你应该设置图层的 contentsScale 与屏幕的比例相同：

You should set the layer's contentsScale to be the same as the scale of your screen:

layer.contentsScale = [UIScreen mainScreen].scale;

这将在所有iOS设备，Retina Display和非Retina Display上正确缩放。除非你有充分的理由这样做，否则你不应该硬编码为2.0（或其他任何事情）。

This will scale it correctly on all iOS devices, Retina Display and non-Retina Display. You shouldn't hard-code it to 2.0 (or anything else for that matter) unless you have a good reason to do so.