axmol/cocos/3d/CCObjLoader.cpp

/****************************************************************************
 Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.
 
 http://www.cocos2d-x.org
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 ****************************************************************************/

#include <cstdlib>
#include <cstring>
#include <cassert>
#include <cmath>
#include <cstddef>

#include <string>
#include <vector>
#include <map>
#include <fstream>
#include <sstream>
#include "platform/CCFileUtils.h"
#include "base/ccUtils.h"

#include "3d/CCObjLoader.h"

namespace tinyobj {
    
#define TINYOBJ_SSCANF_BUFFER_SIZE  (4096)
    
    struct vertex_index {
        int v_idx, vt_idx, vn_idx;
        vertex_index(){};
        vertex_index(int idx) : v_idx(idx), vt_idx(idx), vn_idx(idx){};
        vertex_index(int vidx, int vtidx, int vnidx)
        : v_idx(vidx), vt_idx(vtidx), vn_idx(vnidx){};
    };
    // for std::map
    static inline bool operator<(const vertex_index &a, const vertex_index &b) {
        if (a.v_idx != b.v_idx)
            return (a.v_idx < b.v_idx);
        if (a.vn_idx != b.vn_idx)
            return (a.vn_idx < b.vn_idx);
        if (a.vt_idx != b.vt_idx)
            return (a.vt_idx < b.vt_idx);
        
        return false;
    }
    
    struct obj_shape {
        std::vector<float> v;
        std::vector<float> vn;
        std::vector<float> vt;
    };
    
    static inline bool isSpace(const char c) { return (c == ' ') || (c == '\t'); }
    
    static inline bool isNewLine(const char c) {
        return (c == '\r') || (c == '\n') || (c == '\0');
    }
    
    // Make index zero-base, and also support relative index.
    static inline int fixIndex(int idx, int n) {
        if (idx > 0) return idx - 1;
        if (idx == 0) return 0;
        return n + idx; // negative value = relative
    }
    
    static inline std::string parseString(const char *&token) {
        std::string s;
        token += strspn(token, " \t");
        size_t e = strcspn(token, " \t\r");
        s = std::string(token, &token[e]);
        token += e;
        return s;
    }
    
    static inline int parseInt(const char *&token) {
        token += strspn(token, " \t");
        int i = atoi(token);
        token += strcspn(token, " \t\r");
        return i;
    }
    
    
    // Tries to parse a floating point number located at s.
    //
    // s_end should be a location in the string where reading should absolutely
    // stop. For example at the end of the string, to prevent buffer overflows.
    //
    // Parses the following EBNF grammar:
    //   sign    = "+" | "-" ;
    //   END     = ? anything not in digit ?
    //   digit   = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
    //   integer = [sign] , digit , {digit} ;
    //   decimal = integer , ["." , integer] ;
    //   float   = ( decimal , END ) | ( decimal , ("E" | "e") , integer , END ) ;
    //
    //  Valid strings are for example:
    //   -0	 +3.1417e+2  -0.0E-3  1.0324  -1.41   11e2
    //
    // If the parsing is a success, result is set to the parsed value and true
    // is returned.
    //
    // The function is greedy and will parse until any of the following happens:
    //  - a non-conforming character is encountered.
    //  - s_end is reached.
    //
    // The following situations triggers a failure:
    //  - s >= s_end.
    //  - parse failure.
    //
    static bool tryParseDouble(const char *s, const char *s_end, double *result)
    {
        if (s >= s_end)
        {
            return false;
        }
        
        double mantissa = 0.0;
        // This exponent is base 2 rather than 10.
        // However the exponent we parse is supposed to be one of ten,
        // thus we must take care to convert the exponent/and or the
        // mantissa to a * 2^E, where a is the mantissa and E is the
        // exponent.
        // To get the final double we will use ldexp, it requires the
        // exponent to be in base 2.
        int exponent = 0;
        
        // NOTE: THESE MUST BE DECLARED HERE SINCE WE ARE NOT ALLOWED
        // TO JUMP OVER DEFINITIONS.
        char sign = '+';
        char exp_sign = '+';
        char const *curr = s;
        
        // How many characters were read in a loop.
        int read = 0;
        // Tells whether a loop terminated due to reaching s_end.
        bool end_not_reached = false;
        
