Reducing Vertex Array

Its best to create an indexed mesh to begin with, but here is a naive way to convert a non-indexed mesh to an indexed mesh:

vertex_array = list of final vertices
index_array = list of triplets of indices indicating the triangles

In the end, index_array contains triplets of indices that point into vertex_array, e.g., one triangle is given by the vertices vertex_array[index_array[0]], vertex_array[index_array[1]], vertex_array[index_array[2]]. The next triangle is given by vertex_array[index_array[3]], vertex_array[index_array[4]], vertex_array[index_array[5]], etc.

To build the arrays do this:

int index_accumulator = 0;int found_index = 0;int tri_index = 0;for (i = 0; i < number_triangles; i++){  for (j = 0; j < 3; j++)  {    found_index = find_vertex_in_vertex_array(trivert.x,                         trivert.y, trivert.z)    if (found_index >= 0)    {      index_array[tri_index++] = found_index    }    else    {      vertex_array[index_accumulator] = new_vert(trivert.x,                               trivert.y, trivert.z);      index_array[tri_index++] = index_accumulator;      index_accumulator++;    }  }}// epsilon is a tolerance that will fuse nearly-coincident// verts, to allow for roundoff error.float epsilon = 1.0e-5;int find_vertex_in_vertex_array(x, y, z){  for (i = 0; i < index_accumulator; i++)  {    if (distance(vertex_array[index_accumulator] - vert(x,y,z)           < epsilon)      return(i);  }  return(-1);}

Now, the problem with this is the find_vertex_in_vertex_array method will eventually be too slow if your mesh is complex. If you have meshes with more than a few triangles/vertices, you could more rapidly search for the existing vertices using a hash table of some sort, or a spatial partitioning scheme such as a quadtree.