source/blender/blenkernel/BKE_attribute.h

@@ -42,8 +42,8 @@ typedef enum eAttrDomainMask {
   ATTR_DOMAIN_MASK_FACE = (1 << 2),
   ATTR_DOMAIN_MASK_CORNER = (1 << 3),
   ATTR_DOMAIN_MASK_CURVE = (1 << 4),
-  ATTR_DOMAIN_MASK_GREASE_PENCIL_LAYER = (1 << 5),
-  ATTR_DOMAIN_MASK_ALL = (1 << 6) - 1
+  ATTR_DOMAIN_MASK_GREASE_PENCIL_LAYER = (1 << 6),
+  ATTR_DOMAIN_MASK_ALL = (1 << 7) - 1
 } eAttrDomainMask;
 ENUM_OPERATORS(eAttrDomainMask, ATTR_DOMAIN_MASK_ALL);
 

source/blender/blenkernel/BKE_geometry_set.hh

@@ -719,6 +719,9 @@ class GreasePencilComponent : public GeometryComponent {
   void ensure_owns_direct_data() override;
 
   static constexpr inline GeometryComponent::Type static_type = Type::GreasePencil;
+
+  std::optional<AttributeAccessor> attributes() const final;
+  std::optional<MutableAttributeAccessor> attributes_for_write() final;
 };
 
 }  // namespace blender::bke

source/blender/blenkernel/intern/attribute.cc

@@ -96,6 +96,7 @@ static void get_domains(const ID *id, DomainInfo info[ATTR_DOMAIN_NUM])
       GreasePencil *grease_pencil = (GreasePencil *)id;
       info[ATTR_DOMAIN_GREASE_PENCIL_LAYER].customdata = &grease_pencil->layers_data;
       info[ATTR_DOMAIN_GREASE_PENCIL_LAYER].length = grease_pencil->layers().size();
+      break;
     }
     default:
       break;
@@ -123,6 +124,10 @@ static std::optional<blender::bke::MutableAttributeAccessor> get_attribute_acces
       CurvesGeometry &curves = curves_id.geometry.wrap();
       return curves.attributes_for_write();
     }
+    case ID_GP: {
+      GreasePencil &grease_pencil = reinterpret_cast<GreasePencil &>(id);
+      return grease_pencil.attributes_for_write();
+    }
     default: {
       BLI_assert_unreachable();
       return {};
@@ -717,6 +722,9 @@ int *BKE_id_attributes_active_index_p(ID *id)
     case ID_CV: {
       return &((Curves *)id)->attributes_active_index;
     }
+    case ID_GP: {
+      return &((GreasePencil *)id)->attributes_active_index;
+    }
     default:
       return nullptr;
   }

source/blender/blenkernel/intern/geometry_component_grease_pencil.cc

@@ -197,3 +197,18 @@ blender::bke::MutableAttributeAccessor GreasePencil::attributes_for_write()
   return blender::bke::MutableAttributeAccessor(
       this, blender::bke::get_grease_pencil_accessor_functions_ref());
 }
+
+namespace blender::bke {
+
+std::optional<AttributeAccessor> GreasePencilComponent::attributes() const
+{
+  return AttributeAccessor(grease_pencil_, get_grease_pencil_accessor_functions_ref());
+}
+
+std::optional<MutableAttributeAccessor> GreasePencilComponent::attributes_for_write()
+{
+  GreasePencil *grease_pencil = this->get_for_write();
+  return MutableAttributeAccessor(grease_pencil, get_grease_pencil_accessor_functions_ref());
+}
+
+}  // namespace blender::bke

source/blender/blenkernel/intern/grease_pencil.cc

@@ -126,7 +126,6 @@ static void grease_pencil_copy_data(Main * /*bmain*/,
         grease_pencil_dst->find_layer_by_name(grease_pencil_src->active_layer->wrap().name()));
   }
 
