最直接的方法就是使用如下属性设置：
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（off-screen-rendering），消耗性能的
给UIImage添加生成圆角图片的扩展API：这是on-screen-rendering
- (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;
}
