Sculpt: Enable persistent base for the cloth brush

The cloth brush builds the constraints when the stroke starts usign the
current state of the mesh. This means that deformations profuced by the
simulattion will accumulate after multiple strokes as it will always
start from the previous deformed state. While this is useful in many
cases, for other uses it is convenient to always simulate the same
initial shape, but applying different forces to it.

The persistent base options work like the persistent base in the layer
brush and allows the cloth brush to not accumulate deformation after
each stroke. When enabled, constraints are created for the shape stored
in the persistent base instead of from the current state of the mesh.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8428

1 files changed, 13 insertions, 3 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt_cloth.c b/source/blender/editors/sculpt_paint/sculpt_cloth.c
index 434206c1584..763a765768f 100644
--- a/source/blender/editors/sculpt_paint/sculpt_cloth.c
+++ b/source/blender/editors/sculpt_paint/sculpt_cloth.c
@@ -126,7 +126,8 @@ static void cloth_brush_reallocate_constraints(SculptClothSimulation *cloth_sim)
 static void cloth_brush_add_length_constraint(SculptSession *ss,
                                               SculptClothSimulation *cloth_sim,
                                               const int v1,
-                                              const int v2)
+                                              const int v2,
+                                              const bool use_persistent)
 {
   SculptClothLengthConstraint *length_constraint =
       &cloth_sim->length_constraints[cloth_sim->tot_length_constraints];
@@ -137,7 +138,14 @@ static void cloth_brush_add_length_constraint(SculptSession *ss,
   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));
+  if (use_persistent) {
+    length_constraint->length = len_v3v3(SCULPT_vertex_persistent_co_get(ss, v1),
+                                         SCULPT_vertex_persistent_co_get(ss, v2));
+  }
+  else {
+    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++;
@@ -180,6 +188,8 @@ static void do_cloth_brush_build_constraints_task_cb_ex(
 
   PBVHVertexIter vd;
 
+  const bool use_persistent = brush != NULL && brush->flag & BRUSH_PERSISTENT;
+
   BKE_pbvh_vertex_iter_begin(ss->pbvh, data->nodes[n], vd, PBVH_ITER_UNIQUE)
   {
     if (len_squared_v3v3(vd.co, data->cloth_sim_initial_location) <
@@ -211,7 +221,7 @@ static void do_cloth_brush_build_constraints_task_cb_ex(
           if (c_i != c_j && !cloth_brush_sim_has_length_constraint(
                                 data->cloth_sim, build_indices[c_i], build_indices[c_j])) {
             cloth_brush_add_length_constraint(
-                ss, data->cloth_sim, build_indices[c_i], build_indices[c_j]);
+                ss, data->cloth_sim, build_indices[c_i], build_indices[c_j], use_persistent);
           }
         }
       }