Fix T81915: Draw Face Sets not working with deformed sculpt mesh

The draw face sets brush uses the poly center when used in meshes to increase
its precision when working in low poly geometry. For this to work with deformed
meshes, the deformed coordinates from the PBVH should be used instead.

Reviewed By: sergey

Maniphest Tasks: T81915

Differential Revision: https://developer.blender.org/D9424

3 files changed, 22 insertions, 1 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index 56b5a494df0..875f24837c1 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -292,6 +292,21 @@ void SCULPT_active_vertex_normal_get(SculptSession *ss, float normal[3])
   SCULPT_vertex_normal_get(ss, SCULPT_active_vertex_get(ss), normal);
 }
 
+MVert *SCULPT_mesh_deformed_mverts_get(SculptSession *ss)
+{
+  switch (BKE_pbvh_type(ss->pbvh)) {
+    case PBVH_FACES:
+      if (ss->shapekey_active || ss->deform_modifiers_active) {
+        return BKE_pbvh_get_verts(ss->pbvh);
+      }
+      return ss->mvert;
+    case PBVH_BMESH:
+    case PBVH_GRIDS:
+      return NULL;
+  }
+  return NULL;
+}
+
 float *SCULPT_brush_deform_target_vertex_co_get(SculptSession *ss,
                                                 const int deform_target,
                                                 PBVHVertexIter *iter)
diff --git a/source/blender/editors/sculpt_paint/sculpt_face_set.c b/source/blender/editors/sculpt_paint/sculpt_face_set.c
index af6a06caf69..bfe741d2625 100644
--- a/source/blender/editors/sculpt_paint/sculpt_face_set.c
+++ b/source/blender/editors/sculpt_paint/sculpt_face_set.c
@@ -132,6 +132,8 @@ static void do_draw_face_sets_brush_task_cb_ex(void *__restrict userdata,
       ss, &test, data->brush->falloff_shape);
   const int thread_id = BLI_task_parallel_thread_id(tls);
 
+  MVert *mvert = SCULPT_mesh_deformed_mverts_get(ss);
+
   BKE_pbvh_vertex_iter_begin(ss->pbvh, data->nodes[n], vd, PBVH_ITER_UNIQUE)
   {
     if (BKE_pbvh_type(ss->pbvh) == PBVH_FACES) {
@@ -140,7 +142,7 @@ static void do_draw_face_sets_brush_task_cb_ex(void *__restrict userdata,
         const MPoly *p = &ss->mpoly[vert_map->indices[j]];
 
         float poly_center[3];
-        BKE_mesh_calc_poly_center(p, &ss->mloop[p->loopstart], ss->mvert, poly_center);
+        BKE_mesh_calc_poly_center(p, &ss->mloop[p->loopstart], mvert, poly_center);
 
         if (sculpt_brush_test_sq_fn(&test, poly_center)) {
           const float fade = bstrength * SCULPT_brush_strength_factor(ss,
diff --git a/source/blender/editors/sculpt_paint/sculpt_intern.h b/source/blender/editors/sculpt_paint/sculpt_intern.h
index 6313c934774..1a596909d8d 100644
--- a/source/blender/editors/sculpt_paint/sculpt_intern.h
+++ b/source/blender/editors/sculpt_paint/sculpt_intern.h
@@ -170,6 +170,10 @@ int SCULPT_active_vertex_get(SculptSession *ss);
 const float *SCULPT_active_vertex_co_get(SculptSession *ss);
 void SCULPT_active_vertex_normal_get(SculptSession *ss, float normal[3]);
 
+/* Returns PBVH deformed vertices array if shape keys or deform modifiers are used, otherwise
+ * returns mesh original vertices array. */
+struct MVert *SCULPT_mesh_deformed_mverts_get(SculptSession *ss);
+
 /* Fake Neighbors */
 
 #define FAKE_NEIGHBOR_NONE -1