-  CustomData_free(&grease_pencil_dst->layers_data, grease_pencil_dst->layers().size());
   CustomData_copy(&grease_pencil_src->layers_data,
                   &grease_pencil_dst->layers_data,
                   CD_MASK_ALL,
@@ -1063,8 +1062,10 @@ GreasePencil *BKE_grease_pencil_new_nomain()
 
 GreasePencil *BKE_grease_pencil_copy_for_eval(const GreasePencil *grease_pencil_src)
 {
-  return reinterpret_cast<GreasePencil *>(
+  GreasePencil *grease_pencil = reinterpret_cast<GreasePencil *>(
       BKE_id_copy_ex(nullptr, &grease_pencil_src->id, nullptr, LIB_ID_COPY_LOCALIZE));
+  grease_pencil->runtime->eval_frame = grease_pencil_src->runtime->eval_frame;
+  return grease_pencil;
 }
 
 BoundBox *BKE_grease_pencil_boundbox_get(Object *ob)
@@ -1132,6 +1133,8 @@ void BKE_grease_pencil_data_update(Depsgraph *depsgraph, Scene *scene, Object *o
 
   /* Evaluate modifiers. */
   GreasePencil *grease_pencil = static_cast<GreasePencil *>(object->data);
+  /* Store the frame that this grease pencil is evaluated on. */
+  grease_pencil->runtime->eval_frame = int(DEG_get_ctime(depsgraph));
   GeometrySet geometry_set = GeometrySet::from_grease_pencil(grease_pencil,
                                                              GeometryOwnershipType::ReadOnly);
   grease_pencil_evaluate_modifiers(depsgraph, scene, object, geometry_set);
@@ -1144,9 +1147,6 @@ void BKE_grease_pencil_data_update(Depsgraph *depsgraph, Scene *scene, Object *o
    * would result in a copy when it's shared. So for now, we use a const_cast here. */
   GreasePencil *grease_pencil_eval = const_cast<GreasePencil *>(geometry_set.get_grease_pencil());
 
-  /* Store the frame that this grease pencil data was evaluated on. */
-  grease_pencil_eval->runtime->eval_frame = int(DEG_get_ctime(depsgraph));
-
   /* Assign evaluated object. */
   BKE_object_eval_assign_data(object, &grease_pencil_eval->id, false);
   object->runtime.geometry_set_eval = new GeometrySet(std::move(geometry_set));

source/blender/makesdna/DNA_grease_pencil_types.h

@@ -407,6 +407,11 @@ typedef struct GreasePencil {
    * All attributes stored on the grease pencil layers (#ATTR_DOMAIN_GREASE_PENCIL_LAYER).
    */
   CustomData layers_data;
+  /**
+   * The index of the active attribute in the UI.
+   */
+  int attributes_active_index;
+  char _pad2[4];
 
   /**
    * Pointer to the active layer. Can be NULL.
@@ -419,7 +424,7 @@ typedef struct GreasePencil {
    */
   struct Material **material_array;
   short material_array_num;
-  char _pad2[2];
+  char _pad3[2];
   /**
    * Global flag on the data-block.
    */

source/blender/makesrna/intern/rna_attribute.cc

@@ -88,6 +88,11 @@ const EnumPropertyItem rna_enum_attribute_domain_items[] = {
     // {ATTR_DOMAIN_GRIDS, "GRIDS", 0, "Grids", "Attribute on mesh multires grids"},
     {ATTR_DOMAIN_CURVE, "CURVE", 0, "Spline", "Attribute on spline"},
     {ATTR_DOMAIN_INSTANCE, "INSTANCE", 0, "Instance", "Attribute on instance"},
+    {ATTR_DOMAIN_GREASE_PENCIL_LAYER,
+     "GREASE_PENCIL_LAYER",
+     0,
+     "Grease Pencil Layer",
+     "Attribute on grease pencil layer"},
     {0, nullptr, 0, nullptr, nullptr},
 };