OpenGL ES系列 之 应用 - 1：Wavefront .obj加载

因为Houdini可以直接导出Wavefront .obj，而且该文件格式非常公开，在网上可以找到详细的spec，所以耍了耍。.Obj文件格式在Houdini模型导出那里已经提过。这里再重复一 下，Obj模型结构大致如下：

这个结构有几点跟 GLES不匹配的地方：
1、Facet可能是多边形。每个facet由一个'f'行表示，一行可能会有多个顶点表示是一个多边形。这个可以在导出 模型时预先三角化，也可以取读模型时即时三角化。将多边形分解成对应的一组三角形有两个思路，一个是取任一顶点与其它顶点形成三角扇 (TRIANGLE_FAN)，另一个是按 TRIANGLE_STRIP顺序分解。
2、独立索引。'f'行每个顶点由三个索引组成，分别索引 vertex/texCoord/normal。这种索引的好处是大大减少了texCoord的数量，另外对于多个面的共享顶点也能方便的记录其在每个面 上的uv及n。但是，GLES的DrawElements对每个顶点只接受一个索引，并用这个索引来查看所有的Array。这需要一个转换，将Mat的所 有顶点及相关数据复制成GLES所需要的Array。
3、光照模型。Mat里记录有光照模型，其中模型2跟GLES的硬件光照模型基本一致，其它 模型需要软件模拟，有几个涉及光线追踪的会非常麻烦。
4、多种贴图。DiffuseMap可以直接用一般的贴图来实现，BumpMap可以用 MultiTexture+ dot3RGB combine实现，其它的也都可以模拟但较麻烦。

.Obj文件的格式请google之。 总的说来，这是一个纯文本文件，通常配有.mtl文件汇总用到的所有材质。文件内容是过程式记录的，第一个非"v" 行表示顶点数据结束，这时才知道有多少个顶点，然后是vt/vn。一个usemtl标识着一个新Mesh的开始，这个mesh的材质用usemtl后面跟 的名字去MatLib里查。接着是"f"行，每行是一个facet，可能是多边形。直到下一个usemtl或者文件结束才知道当前mesh结束了，它有多 少个facet了。

写这样一个Parser并不复杂，逐行分析就是了。如果要保持程序清楚简单，直接构造上图所示的对象网络，然后将 GLES可接受格式封装成另一个类似的类树，做一个转换器就好了。

不过我做的时候只能利用零散时间想一点做一点，所以写成一边读一边转 了，相对复杂一点。好在是写着玩的，能工作就好。做为转换器的副产品，还得到了一个 ObjViewer，归功于以前整理的Toolchain和程序框架，这个ObjViewer可以直接编译成PC Emu版本或者X51v WM5版本。这部分的结构如下图所示：

这个程序在PC上工作比较合适，试过打开一个300万个三角形的模型，吃掉了大约800M内存。这个Viewer需要预先把纹理图片转成 PVRTC格式，并且对此不做检查，如果没对应的.pvr，直接出Accessing Violation。这个转换可能得分两步，先缩放成正方形，然后用PVRTextureTool压缩。对于前一步我是用Java imageio kit写了个小程序来处理并保存成未压缩24bit BMP的。

Parser的主要代码如下：

//
//
//  @ Project : Wavefront Obj Loader
//  @ File Name : ObjConverter.cpp
//  @ Date : 2007-9-4
//  @ Author : pinxue
//
//  @ Copyright : 2007-9 Example source license. 
//                  By keep this header comment, 
//                  you may use this source file in your project for non-commicial or commicial purpose.
//

#include "ObjConverter.h"
#include 
#include 

#include "gles/gl.h"
#include "fixmath.h"

#include "Obj.h"
#include "Vertex.h"
#include "UV.h"
#include "Normal.h"
#include "Mesh.h"
#include "Face.h"
#include "MatLib.h"
#include "Mat.h"
#include "Vector3i.h"

#include "Buf.h"


bool debugging = true;
void debug(const char * msg)
{
    if ( debugging )
        printf("%s", msg);
}

#define CLEAN_FGETS(buf) buf[strlen(buf)-2]=0; 
bool ObjConverter::loadWavefrontMtl(const char * src)
{
    char buf[1024];

    Mat curMat;
    Buf matBuf(128);

    matLib->fileName = _strdup(src);

    long matCount = 0;

