python: make it possible to set mesh index buffer.

Heh, funny how this is not there yet.

src/python/magnum/gl.cpp

@@ -944,6 +944,11 @@ void gl(py::module_& m) {
         #endif
         ;
 
+    py::enum_<GL::MeshIndexType>{m, "MeshIndexType", "Mesh index type"}
+        .value("UNSIGNED_BYTE", GL::MeshIndexType::UnsignedByte)
+        .value("UNSIGNED_SHORT", GL::MeshIndexType::UnsignedShort)
+        .value("UNSIGNED_INT", GL::MeshIndexType::UnsignedInt);
+
     /* Class definition above AbstractShaderProgram, since that needs it for
        the draw() signature */
     mesh.def(py::init<GL::MeshPrimitive>(), "Constructor", py::arg("primitive") = GL::MeshPrimitive::Triangles)
@@ -965,6 +970,14 @@ void gl(py::module_& m) {
         .def_property("count", &GL::Mesh::count, [](GL::Mesh& self, UnsignedInt count) {
             self.setCount(count);
         }, "Vertex/index count")
+        .def_property_readonly("is_indexed", &GL::Mesh::isIndexed, "Whether the mesh is indexed")
+        .def_property_readonly("index_type", [](GL::Mesh& self) {
+            if(!self.isIndexed()) {
+                PyErr_SetString(PyExc_RuntimeError, "the mesh is not indexed");
+                throw py::error_already_set{};
+            }
+            return self.indexType();
+        }, "Index type")
 
         /* Using lambdas to avoid method chaining getting into signatures */
 
@@ -975,7 +988,22 @@ void gl(py::module_& m) {
                the mesh */
             pyObjectHolderFor<GL::PyMeshHolder>(self).buffers.emplace_back(pyObjectFromInstance(buffer));
         }, "Add vertex buffer", py::arg("buffer"), py::arg("offset"), py::arg("stride"), py::arg("attribute"))
-        /** @todo more */
+        /** @todo add_vertex_buffer_instanced */
+
+        .def("set_index_buffer", [](GL::Mesh& self, GL::Buffer& buffer, GLintptr offset, GL::MeshIndexType type) {
+            self.setIndexBuffer(buffer, offset, type);
+
+            /* Keep a reference to the buffer to avoid it being deleted before
+               the mesh */
+            pyObjectHolderFor<GL::PyMeshHolder>(self).buffers.emplace_back(pyObjectFromInstance(buffer));
+        }, "Set index buffer", py::arg("buffer"), py::arg("offset"), py::arg("type"))
+        .def("set_index_buffer", [](GL::Mesh& self, GL::Buffer& buffer, GLintptr offset, MeshIndexType type) {
+            self.setIndexBuffer(buffer, offset, type);
+
+            /* Keep a reference to the buffer to avoid it being deleted before
+               the mesh */
+            pyObjectHolderFor<GL::PyMeshHolder>(self).buffers.emplace_back(pyObjectFromInstance(buffer));
+        }, "Set index buffer", py::arg("buffer"), py::arg("offset"), py::arg("type"))
 
         .def_property_readonly("buffers", [](GL::Mesh& self) {
             return pyObjectHolderFor<GL::PyMeshHolder>(self).buffers;

src/python/magnum/test/test_gl_gl.py

@@ -278,7 +278,7 @@ class Mesh(GLTestCase):
         a.count = 15
         self.assertEqual(a.count, 15)
 
-    def test_add_buffer(self):
+    def test_add_vertex_buffer(self):
         buffer = gl.Buffer()
         buffer_refcount = sys.getrefcount(buffer)
 
@@ -293,6 +293,27 @@ class Mesh(GLTestCase):
         del mesh
         self.assertEqual(sys.getrefcount(buffer), buffer_refcount)
 
+    def test_set_index_buffer(self):
+        buffer = gl.Buffer()
+        buffer_refcount = sys.getrefcount(buffer)
+
+        # Adding a buffer to the mesh should increase its ref count
+        mesh = gl.Mesh()
+        mesh.set_index_buffer(buffer, 0, gl.MeshIndexType.UNSIGNED_INT)
+        self.assertEqual(len(mesh.buffers), 1)
+        self.assertIs(mesh.buffers[0], buffer)
+        self.assertEqual(sys.getrefcount(buffer), buffer_refcount + 1)
+
+        # Trying with the generic type as well
+        mesh.set_index_buffer(buffer, 0, MeshIndexType.UNSIGNED_SHORT)
+        self.assertEqual(len(mesh.buffers), 2)
+        self.assertIs(mesh.buffers[1], buffer)
+        self.assertEqual(sys.getrefcount(buffer), buffer_refcount + 2)
+
+        # Deleting the mesh should decrease it again
+        del mesh
+        self.assertEqual(sys.getrefcount(buffer), buffer_refcount)
+
 class Renderbuffer(GLTestCase):
     def test_init(self):
         renderbuffer = gl.Renderbuffer()