Attributes: support setting the active attribute to "None"

Support setting: `object.data.attributes.active = None` for
ID attributes. Use -1 to represent no active index.

Resolves #127691

Ref !128233

----

Backport e21b424eee

Pull Request: https://projects.blender.org/blender/blender/pulls/129036

source/blender/blenkernel/BKE_attribute.h

@@ -92,6 +92,7 @@ int BKE_id_attributes_length(const struct ID *id,
 
 struct CustomDataLayer *BKE_id_attributes_active_get(struct ID *id);
 void BKE_id_attributes_active_set(struct ID *id, const char *name);
+void BKE_id_attributes_active_clear(struct ID *id);
 int *BKE_id_attributes_active_index_p(struct ID *id);
 
 CustomData *BKE_id_attributes_iterator_next_domain(struct ID *id, struct CustomDataLayer *layers);
@@ -109,6 +110,7 @@ int BKE_id_attribute_to_index(const struct ID *id,
 const char *BKE_id_attributes_active_color_name(const struct ID *id);
 const char *BKE_id_attributes_default_color_name(const struct ID *id);
 void BKE_id_attributes_active_color_set(struct ID *id, const char *name);
+void BKE_id_attributes_active_color_clear(struct ID *id);
 void BKE_id_attributes_default_color_set(struct ID *id, const char *name);
 
 const struct CustomDataLayer *BKE_id_attributes_color_find(const struct ID *id, const char *name);

source/blender/blenkernel/intern/attribute.cc

@@ -710,6 +710,9 @@ bool BKE_id_attribute_required(const ID *id, const char *name)
 CustomDataLayer *BKE_id_attributes_active_get(ID *id)
 {
   int active_index = *BKE_id_attributes_active_index_p(id);
+  if (active_index == -1) {
+    return nullptr;
+  }
   if (active_index > BKE_id_attributes_length(id, ATTR_DOMAIN_MASK_ALL, CD_MASK_PROP_ALL)) {
     active_index = 0;
   }
@@ -750,6 +753,11 @@ void BKE_id_attributes_active_set(ID *id, const char *name)
   *BKE_id_attributes_active_index_p(id) = index;
 }
 
+void BKE_id_attributes_active_clear(ID *id)
+{
+  *BKE_id_attributes_active_index_p(id) = -1;
+}
+
 int *BKE_id_attributes_active_index_p(ID *id)
 {
   switch (GS(id->name)) {
@@ -897,6 +905,19 @@ void BKE_id_attributes_active_color_set(ID *id, const char *name)
   }
 }
 
+void BKE_id_attributes_active_color_clear(ID *id)
+{
+  switch (GS(id->name)) {
+    case ID_ME: {
+      Mesh *mesh = reinterpret_cast<Mesh *>(id);
+      MEM_SAFE_FREE(mesh->active_color_attribute);
+      break;
+    }
+    default:
+      break;
+  }
+}
+
 void BKE_id_attributes_default_color_set(ID *id, const char *name)
 {
   switch (GS(id->name)) {

source/blender/makesdna/DNA_curves_types.h

@@ -169,6 +169,8 @@ typedef struct Curves {
   CurvesGeometry geometry;
 
   int flag;
+
+  /** Set to -1 when none is active. */
   int attributes_active_index;
 
   /* Materials. */

source/blender/makesdna/DNA_grease_pencil_types.h

@@ -446,6 +446,8 @@ typedef struct GreasePencil {
   CustomData layers_data;
   /**
    * The index of the active attribute in the UI.
+   *
+   * Set to -1 when none is active.
    */
   int attributes_active_index;
   char _pad2[4];

source/blender/makesdna/DNA_mesh_types.h

@@ -103,6 +103,8 @@ typedef struct Mesh {
   /**
    * The index of the active attribute in the UI. The attribute list is a combination of the
    * generic type attributes from vertex, edge, face, and corner custom data.
+   *
+   * Set to -1 when none is active.
    */
   int attributes_active_index;
 

