private void RefreshZOrdering()
{
uniqueCounter_ = 0;
m_ordering = new SortedList<double, int>();
for (int i = 0; i < m_zPositions.Count; ++i)
{
double zpos = m_zPositions[i];
double fraction = (double)(++uniqueCounter_) / 10000000.0f;
double d = zpos + fraction;
m_ordering.Add(d, i);
}
}