glm.cpp

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    node->index = i;
    node->next  = members[T(i).vindices[0]];
    members[T(i).vindices[0]] = node;

    node = (GLMnode*)malloc(sizeof(GLMnode));
    node->index = i;
    node->next  = members[T(i).vindices[1]];
    members[T(i).vindices[1]] = node;

    node = (GLMnode*)malloc(sizeof(GLMnode));
    node->index = i;
    node->next  = members[T(i).vindices[2]];
    members[T(i).vindices[2]] = node;
  }

  /* calculate the average normal for each vertex */
  numnormals = 1;
  for (i = 1; i <= model->numvertices; i++) {
    /* calculate an average normal for this vertex by averaging the
       facet normal of every triangle this vertex is in */
    node = members[i];
    if (!node)
      fprintf(stderr, "glmVertexNormals(): vertex w/o a triangle\n");
    average[0] = 0.0; average[1] = 0.0; average[2] = 0.0;
    avg = 0;
    while (node) {
      /* only average if the dot product of the angle between the two
         facet normals is greater than the cosine of the threshold
         angle -- or, said another way, the angle between the two
         facet normals is less than (or equal to) the threshold angle */
      dot = glmDot(&model->facetnorms[3 * T(node->index).findex],
 		    &model->facetnorms[3 * T(members[i]->index).findex]);
      if (dot > cos_angle) {
	node->averaged = GL_TRUE;
	average[0] += model->facetnorms[3 * T(node->index).findex + 0];
	average[1] += model->facetnorms[3 * T(node->index).findex + 1];
	average[2] += model->facetnorms[3 * T(node->index).findex + 2];
	avg = 1;			/* we averaged at least one normal! */
      } else {
	node->averaged = GL_FALSE;
      }
      node = node->next;
    }

    if (avg) {
      /* normalize the averaged normal */
      glmNormalize(average);

      /* add the normal to the vertex normals list */
      model->normals[3 * numnormals + 0] = average[0];
      model->normals[3 * numnormals + 1] = average[1];
      model->normals[3 * numnormals + 2] = average[2];
      avg = numnormals;
      numnormals++;
    }

    /* set the normal of this vertex in each triangle it is in */
    node = members[i];
    while (node) {
      if (node->averaged) {
	/* if this node was averaged, use the average normal */
	if (T(node->index).vindices[0] == i)
	  T(node->index).nindices[0] = avg;
	else if (T(node->index).vindices[1] == i)
	  T(node->index).nindices[1] = avg;
	else if (T(node->index).vindices[2] == i)
	  T(node->index).nindices[2] = avg;
      } else {
	/* if this node wasn't averaged, use the facet normal */
	model->normals[3 * numnormals + 0] = 
	  model->facetnorms[3 * T(node->index).findex + 0];
	model->normals[3 * numnormals + 1] = 
	  model->facetnorms[3 * T(node->index).findex + 1];
	model->normals[3 * numnormals + 2] = 
	  model->facetnorms[3 * T(node->index).findex + 2];
	if (T(node->index).vindices[0] == i)
	  T(node->index).nindices[0] = numnormals;
	else if (T(node->index).vindices[1] == i)
	  T(node->index).nindices[1] = numnormals;
	else if (T(node->index).vindices[2] == i)
	  T(node->index).nindices[2] = numnormals;
	numnormals++;
      }
      node = node->next;
    }
  }
  
  model->numnormals = numnormals - 1;

  /* free the member information */
  for (i = 1; i <= model->numvertices; i++) {
    node = members[i];
    while (node) {
      tail = node;
      node = node->next;
      free(tail);
    }
  }
  free(members);

  /* pack the normals array (we previously allocated the maximum
     number of normals that could possibly be created (numtriangles *
     3), so get rid of some of them (usually alot unless none of the
     facet normals were averaged)) */
  normals = model->normals;
  model->normals = (GLfloat*)malloc(sizeof(GLfloat)* 3* (model->numnormals+1));
  for (i = 1; i <= model->numnormals; i++) {
    model->normals[3 * i + 0] = normals[3 * i + 0];
    model->normals[3 * i + 1] = normals[3 * i + 1];
    model->normals[3 * i + 2] = normals[3 * i + 2];
  }
  free(normals);
}