        /*
         BEGIN PARSING.
         */
        
        // Find out what sign we've got.
        if (*curr == '+' || *curr == '-')
        {
            sign = *curr;
            curr++;
        }
        else if (isdigit(*curr)) { /* Pass through. */ }
        else
        {
            goto fail;
        }
        
        // Read the integer part.
        while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
        {
            mantissa *= 10;
            mantissa += static_cast<int>(*curr - 0x30);
            curr++;	read++;
        }
        
        // We must make sure we actually got something.
        if (read == 0)
            goto fail;
        // We allow numbers of form "#", "###" etc.
        if (!end_not_reached)
            goto assemble;
        
        // Read the decimal part.
        if (*curr == '.')
        {
            curr++;
            read = 1;
            while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
            {
                // NOTE: Don't use powf here, it will absolutely murder precision.
                mantissa += static_cast<int>(*curr - 0x30) * pow(10.0, -read);
                read++; curr++;
            }
        }
        else if (*curr == 'e' || *curr == 'E') {}
        else
        {
            goto assemble;
        }
        
        if (!end_not_reached)
            goto assemble;
        
        // Read the exponent part.
        if (*curr == 'e' || *curr == 'E')
        {
            curr++;
            // Figure out if a sign is present and if it is.
            if ((end_not_reached = (curr != s_end)) && (*curr == '+' || *curr == '-'))
            {
                exp_sign = *curr;
                curr++;
            }
            else if (isdigit(*curr)) { /* Pass through. */ }
            else
            {
                // Empty E is not allowed.
                goto fail;
            }
            
            read = 0;
            while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
            {
                exponent *= 10;
                exponent += static_cast<int>(*curr - 0x30);
                curr++;	read++;
            }
            exponent *= (exp_sign == '+'? 1 : -1);
            if (read == 0)
                goto fail;
        }
        
    assemble:
        *result = (sign == '+'? 1 : -1) * ldexp(mantissa * pow(5.0, exponent), exponent);
        return true;
    fail:
        return false;
    }
    static inline float parseFloat(const char *&token) {
        token += strspn(token, " \t");
#ifdef TINY_OBJ_LOADER_OLD_FLOAT_PARSER
        float f = (float)utils::atof(token);
        token += strcspn(token, " \t\r");
#else
        const char *end = token + strcspn(token, " \t\r");
        double val = 0.0;
        tryParseDouble(token, end, &val);
        float f = static_cast<float>(val);
        token = end;
#endif
        return f;
    }
    
    
    static inline void parseFloat2(float &x, float &y, const char *&token) {
        x = parseFloat(token);
        y = parseFloat(token);
    }
    
    static inline void parseFloat3(float &x, float &y, float &z,
                                   const char *&token) {
        x = parseFloat(token);
        y = parseFloat(token);
        z = parseFloat(token);
    }
    
    // Parse triples: i, i/j/k, i//k, i/j
    static vertex_index parseTriple(const char *&token, int vsize, int vnsize,
                                    int vtsize) {
        vertex_index vi(-1);
        
        vi.v_idx = fixIndex(atoi(token), vsize);
        token += strcspn(token, "/ \t\r");
        if (token[0] != '/') {
            return vi;
        }
        token++;
        
        // i//k
        if (token[0] == '/') {
            token++;
            vi.vn_idx = fixIndex(atoi(token), vnsize);
            token += strcspn(token, "/ \t\r");
            return vi;
        }
        
        // i/j/k or i/j
        vi.vt_idx = fixIndex(atoi(token), vtsize);
        token += strcspn(token, "/ \t\r");
        if (token[0] != '/') {
            return vi;
        }
        
        // i/j/k
        token++; // skip '/'
        vi.vn_idx = fixIndex(atoi(token), vnsize);
        token += strcspn(token, "/ \t\r");
        return vi;
    }
    
    static unsigned int
    updateVertex(std::map<vertex_index, unsigned int> &vertexCache,
                 std::vector<float> &positions, std::vector<float> &normals,
                 std::vector<float> &texcoords,
                 const std::vector<float> &in_positions,
                 const std::vector<float> &in_normals,
                 const std::vector<float> &in_texcoords, const vertex_index &i) {
        const std::map<vertex_index, unsigned int>::iterator it = vertexCache.find(i);
        
        if (it != vertexCache.end()) {
            // found cache
            return it->second;
        }
        
        assert(in_positions.size() > (unsigned int)(3 * i.v_idx + 2));
        
