How to find vertices on borders of geometry I trying to highlight vertices which are on "borders", imagine half of sphere for example. Also for example I added image geomtry with triangles and highlighted necessary vertices. Any ideas? Thanks
I'm assuming you are rendering this object as a set of triangles. To do what you are trying to do, you will need to store all your triangles (and vertices) in some sort of buffer or list. Then, for each triangle, test if all three of its sides are matched with another triangle side. If so, it is enclosed and inside the object. Otherwise, it is outside the object. Some basic pseudo-code (I apologize for all the foreach loops :) )

foreach t in triangles:
    all_sides_touched = True
    foreach side_t in t:
        this_side_touched = False
        foreach u in triangles.exclude(t):    // run through all other triangles to test
            foreach side_u in u:
                if side_t.equals(side_u):  this_side_touched = True
        all_sides_touched = all_sides_touched and this_side_touched
    if not all_sides_touched:
        foreach side in t:
            foreach point in side:
                // do whatever you want to do with outside vertices