/* glmLinearTexture: Generates texture coordinates according to a
 * linear projection of the texture map.  It generates these by
 * linearly mapping the vertices onto a square.
 *
 * model - pointer to initialized GLMmodel structure
 */
GLvoid glmLinearTexture(GLMmodel* model)
{
  GLMgroup *group;
  GLfloat dimensions[3];
  GLfloat x, y, scalefactor;
  GLuint i;
  
  assert(model);

  if (model->texcoords)
    free(model->texcoords);
  model->numtexcoords = model->numvertices;
  model->texcoords=(GLfloat*)malloc(sizeof(GLfloat)*2*(model->numtexcoords+1));
  
  glmDimensions(model, dimensions);
  scalefactor = 2.0f / 
    glmAbs(glmMax(glmMax(dimensions[0], dimensions[1]), dimensions[2]));

  /* do the calculations */
  for(i = 1; i <= model->numvertices; i++) {
    x = model->vertices[3 * i + 0] * scalefactor;
    y = model->vertices[3 * i + 2] * scalefactor;
    model->texcoords[2 * i + 0] = (x + 1.0f) / 2.0f;
    model->texcoords[2 * i + 1] = (y + 1.0f) / 2.0f;
  }
  
  /* go through and put texture coordinate indices in all the triangles */
  group = model->groups;
  while(group) {
    for(i = 0; i < group->numtriangles; i++) {
      T(group->triangles[i]).tindices[0] = T(group->triangles[i]).vindices[0];
      T(group->triangles[i]).tindices[1] = T(group->triangles[i]).vindices[1];
      T(group->triangles[i]).tindices[2] = T(group->triangles[i]).vindices[2];
    }    
    group = group->next;
  }

#if 0
  printf("glmLinearTexture(): generated %d linear texture coordinates\n",
	  model->numtexcoords);
#endif
}

/* glmSpheremapTexture: Generates texture coordinates according to a
 * spherical projection of the texture map.  Sometimes referred to as
 * spheremap, or reflection map texture coordinates.  It generates
 * these by using the normal to calculate where that vertex would map
 * onto a sphere.  Since it is impossible to map something flat
 * perfectly onto something spherical, there is distortion at the
 * poles.  This particular implementation causes the poles along the X
 * axis to be distorted.
 *
 * model - pointer to initialized GLMmodel structure
 */
GLvoid glmSpheremapTexture(GLMmodel* model)
{
  GLMgroup* group;
  GLfloat theta, phi, rho, x, y, z, r;
  GLuint i;
  
  assert(model);
  assert(model->normals);

  if (model->texcoords)
    free(model->texcoords);
  model->numtexcoords = model->numnormals;
  model->texcoords=(GLfloat*)malloc(sizeof(GLfloat)*2*(model->numtexcoords+1));
     
  for (i = 1; i <= model->numnormals; i++) {
    z = model->normals[3 * i + 0];	/* re-arrange for pole distortion */
    y = model->normals[3 * i + 1];
    x = model->normals[3 * i + 2];
    r = fsqrt((x * x) + (y * y));
    rho = fsqrt((r * r) + (z * z));
      
    if(r == 0.0f) {
	theta = 0.0f;
	phi = 0.0f;
    } else {
      if(z == 0.0f)
	phi = 3.14159265f / 2.0f;
      else
	phi = facos(z / rho);

      if(y == 0.0)
	theta = 3.141592365f / 2.0f;
      else
	theta = fasin(y / r) + (3.14159265f / 2.0f);
    }
    
    model->texcoords[2 * i + 0] = theta / 3.14159265f;
    model->texcoords[2 * i + 1] = phi / 3.14159265f;
  }
  
  /* go through and put texcoord indices in all the triangles */
  group = model->groups;
  while(group) {
    for (i = 0; i < group->numtriangles; i++) {
      T(group->triangles[i]).tindices[0] = T(group->triangles[i]).nindices[0];
      T(group->triangles[i]).tindices[1] = T(group->triangles[i]).nindices[1];
      T(group->triangles[i]).tindices[2] = T(group->triangles[i]).nindices[2];
    }
    group = group->next;
  }
}

