UIImageView添加圆角

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;}