Calculate bending targets based on the direction of previous segments.

This makes the bending a truely local effect. Eventually target
directions should be based in a local coordinate frame that gets
parallel transported along the curve. This will allow non-straight
rest shapes for hairs as well as supporting twist forces. However,
calculating locally transformed spring forces is more complicated.

4 files changed, 20 insertions, 22 deletions

diff --git a/source/blender/blenkernel/intern/cloth.c b/source/blender/blenkernel/intern/cloth.c
index 1b3b668f524..284107ee4e8 100644
--- a/source/blender/blenkernel/intern/cloth.c
+++ b/source/blender/blenkernel/intern/cloth.c
@@ -1302,9 +1302,9 @@ static int cloth_build_springs ( ClothModifierData *clmd, DerivedMesh *dm )
 						return 0;
 					}
 					
-					spring->ij = tspring->kl;
+					spring->ij = tspring2->ij;
 					spring->kl = tspring->ij;
-					spring->mn = tspring2->ij;
+					spring->mn = tspring->kl;
 					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;
diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 2700f4a0f6d..6a64e17aee2 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -394,7 +394,7 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
 		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);
+		BPH_mass_spring_force_spring_bending_angular(data, s->ij, s->kl, s->mn, s->matrix_index, s->restlen, kb, cb, s->f, s->dfdx, s->dfdv);
 #endif
 	}
 }
diff --git a/source/blender/physics/intern/implicit.h b/source/blender/physics/intern/implicit.h
index ac2c942379b..b11bc5d18a9 100644
--- a/source/blender/physics/intern/implicit.h
+++ b/source/blender/physics/intern/implicit.h
@@ -144,7 +144,7 @@ bool BPH_mass_spring_force_spring_bending(struct Implicit_Data *data, int i, int
                                           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,
+bool BPH_mass_spring_force_spring_bending_angular(struct Implicit_Data *data, int i, int j, int k, 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 */
diff --git a/source/blender/physics/intern/implicit_blender.c b/source/blender/physics/intern/implicit_blender.c
index 84db552d2ff..425dcf9a384 100644
--- a/source/blender/physics/intern/implicit_blender.c
+++ b/source/blender/physics/intern/implicit_blender.c
@@ -1619,28 +1619,32 @@ 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,
+bool BPH_mass_spring_force_spring_bending_angular(Implicit_Data *data, int i, int j, int k, 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], targetdir[3];
-	float extent[3], dir[3], length;
+	float extent[3], dir[3];
 	float dist[3], vel[3];
 	float f[3], dfdx[3][3], dfdv[3][3];
 	
-	target[0] = 0.0f;
-	target[1] = 0.0f;
-	target[2] = restlen;
+	sub_v3_v3v3(targetdir, data->X[j], data->X[i]);
+	normalize_v3(targetdir);
+	mul_v3_v3fl(target, targetdir, restlen);
+	{
+		float x[3], d[3];
+		root_to_world_v3(data, j, x, data->X[j]);
+		root_to_world_v3(data, j, d, target);
+		BKE_sim_debug_data_add_vector(data->debug_data, x, d, 1, 0, 0, "spoint", hash_vertex(935, j));
+	}
 	
 	// 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 = normalize_v3_v3(dir, extent);
-	normalize_v3_v3(targetdir, target);
+	sub_v3_v3v3(extent, data->X[k], data->X[j]);
+	sub_v3_v3v3(vel, data->V[k], data->V[j]);
+	normalize_v3_v3(dir, extent);
 	
 	sub_v3_v3v3(dist, target, extent);
-	mul_v3_v3fl(f, dist, stiffness);
+	mul_v3_v3fl(f, dist, -stiffness);
 	
 	madd_v3_v3fl(vel, dir, -dot_v3v3(vel, dir));
 	madd_v3_v3fl(f, vel, damping);
@@ -1648,13 +1652,7 @@ bool BPH_mass_spring_force_spring_bending_angular(Implicit_Data *data, int i, in
 	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);
+	apply_spring(data, j, k, spring_index, f, dfdx, dfdv);
 	
 	if (r_f) copy_v3_v3(r_f, f);
 	if (r_dfdx) copy_m3_m3(r_dfdx, dfdx);