;
|
||||
spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest);
|
||||
spring->type = CLOTH_SPRING_TYPE_BENDING_ANG;
|
||||
spring->stiffness = (cloth->verts[spring->kl].bend_stiff + cloth->verts[spring->ij].bend_stiff) / 2.0f;
|
||||
bend_springs++;
|
||||
|
||||
BLI_linklist_prepend ( &cloth->springs, spring );
|
||||
}
|
||||
|
||||
spring->ij = tspring2->ij;
|
||||
spring->kl = tspring->kl;
|
||||
spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest);
|
||||
spring->type = CLOTH_SPRING_TYPE_BENDING;
|
||||
spring->stiffness = (cloth->verts[spring->kl].bend_stiff + cloth->verts[spring->ij].bend_stiff) / 2.0f;
|
||||
bend_springs++;
|
||||
|
||||
BLI_linklist_prepend ( &cloth->springs, spring );
|
||||
|
||||
search = search->next;
|
||||
search2 = search2->next;
|
||||
}
|
||||
}
|
||||
else {
|
||||
/* bending springs for hair strands */
|
||||
/* The current algorightm only goes through the edges in order of the mesh edges list */
|
||||
/* and makes springs between the outer vert of edges sharing a vertice. This works just */
|
||||
/* fine for hair, but not for user generated string meshes. This could/should be later */
|
||||
/* extended to work with non-ordered edges so that it can be used for general "rope */
|
||||
/* dynamics" without the need for the vertices or edges to be ordered through the length*/
|
||||
/* of the strands. -jahka */
|
||||
search = cloth->springs;
|
||||
search2 = search->next;
|
||||
while (search && search2) {
|
||||
tspring = search->link;
|
||||
tspring2 = search2->link;
|
||||
|
||||
if (tspring->ij == tspring2->kl) {
|
||||
spring = (ClothSpring *)MEM_callocN ( sizeof ( ClothSpring ), "cloth spring" );
|
||||
|
||||
if (!spring) {
|
||||
cloth_free_errorsprings(cloth, edgelist);
|
||||
return 0;
|
||||
}
|
||||
|
||||
spring->ij = tspring2->ij;
|
||||
spring->kl = tspring->kl;
|
||||
spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest);
|
||||
spring->type = CLOTH_SPRING_TYPE_BENDING;
|
||||
spring->stiffness = (cloth->verts[spring->kl].bend_stiff + cloth->verts[spring->ij].bend_stiff) / 2.0f;
|
||||
bend_springs++;
|
||||
|
||||
BLI_linklist_prepend ( &cloth->springs, spring );
|
||||
}
|
||||
|
||||
search = search->next;
|
||||
search2 = search2->next;
|
||||
}
|
||||
|
||||
search = search->next;
|
||||
search2 = search2->next;
|
||||
}
|
||||
}
|
||||
|
||||
|
|
|
@ -373,7 +373,7 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
|
|||
BPH_mass_spring_force_spring_goal(data, s->ij, s->matrix_index, goal_x, goal_v, k, parms->goalfrict * 0.01f, s->f, s->dfdx, s->dfdv);
|
||||
#endif
|
||||
}
|
||||
else { /* calculate force of bending springs */
|
||||
else if (s->type & CLOTH_SPRING_TYPE_BENDING) { /* calculate force of bending springs */
|
||||
#ifdef CLOTH_FORCE_SPRING_BEND
|
||||
float kb, cb, scaling;
|
||||
|
||||
|
@ -383,6 +383,18 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
|
|||
cb = kb = scaling / (20.0f * (parms->avg_spring_len + FLT_EPSILON));
|
||||
|
||||
BPH_mass_spring_force_spring_bending(data, s->ij, s->kl, s->matrix_index, s->restlen, kb, cb, s->f, s->dfdx, s->dfdv);
|
||||
#endif
|
||||
}
|
||||
else if (s->type & CLOTH_SPRING_TYPE_BENDING_ANG) {
|
||||
#ifdef CLOTH_FORCE_SPRING_BEND
|
||||
float kb, cb, scaling;
|
||||
|
||||
s->flags |= CLOTH_SPRING_FLAG_NEEDED;
|
||||
|
||||
scaling = parms->bending + s->stiffness * fabsf(parms->max_bend - parms->bending);
|
||||
cb = kb = scaling / (20.0f * (parms->avg_spring_len + FLT_EPSILON));
|
||||
|
||||
