Cloth: allow forces to act parallel to cloth.

Currently all force effectors can only act on cloth when the force is
perpendicular to the surface. This makes sense for wind, but not for
other forces; and the user may want even wind to have some friction.

This changes effector code to output two force vectors - although
you of course can pass the same pointer for both. The force is split
between the two outputs based on a new per-effector setting.

Differential Revision: https://developer.blender.org/D8017

9 files changed, 40 insertions, 23 deletions

diff --git a/source/blender/blenkernel/BKE_effect.h b/source/blender/blenkernel/BKE_effect.h
index 6935b3aecce..0518ce8ffa3 100644
--- a/source/blender/blenkernel/BKE_effect.h
+++ b/source/blender/blenkernel/BKE_effect.h
@@ -130,6 +130,7 @@ void BKE_effectors_apply(struct ListBase *effectors,
                          struct EffectorWeights *weights,
                          struct EffectedPoint *point,
                          float *force,
+                         float *wind_force,
                          float *impulse);
 void BKE_effectors_free(struct ListBase *lb);
 
diff --git a/source/blender/blenkernel/intern/boids.c b/source/blender/blenkernel/intern/boids.c
index 639437f8251..d5064629451 100644
--- a/source/blender/blenkernel/intern/boids.c
+++ b/source/blender/blenkernel/intern/boids.c
@@ -1388,6 +1388,7 @@ void boid_body(BoidBrainData *bbd, ParticleData *pa)
                       bbd->part->effector_weights,
                       &epoint,
                       force,
+                      NULL,
                       NULL);
 
   if (ELEM(bpa->data.mode, eBoidMode_OnLand, eBoidMode_Climbing)) {
diff --git a/source/blender/blenkernel/intern/dynamicpaint.c b/source/blender/blenkernel/intern/dynamicpaint.c
index dae8a59fe43..2e1fa519284 100644
--- a/source/blender/blenkernel/intern/dynamicpaint.c
+++ b/source/blender/blenkernel/intern/dynamicpaint.c
@@ -5112,7 +5112,7 @@ static void dynamic_paint_prepare_effect_cb(void *__restrict userdata,
     EffectedPoint epoint;
     pd_point_from_loc(scene, realCoord[bData->s_pos[index]].v, vel, index, &epoint);
     epoint.vel_to_sec = 1.0f;
-    BKE_effectors_apply(effectors, NULL, surface->effector_weights, &epoint, forc, NULL);
+    BKE_effectors_apply(effectors, NULL, surface->effector_weights, &epoint, forc, NULL, NULL);
   }
 
   /* if global gravity is enabled, add it too */
diff --git a/source/blender/blenkernel/intern/effect.c b/source/blender/blenkernel/intern/effect.c
index 7ed04c6976a..235c834fde9 100644
--- a/source/blender/blenkernel/intern/effect.c
+++ b/source/blender/blenkernel/intern/effect.c
@@ -108,7 +108,8 @@ PartDeflect *BKE_partdeflect_new(int type)
       break;
     case PFIELD_WIND:
       pd->shape = PFIELD_SHAPE_PLANE;
-      pd->f_flow = 1.0f; /* realistic wind behavior */
+      pd->f_flow = 1.0f;        /* realistic wind behavior */
+      pd->f_wind_factor = 1.0f; /* only act perpendicularly to a surface */
       break;
     case PFIELD_TEXTURE:
       pd->f_size = 1.0f;
@@ -1072,7 +1073,8 @@ static void do_physical_effector(EffectorCache *eff,
  * scene       = scene where it runs in, for time and stuff
  * lb           = listbase with objects that take part in effecting
  * opco     = global coord, as input
- * force        = force accumulator
+ * force        = accumulator for force
+ * wind_force   = accumulator for force only acting perpendicular to a surface
  * speed        = actual current speed which can be altered
  * cur_time = "external" time in frames, is constant for static particles
  * loc_time = "local" time in frames, range <0-1> for the lifetime of particle
@@ -1085,6 +1087,7 @@ void BKE_effectors_apply(ListBase *effectors,
                          EffectorWeights *weights,
                          EffectedPoint *point,
                          float *force,
+                         float *wind_force,
                          float *impulse)
 {
   /*
@@ -1120,22 +1123,27 @@ void BKE_effectors_apply(ListBase *effectors,
           if (efd.falloff > 0.0f) {
             efd.falloff *= eff_calc_visibility(colliders, eff, &efd, point);
           }
-          if (efd.falloff <= 0.0f) {
-            /* don't do anything */
-          }
-          else if (eff->pd->forcefield == PFIELD_TEXTURE) {
-            do_texture_effector(eff, &efd, point, force);
-          }
-          else {
-            float temp1[3] = {0, 0, 0}, temp2[3];
-            copy_v3_v3(temp1, force);
+          if (efd.falloff > 0.0f) {
+            float out_force[3] = {0, 0, 0};
 
-            do_physical_effector(eff, &efd, point, force);
+            if (eff->pd->forcefield == PFIELD_TEXTURE) {
+              do_texture_effector(eff, &efd, point, out_force);
+            }
+            else {
+              do_physical_effector(eff, &efd, point, out_force);
 
