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一句话理解：使用 mask 层的 alpha，替换原视图的 aplha
为了搞图片蒙板，还得用 ps 搞个图，结果 ps 的蒙板，其实是一个东西
技术这个东西，很多都是相通的，多学习
Layer Mask
image
普通
- (void)viewDidLoad {
[super viewDidLoad];
self.baseView.layer.mask = [self avatorMask:self.baseView];
}
- (CALayer *)avatorMask:(UIView *)baseView {
CAShapeLayer *maskLayer = [CAShapeLayer layer];
maskLayer.frame = baseView.bounds;
CGFloat w = baseView.bounds.size.width;
CGFloat h = baseView.bounds.size.height;
CGFloat radius = h > w ? w/2.0 : h/2.0;
maskLayer.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(radius, radius) radius:radius startAngle:0 endAngle:2*M_PI clockwise:YES].CGPath;
maskLayer.fillColor = [UIColor whiteColor].CGColor;
return maskLayer;
}
渐变（alpha 渐变）
- (void)viewDidLoad {
[super viewDidLoad];
self.baseView.layer.mask = [self avatorMask:self.baseView];
}
- (CALayer *)gradientMask:(UIView *)baseView {
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = baseView.bounds;
gradientLayer.colors = @[(__bridge id)[UIColor colorWithWhite:1 alpha:0.2].CGColor,
(__bridge id)[UIColor colorWithWhite:1 alpha:1].CGColor,
(__bridge id)[UIColor colorWithWhite:1 alpha:0.5].CGColor,
];
gradientLayer.locations = @[@(0.2), @(0.5), @(0.8)];
gradientLayer.startPoint = CGPointMake(0, 0);
gradientLayer.endPoint = CGPointMake(1, 1);
gradientLayer.type = kCAGradientLayerAxial;
return gradientLayer;
}
View Mask
iOS 8 新属性 maskView，使用起来还算方便吧，代码可以少写很多
image
普通图片（只用透明-非透明）
UIImageView *maskView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"mask"]];
maskView.frame = self.baseView.bounds;
self.baseView.maskView = maskView;
渐变图片（alpha 渐变）
UIImageView *maskView2 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"mask2"]];
maskView2.frame = self.baseView2.bounds;
self.baseView2.maskView = maskView2;
附录
