Cloth: Componentize forces

This separates cloth stiffness and damping forces into tension,
compression, and shearing components, allowing more control over the
cloth behaviour.

This also adds a bending model selector (although the new bending model
itself is not implemented in this commit). This is because some of the
features implemented here only make sense within the new bending model,
while the old model is kept for compatibility.

This commit makes non-breaking changes, and thus maintains full
compatibility with existing simulations.

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D3655

1 files changed, 30 insertions, 8 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 2f24231f992..668e40e71cc 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -341,31 +341,53 @@ 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;
-
-	bool no_compress = parms->flags & CLOTH_SIMSETTINGS_FLAG_NO_SPRING_COMPRESS;
+	bool new_compress = parms->bending_model == CLOTH_BENDING_ANGULAR;
+	bool resist_compress = (parms->flags & CLOTH_SIMSETTINGS_FLAG_RESIST_SPRING_COMPRESS) && !new_compress;
 
 	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) ) {
+	if ((s->type & CLOTH_SPRING_TYPE_STRUCTURAL) || (s->type & CLOTH_SPRING_TYPE_SEWING)) {
 #ifdef CLOTH_FORCE_SPRING_STRUCTURAL
-		float k, scaling;
+		float k_tension, scaling_tension;
 
 		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);
+		scaling_tension = parms->tension + s->stiffness * fabsf(parms->max_tension - parms->tension);
+		k_tension = scaling_tension / (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->restlen, k, parms->Cdis, no_compress, parms->max_sewing);
+			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen,
+			                                    k_tension, parms->tension_damp,
+			                                    0.0f, 0.0f, false, false, parms->max_sewing);
 		}
 		else {
-			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen, k, parms->Cdis, no_compress, 0.0f);
+			float k_compression, scaling_compression;
+			scaling_compression = parms->compression + s->stiffness * fabsf(parms->max_compression - parms->compression);
+			k_compression = scaling_compression / (parms->avg_spring_len + FLT_EPSILON);
+
+			BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen,
+			                                    k_tension, parms->tension_damp,
+			                                    k_compression, parms->compression_damp,
+			                                    resist_compress, new_compress, 0.0f);
 		}
 #endif
 	}
+	else if (s->type & CLOTH_SPRING_TYPE_SHEAR) {
+#ifdef CLOTH_FORCE_SPRING_SHEAR
+		float k, scaling;
+
+		s->flags |= CLOTH_SPRING_FLAG_NEEDED;
+
+		scaling = parms->shear + s->stiffness * fabsf(parms->max_shear - parms->shear);
+		k = scaling / (parms->avg_spring_len + FLT_EPSILON);
+
+		BPH_mass_spring_force_spring_linear(data, s->ij, s->kl, s->restlen, k, parms->shear_damp,
+		                                    0.0f, 0.0f, resist_compress, false, 0.0f);
+#endif
+	}
 	else if (s->type & CLOTH_SPRING_TYPE_BENDING) {  /* calculate force of bending springs */
 #ifdef CLOTH_FORCE_SPRING_BEND
 		float kb, cb, scaling;