    FILE *fp = fopen(src, "rb");
    if ( fp == NULL ) {
       printf("File %s cannot open!\n", src);
       return false;
    }

    bool lineReaded = false;
    bool firstMat = true;
    bool readFailed = false;
    while(!feof(fp))
    {
      if ( ! lineReaded ){readFailed = NULL==fgets(buf, 1024, fp); CLEAN_FGETS(buf);}
      else lineReaded = false;

      if ( ! readFailed )
      {
          if ( buf[0] == '#' )
          {
              continue;
          }else if ( 0 == strncmp("newmtl", buf, 6) )
          {
              // finish privious mat
              if ( !firstMat ) { matBuf << curMat; }
              else firstMat = false;
              memset(&curMat, 0, sizeof(Mat));

              // start new mat
              curMat.name = _strdup(& buf[7]);// skip "newmtl "
              // parse mat parameters: Ka, Kd, Ks, illum, Ns
              float r,g,b,a=1.0f;
              while(!feof(fp))
              {
                  readFailed = NULL==fgets(buf, 1024, fp); CLEAN_FGETS(buf);
                  if ( ! readFailed )
                  {
                      // skip tab and space
                      char * bp = buf;
                      while( (*bp == ' ') || (*bp == '\t') ) ++bp;
                      if ( 0 == strncmp("Ka ", bp, 3) )
                      {
                          sscanf(bp + 3, "%f %f %f", &r, &g, &b );
                          curMat.ambient.r = Float2Fixed(r);
                          curMat.ambient.g = Float2Fixed(g);
                          curMat.ambient.b = Float2Fixed(b);
                          curMat.ambient.a = Float2Fixed(a);
                      }else if ( 0 == strncmp("Kd ", bp, 3) )
                      {
                          sscanf(bp + 3, "%f %f %f", &r, &g, &b );
                          curMat.diffuse.r = Float2Fixed(r);
                          curMat.diffuse.g = Float2Fixed(g);
                          curMat.diffuse.b = Float2Fixed(b);
                          curMat.diffuse.a = Float2Fixed(a);
                      }else if ( 0 == strncmp("Ks ", bp, 3) )
                      {
                          curMat.specular.r = Float2Fixed(r);
                          curMat.specular.g = Float2Fixed(g);
                          curMat.specular.b = Float2Fixed(b);
                          curMat.specular.a = Float2Fixed(a);
                      }else if ( 0 == strncmp("Ns ", bp, 3) )
                      {
                          float f;
                          sscanf(bp + 3, "%f", & f);
                          curMat.specularExponent = Float2Fixed(f);
                      }else if ( 0 == strncmp("illum ", bp, 6) )
                      {
                        // not full support yet: illumination mode
                        // 0 : Color and Ambient off { constant color illumination model, color = Kd }
                        // 1 : Color and Ambient on { diffuse illMod with lambertian shading, 
                        //                              color = Ka*Ia + Kd * [SUM j=1..ls, (N * Lj)Ij] }
                        // 2 : Highlight on { GL matching! diffuse and specular illMod 
                        //                      using lambertian shading and Blinn-Phone specular illMod. 
                        //                      color = Ka*Ia + Kd * {SUM j, (N*Lj)Ij} + Ks * {SUM j, ((H*Hj)^Ns)Ij}
                        //   following is too complex if there is no shader support, 
                        //                       i.e. GLES 1.x, refer .mtl spec for details
                        // 3 : Reflection on and Raytrace on
                        // 4 : Transparency: Glass on; Reflection: Raytrace on
                        // 5 : Reflection: Fresnel on and Raytrace on
                        // 6 : Transparentcy: Refraction on; Reflection: Fresnel off and Raytrace on
                        // 7 : Transparency: Refraction on; Reflection: Fresnel on and Raytrace on
                        // 8 : Reflection on and Raytrace off
                        // 9 : Transparenc: Glass on; Reflection: Raytrace off
                        //10 : Cast shadows onto invisible surfaces
                          sscanf(bp + 6, "%d", & curMat.illumMode);
                      }else if ( 0 == strncmp("d ", bp, 2) )
                      {
                         // not support yet: dissolve for current mat
                      }else{
                          // a lot of capability are not supported: sharpness, Ni, Tf and options for the tag supported
                          lineReaded = true;
                          break;
                      }
                  }else{
                      if ( ! feof(fp) )
                      {
                          debug("get next line failed in parsing mat");
                          debug(matBuf.last().name);
                          debug("\n");
                      }
                      break;
                  }
              }
          }
            // texture maps (apply to Ka/Kd/Ks/Ns/d
          else if ( 0 == strncmp("map_bump", buf, 8) || 0 == strncmp("map_Bump", buf, 8) )
          {
              // this is not standard tag, but it does used by some exporter instead of 'bump'
              // and we will use the first one met.
              if ( curMat.bumpMap == 0 )
                      curMat.bumpMap = _strdup(&buf[9]);
          }else if ( 0 == strncmp("map_Ka", buf, 6) || 0 == strncmp("map_kA", buf, 6) )
          {
              curMat.ambientMap = _strdup(&buf[7]);
          }else if ( 0 == strncmp("map_Kd", buf, 6) || 0 == strncmp("map_kD", buf, 6) )
          {
              curMat.diffuseMap = _strdup(&buf[7]);
          }else if ( 0 == strncmp("map_Ks", buf, 6) || 0 == strncmp("map_kS", buf, 6) )
          {
              curMat.specularMap = _strdup(&buf[7]);
          }else if ( 0 == strncmp("map_Ns", buf, 6) || 0 == strncmp("map_nS", buf, 6))
          {
              // not support yet : apply to Ns, specular exponent
          }else if ( 0 == strncmp("bump", buf, 4) )
          {
              if ( curMat.bumpMap == 0 )
                      curMat.bumpMap = _strdup(&buf[5]);
          }else{
              // not support yet: map_d, map_aat on, decal{  tex_color(tv)*decal(tv)+mtl_color*(1.0-decal(tv) }, 
              //                  disp, refl and options
              debug("unknown type");
              debug(buf); debug("\n");
          }
      }else{
          if ( ! feof(fp) )
              debug("read next line failed in mat lib\n");
      }
    }

