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Improved force field effects on hair strands.

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The previous calculation was modulated with the angle between the wind
direction and the segments, which leads to very oscillating behavior.

Now the formula includes an estimate for the geometric cross section
of a hair segment based on the incident angle and the hair thickness
(currently just the particle size). This gives a more stable behavior
and more realistic response to wind.

Conflicts:
	source/blender/blenkernel/intern/particle_system.c
	source/blender/physics/intern/BPH_mass_spring.cpp
This commit is contained in:
Lukas Tönne 2014-12-16 19:40:29 +01:00
parent 658fc3ddbc
commit 5c7adf5be2
5 changed files with 42 additions and 9 deletions
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1
source/blender/blenkernel/BKE_cloth.h
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@ -65,6 +65,7 @@ typedef struct ClothHairData {
float loc[3];
float rot[3][3];
float rest_target[3]; /* rest target direction for each segment */
float radius;
float bending_stiffness;
} ClothHairData;

6
source/blender/blenkernel/intern/particle_system.c
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@ -3007,6 +3007,7 @@ static void hair_create_input_dm(ParticleSimulationData *sim, int totpoint, int
int k, hair_index;
float hairmat[4][4];
float max_length;
float hair_radius;
dm = *r_dm;
if (!dm) {
@ -3034,6 +3035,9 @@ static void hair_create_input_dm(ParticleSimulationData *sim, int totpoint, int
psys->clmd->sim_parms->vgroup_mass = 1;
/* XXX placeholder for more flexible future hair settings */
hair_radius = part->size;
/* make vgroup for pin roots etc.. */
hair_index = 1;
LOOP_PARTICLES {
@ -3063,6 +3067,7 @@ static void hair_create_input_dm(ParticleSimulationData *sim, int totpoint, int
copy_v3_v3(hair->loc, root_mat[3]);
copy_m3_m4(hair->rot, root_mat);
hair->radius = hair_radius;
hair->bending_stiffness = bending_stiffness;
add_v3_v3v3(mvert->co, co, co);
@ -3083,6 +3088,7 @@ static void hair_create_input_dm(ParticleSimulationData *sim, int totpoint, int
copy_v3_v3(hair->loc, root_mat[3]);
copy_m3_m4(hair->rot, root_mat);
hair->radius = hair_radius;
hair->bending_stiffness = bending_stiffness;
copy_v3_v3(mvert->co, co);

8
source/blender/physics/intern/BPH_mass_spring.cpp
View File

@ -497,10 +497,16 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListB
/* Hair has only edges */
if (cloth->numfaces == 0) {
ClothHairData *hairdata = clmd->hairdata;
ClothHairData *hair_ij, *hair_kl;
for (LinkNode *link = cloth->springs; link; link = link->next) {
ClothSpring *spring = (ClothSpring *)link->link;
if (spring->type == CLOTH_SPRING_TYPE_STRUCTURAL)
BPH_mass_spring_force_edge_wind(data, spring->ij, spring->kl, winvec);
hair_ij = &hairdata[spring->ij];
hair_kl = &hairdata[spring->kl];
BPH_mass_spring_force_edge_wind(data, si_ij, si_kl, hair_ij->radius, hair_kl->radius, winvec);
}
}

2
source/blender/physics/intern/implicit.h
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@ -111,7 +111,7 @@ void BPH_mass_spring_force_extern(struct Implicit_Data *data, int i, const float
/* Wind force, acting on a face */
void BPH_mass_spring_force_face_wind(struct Implicit_Data *data, int v1, int v2, int v3, int v4, const float (*winvec)[3]);
/* Wind force, acting on an edge */
void BPH_mass_spring_force_edge_wind(struct Implicit_Data *data, int v1, int v2, const float (*winvec)[3]);
void BPH_mass_spring_force_edge_wind(struct Implicit_Data *data, int v1, int v2, float radius1, float radius2, const float (*winvec)[3]);
/* Linear spring force between two points */
bool BPH_mass_spring_force_spring_linear(struct Implicit_Data *data, int i, int j, float restlen,
float stiffness, float damping, bool no_compress, float clamp_force,

34
source/blender/physics/intern/implicit_blender.c
View File

@ -1461,21 +1461,41 @@ void BPH_mass_spring_force_face_wind(Implicit_Data *data, int v1, int v2, int v3
}
}
void BPH_mass_spring_force_edge_wind(Implicit_Data *data, int v1, int v2, const float (*winvec)[3])
static void edge_wind_vertex(const float dir[3], float length, float radius, const float wind[3], float f[3], float UNUSED(dfdx[3][3]), float UNUSED(dfdv[3][3]))
{
const float effector_scale = 0.01;
float win[3], dir[3], nor[3], length;
const float density = 0.01f; /* XXX arbitrary value, corresponds to effect of air density */
float cos_alpha, sin_alpha, cross_section;
float windlen = len_v3(wind);
if (windlen == 0.0f) {
zero_v3(f);
return;
}
/* angle of wind direction to edge */
cos_alpha = dot_v3v3(wind, dir) / windlen;
sin_alpha = sqrt(1.0 - cos_alpha*cos_alpha);
cross_section = radius * (M_PI * radius * sin_alpha + length * cos_alpha);
mul_v3_v3fl(f, wind, density * cross_section);
}
void BPH_mass_spring_force_edge_wind(Implicit_Data *data, int v1, int v2, float radius1, float radius2, const float (*winvec)[3])
{
float win[3], dir[3], length;
float f[3], dfdx[3][3], dfdv[3][3];
sub_v3_v3v3(dir, data->X[v1], data->X[v2]);
length = normalize_v3(dir);
world_to_root_v3(data, v1, win, winvec[v1]);
madd_v3_v3v3fl(nor, win, dir, -dot_v3v3(win, dir));
madd_v3_v3fl(data->F[v1], nor, effector_scale * length);
edge_wind_vertex(dir, length, radius1, win, f, dfdx, dfdv);
add_v3_v3(data->F[v1], f);
world_to_root_v3(data, v2, win, winvec[v2]);
madd_v3_v3v3fl(nor, win, dir, -dot_v3v3(win, dir));
madd_v3_v3fl(data->F[v2], nor, effector_scale * length);
/* use -length to invert edge direction */
edge_wind_vertex(dir, length, radius2, win, f, dfdx, dfdv);
add_v3_v3(data->F[v2], f);
}
BLI_INLINE void dfdx_spring(float to[3][3], const float dir[3], float length, float L, float k)