iOS性能优化之图片圆角

在Apple官方文档中多次提出开发时,避免触发离屏渲染效果.离屏渲染触发的情况有很多种,具体可参考iOS离屏渲染相关探索,本文主要讲圆角的性能优化

离屏渲染的触发情况

1. 使用mask的 layer (layer.mask)
2. 需要进行裁剪的layer(layer.masksToBounds / view.clipsToBounds)
3. 设置了组透明度为 YES，并且透明度不为 1 的 layer (layer.allowsGroupOpacity/ layer.opacity)
4. 添加了投影的layer(layer.shadow)
5. 采用了 光栅化的layer(layer.shouldRasterize)
6. 绘制了文字的layer(UILabel, CATextLayer, Core Text 等)

方案一

img.layer.cornerRadius = 50;
img.layer.masksToBounds = YES;

设置 border/backgroundColor的情况下不推荐,触发离屏渲染

方案二

//贝塞尔曲线
- (UIImage *)rounderCornerImageWithCornerRadius:(CGFloat)cornerRadius
{
    int w = self.size.width * self.scale;
    int h = self.size.height * self.scale;
    CGRect rect = CGRectMake(0, 0, w, h);
    //使用贝塞尔
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(w, h), false, 1.0);
    [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:c] addClip];
    [self drawInRect:rect];
    UIImage *ret = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return ret;
}

方案三

UIImageView *imageView = [[UIImageViewalloc] initWithFrame:CGRectMake(100,100,100,100)];
imageView.image = [UIImage imageNamed:@"myImg"];
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:imageView.boundsbyRoundingCorners:UIRectCornerAllCornerscornerRadii:imageView.bounds.size];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
//设置大小
maskLayer.frame = imageView.bounds;
//设置图形样子
maskLayer.path = maskPath.CGPath;
imageView.layer.mask = maskLayer;
[self.view addSubview:imageView];

用CAShapeLayer的内存消耗少，渲染速度快

方案四

圆形图片设置图叠加遮罩