tinyobjloader/examples/obj_sticher/obj_writer.cc

//
// Simple wavefront .obj writer
//
#include "obj_writer.h"
#include <cstdio>

static std::string GetFileBasename(const std::string& FileName)
{
    if(FileName.find_last_of(".") != std::string::npos)
        return FileName.substr(0, FileName.find_last_of("."));
    return "";
}

bool WriteMat(const std::string& filename, const std::vector<tinyobj::material_t>& materials) {
  FILE* fp = fopen(filename.c_str(), "w");
  if (!fp) {
    fprintf(stderr, "Failed to open file [ %s ] for write.\n", filename.c_str());
    return false;
  }

  for (size_t i = 0; i < materials.size(); i++) {

    tinyobj::material_t mat = materials[i];

    fprintf(fp, "newmtl %s\n", mat.name.c_str());
    fprintf(fp, "Ka %f %f %f\n", mat.ambient[0], mat.ambient[1], mat.ambient[2]);
    fprintf(fp, "Kd %f %f %f\n", mat.diffuse[0], mat.diffuse[1], mat.diffuse[2]);
    fprintf(fp, "Ks %f %f %f\n", mat.specular[0], mat.specular[1], mat.specular[2]);
    fprintf(fp, "Kt %f %f %f\n", mat.transmittance[0], mat.specular[1], mat.specular[2]);
    fprintf(fp, "Ke %f %f %f\n", mat.emission[0], mat.emission[1], mat.emission[2]);
    fprintf(fp, "Ns %f\n", mat.shininess);
    fprintf(fp, "Ni %f\n", mat.ior);
    fprintf(fp, "illum %d\n", mat.illum);
    fprintf(fp, "\n");
    // @todo { texture }
  }
  
  fclose(fp);

  return true;
}

bool WriteObj(const std::string& filename, const tinyobj::attrib_t& attributes, const std::vector<tinyobj::shape_t>& shapes, const std::vector<tinyobj::material_t>& materials, bool coordTransform) {
  FILE* fp = fopen(filename.c_str(), "w");
  if (!fp) {
    fprintf(stderr, "Failed to open file [ %s ] for write.\n", filename.c_str());
    return false;
  }

  std::string basename = GetFileBasename(filename);
  std::string material_filename = basename + ".mtl";

  int prev_material_id = -1;

  fprintf(fp, "mtllib %s\n\n", material_filename.c_str());

  // facevarying vtx
  for (size_t k = 0; k < attributes.vertices.size(); k+=3) {
    if (coordTransform) {
      fprintf(fp, "v %f %f %f\n",
        attributes.vertices[k + 0],
        attributes.vertices[k + 2],
        -attributes.vertices[k + 1]);
    } else {
      fprintf(fp, "v %f %f %f\n",
        attributes.vertices[k + 0],
        attributes.vertices[k + 1],
        attributes.vertices[k + 2]);
    }
  }

  fprintf(fp, "\n");

  // facevarying normal
  for (size_t k = 0; k < attributes.normals.size(); k += 3) {
    if (coordTransform) {
      fprintf(fp, "vn %f %f %f\n",
        attributes.normals[k + 0],
        attributes.normals[k + 2],
        -attributes.normals[k + 1]);
    } else {
      fprintf(fp, "vn %f %f %f\n",
        attributes.normals[k + 0],
        attributes.normals[k + 1],
        attributes.normals[k + 2]);
    }
  }

  fprintf(fp, "\n");

  // facevarying texcoord
  for (size_t k = 0; k < attributes.texcoords.size(); k += 2) {
    fprintf(fp, "vt %f %f\n",
      attributes.texcoords[k + 0],
      attributes.texcoords[k + 1]);
  }

  for (size_t i = 0; i < shapes.size(); i++) {
    fprintf(fp, "\n");

    if (shapes[i].name.empty()) {
      fprintf(fp, "g Unknown\n");
    } else {
      fprintf(fp, "g %s\n", shapes[i].name.c_str());
    }

    bool has_vn = false;
    bool has_vt = false;
    // Assumes normals and textures are set shape-wise.
    if(shapes[i].mesh.indices.size() > 0){
      has_vn = shapes[i].mesh.indices[0].normal_index != -1;
      has_vt = shapes[i].mesh.indices[0].texcoord_index != -1;
    }

    // face
    int face_index = 0;
    for (size_t k = 0; k < shapes[i].mesh.indices.size(); k += shapes[i].mesh.num_face_vertices[face_index++]) {
      // Check Materials
      int material_id = shapes[i].mesh.material_ids[face_index];
      if (material_id != prev_material_id) {
        std::string material_name = materials[material_id].name;
        fprintf(fp, "usemtl %s\n", material_name.c_str());
        prev_material_id = material_id;
      }

      unsigned char v_per_f = shapes[i].mesh.num_face_vertices[face_index];
      // Imperformant, but if you want to have variable vertices per face, you need some kind of a dynamic loop.
      fprintf(fp, "f");
      for(int l = 0; l < v_per_f; l++){
        const tinyobj::index_t& ref = shapes[i].mesh.indices[k + l];
        if(has_vn && has_vt){
          // v0/t0/vn0
          fprintf(fp, " %d/%d/%d", ref.vertex_index + 1, ref.texcoord_index + 1, ref.normal_index + 1);
          continue;
        }
        if(has_vn && !has_vt){
          // v0//vn0
          fprintf(fp, " %d//%d", ref.vertex_index + 1, ref.normal_index + 1);
          continue;
        }
        if(!has_vn && has_vt){
          // v0/vt0
          fprintf(fp, " %d/%d", ref.vertex_index + 1, ref.texcoord_index + 1);
          continue;
        }
        if(!has_vn && !has_vt){
          // v0 v1 v2
          fprintf(fp, " %d", ref.vertex_index + 1);
          continue;
        }
      }
      fprintf(fp, "\n");
    }
  }

  fclose(fp);

  //
  // Write material file
  //
  bool ret = WriteMat(material_filename, materials);

  return ret;
}