-            /* for softbody backward compatibility */
-            if (point->flag & PE_WIND_AS_SPEED && impulse) {
-              sub_v3_v3v3(temp2, force, temp1);
-              sub_v3_v3v3(impulse, impulse, temp2);
+              /* for softbody backward compatibility */
+              if (point->flag & PE_WIND_AS_SPEED && impulse) {
+                sub_v3_v3v3(impulse, impulse, out_force);
+              }
+            }
+
+            if (wind_force) {
+              madd_v3_v3fl(force, out_force, 1.0f - eff->pd->f_wind_factor);
+              madd_v3_v3fl(wind_force, out_force, eff->pd->f_wind_factor);
+            }
+            else {
+              add_v3_v3(force, out_force);
             }
           }
         }
diff --git a/source/blender/blenkernel/intern/fluid.c b/source/blender/blenkernel/intern/fluid.c
index b75592836e0..521210e7bb5 100644
--- a/source/blender/blenkernel/intern/fluid.c
+++ b/source/blender/blenkernel/intern/fluid.c
@@ -3175,7 +3175,7 @@ static void update_effectors_task_cb(void *__restrict userdata,
 
       /* do effectors */
       pd_point_from_loc(data->scene, voxel_center, vel, index, &epoint);
-      BKE_effectors_apply(data->effectors, NULL, mds->effector_weights, &epoint, retvel, NULL);
+      BKE_effectors_apply(data->effectors, NULL, mds->effector_weights, &epoint, retvel, NULL, NULL);
 
       /* convert retvel to local space */
       mag = len_v3(retvel);
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index c201cb83c44..94b677c649c 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -2262,6 +2262,7 @@ static void do_path_effectors(ParticleSimulationData *sim,
                       sim->psys->part->effector_weights,
                       &epoint,
                       force,
+                      NULL,
                       NULL);
 
   mul_v3_fl(force,
diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 606291a9ae0..d09f9a8eb09 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -2243,8 +2243,13 @@ static void basic_force_cb(void *efdata_v, ParticleKey *state, float *force, flo
   /* add effectors */
   pd_point_from_particle(efdata->sim, efdata->pa, state, &epoint);
   if (part->type != PART_HAIR || part->effector_weights->flag & EFF_WEIGHT_DO_HAIR) {
-    BKE_effectors_apply(
-        sim->psys->effectors, sim->colliders, part->effector_weights, &epoint, force, impulse);
+    BKE_effectors_apply(sim->psys->effectors,
+                        sim->colliders,
+                        part->effector_weights,
+                        &epoint,
+                        force,
+                        NULL,
+                        impulse);
   }
 
   mul_v3_fl(force, efdata->ptex.field);
diff --git a/source/blender/blenkernel/intern/rigidbody.c b/source/blender/blenkernel/intern/rigidbody.c
index 02ce0c6f996..4752782eaeb 100644
--- a/source/blender/blenkernel/intern/rigidbody.c
+++ b/source/blender/blenkernel/intern/rigidbody.c
@@ -1647,7 +1647,7 @@ static void rigidbody_update_sim_ob(
       /* Calculate net force of effectors, and apply to sim object:
        * - we use 'central force' since apply force requires a "relative position"
        *   which we don't have... */
-      BKE_effectors_apply(effectors, NULL, effector_weights, &epoint, eff_force, NULL);
+      BKE_effectors_apply(effectors, NULL, effector_weights, &epoint, eff_force, NULL, NULL);
       if (G.f & G_DEBUG) {
         printf("\tapplying force (%f,%f,%f) to '%s'\n",
                eff_force[0],
diff --git a/source/blender/blenkernel/intern/softbody.c b/source/blender/blenkernel/intern/softbody.c
index 68d0822a223..9c7abbdf876 100644
--- a/source/blender/blenkernel/intern/softbody.c
+++ b/source/blender/blenkernel/intern/softbody.c
@@ -1479,7 +1479,8 @@ static void _scan_for_ext_spring_forces(
             mid_v3_v3v3(pos, sb->bpoint[bs->v1].pos, sb->bpoint[bs->v2].pos);
             mid_v3_v3v3(vel, sb->bpoint[bs->v1].vec, sb->bpoint[bs->v2].vec);
             pd_point_from_soft(scene, pos, vel, -1, &epoint);
-            BKE_effectors_apply(effectors, NULL, sb->effector_weights, &epoint, force, speed);
+            BKE_effectors_apply(
+                effectors, NULL, sb->effector_weights, &epoint, force, NULL, speed);
 
             mul_v3_fl(speed, windfactor);
             add_v3_v3(vel, speed);
@@ -2107,7 +2108,7 @@ static int _softbody_calc_forces_slice_in_a_thread(Scene *scene,
         float eval_sb_fric_force_scale = sb_fric_force_scale(ob);
 
         pd_point_from_soft(scene, bp->pos, bp->vec, sb->bpoint - bp, &epoint);
-        BKE_effectors_apply(effectors, NULL, sb->effector_weights, &epoint, force, speed);
+        BKE_effectors_apply(effectors, NULL, sb->effector_weights, &epoint, force, NULL, speed);
 
         /* apply forcefield*/
         mul_v3_fl(force, fieldfactor * eval_sb_fric_force_scale);