iPhone “slide to unlock” animation

Question

Any ideas as to how Apple implemented the \"slide to unlock\" (also, \"slide to power off\" is another identical example) animation?

I thought about some sort of ani

Answer 1

Maybe it's just a rendered-out animation - you know, a series of stills played one after another. Not necessarily a dynamic effect.

Update: Never mind, the video DrJokepu posted proved it's dynamically generated.

Answer 2

I know, I am a bit late with the answer, but Facebook has great library Shimmer that implements exactly that effect.

Answer 3

I took the best from above solutions and created a neat method that does all for you:

- (void)createSlideToUnlockViewWithText:(NSString *)text
{
    UILabel *label = [[UILabel alloc] init];
    label.text = text;
    [label sizeToFit];
    label.textColor = [UIColor whiteColor];

    //Create an image from the label
    UIGraphicsBeginImageContextWithOptions(label.bounds.size, NO, 0.0);
    [[label layer] renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *textImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CGFloat textWidth = textImage.size.width;
    CGFloat textHeight = textImage.size.height;

    CALayer *textLayer = [CALayer layer];
    textLayer.contents = (id)[textImage CGImage];
    textLayer.frame = CGRectMake(self.view.frame.size.width / 2 - textWidth / 2, self.view.frame.size.height / 2 - textHeight / 2, textWidth, textHeight);

    UIImage *maskImage = [UIImage imageNamed:@"Mask.png"];
    CALayer *maskLayer = [CALayer layer];
    maskLayer.backgroundColor = [[UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.15] CGColor];
    maskLayer.contents = (id)maskImage.CGImage;
    maskLayer.contentsGravity = kCAGravityCenter;
    maskLayer.frame = CGRectMake(-textWidth - maskImage.size.width, 0.0, (textWidth * 2) + maskImage.size.width, textHeight);

    CABasicAnimation *maskAnimation = [CABasicAnimation animationWithKeyPath:@"position.x"];
    maskAnimation.byValue = [NSNumber numberWithFloat:textWidth + maskImage.size.width];
    maskAnimation.repeatCount = HUGE_VALF;
    maskAnimation.duration = 2.0;
    maskAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
    [maskLayer addAnimation:maskAnimation forKey:@"slideAnimation"];

    textLayer.mask = maskLayer;
    self.slideToUnlockLayer = textLayer;
    [self.view.layer addSublayer:self.slideToUnlockLayer];
}

Answer 4

Thanks to rpetrich for the clipping gradient recipe. I am a newbie iPhone and Cocoa developer, so I was real happy to find it.

I've implemented a decent-looking Slide to Cancel UIViewController using rpetrich's method. You can download the Xcode project of my implementation from here.

My implementation uses a repeating NSTimer. I was unable to figure out how use Core (or Gore) Animation to have the iPhone's graphics engine continuously move the highlighting. I think that could be done on OS X with CALayer mask layers, but mask layers are not supported on iPhone OS.

When I play with Apple's "Slide to Unlock" slider on my iPhone's home screen, I occasionally see the animation freeze. So I think Apple may be using a timer as well.

If anyone can figure out how to do a non-timer based implementation using CA or OpenGL, I would love to see it.

Thanks for the help!

Answer 5

not so fresh...but maybe it'll be useful

#define MM_TEXT_TO_DISPLAY          @"default"

#define MM_FONT             [UIFont systemFontOfSize:MM_FONT_SIZE]
#define MM_FONT_SIZE            25
#define MM_FONT_COLOR           [[UIColor darkGrayColor] colorWithAlphaComponent:0.75f];

#define MM_SHADOW_ENABLED           NO
#define MM_SHADOW_COLOR         [UIColor grayColor]
#define MM_SHADOW_OFFSET            CGSizeMake(-1,-1)


#define MM_CONTENT_EDGE_INSETS_TOP      0
#define MM_CONTENT_EDGE_INSETS_LEFT     10
#define MM_CONTENT_EDGE_INSETS_BOTTON   0
#define MM_CONTENT_EDGE_INSETS_RIGHT    10
#define MM_CONTENT_EDGE_INSETS          UIEdgeInsetsMake(MM_CONTENT_EDGE_INSETS_TOP, MM_CONTENT_EDGE_INSETS_LEFT, MM_CONTENT_EDGE_INSETS_BOTTON, MM_CONTENT_EDGE_INSETS_RIGHT)