/* glmDelete: Deletes a GLMmodel structure.
 *
 * model - initialized GLMmodel structure
 */
GLvoid glmDelete(GLMmodel* model)
{
  GLMgroup* group;
  GLuint i;

  assert(model);

  if (model->pathname)   free(model->pathname);
  if (model->mtllibname) free(model->mtllibname);
  if (model->vertices)   free(model->vertices);
  if (model->normals)    free(model->normals);
  if (model->texcoords)  free(model->texcoords);
  if (model->facetnorms) free(model->facetnorms);
  if (model->triangles)  free(model->triangles);
  if (model->materials) {
    for (i = 0; i < model->nummaterials; i++)
      free(model->materials[i].name);
  }
  free(model->materials);
  while(model->groups) {
    group = model->groups;
    model->groups = model->groups->next;
    free(group->name);
    free(group->triangles);
    free(group);
  }

  free(model);
}

/* glmReadOBJ: Reads a model description from a Wavefront .OBJ file.
 * Returns a pointer to the created object which should be free'd with
 * glmDelete().
 *
 * filename - name of the file containing the Wavefront .OBJ format data.  
 */
GLMmodel* glmReadOBJ(char* filename)
{
  GLMmodel* model;
  FILE*     file;
  GLuint i;

  /* open the file */
  file = fopen(filename, "r");
  if (!file) {
    fprintf(stderr, "glmReadOBJ() failed: can't open data file \"%s\".\n",
	    filename);
    exit(1);
  }

  /* allocate a new model */
  model = (GLMmodel*)malloc(sizeof(GLMmodel));
  model->pathname      = strdup(filename);
  model->mtllibname    = NULL;
  model->numvertices   = 0;
  model->vertices      = NULL;
  model->selected      = NULL;
  model->numnormals    = 0;
  model->normals       = NULL;
  model->numtexcoords  = 0;
  model->texcoords     = NULL;
  model->numfacetnorms = 0;
  model->facetnorms    = NULL;
  model->numtriangles  = 0;
  model->triangles     = NULL;
  model->nummaterials  = 0;
  model->materials     = NULL;
  model->numgroups     = 0;
  model->groups        = NULL;
  model->position[0]   = 0.0;
  model->position[1]   = 0.0;
  model->position[2]   = 0.0;

  /* make a first pass through the file to get a count of the number
     of vertices, normals, texcoords & triangles */
  glmFirstPass(model, file);

  /* allocate memory */
  model->vertices = (GLfloat*)malloc(sizeof(GLfloat) *
				     3 * (model->numvertices + 1));
  model->selected = (GLboolean*)malloc(sizeof(GLboolean) *
				     (model->numvertices + 1));
  model->triangles = (GLMtriangle*)malloc(sizeof(GLMtriangle) *
					  model->numtriangles);
  if (model->numnormals) {
    model->normals = (GLfloat*)malloc(sizeof(GLfloat) *
				      3 * (model->numnormals + 1));
  }
  if (model->numtexcoords) {
    model->texcoords = (GLfloat*)malloc(sizeof(GLfloat) *
					2 * (model->numtexcoords + 1));
  }

  /* rewind to beginning of file and read in the data this pass */
  rewind(file);

  glmSecondPass(model, file);
  for (i = 0; i < model->numvertices; i++)
	  model->selected[i] = FALSE;
  /* close the file */
  fclose(file);

  return model;
}

/* glmDraw: Renders the model to the current OpenGL context using the
 * mode specified.
 *
 * model    - initialized GLMmodel structure
 * mode     - a bitwise OR of values describing what is to be rendered.
 *            GLM_NONE     -  render with only vertices
 *            GLM_FLAT     -  render with facet normals
 *            GLM_SMOOTH   -  render with vertex normals
 *            GLM_TEXTURE  -  render with texture coords
 *            GLM_COLOR    -  render with colors (color material)
 *            GLM_MATERIAL -  render with materials
 *            GLM_COLOR and GLM_MATERIAL should not both be specified.  
 *            GLM_FLAT and GLM_SMOOTH should not both be specified.  
 */
GLvoid glmDraw(GLMmodel* model, GLuint mode)
{
  static GLuint i;
  static GLMgroup* group;
  static GLMtriangle* triangle;
  static GLMmaterial* material;

  assert(model);
  assert(model->vertices);

