iOS UILabel两侧加阴影

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.view setBackgroundColor:[UIColor grayColor]];
    // Do any additional setup after loading the view, typically from a nib.
    MarqueeLabel *label = [[MarqueeLabel alloc]initWithFrame:CGRectMake(0, 0, 100, 20)];
    label.backgroundColor = [UIColor clearColor];
    
    float fadeLength = 15.0f;
    CAGradientLayer* gradientMask = [CAGradientLayer layer];
    gradientMask.bounds = label.layer.bounds;
    gradientMask.position = CGPointMake([label bounds].size.width / 2, [label bounds].size.height / 2);
    NSObject *transparent = (NSObject*) [[UIColor clearColor] CGColor];
    NSObject *opaque = (NSObject*) [[UIColor blackColor] CGColor];
    gradientMask.startPoint = CGPointMake(0.0, CGRectGetMidY(label.frame));
    gradientMask.endPoint = CGPointMake(1.0, CGRectGetMidY(label.frame));
    float fadePoint = fadeLength/label.frame.size.width;
    [gradientMask setColors: [NSArray arrayWithObjects: transparent, opaque, opaque, transparent, nil]];
    [gradientMask setLocations: [NSArray arrayWithObjects:
                                 [NSNumber numberWithFloat: 0.0],
                                 [NSNumber numberWithFloat: fadePoint],
                                 [NSNumber numberWithFloat: 1 - fadePoint],
                                 [NSNumber numberWithFloat: 1.0],
                                 nil]];
    label.layer.mask = gradientMask;
    
    label.text = @"者是一个测试程序测试长度适用的滚动的是就是";
    [self.view addSubview:label];
}