    // handle last mat
    matBuf << curMat;
    // to avoid curMat free the file names of last mat
    memset(&curMat, 0, sizeof(Mat));
    matLib->matCount = matBuf.count;
    matLib->mats = matBuf.expose();

    return true;
}

#define UNKNOWN_TYPE 1
#define UNKNOWN_LINE 2
#define BUF_DELTA 1024
bool ObjConverter::loadWavefrontObj(const char * src)
{
    char buf[1024];

    Vertex vertex;
    Buf vertexBuf(4096);
    UV uv;
    Buf uvBuf(1024);
    Normal normal;
    Buf normalBuf(4096);

    Vector3i tri;
    Buf triBuf(1024);

    Mesh mesh;
    Buf meshBuf(4096);
    Face face;
    Buf meshFaceBuf(4096);

    Vertex meshVertex;
    Buf meshVertexBuf(4096);
    UV meshUV;
    Buf meshUVBuf(4096);
    Normal meshNormal;
    Buf meshNormalBuf(4096);

    bool firstMesh = true;
    int error = 0;

    // assume there are enough free memory
    // skip null check for all memory allocation.
    FILE * fp = fopen(src, "rb");
    if ( fp == NULL ) {
       printf("File %s cannot open!\n", src);
       return false;
    }

    bool readFailed = false;
    while(!feof(fp))
    {
      readFailed = NULL == fgets(buf, 1024, fp); CLEAN_FGETS(buf);
      if ( ! readFailed )
      {
          switch(buf[0])
          {
              case '#'://ignore
                  break;
              case 'm'://parse matlib
                  if ( 0 == strncmp("mtllib", buf, 6) )
                  {
                    matLib = new MatLib();
                    matLib->fileName = _strdup(&buf[7]);
                    loadWavefrontMtl( matLib->fileName );
                  }else{
                      error = UNKNOWN_TYPE;
                  }
                  break;
              case 'g'://start of obj, get obj name
                  if ( buf[1] == ' ' )
                  {
                      if ( obj == 0 )
                      {
                              obj = new Obj();
                              obj->name = _strdup( &buf[2] );
                      } // todo : support more than one obj, and handle group of non-object like faces 
                        //           (houdini exports a lot group without name)
                      else {
                        printf("warning: multiple g tag, we don't support yet!\n");
                      }
                  }else{
                      error = UNKNOWN_TYPE;
                  }
                  break;
              case 'v':
                  //'v ' vertex
                  if ( buf[1] == ' ' )
                  {
                      float x,y,z;
                      sscanf( &buf[2], "%f %f %f", &x, &y, &z );
                      vertex.x = Float2Fixed(x);
                      vertex.y = Float2Fixed(y);
                      vertex.z = Float2Fixed(z);
                      vertexBuf << vertex;
                  }else
                  //'vt ' vertex texcoord
                  if ( buf[1] == 't' && buf[2] == ' ' )
                  {
                      float x,y;
                      sscanf( &buf[2], "%f %f", &x, &y );
                      uv.x = Float2Fixed(x);
                      uv.y = Float2Fixed(y);
                      uvBuf << uv;
                  }else
                  //'vn ' vertex normal
                  if ( buf[1] == 'n' && buf[2] == ' ' )
                  {
                      float x,y,z;
                      sscanf( &buf[2], "%f %f %f", &x, &y, &z );
                      normal.x = Float2Fixed(x);
                      normal.y = Float2Fixed(y);
                      normal.z = Float2Fixed(z);
                      normalBuf << normal;
                  }else{
                      error = UNKNOWN_TYPE;
                  }
                  break;
              case 'u'://parse usemtl and mat name
                  // this means a new mesh too
                  if ( 0 == strncmp("usemtl", buf, 6) )
                  {
                      char * matName = & buf[7];
                      Mat * mat = matLib->get( matName );

