Add note on developer build of python binding.

syoyo · syoyo · commit bf3987441dea · 2019-11-17T22:46:49.000+09:00
Add comment on `numpy_indices` of python binding. Fixes tinyobjloader#242
diff --git a/python/README.md b/python/README.md
@@ -52,6 +52,22 @@ Please take a look at `python/sample.py` file in tinyobjloader git repo.
 
 https://github.com/syoyo/tinyobjloader/blob/master/python/sample.py
 
+## How to build
+
+Using `cibuildwheel` is an recommended way to build a python module.
+See $tinyobjloader/azure-pipelines.yml for details.
+
+### Developer build
+
+Edit `setup.py` and uncomment `Developer option` lines
+
+Assume pip is installed.
+
+```
+$ pip install pybind11
+$ python setup.py build
+```
+
 ## License
 
 MIT license.
diff --git a/python/bindings.cc b/python/bindings.cc
@@ -130,6 +130,16 @@ PYBIND11_MODULE(tinyobjloader, tobj_module)
     })
     .def_readonly("indices", &mesh_t::indices)
     .def("numpy_indices", [] (mesh_t &instance) {
+        // Flatten indexes. index_t is composed of 3 ints(vertex_index, normal_index, texcoord_index).
+        // numpy_indices = [0, -1, -1, 1, -1, -1, ...]
+        // C++11 or later should pack POD struct tightly and does not reorder variables, 
+        // so we can memcpy to copy data.
+        // Still, we check the size of struct and byte offsets of each variable just for sure.
+        static_assert(sizeof(index_t) == 12, "sizeof(index_t) must be 12");
+        static_assert(offsetof(index_t, vertex_index) == 0, "offsetof(index_t, vertex_index) must be 0");
+        static_assert(offsetof(index_t, normal_index) == 4, "offsetof(index_t, normal_index) must be 4");
+        static_assert(offsetof(index_t, texcoord_index) == 8, "offsetof(index_t, texcoord_index) must be 8");
+
         auto ret = py::array_t<int>(instance.indices.size() * 3);
         py::buffer_info buf = ret.request();
         memcpy(buf.ptr, instance.indices.data(), instance.indices.size() * 3 * sizeof(int));
diff --git a/python/sample.py b/python/sample.py
@@ -46,6 +46,8 @@
 for (i, v) in enumerate(attrib.texcoords):
     print("vt[{}] = {}".format(i, t))
 
+print("numpy_vertices = {}".format(attrib.numpy_vertices()))
+
 materials = reader.GetMaterials()
 print("Num materials: ", len(materials))
 for m in materials:
@@ -66,8 +68,10 @@
 print("Num shapes: ", len(shapes))
 for shape in shapes:
     print(shape.name)
-    print("num_indices = {}".format(len(shape.mesh.indices)))
+    print("len(num_indices) = {}".format(len(shape.mesh.indices)))
     for (i, idx) in enumerate(shape.mesh.indices):
         print("[{}] v_idx {}".format(i, idx.vertex_index))
         print("[{}] vn_idx {}".format(i, idx.normal_index))
         print("[{}] vt_idx {}".format(i, idx.texcoord_index))
+    print("numpy_indices = {}".format(shape.mesh.numpy_indices()))
+    print("numpy_num_face_vertices = {}".format(shape.mesh.numpy_num_face_vertices()))
diff --git a/python/setup.py b/python/setup.py
@@ -1,4 +1,5 @@
 import setuptools
+import platform
 
 with open("README.md", "r") as fh:
     long_description = fh.read()
@@ -44,10 +45,24 @@ def __str__(self):
             return interpreter_include_path
 
 
+ext_compile_args = ["-std=c++11"]
+ext_link_args = []
+
+# Developer option
+#
+#if platform.system() == "Darwin":
+#    # XCode10 or later does not support libstdc++, so we need to use libc++.
+#    # macosx-version 10.6 does not support libc++, so we require min macosx version 10.9.
+#    ext_compile_args.append("-stdlib=libc++")
+#    ext_compile_args.append("-mmacosx-version-min=10.9")
+#    ext_link_args.append("-stdlib=libc++")
+#    ext_link_args.append("-mmacosx-version-min=10.9")
+
 # `tiny_obj_loader.cc` contains implementation of tiny_obj_loader.
 m = setuptools.Extension(
     "tinyobjloader",
-    extra_compile_args=["-std=c++11"],
+    extra_compile_args=ext_compile_args,
+    extra_link_args=ext_link_args,
     sources=["bindings.cc", "tiny_obj_loader.cc"],
     include_dirs=[
         # Support `build_ext` finding tinyobjloader (without first running