  /* do a bit of warning */
  if (mode & GLM_FLAT && !model->facetnorms) {
    mode &= ~GLM_FLAT;
  }
  if (mode & GLM_SMOOTH && !model->normals) {
    mode &= ~GLM_SMOOTH;
  }
  if (mode & GLM_TEXTURE && !model->texcoords) {
    mode &= ~GLM_TEXTURE;
  }
  if (mode & GLM_FLAT && mode & GLM_SMOOTH) {
    mode &= ~GLM_FLAT;
  }
  if (mode & GLM_COLOR && !model->materials) {
    mode &= ~GLM_COLOR;
  }
  if (mode & GLM_MATERIAL && !model->materials) {
    mode &= ~GLM_MATERIAL;
  }
  if (mode & GLM_COLOR && mode & GLM_MATERIAL) {
    mode &= ~GLM_COLOR;
  }
  if (mode & GLM_COLOR)
    glEnable(GL_COLOR_MATERIAL);
  else if (mode & GLM_MATERIAL)
    glDisable(GL_COLOR_MATERIAL);

  /* perhaps this loop should be unrolled into material, color, flat,
     smooth, etc. loops?  since most cpu's have good branch prediction
     schemes (and these branches will always go one way), probably
     wouldn't gain too much?  */
  group = model->groups;
  while (group) {
    if (mode & GLM_MATERIAL) {
      material = &model->materials[group->material];
      glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, material->ambient);
      glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, material->diffuse);
      glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, material->specular);
      glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, material->shininess);
    }

    if (mode & GLM_COLOR) {
      material = &model->materials[group->material];
      glColor3fv(material->diffuse);
    }
	
    glBegin(GL_TRIANGLES);
    for (i = 0; i < group->numtriangles; i++) {
      triangle = &T(group->triangles[i]);

      if (mode & GLM_FLAT)
	glNormal3fv(&model->facetnorms[3 * triangle->findex]);
      
      if (mode & GLM_SMOOTH)
	glNormal3fv(&model->normals[3 * triangle->nindices[0]]);
      if (mode & GLM_TEXTURE)
	glTexCoord2fv(&model->texcoords[2 * triangle->tindices[0]]);
      glVertex3fv(&model->vertices[3 * triangle->vindices[0]]);
      
      if (mode & GLM_SMOOTH)
	glNormal3fv(&model->normals[3 * triangle->nindices[1]]);
      if (mode & GLM_TEXTURE)
	glTexCoord2fv(&model->texcoords[2 * triangle->tindices[1]]);
      glVertex3fv(&model->vertices[3 * triangle->vindices[1]]);
      
      if (mode & GLM_SMOOTH)
	glNormal3fv(&model->normals[3 * triangle->nindices[2]]);
      if (mode & GLM_TEXTURE)
	glTexCoord2fv(&model->texcoords[2 * triangle->tindices[2]]);
      glVertex3fv(&model->vertices[3 * triangle->vindices[2]]);
    
    }
    glEnd();

    group = group->next;
  }
}

/* glmList: Generates and returns a display list for the model using
 * the mode specified.
 *
 * model    - initialized GLMmodel structure
 * mode     - a bitwise OR of values describing what is to be rendered.
 *            GLM_NONE     -  render with only vertices
 *            GLM_FLAT     -  render with facet normals
 *            GLM_SMOOTH   -  render with vertex normals
 *            GLM_TEXTURE  -  render with texture coords
 *            GLM_COLOR    -  render with colors (color material)
 *            GLM_MATERIAL -  render with materials
 *            GLM_COLOR and GLM_MATERIAL should not both be specified.  
 * GLM_FLAT and GLM_SMOOTH should not both be specified.  */
GLuint glmList(GLMmodel* model, GLuint mode)
{
  GLuint list;

  list = glGenLists(1);
  glNewList(list, GL_COMPILE);
  glmDraw(model, mode);
  glEndList();

  return list;
}

/* glmWeld: eliminate (weld) vectors that are within an epsilon of
 * each other.
 *
 * model      - initialized GLMmodel structure
 * epsilon    - maximum difference between vertices
 *              ( 0.00001 is a good start for a unitized model)
 *
 */