Fixed windows MSVC build compatibility (#9)

Summary:
Fixed a few MSVC compiler (visual studio 2019, MSVC 19.16.27034) compatibility issues
1. Replaced long with int64_t. aten::data_ptr\<long\> is not supported in MSVC
2. pytorch3d/csrc/rasterize_points/rasterize_points_cpu.cpp, inline function is not correctly recognized by MSVC.
3. pytorch3d/csrc/rasterize_meshes/geometry_utils.cuh
const auto kEpsilon = 1e-30;
MSVC does not compile this const into both host and device, change to a MACRO.
4. pytorch3d/csrc/rasterize_meshes/geometry_utils.cuh,
const float area2 = pow(area, 2.0);
2.0 is considered as double by MSVC and raised an error
5. pytorch3d/csrc/rasterize_points/rasterize_points_cpu.cpp
std::tuple<torch::Tensor, torch::Tensor> RasterizePointsCoarseCpu() return type does not match the declaration in rasterize_points_cpu.h.
Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/9

Reviewed By: nikhilaravi

Differential Revision: D19986567

Pulled By: yuanluxu

fbshipit-source-id: f4d98525d088c99c513b85193db6f0fc69c7f017

INSTALL.md

@@ -7,7 +7,7 @@
 
 The core library is written in PyTorch. Several components have underlying implementation in CUDA for improved performance. A subset of these components have CPU implementations in C++/Pytorch. It is advised to use PyTorch3d with GPU support in order to use all the features.
 
-- Linux or macOS
+- Linux or macOS or Windows
 - Python ≥ 3.6
 - PyTorch 1.4
 - torchvision that matches the PyTorch installation. You can install them together at pytorch.org to make sure of this.
@@ -72,3 +72,41 @@ To rebuild after installing from a local clone run, `rm -rf build/ **/*.so` then
 ```
 MACOSX_DEPLOYMENT_TARGET=10.14 CC=clang CXX=clang++ pip install -e .
 ```
+
+**Install from local clone on Windows:**
+
+If you are using pre-compiled pytorch 1.4 and torchvision 0.5, you should make the following changes to the pytorch source code to successfully compile with Visual Studio 2019 (MSVC 19.16.27034) and CUDA 10.1.
+
+Change python/Lib/site-packages/torch/include/csrc/jit/script/module.h
+
+L466, 476, 493, 506, 536
+```
+-static constexpr *
++static const *
+```
+Change python/Lib/site-packages/torch/include/csrc/jit/argument_spec.h
+
+L190
+```
+-static constexpr size_t DEPTH_LIMIT = 128;
++static const size_t DEPTH_LIMIT = 128;
+```
+
+Change python/Lib/site-packages/torch/include/pybind11/cast.h
+
+L1449
+```
+-explicit operator type&() { return *(this->value); }
++explicit operator type& () { return *((type*)(this->value)); }
+```
+
+After patching, you can go to "x64 Native Tools Command Prompt for VS 2019" to compile and install
+```
+cd pytorch3d
+python3 setup.py install
+```
+After installing, verify whether all unit tests have passed
+```
+cd tests
+python3 -m unittest discover -p *.py
+```