                      // finish privous mesh
                      if ( ! firstMesh ) // if this is NOT the first mesh then we have privious mesh
                      {
                          mesh.vertexCount = meshVertexBuf.count;
                          mesh.vertexs = meshVertexBuf.expose();

                          // In current design, uvs and normals have same number of elements as vertexs
                          mesh.uvs = meshUVBuf.expose();
                          mesh.normals = meshNormalBuf.expose();

                          mesh.faceCount = meshFaceBuf.count;
                          mesh.faces = meshFaceBuf.expose();
                          if ( mesh.faceCount > 65536 )
                                printf("warning: mesh with %d faces\n", mesh.faceCount);
                          else { if (debugging) printf("mesh with %d faces\n", mesh.faceCount); }
                          meshBuf << mesh;
                      } else { firstMesh = false; }

                      // create new mesh
                      // by use new Buf wrapper, we just reuse the temporary mesh.
                      //    and as all buffers are exposed, we even need not clean up it (it is reset internally)
                      mesh.mat = mat;
                  }
                  break;
              case 'f'://face
                  if ( buf[1] == ' ' )
                  {
                      // face may contains a series of index
                      // each index contains v/vt/vn
                      // num/num/num num/num/num '\'
#define MAX_FACE_LINE_SIZE 4096
                      char line[MAX_FACE_LINE_SIZE];
                      char *p = line; int num=0, idx=0;
                      strncpy(line, &buf[3], MAX_FACE_LINE_SIZE);
                      bool startNewSet = true;
                      // skip leading space in the line, this is important because we use space to separate set of index
                      //   in fact, we can counting idx to avoid the dependent, but anyway, 
                      //     the set of index is separated by space.
                      while( *p == ' ' || *p == '\t') ++p;
                      while( *p != 0 )
                      {
                          switch( *p )
                          {
                              case ' ': // next triple index set
                                        idx = 0; num = 0; startNewSet = true;
                                        ++p;
                                        break;
                              case '/': // next index of current set
                                        startNewSet = false; // we're handling it.
                                        num = 0; ++idx; ++p;
                                        break;
                              case '\\':// a new new and a new set starting 
                                        startNewSet = true; num = 0; idx = 0;
                                        readFailed = NULL==fgets( line, 1024, fp); CLEAN_FGETS(line);
                                        p=line;
                                        break;
                              default:
                                  startNewSet = false; // we're handling it.
                                  if ( *p == '-' )
                                      num = -num;
                                  else if ( isdigit(*p) )
                                  {
                                      num = num * 10 + (*p - '0');
                                        switch(idx){
                                            case 0:
                                                tri.a = num;
                                                break;
                                            case 1:
                                                tri.b = num;
                                                break;
                                            case 2:
                                                tri.c = num;
                                                break;
                                            default: debug("Warning: face point with more than 3 index!\n");
                                        }
                                  }else{
                                      debug("invalid char in face line\n");
                                  }
                                  ++p;
                          }

                          if ( startNewSet ) {
                                  triBuf << tri;
                          } // what about last set?
                      }
                      // the last tri
                      triBuf << tri;

                      if ( triBuf.count > 3 ) // triangular(triBuf);
                      {
                        // p0, [1, 2] [2,3] [3,4] ..., we will gen  triCount - 2 triangles as FAN
                        // todo : generate TRIANGLE STRIP instead of FAN
                        Buf tmpTriBuf(1024);
                        for ( long i = 0; i < triBuf.count-2; ++i )
                        {
                            // point 0
                            tmpTriBuf << triBuf[0];
                            // point +1
                            tmpTriBuf << triBuf[i+1];
                            // point +2
                            tmpTriBuf << triBuf[i+2];
                        }

