Cloth refactor: Remove goal springs and some other cleanup

This removes the goal springs, in favor of simply calculating the goal forces on the vertices directly. The vertices already store all the necessary data for the goal forces, thus the springs were redundant, and just defined both ends as being the same vertex.

The main advantage of removing the goal springs, is an increase in flexibility, allowing us to much more nicely do some neat dynamic stuff with the goals/pins, such as animated vertex weights. But this also has the advantage of simpler code, and a slightly reduced memory footprint.

This also removes the `f`, `dfdx` and `dfdv` fields from the `ClothSpring` struct, as that data is only used by the solver, and is re-computed on each step, and thus does not need to be stored throughout the simulation.

Reviewers: sergey

Reviewed By: sergey

Tags: #physics

Differential Revision: https://developer.blender.org/D2514

1 files changed, 22 insertions, 29 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 359395b63c4..b694b6e994d 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -333,19 +333,14 @@ 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)
+BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s)
 {
 	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
@@ -361,31 +356,13 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
 		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->restlen, k, parms->Cdis, no_compress, parms->max_sewing, s->f, s->dfdx, s->dfdv);
+			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen, k, parms->Cdis, no_compress, parms->max_sewing);
 		}
 		else {
-			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen, k, parms->Cdis, no_compress, 0.0f, s->f, s->dfdx, s->dfdv);
+			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen, k, parms->Cdis, no_compress, 0.0f);
 		}
 #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)
-		/* divide by time_scale to prevent goal vertices' delta locations from being multiplied */
-		interp_v3_v3v3(goal_x, verts[s->ij].xold, verts[s->ij].xconst, time / parms->time_scale);
-		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, goal_x, goal_v, k, parms->goalfrict * 0.01f, s->f, s->dfdx, s->dfdv);
-#endif
-	}
 	else if (s->type & CLOTH_SPRING_TYPE_BENDING) {  /* calculate force of bending springs */
 #ifdef CLOTH_FORCE_SPRING_BEND
 		float kb, cb, scaling;
@@ -398,7 +375,7 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
 		// Fix for [#45084] for cloth stiffness must have cb proportional to kb
 		cb = kb * parms->bending_damping;
 		
-		BPH_mass_spring_force_spring_bending(data, s->ij, s->kl, s->restlen, kb, cb, s->f, s->dfdx, s->dfdv);
+		BPH_mass_spring_force_spring_bending(data, s->ij, s->kl, s->restlen, kb, cb);
 #endif
 	}
 	else if (s->type & CLOTH_SPRING_TYPE_BENDING_ANG) {
@@ -474,9 +451,24 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListB
 		/* scale gravity force */
 		mul_v3_v3fl(gravity, clmd->scene->physics_settings.gravity, 0.001f * clmd->sim_parms->effector_weights->global_gravity);
 	}
+
 	vert = cloth->verts;
 	for (i = 0; i < cloth->mvert_num; i++, vert++) {
 		BPH_mass_spring_force_gravity(data, i, vert->mass, gravity);
+
+		/* Vertex goal springs */
+		if ((!(vert->flags & CLOTH_VERT_FLAG_PINNED)) && (vert->goal > FLT_EPSILON)) {
+			float goal_x[3], goal_v[3];
+			float k;
+
+			/* divide by time_scale to prevent goal vertices' delta locations from being multiplied */
+			interp_v3_v3v3(goal_x, vert->xold, vert->xconst, time / clmd->sim_parms->time_scale);
+			sub_v3_v3v3(goal_v, vert->xconst, vert->xold); /* distance covered over dt==1 */
+
+			k = vert->goal * clmd->sim_parms->goalspring / (clmd->sim_parms->avg_spring_len + FLT_EPSILON);
+
+			BPH_mass_spring_force_spring_goal(data, i, goal_x, goal_v, k, clmd->sim_parms->goalfrict * 0.01f);
+		}
 	}
 #endif
 
@@ -544,8 +536,9 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), ListB
 	for (LinkNode *link = cloth->springs; link; link = link->next) {
 		ClothSpring *spring = (ClothSpring *)link->link;
 		// only handle active springs
-		if (!(spring->flags & CLOTH_SPRING_FLAG_DEACTIVATE))
-			cloth_calc_spring_force(clmd, spring, time);
+		if (!(spring->flags & CLOTH_SPRING_FLAG_DEACTIVATE)) {
+			cloth_calc_spring_force(clmd, spring);
+		}
 	}
 }