1. 离屏渲染:最简单方式

imgView.layer.cornerRadius = 10;
// 这一行代码是很消耗性能的
imgView.clipsToBounds = YES;
//这是离屏渲染，比较消耗性能，界面比较简单的时候使用（现在苹果手机性能都不错，页面不复杂其实都看不出来）

2. 非离屏渲染：给UIImage添加生成圆角图片

- (UIImage *)imageWithCornerRadius:(CGFloat)radius {
CGRect rect = (CGRect){0.f, 0.f, self.size};

UIGraphicsBeginImageContextWithOptions(self.size, NO, UIScreen.mainScreen.scale);
CGContextAddPath(UIGraphicsGetCurrentContext(),
 [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius].CGPath);
CGContextClip(UIGraphicsGetCurrentContext());

[self drawInRect:rect];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return image;
}