public GPUInstanceCell(GPUInstanceGroup group, int capacity)
 {
     if (capacity < 0)
     {
         throw new ArgumentException("Illegal Capacity: " + capacity);
     }
     m_Group        = group;
     m_Capacity     = capacity;
     m_Items        = new GPUInstanceCellItem[m_Capacity];
     m_TRSMatrices  = new Matrix4x4[m_Capacity];
     m_MatPropBlock = new MaterialPropertyBlock();
     OnCellInit();
 }
        // //==static
        // public static GPUInstanceCell CreateCell(GPUInstanceGroup group)
        // {
        //     return new GPUInstanceCell(group);
        // }
        // //==

        public GPUInstanceCell(GPUInstanceGroup group) : this(group, 64)
        {
        }