python: ability to pass extra attributes to meshtools.interleave().

Yay, finally it's (almost) possible to create custom meshes from pure
Python. Except that there always has to be some initial mesh to add
attributes to, and it's not yet possible to supply index data there.

doc/python/magnum.meshtools.rst

@@ -47,6 +47,10 @@
         :ref:`MeshPrimitive.LINE_LOOP`, :ref:`MeshPrimitive.TRIANGLE_STRIP` or
         :ref:`MeshPrimitive.TRIANGLE_FAN`
 
+.. py:function:: magnum.meshtools.interleave
+    :raise AssertionError: If any attribute in :p:`extra` has the data size
+        different from :p:`mesh` vertex count
+
 .. py:function:: magnum.meshtools.transform2d
     :raise KeyError: If :p:`mesh` doesn't have
         :ref:`trade.MeshAttribute.POSITION` of index :p:`id` (and in morph

doc/python/magnum.trade.rst

@@ -138,8 +138,9 @@
 .. py:class:: magnum.trade.MeshAttributeData
 
     Associates a typed data view with a name, vertex format and other mesh
-    attribute properties. The data view can be either one-dimensional, for
+    attribute properties, which can be subsequently put into a :ref:`MeshData`
-    example a NumPy array:
+    instance, for example with :ref:`meshtools.interleave()`. The data view can
+    be either one-dimensional, for example a NumPy array:
 
     ..
         Just to verify the snippet below actually works (don't want the arrows

src/python/magnum/meshtools.cpp

@@ -169,12 +169,25 @@ void meshtools(py::module_& m) {
 
             return MeshTools::generateIndices(mesh);
         }, "Convert a mesh to plain indexed lines or triangles", py::arg("mesh"))
-        .def("interleave", [](const Trade::MeshData& mesh, MeshTools::InterleaveFlag flags) {
+        /** @todo eugh, find a way w/o the STL vector */
+        .def("interleave", [](const Trade::MeshData& mesh, const std::vector<Trade::MeshAttributeData>& extra, MeshTools::InterleaveFlag flags) {
+            for(std::size_t i = 0; i != extra.size(); ++i) {
+                const Trade::MeshAttributeData& attribute = extra[i];
+                if(attribute.data().size() != mesh.vertexCount()) {
+                    PyErr_Format(PyExc_AssertionError, "extra attribute %zu expected to have %u items but got %zu", i, mesh.vertexCount(), attribute.data().size());
+                    throw py::error_already_set{};
+                }
+            }
             /** @todo check that the vertices/indices aren't impl-specific if
                 the interleaved preservation is disabled, once it's possible to
                 test */
-            return MeshTools::interleave(mesh, {}, flags);
+            return MeshTools::interleave(mesh, extra, flags);
-        }, "Interleave mesh data", py::arg("mesh"), py::arg("flags") = MeshTools::InterleaveFlag::PreserveInterleavedAttributes)
+        }, "Interleave mesh data", py::arg("mesh"),
+            #if PYBIND11_VERSION_MAJOR*100 + PYBIND11_VERSION_MINOR >= 206
+            py::kw_only{}, /* new in pybind11 2.6 */
+            #endif
+            py::arg("extra") = std::vector<Trade::MeshAttributeData>{},
+            py::arg("flags") = MeshTools::InterleaveFlag::PreserveInterleavedAttributes)
         .def("copy", static_cast<Trade::MeshData(*)(const Trade::MeshData&)>(MeshTools::copy), "Make an owned copy of the mesh", py::arg("mesh"))
         /** @todo check that the indices/vertices aren't impl-specific once
             it's possible to test */

src/python/magnum/test/test_meshtools.py

@@ -23,6 +23,7 @@
 #   DEALINGS IN THE SOFTWARE.
 #
 
+import array
 import os
 import sys
 import unittest
@@ -211,11 +212,27 @@ class Interleave(unittest.TestCase):
         # Gap after normals not removed
         self.assertEqual(interleaved.attribute_stride(trade.MeshAttribute.POSITION), 12 + 12 + 8)
 
-        interleaved_packed = meshtools.interleave(mesh, meshtools.InterleaveFlags.NONE)
+        interleaved_packed = meshtools.interleave(mesh, flags=meshtools.InterleaveFlags.NONE)
         self.assertEqual(interleaved_packed.attribute_count(), 2)
         # Gap after normals removed
         self.assertEqual(interleaved_packed.attribute_stride(trade.MeshAttribute.POSITION), 12 + 8)
 
+    def test_extra(self):
+        interleaved = meshtools.interleave(primitives.plane_solid(), extra=[
+            trade.MeshAttributeData(trade.MeshAttribute.OBJECT_ID, VertexFormat.UNSIGNED_SHORT, array.array('H', [3, 176, 2, 14]))
+        ])
+        self.assertEqual(interleaved.attribute_count(), 3)
+        self.assertTrue(interleaved.has_attribute(trade.MeshAttribute.OBJECT_ID))
+        self.assertEqual(interleaved.attribute_format(trade.MeshAttribute.OBJECT_ID), VertexFormat.UNSIGNED_SHORT)
+        self.assertEqual(list(interleaved.attribute(trade.MeshAttribute.OBJECT_ID)), [3, 176, 2, 14])
+
+    def test_extra_invalid(self):
+        with self.assertRaisesRegex(AssertionError, "extra attribute 1 expected to have 4 items but got 5"):
+            meshtools.interleave(primitives.plane_solid(), extra=[
+                trade.MeshAttributeData(trade.MeshAttribute.CUSTOM(33), VertexFormat.UNSIGNED_BYTE, array.array('B', [3, 176, 2, 12])),
+                trade.MeshAttributeData(trade.MeshAttribute.OBJECT_ID, VertexFormat.UNSIGNED_SHORT, array.array('H', [3, 176, 2, 12, 6]))
+            ])
+
 class Copy(unittest.TestCase):
     def test(self):
         mesh = primitives.square_solid()