返回填充边界的，多义线定义数据
[helpstring("method GetPolylines")]
HRESULT GetPolylines([out,retval] IMxDrawResbuf** pData);例如: C# 从文件加载图案
MxDrawResbuf ret = hatch.GetPolylines();
if(ret.Count != 0)
{
MxDrawPolyline pl = (MxDrawPolyline)ret.AtObject(0);
MxDrawPoint pt = pl.GetPointAt(0);
MessageBox.Show(pt.x.ToString() );
MessageBox.Show(pt.y.ToString() );
}