Copy MDeformVert data from old strokes.

@@ -25,0 +34,4 @@
+    const bGPDframe &gpf, const ListBase &vertex_group_names)
+{
+  const int num_vertex_groups = BLI_listbase_count(&vertex_group_names);
+  Vector<int> is_group_used(num_vertex_groups, false);

@@ -25,0 +48,4 @@
+  }
+  ListBase new_names;
+  BLI_listbase_clear(&new_names);
+  Vector<int> index_map(num_vertex_groups);

@@ -25,0 +30,4 @@
+ * - ListBase with used vertex group names (bDeformGroup)
+ * - Vector of indices in the new vertex group list for remapping
+ */
+static std::tuple<ListBase, Vector<int>> find_used_vertex_groups(

@@ -25,0 +42,4 @@
+    Span<MDeformVert> dverts = {gps->dvert, gps->totpoints};
+    for (const MDeformVert &dvert : dverts) {
+      for (const MDeformWeight &weight : Span<MDeformWeight>{dvert.dw, dvert.totweight}) {
+        is_group_used[weight.def_nr] = true;

@@ -57,0 +111,4 @@
+    const MutableSpan<MDeformWeight> vertex_weights = {dst_dvert.dw, dst_dvert.totweight};
+    for (MDeformWeight &weight : vertex_weights) {
+      /* Map def_nr to the reduced vertex group list. */
+      weight.def_nr = stroke_def_nr_map[weight.def_nr];