三维模型obj文件的格式解析与读取

请先看这两个中文博客中对于obj的介绍：

读取Obj格式的模型文件(Dx10)

C++读入obj格式模型文件

更为详细的英文资料(用google或者aol搜索 "obj format"即可得到)：

http://en.wikipedia.org/wiki/Wavefront_.obj_file

Wavefront OBJ File Format Summary

最详细的资料 obj spec: http://www.martinreddy.net/gfx/3d/OBJ.spec

http://people.cs.clemson.edu/~dhouse/courses/405/docs/brief-obj-file-format.html

http://www.scratchapixel.com/lessons/3d-advanced-lessons/obj-file-format/obj-file-format/

看完以上随便一个内容，obj的格式可以说了解了。下面实现对obj文件的读取。

.obj文件中，每一行都有表明该行意义的标志符。对obj的读取中，处理以下标志符

"v"--点的坐标，三维模型为x, y, z的顺序；程序中以

1 typedef struct ObjVector3
2 {
3     ObjFloat x;
4     ObjFloat y;
5     ObjFloat z;
6 } ObjVector3;

结构存储。

"vt"--纹理坐标，程序中以

1 typedef struct ObjVector2
2 {
3     ObjFloat x;
4     ObjFloat y;
5 } ObjVector2;

结构存储

"vn"--法向量坐标，程序中与“v”的存储结构相同

"f"--面所用到的点坐标/纹理坐标/法向量坐标的索引，

"mtllib"--.obj文件用到的material库文件，“usemtl”标志符用到的material都是从material库文件中取出的

"g"--组group的名称，group里面的"f"可以使用0-N个"usemtl"对面的显示渲染进行控制，当使用了大于1个“usemtl”标志符，程序处理时对于已经读取的"f"很难控制；同时查看obj读取的源码，有的用到了这个标志符，有的没有使用该标志，有的使用了"usemtl"标志符对所读取的"f"面进行分割，本文的处理是使用"usemtl"标志符将"f"面分割为mesh，但是考虑到不同的group可以使用相同的"usemtl”标志（即不同的group都使用了 usemtl AAA），因此将"g"与"usemtl"结合起来，二者的名称作为mesh的名称

"usemtl"--参见"mtllib"，"g"。一旦使用了该标志符，则在该标志符后面的"f"全部受影响，直到遇到下一个"usemtl"

mesh结构，解析已经读取的“f”存储所面的点坐标/纹理坐标/法向量坐标，其结构为

 1 struct Mesh
 2 {
 3     string name;        // name
 4     ObjIntd mtl_idx;    // the index of material used by mesh 
 5 
 6     vector<ObjVector3> positions;    // "v" flag
 7     vector<ObjVector2> texcoords;    // "vt" flag
 8     vector<ObjVector3> normals;        // "vn" flag
 9     vector<ObjDword> indices;    // the indices of points of face in positions
10 
11     void reset()
12     { 
13         mtl_idx = -1;
14 
15         name.clear();
16         positions.clear();
17         texcoords.clear();
18         normals.clear();
19         indices.clear();
20     }
21 };

View Code

结构中出现的

ObjFloat ObjIntd

是一组typedef，具体为

 1 typedef int32_t ObjBool;
 2 typedef uint8_t ObjByte;
 3 typedef uint16_t ObjWord;
 4 typedef uint32_t ObjDword;
 5 typedef int8_t ObjIntb;
 6 typedef int16_t ObjIntw;
 7 typedef int32_t ObjIntd;
 8 
 9 typedef float ObjFloat;
10 typedef double ObjDouble;

View Code

对obj文件读取的主体程序如下

 1     ObjBool obj_file_load(const string& objname)
 2     {
 3         if (objname.empty())
 4             return LIBOBJ_FALSE;
 5 
 6         int mesh_count = 0;
 7         Mesh mesh_;
 8         string groupname;
 9         string usemtl;
10         vector<ObjVector3> positions;
11         vector<ObjVector3> normals;
12         vector<ObjVector2> texcoords;
13         vector<vector<ObjVertexIndex> > faces;
14         map<string, ObjIntd> mtlMap;
15 
16         fstream obj_stream;    
17         obj_stream.open(objname.c_str(), std::ios_base::in);
18         if (!obj_stream.is_open())
19             return LIBOBJ_FALSE;
20 
21         string obj_flag;
22         while (obj_stream.good())
23         {
24             obj_stream >> obj_flag;
25 
26             if (obj_flag.empty() || (obj_flag[0] == \'#\'))
27             {
28                 obj_stream.ignore(1024, \'\n\');            // skip line
29                 continue;
30             }
31 
32             if (obj_flag == "v")            // position flag
33                 if (!obj_parse_vector3(obj_stream, positions))
34                     return LIBOBJ_FALSE;
35             else if (obj_flag == "vt")    // texture coordinate flag
36                 if (!obj_parse_vector2(obj_stream, texcoords))
37                     return LIBOBJ_FALSE;
38             else if (obj_flag == "vn")    // normal flag
39                 if (!obj_parse_vector3(obj_stream, normals))
40                     return LIBOBJ_FALSE;
41             else if (obj_flag == "g")        //group name
42                 if (!obj_parse_group(obj_stream, groupname))
43                     return LIBOBJ_FALSE;
44             else if (obj_flag == "f")        // face    flag
45             {
46                 vector<ObjVertexIndex> face;
47 
48                 obj_parse_face(obj_stream, face, positions, texcoords, normals);
49 
50                 faces.push_back(face);
51             }
52             else if (obj_flag == "mtllib")    // Material library
53             {
54                 vector<string> materialnames;
55 
56                 obj_parse_mtllib(obj_stream, materialnames);
57 
58                 for (unsigned i = 0; i < materialnames.size(); i++)
59                     if (!mtl_file_load(get_file_path(objname) + \'/\' + materialnames[i]))
60                         return LIBOBJ_FALSE;
61             }
62             else if (obj_flag == "usemtl")
63             {
64                 if (obj_save_mesh(positions, texcoords, normals, faces, groupname+usemtl, mesh_))
65                 {
66                     m_meshes.back().mtl_idx = mtl_index(usemtl);
67                     
68                     faces.clear();
69                     mesh_.reset();
70                 }
71 
72                 obj_parse_group(obj_stream, usemtl);
73             }
74             else
75             {
76                 obj_stream.ignore(1024, \'\n\');            // skip line
77             }
78         }  
79 
80         if (!obj_stream.eof())
81             return LIBOBJ_FALSE;
82 
83         //save mesh data
84         if (obj_save_mesh(positions, texcoords, normals, faces, groupname+usemtl, mesh_))
85         {
86             m_meshes.back().mtl_idx = mtl_index(usemtl);
87 
88             faces.clear();
89             mesh_.reset();
90         }
91 
92         obj_stream.close();
93 
94         return LIBOBJ_TRUE;
95     }

