Make tinyobj::index_t from tinyobjloader hashable

gistfile1.cpp

#include <unordered_map>

#define TINYOBJLOADER_IMPLEMENTATION
#include "tiny_obj_loader.h"

namespace tinyobj {
  
bool operator==(const index_t& lhs, const index_t& rhs) {
  return
    lhs.vertex_index == rhs.vertex_index &&
    lhs.normal_index == rhs.normal_index &&
    lhs.texcoord_index == rhs.texcoord_index;
}

}

namespace std {

template<>
struct hash<::tinyobj::index_t> {
  std::size_t operator()(const ::tinyobj::index_t& idx) const {
    size_t result = 0;
    hash_combine(result, idx.vertex_index);
    hash_combine(result, idx.normal_index);
    hash_combine(result, idx.texcoord_index);
    return result;
  }
 private:
  // From boost::hash_combine.
  static void hash_combine(size_t& seed, size_t val) {
    std::hash<size_t> h;
    seed ^= (h(val) + 0x9e3779b9 + (seed<<6) + (seed>>2));
  }
};

}