Added back spring force definitions outside the implicit solver.

There are currently 3 types of springs: basic linear springs, goal
springs toward a fixed global target (not recommended, but works) and
bending springs.

These are agnostic to the specific spring definition in the cloth system
so hair systems can use the same API without converting everything to
cloth first.

Conflicts:
	source/blender/physics/intern/implicit_blender.c

1 files changed, 69 insertions, 19 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index abff8f9296e..974fe67011c 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -320,6 +320,72 @@ static int UNUSED_FUNCTION(cloth_calc_helper_forces)(Object *UNUSED(ob), ClothMo
 	return 1;
 }
 
+BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s, float time)
+{
+	Cloth *cloth = clmd->clothObject;
+	ClothSimSettings *parms = clmd->sim_parms;
+	Implicit_Data *data = cloth->implicit;
+	ClothVertex *verts = cloth->verts;
+	
+	bool no_compress = parms->flags & CLOTH_SIMSETTINGS_FLAG_NO_SPRING_COMPRESS;
+	
+	zero_v3(s->f);
+	zero_m3(s->dfdx);
+	zero_m3(s->dfdv);
+	
+	s->flags &= ~CLOTH_SPRING_FLAG_NEEDED;
+	
+	// calculate force of structural + shear springs
+	if ((s->type & CLOTH_SPRING_TYPE_STRUCTURAL) || (s->type & CLOTH_SPRING_TYPE_SHEAR) || (s->type & CLOTH_SPRING_TYPE_SEWING) ) {
+#ifdef CLOTH_FORCE_SPRING_STRUCTURAL
+		float k, scaling;
+		
+		s->flags |= CLOTH_SPRING_FLAG_NEEDED;
+		
+		scaling = parms->structural + s->stiffness * fabsf(parms->max_struct - parms->structural);
+		k = scaling / (parms->avg_spring_len + FLT_EPSILON);
+		
+		if (s->type & CLOTH_SPRING_TYPE_SEWING) {
+			// TODO: verify, half verified (couldn't see error)
+			// sewing springs usually have a large distance at first so clamp the force so we don't get tunnelling through colission objects
+			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->matrix_index, s->restlen, k, parms->Cdis, no_compress, parms->max_sewing, s->f, s->dfdx, s->dfdv);
+		}
+		else {
+			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->matrix_index, s->restlen, k, parms->Cdis, no_compress, 0.0f, s->f, s->dfdx, s->dfdv);
+		}
+#endif
+	}
+	else if (s->type & CLOTH_SPRING_TYPE_GOAL) {
+#ifdef CLOTH_FORCE_SPRING_GOAL
+		float goal_x[3], goal_v[3];
+		float k, scaling;
+		
+		s->flags |= CLOTH_SPRING_FLAG_NEEDED;
+		
+		// current_position = xold + t * (newposition - xold)
+		interp_v3_v3v3(goal_x, verts[s->ij].xold, verts[s->ij].xconst, time);
+		sub_v3_v3v3(goal_v, verts[s->ij].xconst, verts[s->ij].xold); // distance covered over dt==1
+		
+		scaling = parms->goalspring + s->stiffness * fabsf(parms->max_struct - parms->goalspring);
+		k = verts[s->ij].goal * scaling / (parms->avg_spring_len + FLT_EPSILON);
+		
+		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 */
+#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(data, s->ij, s->kl, s->matrix_index, s->restlen, kb, cb, s->f, s->dfdx, s->dfdv);
+#endif
+	}
+}
+
 static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListBase *effectors, float time)
 {
 	/* Collect forces and derivatives:  F, dFdX, dFdV */
@@ -382,29 +448,13 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListB
 		MEM_freeN(winvec);
 	}
 	
-#if 0
 	// calculate spring forces
-	link = cloth->springs;
-	while (link) {
-		// only handle active springs
-		ClothSpring *spring = link->link;
-		if (!(spring->flags & CLOTH_SPRING_FLAG_DEACTIVATE))
-			cloth_calc_spring_force(clmd, link->link, lF, lX, lV, dFdV, dFdX, time);
-
-		link = link->next;
-	}
-	
-	// apply spring forces
-	link = cloth->springs;
-	while (link) {
+	for (LinkNode *link = cloth->springs; link; link = link->next) {
+		ClothSpring *spring = (ClothSpring *)link->link;
 		// only handle active springs
-		ClothSpring *spring = link->link;
 		if (!(spring->flags & CLOTH_SPRING_FLAG_DEACTIVATE))
-			cloth_apply_spring_force(clmd, link->link, lF, lX, lV, dFdV, dFdX);
-		link = link->next;
+			cloth_calc_spring_force(clmd, spring, time);
 	}
-	// printf("\n");
-#endif
 }
 
 int BPH_cloth_solve(Object *ob, float frame, ClothModifierData *clmd, ListBase *effectors)