source/blender/blenkernel/intern/customdata.cc

@@ -2289,26 +2289,12 @@ bool CustomData_merge(const CustomData *source,
   return changed;
 }
 
-static bool attribute_stored_in_bmesh_flag(const StringRef name)
-{
-  return ELEM(name,
-              "position",
-              ".hide_vert",
-              ".hide_edge",
-              ".hide_poly",
-              ".select_vert",
-              ".select_edge",
-              ".select_poly",
-              "material_index",
-              "sharp_edge");
-}
-
 CustomData CustomData_shallow_copy_remove_non_bmesh_attributes(const CustomData *src,
                                                                const eCustomDataMask mask)
 {
   Vector<CustomDataLayer> dst_layers;
   for (const CustomDataLayer &layer : Span<CustomDataLayer>{src->layers, src->totlayer}) {
-    if (attribute_stored_in_bmesh_flag(layer.name)) {
+    if (BM_attribute_stored_in_bmesh_builtin(layer.name)) {
       continue;
     }
     if (!(mask & CD_TYPE_AS_MASK(layer.type))) {

source/blender/bmesh/intern/bmesh_mesh_convert.cc

@@ -133,6 +133,20 @@ static char bm_face_flag_to_mflag(const BMFace *f)
   return ((hflag & BM_ELEM_SMOOTH) ? ME_SMOOTH : 0);
 }
 
+bool BM_attribute_stored_in_bmesh_builtin(const StringRef name)
+{
+  return ELEM(name,
+              "position",
+              ".hide_vert",
+              ".hide_edge",
+              ".hide_poly",
+              ".select_vert",
+              ".select_edge",
+              ".select_poly",
+              "material_index",
+              "sharp_edge");
+}
+
 /* Static function for alloc (duplicate in modifiers_bmesh.c) */
 static BMFace *bm_face_create_from_mpoly(BMesh &bm,
                                          Span<MLoop> loops,

source/blender/bmesh/intern/bmesh_mesh_convert.h

@@ -9,6 +9,16 @@
 
 #include "bmesh.h"
 
+#ifdef __cplusplus
+#  include "BLI_string_ref.hh"
+
+/**
+ * \return Whether attributes with the given name are stored in special flags or fields in BMesh
+ * rather than in the regular custom data blocks.
+ */
+bool BM_attribute_stored_in_bmesh_builtin(const blender::StringRef name);
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif

source/blender/editors/sculpt_paint/sculpt_dyntopo.cc

@@ -28,6 +28,8 @@
 #include "BKE_pointcache.h"
 #include "BKE_scene.h"
 
+#include "BLI_index_range.hh"
+
 #include "DEG_depsgraph.h"
 
 #include "WM_api.h"
@@ -42,6 +44,8 @@
 #include "bmesh.h"
 #include "bmesh_tools.h"
 
+using blender::IndexRange;
+
 void SCULPT_dynamic_topology_triangulate(BMesh *bm)
 {
   if (bm->totloop != bm->totface * 3) {
@@ -281,8 +285,8 @@ static int dyntopo_warning_popup(bContext *C, wmOperatorType *ot, enum eDynTopoW
   uiLayout *layout = UI_popup_menu_layout(pup);
 
   if (flag & (DYNTOPO_WARN_VDATA | DYNTOPO_WARN_EDATA | DYNTOPO_WARN_LDATA)) {
-    const char *msg_error = TIP_("Vertex Data Detected!");
-    const char *msg = TIP_("Dyntopo will not preserve vertex colors, UVs, or other customdata");
+    const char *msg_error = TIP_("Attribute Data Detected");
+    const char *msg = TIP_("Dyntopo will not preserve colors, UVs, or other attributes");
     uiItemL(layout, msg_error, ICON_INFO);
     uiItemL(layout, msg, ICON_NONE);
     uiItemS(layout);
@@ -305,6 +309,39 @@ static int dyntopo_warning_popup(bContext *C, wmOperatorType *ot, enum eDynTopoW
   return OPERATOR_INTERFACE;
 }
 
+static bool dyntopo_supports_customdata_layers(const blender::Span<CustomDataLayer> layers,
+                                               int totelem)
+{
+  for (const CustomDataLayer &layer : layers) {
+    if (CD_TYPE_AS_MASK(layer.type) & CD_MASK_PROP_ALL) {
+      if (layer.name[0] == '\0') {
+        return false;
+      }
+
+      if (STREQ(layer.name, ".sculpt_face_sets") && totelem > 0) {
+        int *fsets = static_cast<int *>(layer.data);
+        int fset = fsets[0];
+
+        /* Check if only one face set exists. */
+        for (int i : IndexRange(totelem)) {
+          if (fsets[i] != fset) {
+            return false;
+          }
+        }
+
+        return true;
+      }
+
+      /* Some data is stored as generic attributes on #Mesh but in flags or field on #BMesh. */
+      return BM_attribute_stored_in_bmesh_builtin(layer.name);
+    }
+    /* Some layers just encode #Mesh topology or are handled as special cases for dyntopo. */
+    return ELEM(layer.type, CD_MEDGE, CD_MFACE, CD_MLOOP, CD_MPOLY, CD_PAINT_MASK, CD_ORIGINDEX);
+  }
+
+  return true;
+}
+
 enum eDynTopoWarnFlag SCULPT_dynamic_topology_check(Scene *scene, Object *ob)
 {
   Mesh *me = static_cast<Mesh *>(ob->data);
@@ -315,18 +352,17 @@ enum eDynTopoWarnFlag SCULPT_dynamic_topology_check(Scene *scene, Object *ob)
   BLI_assert(ss->bm == nullptr);
   UNUSED_VARS_NDEBUG(ss);
 
-  for (int i = 0; i < CD_NUMTYPES; i++) {
-    if (!ELEM(i, CD_MEDGE, CD_MFACE, CD_MLOOP, CD_MPOLY, CD_PAINT_MASK, CD_ORIGINDEX)) {
-      if (CustomData_has_layer(&me->vdata, i)) {
-        flag |= DYNTOPO_WARN_VDATA;
-      }
-      if (CustomData_has_layer(&me->edata, i)) {
-        flag |= DYNTOPO_WARN_EDATA;
-      }
-      if (CustomData_has_layer(&me->ldata, i)) {
-        flag |= DYNTOPO_WARN_LDATA;
-      }
-    }
+  if (!dyntopo_supports_customdata_layers({me->vdata.layers, me->vdata.totlayer}, me->totvert)) {
+    flag |= DYNTOPO_WARN_VDATA;
+  }
+  if (!dyntopo_supports_customdata_layers({me->edata.layers, me->edata.totlayer}, me->totedge)) {
+    flag |= DYNTOPO_WARN_EDATA;
+  }
+  if (!dyntopo_supports_customdata_layers({me->pdata.layers, me->pdata.totlayer}, me->totpoly)) {
+    flag |= DYNTOPO_WARN_LDATA;
+  }
+  if (!dyntopo_supports_customdata_layers({me->ldata.layers, me->ldata.totlayer}, me->totloop)) {
+    flag |= DYNTOPO_WARN_LDATA;
   }
 
   {