scripts/startup/bl_ui/node_add_menu_geometry.py

@@ -307,6 +307,7 @@ class NODE_MT_geometry_node_GEO_MATERIAL(Menu):
     def draw(self, _context):
         layout = self.layout
         node_add_menu.add_node_type(layout, "GeometryNodeReplaceMaterial")
+        node_add_menu.add_node_type(layout, "GeometryNodeSampleMaterial")
         layout.separator()
         node_add_menu.add_node_type(layout, "GeometryNodeInputMaterialIndex")
         node_add_menu.add_node_type(layout, "GeometryNodeMaterialSelection")

source/blender/blenkernel/BKE_node.h

@@ -1575,6 +1575,7 @@ void BKE_nodetree_remove_layer_n(struct bNodeTree *ntree, struct Scene *scene, i
 #define GEO_NODE_SDF_VOLUME_SPHERE 1196
 #define GEO_NODE_MEAN_FILTER_SDF_VOLUME 1197
 #define GEO_NODE_OFFSET_SDF_VOLUME 1198
+#define GEO_NODE_SAMPLE_MATERIAL 1199
 
 /** \} */
 

source/blender/nodes/NOD_static_types.h

@@ -397,6 +397,7 @@ DefNode(GeometryNode, GEO_NODE_REVERSE_CURVE, 0, "REVERSE_CURVE", ReverseCurve,
 DefNode(GeometryNode, GEO_NODE_ROTATE_INSTANCES, 0, "ROTATE_INSTANCES", RotateInstances, "Rotate Instances", "Rotate geometry instances in local or global space")
 DefNode(GeometryNode, GEO_NODE_SAMPLE_CURVE, def_geo_curve_sample, "SAMPLE_CURVE", SampleCurve, "Sample Curve", "Retrieve data from a point on a curve at a certain distance from its start")
 DefNode(GeometryNode, GEO_NODE_SAMPLE_INDEX, def_geo_sample_index, "SAMPLE_INDEX", SampleIndex, "Sample Index", "Retrieve values from specific geometry elements")
+DefNode(GeometryNode, GEO_NODE_SAMPLE_MATERIAL, 0, "SAMPLE_MATERIAL", SampleMaterial, "Sample Material", "")
 DefNode(GeometryNode, GEO_NODE_SAMPLE_NEAREST_SURFACE, def_geo_sample_nearest_surface, "SAMPLE_NEAREST_SURFACE", SampleNearestSurface, "Sample Nearest Surface", "Calculate the interpolated value of a mesh attribute on the closest point of its surface")
 DefNode(GeometryNode, GEO_NODE_SAMPLE_NEAREST, def_geo_sample_nearest, "SAMPLE_NEAREST", SampleNearest, "Sample Nearest", "Find the element of a geometry closest to a position")
 DefNode(GeometryNode, GEO_NODE_SAMPLE_UV_SURFACE, def_geo_sample_uv_surface, "SAMPLE_UV_SURFACE", SampleUVSurface, "Sample UV Surface", "Calculate the interpolated values of a mesh attribute at a UV coordinate")

source/blender/nodes/geometry/CMakeLists.txt

@@ -148,6 +148,7 @@ set(SRC
   nodes/node_geo_remove_attribute.cc
   nodes/node_geo_rotate_instances.cc
   nodes/node_geo_sample_index.cc
+  nodes/node_geo_sample_material.cc
   nodes/node_geo_sample_nearest.cc
   nodes/node_geo_sample_nearest_surface.cc
   nodes/node_geo_sample_uv_surface.cc

source/blender/nodes/geometry/node_geometry_register.cc

@@ -132,6 +132,7 @@ void register_geometry_nodes()
   register_node_type_geo_remove_attribute();
   register_node_type_geo_rotate_instances();
   register_node_type_geo_sample_index();
+  register_node_type_geo_sample_material();
   register_node_type_geo_sample_nearest_surface();
   register_node_type_geo_sample_nearest();
   register_node_type_geo_sample_uv_surface();