                        triBuf.exchange(tmpTriBuf);
                      }

                      // put the face into mesh including append v/vt/vn pointed by face into mesh
                      bool existed=false;
                      long j = 0;
                      Vertex * cv;
                      for ( long i = 0; i < triBuf.count; ++i )
                      {
                          cv = &vertexBuf[triBuf[i].a -1]; // Wavefront Obj face index start from 1
                          existed=false;
                          for ( j = 0 ; j < meshVertexBuf.count; ++j )
                          {
                              if (  meshVertexBuf[j].x == cv->x
                                 && meshVertexBuf[j].y == cv->y
                                 && meshVertexBuf[j].z == cv->z )
                              { existed = true; break; }
                          }
                          if ( existed )
                          {
                              // todo : check normal and uv at j is same
                          }else{
                              // append it
                              meshVertexBuf << *cv;
                              meshUVBuf << uvBuf[triBuf[i].b-1]; // Wavefront Obj face index start from 1
                              meshNormalBuf << normalBuf[triBuf[i].c-1]; // Wavefront Obj face index start from 1
                          }

                          switch(i % 3)
                          {
                              case 0: face.a = j; break;
                              case 1: face.b = j; break;
                              case 2: face.c = j;
                                      // record the face
                                      meshFaceBuf << face;
                                      break;
                          }
                      }
                      triBuf.cleanup();

                      //++ faceGroup;
                  }
                  break;
              default:
                  // ignore
                  debug("\nignore unknown line: ");
                  debug(buf); debug("\n");
                  ;

          }
      }else{
        if ( ! feof(fp) ){
          printf( "failed to read a line!\n");
          return false;
        }
      }
    }

    // finish last mesh
        mesh.vertexCount = meshVertexBuf.count;
        mesh.vertexs = meshVertexBuf.expose();
        mesh.uvs = meshUVBuf.expose();
        mesh.normals = meshNormalBuf.expose();
        mesh.faceCount = meshFaceBuf.count;
        mesh.faces = meshFaceBuf.expose();
        meshBuf << mesh;
        if ( mesh.faceCount > 65536 )
           printf( "warning: mesh with %d faces!", mesh.faceCount);
        else { if (debugging) printf("mesh with %d faces.\n"); }

    // we got it!
        obj->meshCount = meshBuf.count;
        obj->meshs = meshBuf.expose();

    return true;
}

这里面大量使用的Buf是个短小但实用的小容器，其实你也完全可以用STL库的，不过eVC4好象没带STL的实现。

//
//
//  @ Project : Wavefront Obj Loader
//  @ File Name : Main.cpp
//  @ Date : 2007-9-12
//  @ Author : pinxue
//
//  @ Copyright : 2007-8 Example source license. 
                  By keep this header comment, 
                  you may use this source file in your project for non-commicial or commicial purpose.
//
#ifndef BUF_H
#define BUF_H
#include 
#include 

template <typename T>
class Buf
{
   private:
        T * _buf;
        long cap;
   public:
        long count;

   private:
        void enlargeBuf() { cap += 1024; _buf = (T *) realloc( _buf, cap * sizeof(T) ); }
        void reset(long initCap){cap=initCap; count=0; _buf = (T *) malloc( cap * sizeof(T) ); memset( _buf, 0, cap * sizeof(T)); }

    public:
        Buf(long initCap){ reset(initCap); }
        ~Buf(){ if ( _buf != 0 ) free( _buf ); }
        void cleanup(void){ count = 0; };

        const Buf* append(const T & t)
        {
                //_buf[count] = t; 
                memcpy( & _buf[count], &t , sizeof(T) );
                ++count;
                if ( count >= cap ) enlargeBuf();
                return this;
        }
        const Buf* operator <<(const T& t){ return append(t); }

        T& operator [](long idx) { return  _buf[idx]; }

        const T* getBuf(void){ return _buf; }
        T& firstFree(void){ return _buf[count]; }
        /** User promise there has at least one element by calling this function */
        T& first(void){ return _buf[0]; }
        /** User promise there has at least one element by calling this function */
        T& last(void){ return _buf[count-1]; }

        T* expose(void){
                T* tmp = (T*) realloc(_buf, count * sizeof(T)) ;
                reset(cap);
                return tmp;
        }

        void exchange(Buf & b){
                long t; T * p;
                p = _buf; _buf = b._buf; b._buf = p;
                t = count; count = b.count; b.count = t;
                t = cap; cap = b.cap; b.cap = t;
        }
};

#endif //ifndef BUF_H