BPH_mass_spring_force_spring_bending_angular(data, s->ij, s->kl, s->matrix_index, s->restlen, kb, cb, s->f, s->dfdx, s->dfdv);
|
||||
#endif
|
||||
}
|
||||
}
|
||||
|
|
|
@ -140,6 +140,10 @@ bool BPH_mass_spring_force_spring_linear(struct Implicit_Data *data, int i, int
|
|||
bool BPH_mass_spring_force_spring_bending(struct Implicit_Data *data, int i, int j, int spring_index, float restlen,
|
||||
float kb, float cb,
|
||||
float r_f[3], float r_dfdx[3][3], float r_dfdv[3][3]);
|
||||
/* Angular bending force based on local target vectors */
|
||||
bool BPH_mass_spring_force_spring_bending_angular(struct Implicit_Data *data, int i, int j, int spring_index, float restlen,
|
||||
float stiffness, float damping,
|
||||
float r_f[3], float r_dfdx[3][3], float r_dfdv[3][3]);
|
||||
/* Global goal spring */
|
||||
bool BPH_mass_spring_force_spring_goal(struct Implicit_Data *data, int i, int spring_index, const float goal_x[3], const float goal_v[3],
|
||||
float stiffness, float damping,
|
||||
|
|
|
@ -1181,12 +1181,12 @@ int BPH_mass_spring_init_spring(Implicit_Data *data, int index, int v1, int v2)
|
|||
{
|
||||
int s = data->M[0].vcount + index; /* index from array start */
|
||||
|
||||
/* tfm and S don't have spring entries (diagonal blocks only) */
|
||||
init_fmatrix(data->bigI + s, v1, v2);
|
||||
init_fmatrix(data->M + s, v1, v2);
|
||||
init_fmatrix(data->dFdX + s, v1, v2);
|
||||
init_fmatrix(data->dFdV + s, v1, v2);
|
||||
init_fmatrix(data->A + s, v1, v2);
|
||||
// init_fmatrix(data->S + s, v1, v2); // has no off-diagonal spring entries
|
||||
init_fmatrix(data->P + s, v1, v2);
|
||||
init_fmatrix(data->Pinv + s, v1, v2);
|
||||
|
||||
|
@ -1609,6 +1609,48 @@ bool BPH_mass_spring_force_spring_bending(Implicit_Data *data, int i, int j, int
|
|||
}
|
||||
}
|
||||
|
||||
/* Angular spring that pulls the vertex toward the local target
|
||||
* See "Artistic Simulation of Curly Hair" (Pixar technical memo #12-03a)
|
||||
*/
|
||||
bool BPH_mass_spring_force_spring_bending_angular(Implicit_Data *data, int i, int j, int spring_index, float restlen,
|
||||
float stiffness, float damping,
|
||||
float r_f[3], float r_dfdx[3][3], float r_dfdv[3][3])
|
||||
{
|
||||
float target[3], dist[3], extent[3], length, dir[3], vel[3];
|
||||
float f[3], dfdx[3][3], dfdv[3][3];
|
||||
|
||||
target[0] = 0.0f;
|
||||
target[1] = 0.0f;
|
||||
target[2] = restlen;
|
||||
|
||||
// calculate elonglation
|
||||
// spring_length(data, i, j, extent, dir, &length, vel);
|
||||
sub_v3_v3v3(extent, data->X[j], data->X[i]);
|
||||
sub_v3_v3v3(vel, data->V[j], data->V[i]);
|
||||
length = len_v3(extent);
|
||||
|
||||
sub_v3_v3v3(dist, target, extent);
|
||||
mul_v3_v3fl(f, dist, stiffness);
|
||||
// mul_v3_v3fl(f, dir, fbstar(length, restlen, kb, cb));
|
||||
|
||||
zero_m3(dfdx);
|
||||
zero_m3(dfdv);
|
||||
|
||||
// outerproduct(dfdx, dir, dir);
|
||||
// mul_m3_fl(dfdx, fbstar_jacobi(length, restlen, kb, cb));
|
||||
|
||||
/* XXX damping not supported */
|
||||
// zero_m3(dfdv);
|
||||
|
||||
apply_spring(data, i, j, spring_index, f, dfdx, dfdv);
|
||||
|
||||
if (r_f) copy_v3_v3(r_f, f);
|
||||
if (r_dfdx) copy_m3_m3(r_dfdx, dfdx);
|
||||
if (r_dfdv) copy_m3_m3(r_dfdv, dfdv);
|
||||
|
||||
return true;
|
||||
}
|
||||
|
||||
bool BPH_mass_spring_force_spring_goal(Implicit_Data *data, int i, int UNUSED(spring_index), const float goal_x[3], const float goal_v[3],
|
||||
float stiffness, float damping,
|
||||
float r_f[3], float r_dfdx[3][3], float r_dfdv[3][3])
|
||||
|
|
Loading…
Reference in New Issue