1、設(shè)置簡單，性能差別不明顯，簡單圓角場景下推薦使用。

       // 設(shè)置 layer 的 cornerRadius
      view.layer.masksToBounds = YES;
      view.layer.cornerRadius = imgSize.width / 2;

蘋果在iOS9后優(yōu)化了 cornerRadius 的繪圖方式，此種方式不再需要離屏渲染。

2、在位圖尺寸很大，數(shù)量很多的情況下，但要注意內(nèi)存警告，最好配合緩存機(jī)制使用，避免因內(nèi)存溢出而崩潰。

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                UIImage *image = view.image;
                image = [image drawCircleImage];
                dispatch_async(dispatch_get_main_queue(), ^{
                    view.image = image;
                });
            });
////////////////////////
@implementation UIImage (RoundedCorner)

- (UIImage *)drawCircleImage {
    CGFloat side = MIN(self.size.width, self.size.height);
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(side, side), false, [UIScreen mainScreen].scale);
    CGContextAddPath(UIGraphicsGetCurrentContext(),
                     [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, side, side)].CGPath);
    CGContextClip(UIGraphicsGetCurrentContext());
    CGFloat marginX = -(self.size.width - side) / 2.f;
    CGFloat marginY = -(self.size.height - side) / 2.f;
    [self drawInRect:CGRectMake(marginX, marginY, self.size.width, self.size.height)];
    CGContextDrawPath(UIGraphicsGetCurrentContext(), kCGPathFillStroke);
    UIImage *output = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return output;
}