Integrate hair collisions with cloth collision

This integrates hair collisions with the new cloth collision system,
greatly improving reliability, and reducing the amount of hair-specific
code paths in the cloth code.

The removes all the point constraint based collision stuff, instead
implementing segment impulse based collisions, using the same collision
response code as the normal cloth solver.

The hair system can now also collide with the emitter if it is a
collision object.

Reviewed By: mano-wii, Sebastian Parborg

Differential Revision: https://developer.blender.org/D6545

1 files changed, 10 insertions, 146 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 999cefde104..94eaffd1f91 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -83,7 +83,7 @@ static float cloth_calc_volume(ClothModifierData *clmd)
   float vol = 0;
 
   if (clmd->sim_parms->vgroup_pressure > 0) {
-    for (unsigned int i = 0; i < cloth->tri_num; i++) {
+    for (unsigned int i = 0; i < cloth->primitive_num; i++) {
       bool skip_face = false;
       /* We have custom vertex weights for pressure. */
       const MVertTri *vt = &tri[i];
@@ -103,7 +103,7 @@ static float cloth_calc_volume(ClothModifierData *clmd)
     }
   }
   else {
-    for (unsigned int i = 0; i < cloth->tri_num; i++) {
+    for (unsigned int i = 0; i < cloth->primitive_num; i++) {
       const MVertTri *vt = &tri[i];
       vol += BPH_tri_tetra_volume_signed_6x(data, vt->tri[0], vt->tri[1], vt->tri[2]);
     }
@@ -174,96 +174,17 @@ void BKE_cloth_solver_set_volume(ClothModifierData *clmd)
   cloth->initial_mesh_volume = cloth_calc_volume(clmd);
 }
 
-static bool collision_response(ClothModifierData *clmd,
-                               CollisionModifierData *collmd,
-                               CollPair *collpair,
-                               float dt,
-                               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_get_epsilon(collmd->bvhtree);
-
-  float margin_distance = (float)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);
-
-    bounce = -v_nor_old * restitution;
-
-    repulse = -margin_distance / dt; /* base repulsion velocity in normal direction */
-    /* XXX this clamping factor is quite arbitrary ...
-     * not sure if there is a more scientific approach, but seems to give good results
-     */
-    CLAMP(repulse, 0.0f, 4.0f * bounce);
-
-    if (margin_distance < -epsilon2) {
-      mul_v3_v3fl(r_impulse, collpair->normal, max_ff(repulse, bounce) - v_nor_new);
-    }
-    else {
-      bounce = 0.0f;
-      mul_v3_v3fl(r_impulse, collpair->normal, repulse - v_nor_new);
-    }
-
-    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)
  */
-static void cloth_setup_constraints(ClothModifierData *clmd,
-                                    ColliderContacts *contacts,
-                                    int totcolliders,
-                                    float dt)
+static void cloth_setup_constraints(ClothModifierData *clmd)
 {
   Cloth *cloth = clmd->clothObject;
   Implicit_Data *data = cloth->implicit;
   ClothVertex *verts = cloth->verts;
   int mvert_num = cloth->mvert_num;
-  int i, j, v;
+  int v;
 
   const float ZERO[3] = {0.0f, 0.0f, 0.0f};
 
@@ -277,37 +198,6 @@ static void cloth_setup_constraints(ClothModifierData *clmd,
 
     verts[v].impulse_count = 0;
   }
-
-  for (i = 0; i < totcolliders; i++) {
-    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);
-      float restitution = 0.0f;
-      int v = collpair->face1;
-      float impulse[3];
-
-      /* pinned verts handled separately */
-      if (verts[v].flags & CLOTH_VERT_FLAG_PINNED) {
-        continue;
-      }
-
-      /* XXX cheap way of avoiding instability from multiple collisions in the same step
-       * this should eventually be supported ...
-       */
-      if (verts[v].impulse_count > 0) {
-        continue;
-      }
-
-      /* calculate collision response */
-      if (!collision_response(clmd, ct->collmd, collpair, dt, restitution, impulse)) {
-        continue;
-      }
-
-      BPH_mass_spring_add_constraint_ndof2(data, v, collpair->normal, impulse);
-      ++verts[v].impulse_count;
-    }
-  }
 }
 