        positions.push_back(in_positions[3 * i.v_idx + 0]);
        positions.push_back(in_positions[3 * i.v_idx + 1]);
        positions.push_back(in_positions[3 * i.v_idx + 2]);
        
        if (i.vn_idx >= 0) {
            normals.push_back(in_normals[3 * i.vn_idx + 0]);
            normals.push_back(in_normals[3 * i.vn_idx + 1]);
            normals.push_back(in_normals[3 * i.vn_idx + 2]);
        }
        
        if (i.vt_idx >= 0) {
            texcoords.push_back(in_texcoords[2 * i.vt_idx + 0]);
            texcoords.push_back(in_texcoords[2 * i.vt_idx + 1]);
        }
        
        unsigned int idx = static_cast<unsigned int>(positions.size() / 3 - 1);
        vertexCache[i] = idx;
        
        return idx;
    }
    
    void InitMaterial(material_t &material) {
        material.name = "";
        material.ambient_texname = "";
        material.diffuse_texname = "";
        material.specular_texname = "";
        material.normal_texname = "";
        for (int i = 0; i < 3; i++) {
            material.ambient[i] = 0.f;
            material.diffuse[i] = 0.f;
            material.specular[i] = 0.f;
            material.transmittance[i] = 0.f;
            material.emission[i] = 0.f;
        }
        material.illum = 0;
        material.dissolve = 1.f;
        material.shininess = 1.f;
        material.ior = 1.f;
        material.unknown_parameter.clear();
    }
    
    static bool exportFaceGroupToShape(
                                       shape_t &shape, std::map<vertex_index, unsigned int> vertexCache,
                                       const std::vector<float> &in_positions,
                                       const std::vector<float> &in_normals,
                                       const std::vector<float> &in_texcoords,
                                       const std::vector<std::vector<vertex_index> > &faceGroup,
                                       const int material_id, const std::string &name, bool clearCache) {
        if (faceGroup.empty()) {
            return false;
        }
        
        // Flatten vertices and indices
        for (size_t i = 0, size = faceGroup.size(); i < size; ++i) {
            const std::vector<vertex_index> &face = faceGroup[i];
            
            vertex_index i0 = face[0];
            vertex_index i1(-1);
            vertex_index i2 = face[1];
            
            size_t npolys = face.size();
            
            // Polygon -> triangle fan conversion
            for (size_t k = 2; k < npolys; k++) {
                i1 = i2;
                i2 = face[k];
                
                unsigned int v0 = updateVertex(
                                               vertexCache, shape.mesh.positions, shape.mesh.normals,
                                               shape.mesh.texcoords, in_positions, in_normals, in_texcoords, i0);
                unsigned int v1 = updateVertex(
                                               vertexCache, shape.mesh.positions, shape.mesh.normals,
                                               shape.mesh.texcoords, in_positions, in_normals, in_texcoords, i1);
                unsigned int v2 = updateVertex(
                                               vertexCache, shape.mesh.positions, shape.mesh.normals,
                                               shape.mesh.texcoords, in_positions, in_normals, in_texcoords, i2);
                
                shape.mesh.indices.push_back(v0);
                shape.mesh.indices.push_back(v1);
                shape.mesh.indices.push_back(v2);
                
                shape.mesh.material_ids.push_back(material_id);
            }
        }
        
        shape.name = name;
        
        if (clearCache)
            vertexCache.clear();
        
        return true;
    }
    
    static std::string& replacePathSeperator(std::string& path)
    {
        for (std::string::size_type i = 0, size = path.size(); i < size; ++i) {
            if (path[i] == '\\')
                path[i] = '/';
        }
        return path;
    }
    
    std::string LoadMtl(std::map<std::string, int> &material_map,
                        std::vector<material_t> &materials,
                        std::istream &inStream) {
        std::stringstream err;
        
        // Create a default material anyway.
        material_t material;
        InitMaterial(material);
        
        int maxchars = 8192;             // Alloc enough size.
        std::vector<char> buf(maxchars); // Alloc enough size.
        while (inStream.peek() != -1) {
            inStream.getline(&buf[0], maxchars);
            
            std::string linebuf(&buf[0]);
            
