Sculpt: Cloth Brush Soft Body Influence property

This property adds constraints to the simulation using the initial
location of the vertices, making it behave like a soft body. The
strength of these constraints can be modified with the brush parameter.
This makes some deformation modes more subtle and predictable, making it
possible to use the cloth brush to add surface detail in a more
controllable way without loosing completely the original shape of the
mesh.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7845

1 files changed, 62 insertions, 16 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt_cloth.c b/source/blender/editors/sculpt_paint/sculpt_cloth.c
index 4232be91034..91293b78dae 100644
--- a/source/blender/editors/sculpt_paint/sculpt_cloth.c
+++ b/source/blender/editors/sculpt_paint/sculpt_cloth.c
@@ -113,36 +113,71 @@ static bool cloth_brush_sim_has_length_constraint(SculptClothSimulation *cloth_s
   return BLI_edgeset_haskey(cloth_sim->created_length_constraints, v1, v2);
 }
 
+static void cloth_brush_reallocate_constraints(SculptClothSimulation *cloth_sim)
+{
+  if (cloth_sim->tot_length_constraints >= cloth_sim->capacity_length_constraints) {
+    cloth_sim->capacity_length_constraints += CLOTH_LENGTH_CONSTRAINTS_BLOCK;
+    cloth_sim->length_constraints = MEM_reallocN_id(cloth_sim->length_constraints,
+                                                    cloth_sim->capacity_length_constraints *
+                                                        sizeof(SculptClothLengthConstraint),
+                                                    "length constraints");
+  }
+}
+
 static void cloth_brush_add_length_constraint(SculptSession *ss,
                                               SculptClothSimulation *cloth_sim,
                                               const int v1,
                                               const int v2)
 {
-  cloth_sim->length_constraints[cloth_sim->tot_length_constraints].v1 = v1;
-  cloth_sim->length_constraints[cloth_sim->tot_length_constraints].v2 = v2;
-  cloth_sim->length_constraints[cloth_sim->tot_length_constraints].length = len_v3v3(
-      SCULPT_vertex_co_get(ss, v1), SCULPT_vertex_co_get(ss, v2));
+  SculptClothLengthConstraint *length_constraint =
+      &cloth_sim->length_constraints[cloth_sim->tot_length_constraints];
+
+  length_constraint->elem_index_a = v1;
+  length_constraint->elem_index_b = v2;
+
+  length_constraint->elem_position_a = cloth_sim->pos[v1];
+  length_constraint->elem_position_b = cloth_sim->pos[v2];
+
+  length_constraint->length = len_v3v3(SCULPT_vertex_co_get(ss, v1), SCULPT_vertex_co_get(ss, v2));
+  length_constraint->strength = 1.0f;
 
   cloth_sim->tot_length_constraints++;
 
   /* Reallocation if the array capacity is exceeded. */
-  if (cloth_sim->tot_length_constraints >= cloth_sim->capacity_length_constraints) {
-    cloth_sim->capacity_length_constraints += CLOTH_LENGTH_CONSTRAINTS_BLOCK;
-    cloth_sim->length_constraints = MEM_reallocN_id(cloth_sim->length_constraints,
-                                                    cloth_sim->capacity_length_constraints *
-                                                        sizeof(SculptClothLengthConstraint),
-                                                    "length constraints");
-  }
+  cloth_brush_reallocate_constraints(cloth_sim);
 
   /* Add the constraint to the GSet to avoid creating it again. */
   BLI_edgeset_add(cloth_sim->created_length_constraints, v1, v2);
 }
 
+static void cloth_brush_add_softbody_constraint(SculptClothSimulation *cloth_sim,
+                                                const int v,
+                                                const float strength)
+{
+  SculptClothLengthConstraint *length_constraint =
+      &cloth_sim->length_constraints[cloth_sim->tot_length_constraints];
+
+  length_constraint->elem_index_a = v;
+  length_constraint->elem_index_b = v;
+
+  length_constraint->elem_position_a = cloth_sim->pos[v];
+  length_constraint->elem_position_b = cloth_sim->init_pos[v];
+
+  length_constraint->length = 0.0f;
+  length_constraint->strength = strength;
+
+  cloth_sim->tot_length_constraints++;
+
+  /* Reallocation if the array capacity is exceeded. */
+  cloth_brush_reallocate_constraints(cloth_sim);
+}
+
 static void do_cloth_brush_build_constraints_task_cb_ex(
     void *__restrict userdata, const int n, const TaskParallelTLS *__restrict UNUSED(tls))
 {
   SculptThreadedTaskData *data = userdata;
   SculptSession *ss = data->ob->sculpt;
+  Brush *brush = data->brush;
 
   PBVHVertexIter vd;
 
@@ -162,6 +197,11 @@ static void do_cloth_brush_build_constraints_task_cb_ex(
       }
       SCULPT_VERTEX_NEIGHBORS_ITER_END(ni);
 
+      if (brush->cloth_constraint_softbody_strength > 0.0f) {
+        cloth_brush_add_softbody_constraint(
+            data->cloth_sim, vd.index, brush->cloth_constraint_softbody_strength);
+      }
+
       /* As we don't know the order of the neighbor vertices, we create all possible combinations
        * between the neighbor and the original vertex as length constraints. */
       /* This results on a pattern that contains structural, shear and bending constraints for all
@@ -484,11 +524,11 @@ static void cloth_brush_satisfy_constraints(SculptSession *ss,
     for (int i = 0; i < cloth_sim->tot_length_constraints; i++) {
 
       const SculptClothLengthConstraint *constraint = &cloth_sim->length_constraints[i];
-      const int v1 = constraint->v1;
-      const int v2 = constraint->v2;
+      const int v1 = constraint->elem_index_a;
+      const int v2 = constraint->elem_index_b;
 
       float v1_to_v2[3];
-      sub_v3_v3v3(v1_to_v2, cloth_sim->pos[v2], cloth_sim->pos[v1]);
+      sub_v3_v3v3(v1_to_v2, constraint->elem_position_b, constraint->elem_position_a);
       const float current_distance = len_v3(v1_to_v2);
       float correction_vector[3];
       float correction_vector_half[3];
@@ -524,8 +564,14 @@ static void cloth_brush_satisfy_constraints(SculptSession *ss,
                                                   cloth_sim->init_pos[v2]) :
                                               1.0f;
 
-      madd_v3_v3fl(cloth_sim->pos[v1], correction_vector_half, 1.0f * mask_v1 * sim_factor_v1);
-      madd_v3_v3fl(cloth_sim->pos[v2], correction_vector_half, -1.0f * mask_v2 * sim_factor_v2);
+      madd_v3_v3fl(cloth_sim->pos[v1],
+                   correction_vector_half,
+                   1.0f * mask_v1 * sim_factor_v1 * constraint->strength);
+      if (v1 != v2) {
+        madd_v3_v3fl(cloth_sim->pos[v2],
+                     correction_vector_half,
+                     -1.0f * mask_v2 * sim_factor_v2 * constraint->strength);
+      }
     }
   }
 }