/// <summary>
/// �R���X�g���N�^
/// </summary>
/// <param name="id">�h�L�������gID</param>
public Document(Int32 id)
{
_id = id;
_penSize = 1;
_fileName = "";
_dirty = false;
_surface = new Surface(50, 50);
_backSurface = _surface.Clone() as Surface;
_historyList = new HistoryActionList();
}