#define MM_TEXT_ALIGNMENT           UITextAlignmentCenter
#define MM_BACKGROUND_COLOR         [UIColor clearColor]

#define MM_TIMER_INTERVAL           0.05f
#define MM_HORIZONTAL_SPAN          5


@interface MMAnimatedGradientLabel : UILabel {  

    NSString *textToDisplay;
    int text_length;

    CGGradientRef gradient;

    int current_position_x;
    NSTimer *timer;

    CGPoint alignment;

    CGGlyph *_glyphs;
}

- (id)initWithString:(NSString *)_string;

- (void)startAnimation;
- (void)toggle;
- (BOOL)isAnimating;

@end

#define RGB_COMPONENTS(r, g, b, a)  (r) / 255.0f, (g) / 255.0f, (b) / 255.0f, (a)

@interface MMAnimatedGradientLabel (Private)
- (CGRect)calculateFrame;
@end


@implementation MMAnimatedGradientLabel

// Missing in standard headers.
extern void CGFontGetGlyphsForUnichars(CGFontRef, const UniChar[], const CGGlyph[], size_t);

- (id)init {
    textToDisplay = MM_TEXT_TO_DISPLAY;
    return [self initWithFrame:[self calculateFrame]];
}

- (id)initWithString:(NSString *)_string {
    textToDisplay = _string;
    return [self initWithFrame:[self calculateFrame]];
}

-(id)initWithFrame:(CGRect)frame {  
    if (self = [super initWithFrame:frame]) {

        // set default values
        //
        self.textAlignment      = MM_TEXT_ALIGNMENT;
        self.backgroundColor    = MM_BACKGROUND_COLOR;
        self.font               = MM_FONT;
        self.text               = textToDisplay;
        self.textColor          = MM_FONT_COLOR;

        if (MM_SHADOW_ENABLED) {
            self.shadowColor        = MM_SHADOW_COLOR;
            self.shadowOffset       = MM_SHADOW_OFFSET;
        }

        text_length = -1;

        CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
        CGFloat colors[] =
        {       
            RGB_COMPONENTS(255.0, 255.0, 255.0, 0.00),
//          RGB_COMPONENTS(255.0, 255.0, 255.0, 0.15),
            RGB_COMPONENTS(255.0, 255.0, 255.0, 0.95),
//          RGB_COMPONENTS(255.0, 255.0, 255.0, 0.15),
            RGB_COMPONENTS(255.0, 255.0, 255.0, 0.00)
        };

        gradient = CGGradientCreateWithColorComponents(rgb, colors, NULL, sizeof(colors)/(sizeof(colors[0])*4));
        CGColorSpaceRelease(rgb);

        current_position_x = -(frame.size.width/2);// - MM_CONTENT_EDGE_INSETS.left - MM_CONTENT_EDGE_INSETS.right); 
    }

    return self;
}

- (CGRect)calculateFrame {
    CGSize size = [textToDisplay sizeWithFont:MM_FONT];
    NSLog(@"size: %f, %f", size.width, size.height);
    return CGRectMake(0, 0, size.width + MM_CONTENT_EDGE_INSETS.left + MM_CONTENT_EDGE_INSETS.right, size.height + MM_CONTENT_EDGE_INSETS.top + MM_CONTENT_EDGE_INSETS.bottom);
}

- (void)tick:(NSTimer*)theTimer {
    if (current_position_x < self.frame.size.width)
        current_position_x = current_position_x + MM_HORIZONTAL_SPAN;
    else
        current_position_x = -(self.frame.size.width/2); // - MM_CONTENT_EDGE_INSETS.left - MM_CONTENT_EDGE_INSETS.right);

    [self setNeedsDisplay]; 
}

- (void)startAnimation {    
    timer = [[NSTimer alloc] initWithFireDate:[NSDate date] 
                                     interval:MM_TIMER_INTERVAL
                                       target:self 
                                     selector:@selector(tick:)
                                     userInfo:nil
                                      repeats:YES];