            // Trim newline '\r\n' or '\n'
            if (!linebuf.empty()) {
                if (linebuf[linebuf.size() - 1] == '\n')
                    linebuf.erase(linebuf.size() - 1);
            }
            if (!linebuf.empty()) {
                if (linebuf[linebuf.size() - 1] == '\r')
                    linebuf.erase(linebuf.size() - 1);
            }
            
            // Skip if empty line.
            if (linebuf.empty()) {
                continue;
            }
            
            // Skip leading space.
            const char *token = linebuf.c_str();
            token += strspn(token, " \t");
            
            assert(token);
            if (token[0] == '\0')
                continue; // empty line
            
            if (token[0] == '#')
                continue; // comment line
            
            // new mtl
            if ((0 == strncmp(token, "newmtl", 6)) && isSpace((token[6]))) {
                // flush previous material.
                if (!material.name.empty()) {
                    material_map.insert(
                                        std::pair<std::string, int>(material.name, static_cast<int>(materials.size())));
                    materials.push_back(material);
                }
                
                // initial temporary material
                InitMaterial(material);
                
                // set new mtl name
                char namebuf[TINYOBJ_SSCANF_BUFFER_SIZE];
                token += 7;
#ifdef _MSC_VER
                sscanf_s(token, "%s", namebuf, _countof(namebuf));
#else
                sscanf(token, "%s", namebuf);
#endif
                material.name = namebuf;
                continue;
            }
            
            // ambient
            if (token[0] == 'K' && token[1] == 'a' && isSpace((token[2]))) {
                token += 2;
                float r, g, b;
                parseFloat3(r, g, b, token);
                material.ambient[0] = r;
                material.ambient[1] = g;
                material.ambient[2] = b;
                continue;
            }
            
            // diffuse
            if (token[0] == 'K' && token[1] == 'd' && isSpace((token[2]))) {
                token += 2;
                float r, g, b;
                parseFloat3(r, g, b, token);
                material.diffuse[0] = r;
                material.diffuse[1] = g;
                material.diffuse[2] = b;
                continue;
            }
            
            // specular
            if (token[0] == 'K' && token[1] == 's' && isSpace((token[2]))) {
                token += 2;
                float r, g, b;
                parseFloat3(r, g, b, token);
                material.specular[0] = r;
                material.specular[1] = g;
                material.specular[2] = b;
                continue;
            }
            
            // transmittance
            if (token[0] == 'K' && token[1] == 't' && isSpace((token[2]))) {
                token += 2;
                float r, g, b;
                parseFloat3(r, g, b, token);
                material.transmittance[0] = r;
                material.transmittance[1] = g;
                material.transmittance[2] = b;
                continue;
            }
            
            // ior(index of refraction)
            if (token[0] == 'N' && token[1] == 'i' && isSpace((token[2]))) {
                token += 2;
                material.ior = parseFloat(token);
                continue;
            }
            
            // emission
            if (token[0] == 'K' && token[1] == 'e' && isSpace(token[2])) {
                token += 2;
                float r, g, b;
                parseFloat3(r, g, b, token);
                material.emission[0] = r;
                material.emission[1] = g;
                material.emission[2] = b;
                continue;
            }
            
            // shininess
            if (token[0] == 'N' && token[1] == 's' && isSpace(token[2])) {
                token += 2;
                material.shininess = parseFloat(token);
                continue;
            }
            
            // illum model
            if (0 == strncmp(token, "illum", 5) && isSpace(token[5])) {
                token += 6;
                material.illum = parseInt(token);
                continue;
            }
            
            // dissolve
            if ((token[0] == 'd' && isSpace(token[1]))) {
                token += 1;
                material.dissolve = parseFloat(token);
                continue;
            }
            if (token[0] == 'T' && token[1] == 'r' && isSpace(token[2])) {
                token += 2;
                // Invert value of Tr(assume Tr is in range [0, 1])
                material.dissolve = 1.0f - parseFloat(token);
                continue;
            }
            
            // ambient texture
            if ((0 == strncmp(token, "map_Ka", 6)) && isSpace(token[6])) {
                token += 7;
                material.ambient_texname = token;
                replacePathSeperator(material.ambient_texname);
                continue;
            }
            
            // diffuse texture
            if ((0 == strncmp(token, "map_Kd", 6)) && isSpace(token[6])) {
                token += 7;
                material.diffuse_texname = token;
                replacePathSeperator(material.diffuse_texname);
                continue;
            }
            