source/blender/makesdna/DNA_pointcloud_types.h

@@ -44,6 +44,7 @@ typedef struct PointCloud {
 
   /* Custom Data */
   struct CustomData pdata;
+  /** Set to -1 when none is active. */
   int attributes_active_index;
   int _pad4;
 

source/blender/makesrna/intern/rna_attribute.cc

@@ -594,18 +594,23 @@ static void rna_AttributeGroup_active_set(PointerRNA *ptr,
 {
   ID *id = ptr->owner_id;
   CustomDataLayer *layer = static_cast<CustomDataLayer *>(attribute_ptr.data);
-  BKE_id_attributes_active_set(id, layer->name);
+  if (layer) {
+    BKE_id_attributes_active_set(id, layer->name);
+  }
+  else {
+    BKE_id_attributes_active_clear(id);
+  }
 }
 
 static void rna_AttributeGroup_active_index_set(PointerRNA *ptr, int value)
 {
-  *BKE_id_attributes_active_index_p(ptr->owner_id) = value;
+  *BKE_id_attributes_active_index_p(ptr->owner_id) = std::max(-1, value);
 }
 
 static void rna_AttributeGroup_active_index_range(
     PointerRNA *ptr, int *min, int *max, int *softmin, int *softmax)
 {
-  *min = 0;
+  *min = -1;
   *max = BKE_id_attributes_length(ptr->owner_id, ATTR_DOMAIN_MASK_ALL, CD_MASK_PROP_ALL);
 
   *softmin = *min;
@@ -636,7 +641,12 @@ static void rna_AttributeGroup_active_color_set(PointerRNA *ptr,
 {
   ID *id = ptr->owner_id;
   CustomDataLayer *layer = static_cast<CustomDataLayer *>(attribute_ptr.data);
-  BKE_id_attributes_active_color_set(id, layer->name);
+  if (layer) {
+    BKE_id_attributes_active_color_set(id, layer->name);
+  }
+  else {
+    BKE_id_attributes_active_color_clear(ptr->owner_id);
+  }
 }
 
 static int rna_AttributeGroup_active_color_index_get(PointerRNA *ptr)
@@ -656,18 +666,18 @@ static void rna_AttributeGroup_active_color_index_set(PointerRNA *ptr, int value
   CustomDataLayer *layer = BKE_id_attribute_from_index(
       ptr->owner_id, value, ATTR_DOMAIN_MASK_COLOR, CD_MASK_COLOR_ALL);
 
-  if (!layer) {
-    fprintf(stderr, "%s: error setting active color index to %d\n", __func__, value);
-    return;
+  if (layer) {
+    BKE_id_attributes_active_color_set(ptr->owner_id, layer->name);
+  }
+  else {
+    BKE_id_attributes_active_color_clear(ptr->owner_id);
   }
-
-  BKE_id_attributes_active_color_set(ptr->owner_id, layer->name);
 }
 
 static void rna_AttributeGroup_active_color_index_range(
     PointerRNA *ptr, int *min, int *max, int *softmin, int *softmax)
 {
-  *min = 0;
+  *min = -1;
   *max = BKE_id_attributes_length(ptr->owner_id, ATTR_DOMAIN_MASK_COLOR, CD_MASK_COLOR_ALL);
 
   *softmin = *min;
@@ -1323,7 +1333,9 @@ static void rna_def_attribute_group(BlenderRNA *brna)
   RNA_def_property_update(prop, 0, "rna_AttributeGroup_update_active");
 
   prop = RNA_def_property(srna, "active_index", PROP_INT, PROP_NONE);
-  RNA_def_property_ui_text(prop, "Active Attribute Index", "Active attribute index");
+  RNA_def_property_ui_text(
+      prop, "Active Attribute Index", "Active attribute index or -1 when none are active");
+  RNA_def_property_range(prop, -1, INT_MAX);
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
   RNA_def_property_int_funcs(prop,
                              "rna_AttributeGroup_active_index_get",