gistfile1.cpp

void load_obj(const char* filename, Mesh* mesh) {
  ifstream in(filename, ios::in);
  if (!in) { cerr << "Cannot open " << filename << endl; exit(1); }
  vector<int> nb_seen;

  string line;
  while (getline(in, line)) {
    if (line.substr(0,2) == "v ") {
      istringstream s(line.substr(2));
      glm::vec4 v; s >> v.x; s >> v.y; s >> v.z; v.w = 1.0;
      mesh->vertices.push_back(v);
    }  else if (line.substr(0,2) == "f ") {
      istringstream s(line.substr(2));
      GLushort a,b,c;
      s >> a; s >> b; s >> c;
      a--; b--; c--;
      mesh->elements.push_back(a); mesh->elements.push_back(b); mesh->elements.push_back(c);
    }
    else if (line[0] == '#') { /* ignoring this line */ }
    else { /* ignoring this line */ }
  }

  mesh->normals.resize(mesh->vertices.size(), glm::vec3(0.0, 0.0, 0.0));
  nb_seen.resize(mesh->vertices.size(), 0);
  for (unsigned int i = 0; i < mesh->elements.size(); i+=3) {
    GLushort ia = mesh->elements[i];
    GLushort ib = mesh->elements[i+1];
    GLushort ic = mesh->elements[i+2];
    glm::vec3 normal = glm::normalize(glm::cross(
      glm::vec3(mesh->vertices[ib]) - glm::vec3(mesh->vertices[ia]),
      glm::vec3(mesh->vertices[ic]) - glm::vec3(mesh->vertices[ia])));

    int v[3];  v[0] = ia;  v[1] = ib;  v[2] = ic;
    for (int j = 0; j < 3; j++) {
      GLushort cur_v = v[j];
      nb_seen[cur_v]++;
      if (nb_seen[cur_v] == 1) {
	mesh->normals[cur_v] = normal;
      } else {
	// average
	mesh->normals[cur_v].x = mesh->normals[cur_v].x * (1.0 - 1.0/nb_seen[cur_v]) + normal.x * 1.0/nb_seen[cur_v];
	mesh->normals[cur_v].y = mesh->normals[cur_v].y * (1.0 - 1.0/nb_seen[cur_v]) + normal.y * 1.0/nb_seen[cur_v];
	mesh->normals[cur_v].z = mesh->normals[cur_v].z * (1.0 - 1.0/nb_seen[cur_v]) + normal.z * 1.0/nb_seen[cur_v];
	mesh->normals[cur_v] = glm::normalize(mesh->normals[cur_v]);
      }
    }
  }
}