void InitHeightMap()
 {
     if (heightMapCache == null)
     {
         heightMapCache = new HeightMapCache();
     }
     else
     {
         heightMapCache.Clear();
     }
 }
 void InitHeightMap()
 {
     if (heightMapCache == null)
     {
         int poolSize = (visibleChunksDistance + 10) * 2 * CHUNK_SIZE / 128 + 1;
         poolSize      *= poolSize;
         heightMapCache = new HeightMapCache(poolSize);
     }
     else
     {
         heightMapCache.Clear();
     }
 }