            // specular texture
            if ((0 == strncmp(token, "map_Ks", 6)) && isSpace(token[6])) {
                token += 7;
                material.specular_texname = token;
                replacePathSeperator(material.specular_texname);
                continue;
            }
            
            // normal texture
            if ((0 == strncmp(token, "map_Ns", 6)) && isSpace(token[6])) {
                token += 7;
                material.normal_texname = token;
                replacePathSeperator(material.normal_texname);
                continue;
            }
            
            // unknown parameter
            const char *_space = strchr(token, ' ');
            if (!_space) {
                _space = strchr(token, '\t');
            }
            if (_space) {
                std::ptrdiff_t len = _space - token;
                std::string key(token, len);
                std::string value = _space + 1;
                material.unknown_parameter.insert(
                                                  std::pair<std::string, std::string>(key, value));
            }
        }
        // flush last material.
        material_map.insert(
                            std::pair<std::string, int>(material.name, static_cast<int>(materials.size())));
        materials.push_back(material);
        
        return err.str();
    }
    
    std::string MaterialFileReader::operator()(const std::string &matId,
                                               std::vector<material_t> &materials,
                                               std::map<std::string, int> &matMap) {
        std::string filepath;
        
        if (!m_mtlBasePath.empty()) {
            filepath = std::string(m_mtlBasePath) + matId;
        } else {
            filepath = matId;
        }
        
        std::string err = "";
        
        std::istringstream matIStream(cocos2d::FileUtils::getInstance()->getStringFromFile(filepath));
        if (!matIStream) {
            std::stringstream ss;
            ss << "WARN: Material file [ " << filepath << " ] not found. Created a default material.";
            err += ss.str();
        }
        err += LoadMtl(matMap, materials, matIStream);

        return err;
    }
    
    std::string LoadObj(std::vector<shape_t> &shapes,
                        std::vector<material_t> &materials, // [output]
                        const char *filename, const char *mtl_basepath) {
        
        shapes.clear();
        
        std::stringstream err;
        
        std::istringstream ifs(cocos2d::FileUtils::getInstance()->getStringFromFile(filename));
        if (!ifs) {
            err << "Cannot open file [" << filename << "]" << std::endl;
            return err.str();
        }
        
        std::string basePath;
        if (mtl_basepath) {
            basePath = mtl_basepath;
        }
        MaterialFileReader matFileReader(basePath);
        
        return LoadObj(shapes, materials, ifs, matFileReader);
    }
    
    std::string LoadObj(std::vector<shape_t> &shapes,
                        std::vector<material_t> &materials, // [output]
                        std::istream &inStream, MaterialReader &readMatFn) {
        std::stringstream err;
        
        std::vector<float> v;
        std::vector<float> vn;
        std::vector<float> vt;
        std::vector<std::vector<vertex_index> > faceGroup;
        std::string name;
        
        // material
        std::map<std::string, int> material_map;
        std::map<vertex_index, unsigned int> vertexCache;
        int material = -1;
        
        shape_t shape;
        
        int maxchars = 8192;             // Alloc enough size.
        std::vector<char> buf(maxchars); // Alloc enough size.
        while (inStream.peek() != -1) {
            inStream.getline(&buf[0], maxchars);
            
            std::string linebuf(&buf[0]);
            
            // Trim newline '\r\n' or '\n'
            if (!linebuf.empty()) {
                if (linebuf[linebuf.size() - 1] == '\n')
                    linebuf.erase(linebuf.size() - 1);
            }
            if (!linebuf.empty()) {
                if (linebuf[linebuf.size() - 1] == '\r')
                    linebuf.erase(linebuf.size() - 1);
            }
            
            // Skip if empty line.
            if (linebuf.empty()) {
                continue;
            }
            
            // Skip leading space.
            const char *token = linebuf.c_str();
            token += strspn(token, " \t");
            
            assert(token);
            if (token[0] == '\0')
                continue; // empty line
            
            if (token[0] == '#')
                continue; // comment line
            
            // vertex
            if (token[0] == 'v' && isSpace((token[1]))) {
                token += 2;
                float x, y, z;
                parseFloat3(x, y, z, token);
                v.push_back(x);
                v.push_back(y);
                v.push_back(z);
                continue;
            }
            
            // normal
            if (token[0] == 'v' && token[1] == 'n' && isSpace((token[2]))) {
                token += 3;
                float x, y, z;
                parseFloat3(x, y, z, token);
                vn.push_back(x);
                vn.push_back(y);
                vn.push_back(z);
                continue;
            }
            
