Moved collision response into the main cloth sim source file and fixed

some coordinate transform issues.

Collision response should be regarded as part of the dynamics system
instead of the basic collision detection.

1 files changed, 75 insertions, 14 deletions

diff --git a/source/blender/blenkernel/intern/implicit.c b/source/blender/blenkernel/intern/implicit.c
index 68aaab09576..f60a0ccac82 100644
--- a/source/blender/blenkernel/intern/implicit.c
+++ b/source/blender/blenkernel/intern/implicit.c
@@ -2090,6 +2090,74 @@ bool implicit_hair_volume_get_texture_data(Object *UNUSED(ob), ClothModifierData
 
 /* ================================ */
 
+static bool collision_response(ClothModifierData *clmd, CollisionModifierData *collmd, CollPair *collpair, float restitution, float r_impulse[3])
+{
+	Cloth *cloth = clmd->clothObject;
+	int index = collpair->ap1;
+	bool result = false;
+	
+	float v1[3], v2_old[3], v2_new[3], v_rel_old[3], v_rel_new[3];
+	float epsilon2 = BLI_bvhtree_getepsilon(collmd->bvhtree);
+
+	float margin_distance = collpair->distance - epsilon2;
+	float mag_v_rel;
+	
+	zero_v3(r_impulse);
+	
+	if (margin_distance > 0.0f)
+		return false; /* XXX tested before already? */
+	
+	/* only handle static collisions here */
+	if ( collpair->flag & COLLISION_IN_FUTURE )
+		return false;
+	
+	/* velocity */
+	copy_v3_v3(v1, cloth->verts[index].v);
+	collision_get_collider_velocity(v2_old, v2_new, collmd, collpair);
+	/* relative velocity = velocity of the cloth point relative to the collider */
+	sub_v3_v3v3(v_rel_old, v1, v2_old);
+	sub_v3_v3v3(v_rel_new, v1, v2_new);
+	/* normal component of the relative velocity */
+	mag_v_rel = dot_v3v3(v_rel_old, collpair->normal);
+	
+	/* only valid when moving toward the collider */
+	if (mag_v_rel < -ALMOST_ZERO) {
+		float v_nor_old, v_nor_new;
+		float v_tan_old[3], v_tan_new[3];
+		float bounce, repulse;
+		
+		/* Collision response based on
+		 * "Simulating Complex Hair with Robust Collision Handling" (Choe, Choi, Ko, ACM SIGGRAPH 2005)
+		 * http://graphics.snu.ac.kr/publications/2005-choe-HairSim/Choe_2005_SCA.pdf
+		 */
+		
+		v_nor_old = mag_v_rel;
+		v_nor_new = dot_v3v3(v_rel_new, collpair->normal);
+		
+		madd_v3_v3v3fl(v_tan_old, v_rel_old, collpair->normal, -v_nor_old);
+		madd_v3_v3v3fl(v_tan_new, v_rel_new, collpair->normal, -v_nor_new);
+		
+		/* TODO repulsion forces can easily destabilize the system,
+		 * have to clamp them or construct a linear spring instead
+		 */
+//		repulse = -margin_distance / dt + dot_v3v3(v1, collpair->normal);
+		repulse = 0.0f;
+		
+		if (margin_distance < -epsilon2) {
+			bounce = -(v_nor_new + v_nor_old * restitution);
+			mul_v3_v3fl(r_impulse, collpair->normal, max_ff(repulse, bounce));
+		}
+		else {
+			bounce = 0.0f;
+			mul_v3_v3fl(r_impulse, collpair->normal, repulse);
+		}
+		
+		result = true;
+	}
+	
+	return result;
+}
+
 /* Init constraint matrix
  * This is part of the modified CG method suggested by Baraff/Witkin in
  * "Large Steps in Cloth Simulation" (Siggraph 1998)
@@ -2120,8 +2188,9 @@ static void setup_constraint_matrix(ClothModifierData *clmd, ColliderContacts *c
 		ColliderContacts *ct = &contacts[i];
 		for (j = 0; j < ct->totcollisions; ++j) {
 			CollPair *collpair = &ct->collisions[j];
+			float restitution = (1.0f - clmd->coll_parms->damping) * (1.0f - ct->ob->pd->pdef_sbdamp);
 			int v = collpair->face1;
-			float cmat[3][3];
+			float cnor[3], cmat[3][3];
 			float impulse[3];
 			
 			/* pinned verts handled separately */
@@ -2129,13 +2198,16 @@ static void setup_constraint_matrix(ClothModifierData *clmd, ColliderContacts *c
 				continue;
 			
 			/* calculate collision response */
-			if (!cloth_points_collpair_response(clmd, ct->collmd, ct->ob->pd, collpair, dt, impulse))
+			if (!collision_response(clmd, ct->collmd, collpair, restitution, impulse))
 				continue;
 			
+			vel_world_to_root(impulse, X[v], impulse, &roots[v]);
 			add_v3_v3(z[v], impulse);
 			
 			/* modify S to enforce velocity constraint in normal direction */
-			mul_fvectorT_fvector(cmat, collpair->normal, collpair->normal);
+			copy_v3_v3(cnor, collpair->normal);
+			mul_transposed_m3_v3(roots[v].rot, cnor);
+			mul_fvectorT_fvector(cmat, cnor, cnor);
 			sub_m3_m3m3(S[v].m, I, cmat);
 			
 			BKE_sim_debug_data_add_dot(clmd->debug_data, collpair->pa, 0, 1, 0, "collision", hash_collpair(936, collpair));
@@ -2151,17 +2223,6 @@ static void setup_constraint_matrix(ClothModifierData *clmd, ColliderContacts *c
 			}
 		}
 	}
-	
-	/* transform to root space */
-	for (v = 0; v < numverts; v++) {
-		float t[3][3];
-		copy_m3_m3(t, roots[v].rot);
-		transpose_m3(t);
-		mul_m3_m3m3(S[v].m, S[v].m, roots[v].rot);
-		mul_m3_m3m3(S[v].m, t, S[v].m);
-		
-		vel_world_to_root(z[v], X[v], z[v], &roots[v]);
-	}
 }
 
 static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), lfVector *lF, lfVector *lX, lfVector *lV, fmatrix3x3 *dFdV, fmatrix3x3 *dFdX, ListBase *effectors, float time, fmatrix3x3 *M)