Geometry Nodes: Set Grid Background node

It's useful when creating a grid procedurally to be explicit
about what background value it gets. This PR adds a very
simple node just to do that.

Pull Request: https://projects.blender.org/blender/blender/pulls/147235

scripts/startup/bl_ui/node_add_menu_geometry.py

@@ -911,7 +911,6 @@ class NODE_MT_gn_volume_read_base(node_add_menu.NodeMenu):
         layout = self.layout
         self.node_operator(layout, "GeometryNodeGetNamedGrid")
         self.node_operator(layout, "GeometryNodeGridInfo")
-        self.node_operator(layout, "GeometryNodeSetGridTransform")
 
         self.draw_assets_for_catalog(layout, self.menu_path)
 
@@ -923,6 +922,8 @@ class NODE_MT_gn_volume_write_base(node_add_menu.NodeMenu):
     def draw(self, context):
         layout = self.layout
         self.node_operator(layout, "GeometryNodeStoreNamedGrid")
+        self.node_operator(layout, "GeometryNodeSetGridBackground")
+        self.node_operator(layout, "GeometryNodeSetGridTransform")
 
         self.draw_assets_for_catalog(layout, self.menu_path)
 

source/blender/makesrna/intern/rna_nodetree.cc

@@ -10284,6 +10284,7 @@ static void rna_def_nodes(BlenderRNA *brna)
   define("GeometryNode", "GeometryNodeSetGreasePencilColor");
   define("GeometryNode", "GeometryNodeSetGreasePencilDepth");
   define("GeometryNode", "GeometryNodeSetGreasePencilSoftness");
+  define("GeometryNode", "GeometryNodeSetGridBackground");
   define("GeometryNode", "GeometryNodeSetGridTransform");
   define("GeometryNode", "GeometryNodeSetID");
   define("GeometryNode", "GeometryNodeSetInstanceTransform");

source/blender/nodes/geometry/CMakeLists.txt

@@ -221,6 +221,7 @@ set(SRC
   nodes/node_geo_set_grease_pencil_color.cc
   nodes/node_geo_set_grease_pencil_depth_mode.cc
   nodes/node_geo_set_grease_pencil_softness.cc
+  nodes/node_geo_set_grid_background.cc
   nodes/node_geo_set_grid_transform.cc
   nodes/node_geo_set_id.cc
   nodes/node_geo_set_instance_transform.cc

source/blender/nodes/geometry/nodes/node_geo_set_grid_background.cc

@@ -0,0 +1,101 @@
+/* SPDX-FileCopyrightText: 2025 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "node_geometry_util.hh"
+
+#include "BKE_volume_grid_process.hh"
+
+#include "NOD_rna_define.hh"
+
+#include "UI_interface_layout.hh"
+#include "UI_resources.hh"
+
+#include "RNA_enum_types.hh"
+
+namespace blender::nodes::node_geo_set_grid_background {
+
+static void node_declare(NodeDeclarationBuilder &b)
+{
+  const bNode *node = b.node_or_null();
+  if (!node) {
+    return;
+  }
+
+  const eNodeSocketDatatype data_type = eNodeSocketDatatype(node->custom1);
+
+  b.use_custom_socket_order();
+  b.allow_any_socket_order();
+  b.add_default_layout();
+  b.add_input(data_type, "Grid")
+      .hide_value()
+      .structure_type(StructureType::Grid)
+      .is_default_link_socket();
+  b.add_output(data_type, "Grid").structure_type(StructureType::Grid).align_with_previous();
+  b.add_input(data_type, "Background").structure_type(StructureType::Single);
+}
+
+static void node_layout(uiLayout *layout, bContext * /*C*/, PointerRNA *ptr)
+{
+  layout->use_property_split_set(true);
+  layout->use_property_decorate_set(false);
+  layout->prop(ptr, "data_type", UI_ITEM_NONE, "", ICON_NONE);
+}
+
+static void node_geo_exec(GeoNodeExecParams params)
+{
+#ifdef WITH_OPENVDB
+  bke::GVolumeGrid grid = params.extract_input<bke::GVolumeGrid>("Grid");
+  if (!grid) {
+    params.set_default_remaining_outputs();
+    return;
+  }
+
+  const auto background = params.extract_input<bke::SocketValueVariant>("Background");
+
+  bke::VolumeTreeAccessToken tree_token;
+  openvdb::GridBase &grid_base = grid.get_for_write().grid_for_write(tree_token);
+  bke::volume_grid::set_grid_background(grid_base, background.get_single_ptr());
+
+  params.set_output("Grid", std::move(grid));
+#else
+  node_geo_exec_with_missing_openvdb(params);
+#endif
+}
+
+static void node_init(bNodeTree * /*tree*/, bNode *node)
+{
+  node->custom1 = SOCK_FLOAT;
+}
+
+static void node_rna(StructRNA *srna)
+{
+  RNA_def_node_enum(srna,
+                    "data_type",
+                    "Data Type",
+                    "Node socket data type",
+                    rna_enum_node_socket_data_type_items,
+                    NOD_inline_enum_accessors(custom1),
+                    SOCK_FLOAT,
+                    grid_socket_type_items_filter_fn);
+}
+
+static void node_register()
+{
+  static blender::bke::bNodeType ntype;
+
+  geo_node_type_base(&ntype, "GeometryNodeSetGridBackground");
+  ntype.ui_name = "Set Grid Background";
+  ntype.ui_description = "Set the background value used for inactive voxels and tiles";
+  ntype.nclass = NODE_CLASS_GEOMETRY;
+  ntype.initfunc = node_init;
+  ntype.geometry_node_execute = node_geo_exec;
+  ntype.draw_buttons = node_layout;
+  ntype.declare = node_declare;
+  blender::bke::node_register_type(ntype);
+
+  node_rna(ntype.rna_ext.srna);
+}
+NOD_REGISTER_NODE(node_register)
+
+}  // namespace blender::nodes::node_geo_set_grid_background