 /* computes where the cloth would be if it were subject to perfectly stiff edges
@@ -691,7 +581,7 @@ static void cloth_calc_force(
 
     pressure_difference *= clmd->sim_parms->pressure_factor;
 
-    for (i = 0; i < cloth->tri_num; i++) {
+    for (i = 0; i < cloth->primitive_num; i++) {
       const MVertTri *vt = &tri[i];
       if (fabs(pressure_difference) > 1E-6f) {
         if (clmd->sim_parms->vgroup_pressure > 0) {
@@ -744,13 +634,13 @@ static void cloth_calc_force(
           effectors, NULL, clmd->sim_parms->effector_weights, &epoint, winvec[i], NULL);
     }
 
-    for (i = 0; i < cloth->tri_num; i++) {
+    for (i = 0; i < cloth->primitive_num; i++) {
       const MVertTri *vt = &tri[i];
       BPH_mass_spring_force_face_wind(data, vt->tri[0], vt->tri[1], vt->tri[2], winvec);
     }
 
     /* Hair has only edges */
-    if (cloth->tri_num == 0) {
+    if (cloth->primitive_num == 0) {
 #if 0
       ClothHairData *hairdata = clmd->hairdata;
       ClothHairData *hair_ij, *hair_kl;
@@ -1241,8 +1131,6 @@ int BPH_cloth_solve(
   unsigned int mvert_num = cloth->mvert_num;
   float dt = clmd->sim_parms->dt * clmd->sim_parms->timescale;
   Implicit_Data *id = cloth->implicit;
-  ColliderContacts *contacts = NULL;
-  int totcolliders = 0;
 
   BKE_sim_debug_data_clear_category("collision");
 
@@ -1269,25 +1157,8 @@ int BPH_cloth_solve(
   while (step < tf) {
     ImplicitSolverResult result;
 
-    if (is_hair) {
-      /* copy velocities for collision */
-      for (i = 0; i < mvert_num; i++) {
-        BPH_mass_spring_get_motion_state(id, i, NULL, verts[i].tv);
-        copy_v3_v3(verts[i].v, verts[i].tv);
-      }
-
-      /* determine contact points */
-      if (clmd->coll_parms->flags & CLOTH_COLLSETTINGS_FLAG_ENABLED) {
-        cloth_find_point_contacts(depsgraph, ob, clmd, 0.0f, tf, &contacts, &totcolliders);
-      }
-
-      /* setup vertex constraints for pinned vertices and contacts */
-      cloth_setup_constraints(clmd, contacts, totcolliders, dt);
-    }
-    else {
-      /* setup vertex constraints for pinned vertices */
-      cloth_setup_constraints(clmd, NULL, 0, dt);
-    }
+    /* setup vertex constraints for pinned vertices */
+    cloth_setup_constraints(clmd);
 
     /* initialize forces to zero */
     BPH_mass_spring_clear_forces(id);
@@ -1300,9 +1171,7 @@ int BPH_cloth_solve(
     cloth_record_result(clmd, &result, dt);
 
     /* Calculate collision impulses. */
-    if (!is_hair) {
-      cloth_solve_collisions(depsgraph, ob, clmd, step, dt);
-    }
+    cloth_solve_collisions(depsgraph, ob, clmd, step, dt);
 
     if (is_hair) {
       cloth_continuum_step(clmd, dt);
@@ -1327,11 +1196,6 @@ int BPH_cloth_solve(
       BPH_mass_spring_get_motion_state(id, i, verts[i].txold, NULL);
     }
 
-    /* free contact points */
-    if (contacts) {
-      cloth_free_contacts(contacts, totcolliders);
-    }
-
     step += dt;
   }