DotSlashSlash DotSlashSlash - 6 days ago 6
Objective-C Question

How do I add a gradient to the text of a UILabel, but not the background?

hey, I want to be able to have a gradient fill on the text in a UILabel I know about CGGradient but i dont know how i would use it on a UILabel's text

i found this on google but i cant manage to get it to work

http://silverity.livejournal.com/26436.html

Answer

(Skip to bottom for full class source code)

Really useful answers by both Brad Larson and Bach. The second worked for me but it requires an image to be present in advance. I wanted something more dynamic so I combined both solutions into one:

  • draw the desired gradient on a UIImage
  • use the UIImage to set the color pattern

The result works and in the screenshot below you can see some Greek characters rendered fine too. (I have also added a stroke and a shadow on top of the gradient)

iOS stylized UILabel, the big brown fox

Here's the custom init method of my label along with the method that renders a gradient on a UIImage (part of the code for that functionality I got from a blog post I can not find now to reference it):

- (id)initWithFrame:(CGRect)frame text:(NSString *)aText {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
        self.text = aText;

        self.textColor = [UIColor colorWithPatternImage:[self gradientImage]];

    }
    return self;
}

- (UIImage *)gradientImage
{
    CGSize textSize = [self.text sizeWithFont:self.font];
    CGFloat width = textSize.width;         // max 1024 due to Core Graphics limitations
    CGFloat height = textSize.height;       // max 1024 due to Core Graphics limitations

    // create a new bitmap image context
    UIGraphicsBeginImageContext(CGSizeMake(width, height));

    // get context
    CGContextRef context = UIGraphicsGetCurrentContext();       

    // push context to make it current (need to do this manually because we are not drawing in a UIView)
    UIGraphicsPushContext(context);                             

    //draw gradient    
    CGGradientRef glossGradient;
    CGColorSpaceRef rgbColorspace;
    size_t num_locations = 2;
    CGFloat locations[2] = { 0.0, 1.0 };
    CGFloat components[8] = { 0.0, 1.0, 1.0, 1.0,  // Start color
                            1.0, 1.0, 0.0, 1.0 }; // End color
    rgbColorspace = CGColorSpaceCreateDeviceRGB();
    glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations);
    CGPoint topCenter = CGPointMake(0, 0);
    CGPoint bottomCenter = CGPointMake(0, textSize.height);
    CGContextDrawLinearGradient(context, glossGradient, topCenter, bottomCenter, 0);

    CGGradientRelease(glossGradient);
    CGColorSpaceRelease(rgbColorspace); 

    // pop context 
    UIGraphicsPopContext();                             

    // get a UIImage from the image context
    UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();

    // clean up drawing environment
    UIGraphicsEndImageContext();

    return  gradientImage;
}

I'll try to complete that UILabel subclass and post it.

EDIT:

The class is done and it's on my GitHub repository. Read about it here!

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