设置一个负值的y轴偏移转将阴影转移到顶部。
Set a negative value for y-offset to shift the shadow to the top.
接下来,旋转和恢复这个矩阵;然后,使用translate设置与当前坐标系统的偏移量(这是从之前旋转和转换的矩阵应用的),并绘制一个红色椭圆。
Next, rotate and store this matrix; then, offset from the current coordinate system with translate (which is applied from the previously rotated and translated matrices), and draw a red ellipse.
最后,我们将当前的结束偏移量设置为下一个循环的开始偏移量。
Finally, we make the starting offset for the next loop the ending offset of the current one.
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