build flat_vertices collection for VBO

WFObj.cc

@@ -442,12 +442,28 @@ bool WFObj::loadfile(const char *path, Buffer & buff)
 
 void WFObj::buildVBO()
 {
+    map<VertexRef, int> flat_vertices;
+    int vid = 0;
     glGenBuffers(1, &m_vbo);
     bool do_textures = m_loadtexture != NULL
         && m_vertices[VERTEX_TEXTURE].size() > 0;
+    for (map<string, vector<Face> >::iterator it = m_faces.begin();
+            it != m_faces.end();
+            it++)
+    {
+        for (vector<Face>::iterator fit = it->second.begin();
+                fit != it->second.end();
+                fit++)
+        {
+            for (int i = 0; i < 3; i++)
+            {
+                flat_vertices[fit->vertices[i]] = vid++;
+            }
+        }
+    }
 }
 
-bool WFObj::VertexRef::operator<(const VertexRef & other)
+bool WFObj::VertexRef::operator<(const VertexRef & other) const
 {
     if (vertex != other.vertex)
         return vertex < other.vertex;

WFObj.h

@@ -61,7 +61,7 @@ protected:
             int vertex;
             int texture;
             int normal;
-            bool operator<(const VertexRef & other);
+            bool operator<(const VertexRef & other) const;
     };
 
     class Face