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diff --git a/source/blender/geometry/GEO_realize_instances.hh b/source/blender/geometry/GEO_realize_instances.hh
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+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#pragma once
+
+#include "BKE_geometry_set.hh"
+
+namespace blender::geometry {
+
+struct RealizeInstancesOptions {
+  /**
+   * The default is to generate new ids for every element (when there was any id attribute in the
+   * input). This avoids having a geometry that contains the same id many times.
+   * When this is `true` the ids on the original geometries are kept unchanged and ids on instances
+   * are ignored. Ids are zero initialized when the original geometry did not have an id.
+   */
+  bool keep_original_ids = false;
+  /**
+   * When `true` the output geometry will contain all the generic attributes that existed on
+   * instances. Otherwise, instance attributes are ignored.
+   */
+  bool realize_instance_attributes = true;
+};
+
+/**
+ * Join all instances into a single geometry component for each geometry type. For example, all
+ * mesh instances (including the already realized mesh) are joined into a single mesh. The output
+ * geometry set does not contain any instances. If the input did not contain any instances, it is
+ * returned directly.
+ *
+ * The `id` attribute has special handling. If there is an id attribute on any component, the
+ * output will contain an `id` attribute as well. The output id is generated by mixing/hashing ids
+ * of instances and of the instanced geometry data.
+ */
+GeometrySet realize_instances(GeometrySet geometry_set, const RealizeInstancesOptions &options);
+
+GeometrySet realize_instances_legacy(GeometrySet geometry_set);
+
+}  // namespace blender::geometry