public int ToContentIndex(IRowCol RowCol, int Offset = 0)
{
if (RowCol.LocationFrame == LocationFrame.OneBased)
{
RowCol = RowCol.ToZeroRowCol();
}
var ix = RowCol.RowNum * this.ScreenDim.Width + RowCol.ColNum;
ix += Offset;
return(ix);
}