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 animating mask - but masking is not available on the iPhone OS for performance reasons.

Is there some private API effect (like SuckEffect) that they might have used? A spotlight type of effect? Some Core Animation thing?

Edit: It's definitely not a series of stills. I've seen examples of being edit a plist value or something and customize the string on jailbroken iphones.

Answer 1

Good question. It might be getting drawn with ordinary Quartz stuff (context clipping or similar), but I can't imagine that that'd have decent performance. Probably a private API.

Answer 2

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 3

I guess this is CoreAnimation, which relies on openGL.

Answer 4

You can use the kCGTextClip drawing mode to set the clipping path and then fill with a gradient.

// Get Context
CGContextRef context = UIGraphicsGetCurrentContext();
// Set Font
CGContextSelectFont(context, "Helvetica", 24.0, kCGEncodingMacRoman);
// Set Text Matric
CGAffineTransform xform = CGAffineTransformMake(1.0,  0.0,
            0.0, -1.0,
            0.0,  0.0);
CGContextSetTextMatrix(context, xform);
// Set Drawing Mode to set clipping path
CGContextSetTextDrawingMode (context, kCGTextClip);
// Draw Text
CGContextShowTextAtPoint (context, 0, 20, "Gradient", strlen("Gradient")); 
// Calculate Text width
CGPoint textEnd = CGContextGetTextPosition(context);
// Generate Gradient locations & colors
size_t num_locations = 3;
CGFloat locations[3] = { 0.3, 0.5, 0.6 };
CGFloat components[12] = { 
 1.0, 1.0, 1.0, 0.5,
 1.0, 1.0, 1.0, 1.0,
 1.0, 1.0, 1.0, 0.5,
};
// Load Colorspace
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
// Create Gradient
CGGradientRef gradient = CGGradientCreateWithColorComponents (colorspace, components,
                 locations, num_locations);
// Draw Gradient (using clipping path
CGContextDrawLinearGradient (context, gradient, rect.origin, textEnd, 0);
// Cleanup (exercise for reader)

Setup an NSTimer and vary the values in locations, or use GoreAnimation to do the same.

Answer 5

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 6

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 7

It can be easilly done by using Core Animation, animating a mask layer on the layer displaying the text.

Try this in any plain UIViewController (you can start with a new Xcode project based on the View-based application project template), or grab my Xcode project here:

Note that the CALayer.mask property is only available in iPhone OS 3.0 and later.

- (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 = 1e100f;
  maskAnim.duration = 1.0f;
  [maskLayer addAnimation:maskAnim forKey:@"slideAnim"];

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

  [super viewDidLoad];
}

The images used by this code are:

Answer 8

First, a HUGE thank you to marcio for his solution. This worked almost perfectly, saved me hours of effort, and made a huge splash in my app. My boss loved it. I owe you beer. Or several.

One small correction for iPhone 4 only. I mean the hardware itself, not just iOS 4. They changed the system font on the iPhone 4 from Helvetica (iPhone 3Gs and below) to Helvetic Neue. This caused the translation you're doing from character to glyphs to be off by exactly 4 spots. For example the string "fg" would appear as "bc". I fixed this by explicitly setting the font to "Helvetica" rather than using "systemFontofSize". Now it works like a charm.

Again...THANK YOU!