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copied!<p>It can be easilly done by using Core Animation, animating a mask layer on the layer displaying the text.</p> <p>Try this in any plain UIViewController (you can start with a new Xcode project based on the <em>View-based application</em> project template), or grab my Xcode project <a href="http://dl.dropbox.com/u/713729/SlideToUnlock.zip" rel="nofollow noreferrer">here</a>:</p> <p><em>Note that the <code>CALayer.mask</code> property is only available in iPhone OS 3.0 and later.</em></p> <pre><code>- (void)viewDidLoad { self.view.layer.backgroundColor = [[UIColor blackColor] CGColor]; UIImage *textImage = [UIImage imageNamed:@"SlideToUnlock.png"]; CGFloat textWidth = textImage.size.width; CGFloat textHeight = textImage.size.height; CALayer *textLayer = [CALayer layer]; textLayer.contents = (id)[textImage CGImage]; textLayer.frame = CGRectMake(10.0f, 215.0f, textWidth, textHeight); CALayer *maskLayer = [CALayer layer]; // Mask image ends with 0.15 opacity on both sides. Set the background color of the layer // to the same value so the layer can extend the mask image. maskLayer.backgroundColor = [[UIColor colorWithRed:0.0f green:0.0f blue:0.0f alpha:0.15f] CGColor]; maskLayer.contents = (id)[[UIImage imageNamed:@"Mask.png"] CGImage]; // Center the mask image on twice the width of the text layer, so it starts to the left // of the text layer and moves to its right when we translate it by width. maskLayer.contentsGravity = kCAGravityCenter; maskLayer.frame = CGRectMake(-textWidth, 0.0f, textWidth * 2, textHeight); // Animate the mask layer's horizontal position CABasicAnimation *maskAnim = [CABasicAnimation animationWithKeyPath:@"position.x"]; maskAnim.byValue = [NSNumber numberWithFloat:textWidth]; maskAnim.repeatCount = HUGE_VALF; maskAnim.duration = 1.0f; [maskLayer addAnimation:maskAnim forKey:@"slideAnim"]; textLayer.mask = maskLayer; [self.view.layer addSublayer:textLayer]; [super viewDidLoad]; } </code></pre> <p>The images used by this code are:</p> <p><a href="https://i.stack.imgur.com/kmq78.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kmq78.png" alt="Mask Layer"></a> <a href="https://i.stack.imgur.com/RFLIl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RFLIl.png" alt="Text Layer"></a></p>

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