View Code

obj文件用到了.mtl格式的material，在对“mtllib”标志符解析时开始读取该.mtl文件，

对于.mtl文件的介绍，请阅读

更为详细的英文资料：

http://www.fileformat.info/format/material/

http://people.cs.clemson.edu/~dhouse/courses/405/docs/brief-mtl-file-format.html

本程序中存储mtl文件的结构较为简单，只使用了mtl文件中的几个结构而没有全部处理

 1 struct ObjMaterial
 2 {
 3     string name;
 4     
 5     ObjRgb ambient;
 6     ObjRgb diffuse;
 7     ObjRgb specular;
 8 
 9     ObjWord shininess;
10     ObjByte illumination_model;
11     ObjFloat transparency;
12 
13     string ambient_texture;
14     string diffuse_texture;
15     string specular_texture;
16 };

View Code

对mtl文件的解析代码：

 1     ObjBool mtl_file_load(const string& mtlname)
 2     {
 3         if (mtlname.empty())        // if obj has no material
 4             return LIBOBJ_FALSE;
 5 
 6         ObjMaterial* pmaterial = NULL;
 7 
 8         fstream mtlstream;
 9         mtlstream.open(mtlname.c_str(), std::ios_base::in);    //open strFileName file
10         if (!mtlstream.is_open())
11             return LIBOBJ_FALSE;
12         
13         string mtlflag;
14         while (mtlstream.good())
15         {
16             mtlstream >> mtlflag;
17 
18             if (mtlflag == "newmtl")
19             {
20                 string materialname;
21                 mtlstream >> materialname;
22                 if (mtl_index(materialname) != -1)
23                     continue;
24 
25                 pmaterial = new ObjMaterial;
26                 pmaterial->name = materialname;
27                 m_materials.push_back(pmaterial);
28             }
29             else if (mtlflag == "Ka")        //Ambient color
30                 if (!mtl_parse_color(mtlstream, pmaterial->ambient))
31                     return LIBOBJ_FALSE;
32             else if (mtlflag == "Kd")        //Diffuse color
33                 if (!mtl_parse_color(mtlstream, pmaterial->diffuse))
34                     return LIBOBJ_FALSE;
35             else if (mtlflag == "Ks")        //Specular color
36                 if (!mtl_parse_color(mtlstream, pmaterial->specular))
37                     return LIBOBJ_FALSE;
38             else if (mtlflag == "Tr"/*"d"*/)        // Alpha, that is transparent
39                 if (!mtl_parse_light(mtlstream, pmaterial->transparency))
40                     return LIBOBJ_FALSE;
41             else if (mtlflag == "Ns")        //Shininess
42                 if (!mtl_parse_light(mtlstream, pmaterial->shininess))
43                     return LIBOBJ_FALSE;
44             else if (mtlflag == "illum")        //Illumination type
45                 if (!mtl_parse_light(mtlstream, pmaterial->illumination_model))
46                     return LIBOBJ_FALSE;
47             else if (mtlflag == "map_Ka")    //ambient Texture
48                 if (!mtl_parse_texture(mtlstream, pmaterial->ambient_texture))
49                     return LIBOBJ_FALSE;
50             else if (mtlflag == "map_Kd")    //diffuse Texture
51                 if (!mtl_parse_texture(mtlstream, pmaterial->diffuse_texture))
52                     return LIBOBJ_FALSE;
53             else if (mtlflag == "map_Ks")    //specular Texture
54                 if (!mtl_parse_texture(mtlstream, pmaterial->specular_texture))
55                     return LIBOBJ_FALSE;
56             else
57                 mtlstream.ignore(1024, \'\n\');    // ignore this line, on the assumption that the max characters at this line is 1024.                
58         }
59 
60         if (!mtlstream.eof())
61             return LIBOBJ_FALSE;
62 
63         mtlstream.close();
64         return LIBOBJ_TRUE;
65     }

View Code

完整的代码放在了https://github.com/priseup/obj_load

ps: 手上没有数据，还没有进行测试

秒客网

三维模型obj文件的格式解析与读取

相关文章