Modeling: Add Auto Normalize when Assigning vertex weights

Part of #135062.

This PR adds an Auto Normalize option in the Vertex Group panel that
when checked will normalize the other deform-bone vertex groups' weights
when assigning the weight of a deform-bone vertex group. For example if
a selected vertex has the following weights:

| Name    | Weight |
|---------|--------|
| Group 1 | 0.2    |
| Group 2 | 0.2    |
| Group 3 | 0.6    |

And the user selects Group 3, checks the Auto Normalize checkbox, sets
the weight to 0.8, and clicks Assign, the new weights will be:

| Name    | Weight |
|---------|--------|
| Group 1 | 0.1    |
| Group 2 | 0.1    |
| Group 3 | 0.8    |

Co-authored-by: Andy Beers <acbeers1@gmail.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/138133

scripts/startup/bl_ui/properties_data_mesh.py

@@ -272,7 +272,11 @@ class DATA_PT_vertex_groups(MeshButtonsPanel, Panel):
             sub.operator("object.vertex_group_select", text="Select")
             sub.operator("object.vertex_group_deselect", text="Deselect")
 
-            layout.prop(context.tool_settings, "vertex_group_weight", text="Weight")
+            col = layout.column(align=True)
+            col.use_property_split = True
+            col.separator()
+            col.prop(context.tool_settings, "vertex_group_weight", text="Weight")
+            col.prop(context.tool_settings, "use_auto_normalize", text="Auto Normalize")
 
         draw_attribute_warnings(context, layout, None)
 

source/blender/editors/object/object_vgroup.cc

@@ -1341,21 +1341,14 @@ static void vgroup_levels_subset(Object *ob,
 static bool vgroup_normalize_all(Object *ob,
                                  const bool *vgroup_validmap,
                                  const int vgroup_tot,
-                                 const int subset_count,
                                  const bool lock_active,
                                  ReportList *reports)
 {
   MDeformVert *dv, **dvert_array = nullptr;
   int i, dvert_tot = 0;
   const int def_nr = BKE_object_defgroup_active_index_get(ob) - 1;
-
   const bool use_vert_sel = vertex_group_use_vert_sel(ob);
 
-  if (subset_count == 0) {
-    BKE_report(reports, RPT_ERROR, "No vertex groups to operate on");
-    return false;
-  }
-
   vgroup_parray_alloc(static_cast<ID *>(ob->data), &dvert_array, &dvert_tot, use_vert_sel);
 
   if (dvert_array) {
@@ -1411,6 +1404,35 @@ static bool vgroup_normalize_all(Object *ob,
   return false;
 }
 
+/**
+ * If the currently active vertex group is for a deform bone, normalize all
+ * vertex groups that are for deform bones.
+ *
+ * \param lock_active: If true, the active vertex group will be left untouched,
+ * and the remaining deform groups will be normalized to occupy the remaining
+ * weight not used by it.
+ */
+static void vgroup_normalize_all_deform_if_active_is_deform(Object *ob,
+                                                            const bool lock_active,
+                                                            ReportList *reports)
+{
+  int r_defgroup_tot = BKE_object_defgroup_count(ob);
+  bool *defgroup_validmap = BKE_object_defgroup_validmap_get(ob, r_defgroup_tot);
+  const int def_nr = BKE_object_defgroup_active_index_get(ob) - 1;
+
+  /* Only auto-normalize if the active group is bone-deforming. */
+  if (defgroup_validmap[def_nr] == true) {
+    int subset_count, vgroup_tot;
+    const bool *vgroup_validmap = BKE_object_defgroup_subset_from_select_type(
+        ob, WT_VGROUP_BONE_DEFORM, &vgroup_tot, &subset_count);
+
+    vgroup_normalize_all(ob, vgroup_validmap, vgroup_tot, lock_active, reports);
+    MEM_SAFE_FREE(vgroup_validmap);
+  }
+
+  MEM_SAFE_FREE(defgroup_validmap);
+}
+
 enum {
   VGROUP_TOGGLE,
   VGROUP_LOCK,
@@ -2714,13 +2736,18 @@ void OBJECT_OT_vertex_group_remove(wmOperatorType *ot)
 /** \name Vertex Group Assign Operator
  * \{ */
 
-static wmOperatorStatus vertex_group_assign_exec(bContext *C, wmOperator * /*op*/)
+static wmOperatorStatus vertex_group_assign_exec(bContext *C, wmOperator *op)
 {
   ToolSettings *ts = CTX_data_tool_settings(C);
   Object *ob = context_object(C);
   Scene &scene = *CTX_data_scene(C);
 
   vgroup_assign_verts(ob, scene, ts->vgroup_weight);
+
+  if (ts->auto_normalize) {
+    vgroup_normalize_all_deform_if_active_is_deform(ob, true, op->reports);
+  }
+
   DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
   WM_event_add_notifier(C, NC_GEOM | ND_DATA, ob->data);
 
@@ -2818,6 +2845,11 @@ static wmOperatorStatus vertex_group_remove_from_exec(bContext *C, wmOperator *o
     }
   }
 
+  ToolSettings *ts = CTX_data_tool_settings(C);
+  if (ts->auto_normalize) {
+    vgroup_normalize_all_deform_if_active_is_deform(ob, false, op->reports);
+  }
+
   DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
   WM_event_add_notifier(C, NC_GEOM | ND_DATA, ob->data);
 
@@ -3096,8 +3128,14 @@ static wmOperatorStatus vertex_group_normalize_all_exec(bContext *C, wmOperator
   const bool *vgroup_validmap = BKE_object_defgroup_subset_from_select_type(
       ob, subset_type, &vgroup_tot, &subset_count);
 
-  changed = vgroup_normalize_all(
-      ob, vgroup_validmap, vgroup_tot, subset_count, lock_active, op->reports);
+  if (subset_count == 0) {
+    BKE_report(op->reports, RPT_ERROR, "No vertex groups to operate on");
+    changed = false;
+  }
+  else {
+    changed = vgroup_normalize_all(ob, vgroup_validmap, vgroup_tot, lock_active, op->reports);
+  }
+
   MEM_freeN(vgroup_validmap);
 
   if (changed) {

source/blender/makesrna/intern/rna_scene.cc

@@ -3272,7 +3272,7 @@ static void rna_def_tool_settings(BlenderRNA *brna)
   RNA_def_property_ui_text(prop,
                            "Weight Paint Auto-Normalize",
                            "Ensure all bone-deforming vertex groups add up "
-                           "to 1.0 while weight painting");
+                           "to 1.0 while weight painting or assigning to vertices");
   RNA_def_property_update(prop, 0, "rna_Scene_update_active_object_data");
 
   prop = RNA_def_property(srna, "use_lock_relative", PROP_BOOLEAN, PROP_NONE);