iOS-CALayer遮罩效果

   self.view.backgroundColor = [UIColor blackColor];
    //获取图片
    self.imageContents = [UIImage imageNamed:@"原始图片"];
    self.maskContents = [UIImage imageNamed:@"maskLayerContents"];
    
    //创建图片layer
    self.imageLayer = [CALayer layer];
    self.imageLayer.frame = CGRectMake(50, 50, 200, 200);
    self.imageLayer.contents = (__bridge id)(self.imageContents.CGImage);
    [self.view.layer addSublayer:self.imageLayer];
    
    //创建遮住layer
    self.maskLayer = [CALayer layer];
    self.maskLayer.frame = self.imageLayer.bounds;
    self.maskLayer.contents = (__bridge id)(self.maskContents.CGImage);
    
    //黑色表示通过，白色表示不通过(给图片layer提供遮罩)
    self.imageLayer.mask = self.maskLayer;

 效果图：