source/blender/nodes/geometry/node_geometry_register.hh

@@ -129,6 +129,7 @@ void register_node_type_geo_realize_instances();
 void register_node_type_geo_remove_attribute();
 void register_node_type_geo_rotate_instances();
 void register_node_type_geo_sample_index();
+void register_node_type_geo_sample_material();
 void register_node_type_geo_sample_nearest_surface();
 void register_node_type_geo_sample_nearest();
 void register_node_type_geo_sample_uv_surface();

source/blender/nodes/geometry/nodes/node_geo_sample_material.cc

@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "DEG_depsgraph_query.h"
+
+#include "BLI_task.hh"
+
+#include "DNA_mesh_types.h"
+#include "DNA_meshdata_types.h"
+
+#include "BKE_curves.hh"
+#include "BKE_mesh.hh"
+
+#include "node_geometry_util.hh"
+
+namespace blender::nodes::node_geo_sample_material_cc {
+
+static void node_declare(NodeDeclarationBuilder &b)
+{
+  b.add_input<decl::Geometry>(N_("Geometry"));
+  b.add_input<decl::Geometry>(N_("Material Source"));
+  b.add_input<decl::Bool>(N_("Selection")).default_value(true).hide_value().field_on({0});
+  b.add_input<decl::Int>(N_("Material Index")).default_value(1).field_on({0});
+  /* TODO: It's possible to avoid propagation from second geometry input? Or i miss something? */
+  b.add_output<decl::Geometry>(N_("Geometry")).propagate_all();
+}
+
+static void node_geo_exec(GeoNodeExecParams params)
+{
+  GeometrySet geometry = params.extract_input<GeometrySet>("Geometry");
+  Field<bool> selection_field = params.extract_input<Field<bool>>("Selection");
+  Field<int> index_field = params.extract_input<Field<int>>("Material Index");
+
+  geometry.modify_geometry_sets([&](GeometrySet &geometry_set) {
+    const MeshComponent *component = geometry_set.get_component_for_read<MeshComponent>();
+    Mesh *mesh = geometry_set.get_mesh_for_write();
+    if (!mesh) {
+      return;
+    }
+
+    bke::GeometryFieldContext field_context{*component, ATTR_DOMAIN_FACE};
+    fn::FieldEvaluator evaluator{field_context, mesh->totpoly};
+    evaluator.set_selection(selection_field);
+    evaluator.add(index_field);
+    evaluator.evaluate();
+
+    const IndexMask selection = evaluator.get_evaluated_selection_as_mask();
+    if (selection.is_empty()) {
+      return;
+    }
+    
+    bke::MutableAttributeAccessor attributes = mesh->attributes_for_write();
+    SpanAttributeWriter<int> dst_indices_attribute = attributes.lookup_or_add_for_write_only_span<int>("material_index", ATTR_DOMAIN_FACE);
+    MutableSpan<int> dst_indices = dst_indices_attribute.span;
+    
+    const VArray<int> &indices = evaluator.get_evaluated<int>(0);
+    
+    indices.materialize(selection, dst_indices);
+    
+    dst_indices_attribute.finish();
+  });
+
+  params.set_output("Geometry", std::move(geometry));
+}
+
+}  // namespace blender::nodes::node_geo_sample_material_cc
+
+void register_node_type_geo_sample_material()
+{
+  namespace file_ns = blender::nodes::node_geo_sample_material_cc;
+
+  static bNodeType ntype;
+
+  geo_node_type_base(&ntype, GEO_NODE_SAMPLE_MATERIAL, "Sample Material", NODE_CLASS_GEOMETRY);
+  ntype.geometry_node_execute = file_ns::node_geo_exec;
+  ntype.declare = file_ns::node_declare;
+  nodeRegisterType(&ntype);
+}