与iOS相比，打开的GL ES坐标在y轴上翻转。通过glreadpixels保存数据（到视频中）可以进行适当的转换，但在UIView中显示会翻转y轴。将其翻转回来进行演示的最佳方式是什么？
到目前为止，我看到了三种方式：
1） 在opengl中渲染两次，将非翻转版本发送到glreadpixels，将翻转版本发送给CAEAGLLayer（presentRenderbuffer）。
2） 翻转opengl中的像素，使其正确显示；一旦我通过glreadpixels读取了它们，请移动这些位，然后将其保存到文件中。
3） 翻转opengl中的像素，使其正确显示；对视频本身应用某种类型的变换（使其在播放时翻转）。
我不确定这些是否是正确的道路。寻找最具性能的路径。
看起来最好的方法是在opengl中使用翻转的顶点。
只需对UIView应用转换即可翻转它。例如：
view.transform = CGAffineTransformMakeScale(1.0, -1.0);
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