Geometry Nodes: Sample Volume node

This patch adds a `Sample Volume` node that can sample the value
of a volume at a specified position.
It supports Float, Int32, Boolean and Vector grids.
The `Grid` input expects a named attribute with the name of the grid.

@@ -11004,0 +11013,4 @@
+  PropertyRNA *prop;
+
+  RNA_def_struct_sdna_from(srna, "NodeGeometrySampleVolume", "storage");
+

@@ -11004,0 +11021,4 @@
+
+  prop = RNA_def_property(srna, "grid_type", PROP_ENUM, PROP_NONE);
+  RNA_def_property_enum_items(prop, rna_enum_attribute_type_items);
+  RNA_def_property_enum_funcs(

@@ -0,0 +101,4 @@
+{
+  StringRefNull grid_name;
+
+  if (field.node().field_inputs() != nullptr) {

@@ -0,0 +190,4 @@
+  {
+    const VArray<float3> &positions = params.readonly_single_input<float3>(0, "Position");
+    GMutableSpan dst = params.uninitialized_single_output(1, "Value");
+    const VolumeGridType grid_type = BKE_volume_grid_type_openvdb(*base_grid_);

@@ -0,0 +195,4 @@
+    switch (grid_type) {
+      case VOLUME_GRID_FLOAT: {
+        sample_grid<openvdb::FloatGrid>(base_grid_, positions, mask, dst, sampling_mode_);
+        break;

@@ -0,0 +320,4 @@
+  if (volume_grid == nullptr) {
+    char *message = BLI_sprintfN(TIP_("Grid not found in the volume: \"%s\""), grid_name.c_str());
+    params.error_message_add(NodeWarningType::Error, message);
+    params.set_default_remaining_outputs();

@@ -0,0 +329,4 @@
+  /* Check that the input grid socket type matches the grid type. */
+  if (!((grid_type == VOLUME_GRID_FLOAT && input_grid_type == CD_PROP_FLOAT) ||
+        (grid_type == VOLUME_GRID_INT && input_grid_type == CD_PROP_INT32) ||
+        (grid_type == VOLUME_GRID_BOOLEAN && input_grid_type == CD_PROP_BOOL) ||

@@ -0,0 +346,4 @@
+        NodeWarningType::Warning,
+        TIP_("Using the Point Sampler because of Boolean Grid type limitation"));
+    sampling_mode = GEO_NODE_SAMPLE_VOLUME_SAMPLING_MODE_POINT;
+  }

@@ -0,0 +351,4 @@
+  GField output_field;
+  if (position_value_or_field.is_field()) {
+    auto fn = std::make_shared<SampleVolumeFunction>(
+        std::move(base_grid), std::move(grid_field), sampling_mode);

@@ -0,0 +270,4 @@
+  }
+  BLI_assert_unreachable();
+  return std::nullopt;
+}

@@ -0,0 +283,4 @@
+  }
+  const NodeGeometrySampleVolume &storage = node_storage(params.node());
+  const eCustomDataType input_grid_type = eCustomDataType(storage.grid_type);
+  auto interpolation_mode = (const GeometryNodeSampleVolumeInterpolationMode)

@@ -0,0 +329,4 @@
+  GField output_field = GField(std::move(op));
+
+  output_attribute_field(params, std::move(output_field));
+  params.set_default_remaining_outputs();

@@ -0,0 +4,4 @@
+
+#include "BKE_volume.h"
+#include "BLI_virtual_array.hh"
+#include "NOD_add_node_search.hh"

@@ -0,0 +123,4 @@
+{
+  using ValueT = typename GridT::ValueType;
+  using AccessorT = typename GridT::ConstAccessor;
+  const GridT::ConstPtr grid = openvdb::gridConstPtrCast<GridT>(base_grid);

@@ -0,0 +231,4 @@
+  switch (data_type) {
+    case CD_PROP_FLOAT:
+      return params.extract_input<Field<float>>("Grid_Float");
+    case CD_PROP_FLOAT3:

@@ -0,0 +310,4 @@
+  const VolumeComponent *component = geometry_set.get_component_for_read<VolumeComponent>();
+  const Volume *volume = component->get_for_read();
+  BKE_volume_load(volume, DEG_get_bmain(params.depsgraph()));
+  const VolumeGrid *volume_grid = BKE_volume_grid_find_for_read(volume, grid_name.c_str());

@@ -0,0 +64,4 @@
+static void search_link_ops(GatherLinkSearchOpParams &params)
+{
+  if (U.experimental.use_new_volume_nodes) {
+    blender::nodes::search_link_ops_for_basic_node(params);

@@ -0,0 +114,4 @@
+  bNodeSocket *socket_value_boolean = socket_value_float->next;
+  bNodeSocket *socket_value_int32 = socket_value_boolean->next;
+
+  nodeSetSocketAvailability(ntree, socket_value_vector, grid_type == CD_PROP_FLOAT3);

@@ -0,0 +148,4 @@
+  return "";
+}
+
+static std::optional<eCustomDataType> vdb_grid_type_to_customdata_type(

@@ -0,0 +179,4 @@
+  const GridT::ConstPtr grid = openvdb::gridConstPtrCast<GridT>(base_grid);
+  AccessorT accessor = grid->getConstAccessor();
+
+  auto copy_data = [&](auto sampler) {

@@ -0,0 +356,4 @@
+  auto op = FieldOperation::Create(std::move(fn), {position_field});
+  GField output_field = GField(std::move(op));
+
+  if (grid_customdata_type.value() != output_field_type) {

@@ -0,0 +134,4 @@
+
+static const StringRefNull get_grid_name(GField &field)
+{
+  if (field.node().field_inputs() != nullptr) {