UPDATE FOR iOS 7.0
In iOS 7.0, Apple added a new attribute, NSTextEffectAttributeName
, for attributed strings. If your deployment target is iOS 7.0 or later, you can set this attribute to NSTextEffectLetterpressStyle
to draw an attributed string in an embossed style.
ORIGINAL
I can’t say for certain how Apple draws the embossed text. It looks to me like they fill the string glyphs with a reddish color, then apply a shadow around the interior edges of the glyphs, and also apply a very faint shadow along the top outside edges of the glyphs. I tried it out and here’s what it looks like:
On top is my rendering. Below that is a simple UILabel with shadow as Chris suggested in his answer. I put a screen shot of the Reminders app in the background.
Here’s my code.
First, you need a function that creates an image mask of your string. You’ll use the mask to draw the string itself, and then to draw a shadow that only appears around the inside edges of the string. This image just has an alpha channel and no RGB channels.
- (UIImage *)maskWithString:(NSString *)string font:(UIFont *)font size:(CGSize)size
{
CGRect rect = { CGPointZero, size };
CGFloat scale = [UIScreen mainScreen].scale;
CGColorSpaceRef grayscale = CGColorSpaceCreateDeviceGray();
CGContextRef gc = CGBitmapContextCreate(NULL, size.width * scale, size.height * scale, 8, size.width * scale, grayscale, kCGImageAlphaOnly);
CGContextScaleCTM(gc, scale, scale);
CGColorSpaceRelease(grayscale);
UIGraphicsPushContext(gc); {
[[UIColor whiteColor] setFill];
[string drawInRect:rect withFont:font];
} UIGraphicsPopContext();
CGImageRef cgImage = CGBitmapContextCreateImage(gc);
CGContextRelease(gc);
UIImage *image = [UIImage imageWithCGImage:cgImage scale:scale orientation:UIImageOrientationDownMirrored];
CGImageRelease(cgImage);
return image;
}
Second, you need a function that inverts that mask. You’ll use this to make CoreGraphics draw a shadow around the inside edges of the string. This needs to be a full RGBA image. (iOS doesn’t seem to support grayscale+alpha images.)
- (UIImage *)invertedMaskWithMask:(UIImage *)mask
{
CGRect rect = { CGPointZero, mask.size };
UIGraphicsBeginImageContextWithOptions(rect.size, NO, mask.scale); {
[[UIColor blackColor] setFill];
UIRectFill(rect);
CGContextClipToMask(UIGraphicsGetCurrentContext(), rect, mask.CGImage);
CGContextClearRect(UIGraphicsGetCurrentContext(), rect);
}
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
You can use those in a function that draws the string in red and applies a shadow to its interior edges.
-(UIImage *)imageWithInteriorShadowAndString:(NSString *)string font:(UIFont *)font textColor:(UIColor *)textColor size:(CGSize)size
{
CGRect rect = { CGPointZero, size };
UIImage *mask = [self maskWithString:string font:font size:rect.size];
UIImage *invertedMask = [self invertedMaskWithMask:mask];
UIImage *image;
UIGraphicsBeginImageContextWithOptions(rect.size, NO, [UIScreen mainScreen].scale); {
CGContextRef gc = UIGraphicsGetCurrentContext();
// Clip to the mask that only allows drawing inside the string's image.
CGContextClipToMask(gc, rect, mask.CGImage);
// We apply the mask twice because we're going to draw through it twice.
// Only applying it once would make the edges too sharp.
CGContextClipToMask(gc, rect, mask.CGImage);
mask = nil; // done with mask; let ARC free it
// Draw the red text.
[textColor setFill];
CGContextFillRect(gc, rect);
// Draw the interior shadow.
CGContextSetShadowWithColor(gc, CGSizeZero, 1.6, [UIColor colorWithWhite:.3 alpha:1].CGColor);
[invertedMask drawAtPoint:CGPointZero];
invertedMask = nil; // done with invertedMask; let ARC free it
image = UIGraphicsGetImageFromCurrentImageContext();
}
UIGraphicsEndImageContext();
return image;
}
Next you need a function that takes an image and returns a copy with a faint upward shadow.
- (UIImage *)imageWithUpwardShadowAndImage:(UIImage *)image
{
UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale); {
CGContextSetShadowWithColor(UIGraphicsGetCurrentContext(), CGSizeMake(0, -1), 1, [UIColor colorWithWhite:0 alpha:.15].CGColor);
[image drawAtPoint:CGPointZero];
}
UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultImage;
}
Finally, you can combine those functions to create an embossed image of your string. I put my final image into a UIImageView
for easy testing.
- (void)viewDidLoad
{
[super viewDidLoad];
CGRect rect = self.imageView.bounds;
NSString *string = @"Reminders";
UIFont *font = [UIFont systemFontOfSize:33];
UIImage *interiorShadowImage = [self imageWithInteriorShadowAndString:string
font:font
textColor:[UIColor colorWithHue:0 saturation:.9 brightness:.7 alpha:1]
size:rect.size];
UIImage *finalImage = [self imageWithUpwardShadowAndImage:interiorShadowImage];
self.imageView.image = finalImage;
}