绘制一个多边形,实现以下变换:a) 按字母U或u进行旋转轴的切换：旋转轴为垂直于屏幕的直线，过当前窗口中心或者过物体中心（通过按U/u在两种可能中切换）。改变旋转轴后的变换是在以前发生所有变换的基础上累加进行的。b) 按字母R或r, 物体绕旋转轴分别旋转一个小角度d0或者-d0。

c) 按向上、下、左、或右方向键，物体相对于屏幕向上、下、左、或右平移固定长度L0。d) 按S或s实现物体绕自身中心放大为原来的k或1/k倍，其中k>1为放缩因子。e) 如果按字母i或I, 则取消之前b,c,d中的所有变换。-Draw a polygon, transformation to achieve the following: a) by letter U or u switch to the axis of rotation: rotation axis is perpendicular to the screen line, over the current window center or off center of the body (by pressing the U/u switch in the two possible ). After changing the axis of rotation occurred before the transformation is based on the accumulation of all transformations carried out. b) by the letter R or r, objects were rotating around the axis of rotation of a small angle d0 or-d0. The specific value of custom d0