            // texcoord
            if (token[0] == 'v' && token[1] == 't' && isSpace((token[2]))) {
                token += 3;
                float x, y;
                parseFloat2(x, y, token);
                vt.push_back(x);
                vt.push_back(y);
                continue;
            }
            
            // face
            if (token[0] == 'f' && isSpace((token[1]))) {
                token += 2;
                token += strspn(token, " \t");
                
                std::vector<vertex_index> face;
                auto first = static_cast<int>(v.size() / 3);
                auto second = static_cast<int>(vn.size() / 3);
                auto third = static_cast<int>(vt.size() / 2);
                while (!isNewLine(token[0])) {
                    vertex_index vi =
                    parseTriple(token, first, second, third);
                    face.push_back(vi);
                    size_t n = strspn(token, " \t\r");
                    token += n;
                }
                
                faceGroup.push_back(face);
                
                continue;
            }
            
            // use mtl
            if ((0 == strncmp(token, "usemtl", 6)) && isSpace((token[6]))) {
                
                char namebuf[TINYOBJ_SSCANF_BUFFER_SIZE];
                token += 7;
#ifdef _MSC_VER
                sscanf_s(token, "%s", namebuf, _countof(namebuf));
#else
                sscanf(token, "%s", namebuf);
#endif
                
                // Create face group per material.
                bool ret = exportFaceGroupToShape(shape, vertexCache, v, vn, vt,
                                                  faceGroup, material, name, true);
                if (ret) {
                    shapes.push_back(shape);
                }
                shape = shape_t();
                faceGroup.clear();
                
                if (material_map.find(namebuf) != material_map.end()) {
                    material = material_map[namebuf];
                } else {
                    // { error!! material not found }
                    material = -1;
                }
                
                continue;
            }
            
            // load mtl
            if ((0 == strncmp(token, "mtllib", 6)) && isSpace((token[6]))) {
                char namebuf[TINYOBJ_SSCANF_BUFFER_SIZE];
                token += 7;
#ifdef _MSC_VER
                sscanf_s(token, "%s", namebuf, _countof(namebuf));
#else
                sscanf(token, "%s", namebuf);
#endif
                
                std::string err_mtl = readMatFn(namebuf, materials, material_map);
                if (!err_mtl.empty()) {
                    faceGroup.clear(); // for safety
                    return err_mtl;
                }
                
                continue;
            }
            
            // group name
            if (token[0] == 'g' && isSpace((token[1]))) {
                
                // flush previous face group.
                bool ret = exportFaceGroupToShape(shape, vertexCache, v, vn, vt,
                                                  faceGroup, material, name, true);
                if (ret) {
                    shapes.push_back(shape);
                }
                
                shape = shape_t();
                
                // material = -1;
                faceGroup.clear();
                
                std::vector<std::string> names;
                while (!isNewLine(token[0])) {
                    std::string str = parseString(token);
                    names.push_back(str);
                    token += strspn(token, " \t\r"); // skip tag
                }
                
                assert(!names.empty());
                
                // names[0] must be 'g', so skip the 0th element.
                if (names.size() > 1) {
                    name = names[1];
                } else {
                    name = "";
                }
                
                continue;
            }
            
            // object name
            if (token[0] == 'o' && isSpace((token[1]))) {
                
                // flush previous face group.
                bool ret = exportFaceGroupToShape(shape, vertexCache, v, vn, vt,
                                                  faceGroup, material, name, true);
                if (ret) {
                    shapes.push_back(shape);
                }
                
                // material = -1;
                faceGroup.clear();
                shape = shape_t();
                
                // @todo { multiple object name? }
                char namebuf[TINYOBJ_SSCANF_BUFFER_SIZE];
                token += 2;
#ifdef _MSC_VER
                sscanf_s(token, "%s", namebuf, _countof(namebuf));
#else
                sscanf(token, "%s", namebuf);
#endif
                name = std::string(namebuf);
                
                continue;
            }
            
            // Ignore unknown command.
        }
        
        bool ret = exportFaceGroupToShape(shape, vertexCache, v, vn, vt, faceGroup,
                                          material, name, true);
        if (ret) {
            shapes.push_back(shape);
        }
        faceGroup.clear(); // for safety
        
        return err.str();
    }
}