Mesh RNA API: Expose contiguous normal arrays

Since vertex and face normals are now stored on the mesh when necessary,
we can expose them as contiguous arrays of vectors in the Python API.
This can give render engines and other addons easy access to they data
for fast access through a regular collection property.

While "Mesh Vertex" still has a "normal" property in RNA, that is only
maintained in order to avoid breaking the existing API, and accessing
it is less efficient than accessing the normals directly.

I made the normal arrays read-only, because modifying them could
put them in an invalid state. This is inline with how we treat the data
internally, and helps keep relationships between data clear.

Differential Revision: https://developer.blender.org/D13839

1 files changed, 74 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_mesh.c b/source/blender/makesrna/intern/rna_mesh.c
index c1aea33b9a5..7d43d500760 100644
--- a/source/blender/makesrna/intern/rna_mesh.c
+++ b/source/blender/makesrna/intern/rna_mesh.c
@@ -1288,6 +1288,32 @@ static char *rna_LoopCustomData_data_path(PointerRNA *ptr, const char *collectio
   return NULL;
 }
 
+static void rna_Mesh_vertex_normals_begin(CollectionPropertyIterator *iter, PointerRNA *ptr)
+{
+  const Mesh *mesh = rna_mesh(ptr);
+  const float(*normals)[3] = BKE_mesh_vertex_normals_ensure(mesh);
+  rna_iterator_array_begin(iter, (void *)normals, sizeof(float[3]), mesh->totvert, false, NULL);
+}
+
+static int rna_Mesh_vertex_normals_length(PointerRNA *ptr)
+{
+  const Mesh *mesh = rna_mesh(ptr);
+  return mesh->totvert;
+}
+
+static void rna_Mesh_poly_normals_begin(CollectionPropertyIterator *iter, PointerRNA *ptr)
+{
+  const Mesh *mesh = rna_mesh(ptr);
+  const float(*normals)[3] = BKE_mesh_poly_normals_ensure(mesh);
+  rna_iterator_array_begin(iter, (void *)normals, sizeof(float[3]), mesh->totpoly, false, NULL);
+}
+
+static int rna_Mesh_poly_normals_length(PointerRNA *ptr)
+{
+  const Mesh *mesh = rna_mesh(ptr);
+  return mesh->totpoly;
+}
+
 static char *rna_MeshUVLoop_path(PointerRNA *ptr)
 {
   return rna_LoopCustomData_data_path(ptr, "uv_layers", CD_MLOOPUV);
@@ -2520,6 +2546,20 @@ static void rna_def_mesh_polygons(BlenderRNA *brna, PropertyRNA *cprop)
   RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
 }
 
+/* Defines a read-only vector type since normals should not be modified manually. */
+static void rna_def_normal_layer_value(BlenderRNA *brna)
+{
+  StructRNA *srna = RNA_def_struct(brna, "MeshNormalValue", NULL);
+  RNA_def_struct_sdna(srna, "vec3f");
+  RNA_def_struct_ui_text(srna, "Mesh Normal Vector", "Vector in a mesh normal array");
+
+  PropertyRNA *prop = RNA_def_property(srna, "vector", PROP_FLOAT, PROP_DIRECTION);
+  RNA_def_property_ui_text(prop, "Vector", "3D vector");
+  RNA_def_property_float_sdna(prop, NULL, "x");
+  RNA_def_property_array(prop, 3);
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+}
+
 static void rna_def_loop_colors(BlenderRNA *brna, PropertyRNA *cprop)
 {
   StructRNA *srna;
@@ -3017,6 +3057,40 @@ static void rna_def_mesh(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Polygons", "Polygons of the mesh");
   rna_def_mesh_polygons(brna, prop);
 
+  rna_def_normal_layer_value(brna);
+
+  prop = RNA_def_property(srna, "vertex_normals", PROP_COLLECTION, PROP_NONE);
+  RNA_def_property_struct_type(prop, "MeshNormalValue");
+  RNA_def_property_ui_text(prop,
+                           "Vertex Normals",
+                           "The normal direction of each vertex, defined as the average of the "
+                           "surrounding face normals");
+  RNA_def_property_collection_funcs(prop,
+                                    "rna_Mesh_vertex_normals_begin",
+                                    "rna_iterator_array_next",
+                                    "rna_iterator_array_end",
+                                    "rna_iterator_array_get",
+                                    "rna_Mesh_vertex_normals_length",
+                                    NULL,
+                                    NULL,
+                                    NULL);
+
+  prop = RNA_def_property(srna, "polygon_normals", PROP_COLLECTION, PROP_NONE);
+  RNA_def_property_struct_type(prop, "MeshNormalValue");
+  RNA_def_property_ui_text(prop,
+                           "Polygon Normals",
+                           "The normal direction of each polygon, defined by the winding order "
+                           "and position of its vertices");
+  RNA_def_property_collection_funcs(prop,
+                                    "rna_Mesh_poly_normals_begin",
+                                    "rna_iterator_array_next",
+                                    "rna_iterator_array_end",
+                                    "rna_iterator_array_get",
+                                    "rna_Mesh_poly_normals_length",
+                                    NULL,
+                                    NULL,
+                                    NULL);
+
   prop = RNA_def_property(srna, "loop_triangles", PROP_COLLECTION, PROP_NONE);
   RNA_def_property_collection_sdna(prop, NULL, "runtime.looptris.array", "runtime.looptris.len");
   RNA_def_property_struct_type(prop, "MeshLoopTriangle");