本文讨论了在UIKit中使用-drawInRect:方法绘制图片时存在的性能问题。该方法会根据图片的方向旋转并翻转图片以适配坐标系，这可能导致绘制速度较慢。文章进一步探讨了使用CGContextDrawImage进行手动坐标转换的方法，尽管这样做可能会增加维护成本。
Internally, -drawInRect: will rotate the image into the correct orientation according to the imageOrientation property, then flip the image upside down to convert UIKit coordinates into CoreGraphics coordinates. Then it will call CGContextDrawImage. In this sense, -drawInRect: is surely slower.
But using CGContextDrawImage to target UIKit requires one to do the transformation hassles which may not worth for maintenance.
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