    [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
}

- (void)toggle {

    if (!timer) {
        timer = [[NSTimer alloc] initWithFireDate:[NSDate date] 
                                         interval:MM_TIMER_INTERVAL
                                           target:self 
                                         selector:@selector(tick:)
                                         userInfo:nil
                                          repeats:YES];

        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
    } else {
        [timer invalidate];
        [timer release];
        timer = nil;

        current_position_x = -(self.frame.size.width/2);
        [self setNeedsDisplay]; 
    }
}

- (BOOL)isAnimating {

    if (timer) 
        return YES;
    else
        return NO;
}

- (void)drawRect:(CGRect)rect {
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    // Get drawing font.
    CGFontRef font = CGFontCreateWithFontName((CFStringRef)[[self font] fontName]);
    CGContextSetFont(ctx, font);
    CGContextSetFontSize(ctx, [[self font] pointSize]);

    // Calculate text drawing point only first time
    // 
    if (text_length == -1) {    

        // Transform text characters to unicode glyphs.
        text_length = [[self text] length];
        unichar chars[text_length];
        [[self text] getCharacters:chars range:NSMakeRange(0, text_length)];

        _glyphs = malloc(sizeof(CGGlyph) * text_length);
        for (int i=0; i<text_length;i ++)
            _glyphs[i] = chars[i] - 29;

        // Measure text dimensions.
        CGContextSetTextDrawingMode(ctx, kCGTextInvisible); 
        CGContextSetTextPosition(ctx, 0, 0);
        CGContextShowGlyphs(ctx, _glyphs, text_length);
        CGPoint textEnd = CGContextGetTextPosition(ctx);

        // Calculate text drawing point.        
        CGPoint anchor = CGPointMake(textEnd.x * (-0.5), [[self font] pointSize] * (-0.25));  
        CGPoint p = CGPointApplyAffineTransform(anchor, CGAffineTransformMake(1, 0, 0, -1, 0, 1));

        if ([self textAlignment] == UITextAlignmentCenter) 
            alignment.x = [self bounds].size.width * 0.5 + p.x;
        else if ([self textAlignment] == UITextAlignmentLeft) 
            alignment.x = 0;
        else 
            alignment.x = [self bounds].size.width - textEnd.x;

        alignment.y = [self bounds].size.height * 0.5 + p.y;
    }

    // Flip back mirrored text.
    CGContextSetTextMatrix(ctx, CGAffineTransformMakeScale(1, -1));

    // Draw shadow.
    CGContextSaveGState(ctx);
    CGContextSetTextDrawingMode(ctx, kCGTextFill);
    CGContextSetFillColorWithColor(ctx, [[self textColor] CGColor]);
    CGContextSetShadowWithColor(ctx, [self shadowOffset], 0, [[self shadowColor] CGColor]);
    CGContextShowGlyphsAtPoint(ctx, alignment.x, alignment.y, _glyphs, text_length);
    CGContextRestoreGState(ctx);

    // Draw text clipping path.
    CGContextSetTextDrawingMode(ctx, kCGTextClip);
    CGContextShowGlyphsAtPoint(ctx, alignment.x, alignment.y, _glyphs, text_length);

    // Restore text mirroring.
    CGContextSetTextMatrix(ctx, CGAffineTransformIdentity);

    if ([self isAnimating]) {
        // Fill text clipping path with gradient.
        CGPoint start = CGPointMake(rect.origin.x + current_position_x, rect.origin.y);
        CGPoint end = CGPointMake(rect.size.width/3*2 + current_position_x, rect.origin.y);

        CGContextDrawLinearGradient(ctx, gradient, start, end, 0);
    }
}


- (void) dealloc {
    free(_glyphs);
    [timer invalidate];
    [timer release];

    CGGradientRelease(gradient);
    [super dealloc];
}

Answer 6

I uploaded to GitHub a mini project who helps with the “slide to unlock” animation.

https://github.com/GabrielMassana/GM_FSHighlightAnimationAdditions

The project have LTR, RTL, Up to Down and Down to Up animations and it is based in the posts:

Pascal Bourque: https://stackoverflow.com/a/2778232/1381708

cberkley: https://stackoverflow.com/a/5710097/1381708

Cheers