UIImage任意形状的不规则裁剪

 
UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(0,0, 320, 480)];
imageView.image = [UIImage imageNamed:@"ddd.png"];
[self.view.addSubview:imageView];
CALayer * maskLayer = [CALayer layer];
 maskLayer.frame  = imageView.bounds; 
maskLayer.contents = (id)[[UIImage imageNamed:@"maskcover"] CGImage];
[imageView.layer setMask:maskLayer];