渐变的高斯模糊效果

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 200, CGRectGetWidth(self.view.frame), 400)];
imageView.image = [UIImage imageNamed:@"home_testImg"];
[self.view addSubview:imageView];
    
CAGradientLayer *gl = [CAGradientLayer layer];
gl.frame = CGRectMake(0,0,CGRectGetWidth(imageView.frame),CGRectGetHeight(imageView.frame));
gl.startPoint = CGPointMake(0.5, 0.0);
gl.endPoint = CGPointMake(0.5, 1);
gl.colors = @[(__bridge id)[UIColor colorWithWhite:0 alpha:0].CGColor,(__bridge id)[UIColor colorWithWhite:0 alpha:0.9].CGColor, (__bridge id)[UIColor colorWithWhite:0 alpha:1].CGColor];
gl.locations = @[@(0),@(0.7), @(1.0f)];

UIBlurEffect *blur = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];
UIVisualEffectView *maskView = [[UIVisualEffectView alloc] initWithEffect:blur];
maskView.frame = CGRectMake(0,0, CGRectGetWidth(imageView.frame), CGRectGetHeight(imageView.frame));
maskView.layer.mask = gl;
[imageView addSubview:maskView];