正如你看到的，我只是使例子更加健壮，但是对于实际业务代码影响最小。

As you can see, I just made the example more robust with minimal impact on the actual business code.

youdao

到目前为止我做到了这一点。但问题是，当我最小化或鼠标窗口的大小改变输出窗口，它只是再次油漆的三角1而非三角2。

I have achieved it so far. but problem is when I minimize or change size of window with mouse the output window, it just paint again Triangle 1 rather than Triangle 2.

youdao