这是一个图形的旋转，每次旋转的角度是90度，就是这个功能。
This is a graph of the rotation Angle of each rotation is 90 degrees, is this function.
您首先要画出正方形，然后再指定该显示窗口后面绘制图形的旋转操作。
You draw your square first, then specify the rotation operation that is applied to the subsequent shapes drawn to the display window.
这样，当我在旋转图形时，直线的中心将发生旋转。
That way, when I rotate the shape, the rotation occurs from the center of the line.
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