Radical simplification of the wind effect on hair, since the previous
approach does not work very well. Using a cross section estimate still causes large oscillations due to varying hair force based on angles. It also requires a sensible hair thickness value (particle radius) which is difficult to control and visualize at this point. The new model is based purely on per-vertex forces, which seems to be much more stable. It's also somewhat justified by the fact that each hair vertex represents a certain mass. Conflicts: source/blender/physics/intern/BPH_mass_spring.cpp
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@ -497,6 +497,7 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListB
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/* Hair has only edges */
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if (cloth->numfaces == 0) {
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#if 0
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ClothHairData *hairdata = clmd->hairdata;
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ClothHairData *hair_ij, *hair_kl;
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@ -508,6 +509,16 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListB
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BPH_mass_spring_force_edge_wind(data, spring->ij, spring->kl, hair_ij->radius, hair_kl->radius, winvec);
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}
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}
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#else
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ClothHairData *hairdata = clmd->hairdata;
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vert = cloth->verts;
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for (i = 0; i < cloth->numverts; i++, vert++) {
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ClothHairData *hair = &hairdata[i];
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BPH_mass_spring_force_vertex_wind(data, i, hair->radius, winvec);
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}
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#endif
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MEM_freeN(winvec);
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}
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@ -112,6 +112,8 @@ void BPH_mass_spring_force_extern(struct Implicit_Data *data, int i, const float
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void BPH_mass_spring_force_face_wind(struct Implicit_Data *data, int v1, int v2, int v3, int v4, const float (*winvec)[3]);
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/* Wind force, acting on an edge */
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void BPH_mass_spring_force_edge_wind(struct Implicit_Data *data, int v1, int v2, float radius1, float radius2, const float (*winvec)[3]);
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/* Wind force, acting on a vertex */
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void BPH_mass_spring_force_vertex_wind(struct Implicit_Data *data, int v, float radius, const float (*winvec)[3]);
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/* Linear spring force between two points */
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bool BPH_mass_spring_force_spring_linear(struct Implicit_Data *data, int i, int j, float restlen,
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float stiffness, float damping, bool no_compress, float clamp_force,
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@ -1493,11 +1493,22 @@ void BPH_mass_spring_force_edge_wind(Implicit_Data *data, int v1, int v2, float
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add_v3_v3(data->F[v1], f);
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world_to_root_v3(data, v2, win, winvec[v2]);
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/* use -length to invert edge direction */
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edge_wind_vertex(dir, length, radius2, win, f, dfdx, dfdv);
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add_v3_v3(data->F[v2], f);
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}
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void BPH_mass_spring_force_vertex_wind(Implicit_Data *data, int v, float UNUSED(radius), const float (*winvec)[3])
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{
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const float density = 0.01f; /* XXX arbitrary value, corresponds to effect of air density */
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float wind[3];
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float f[3];
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world_to_root_v3(data, v, wind, winvec[v]);
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mul_v3_v3fl(f, wind, density);
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add_v3_v3(data->F[v], f);
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}
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BLI_INLINE void dfdx_spring(float to[3][3], const float dir[3], float length, float L, float k)
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{
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// dir is unit length direction, rest is spring's restlength, k is spring constant.
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