public override void AddCellBeforeModification(TerrainCell cellBefore)
{
TerrainCellAlterationPair pair;
if (!_alterationPairs.TryGetValue(cellBefore.Position, out pair))
{
pair = new TerrainCellAlterationPair {
Before = cellBefore.GetAlteration(true, false)
};
_alterationPairs.Add(cellBefore.Position, pair);
}
}