Preventing a UITabBar from applying a gradient to its icon images

Adding gradient is very simple, add the following lines of code:

CGFloat components[8] = {0.0,0.4,1.0,0.2,0.0,0.6,1.0,1.0};
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();  
CGGradientRef colorGradient = CGGradientCreateWithColorComponents(colorSpace, components, NULL, 2);
CGContextDrawLinearGradient(cxt, colorGradient,CGPointZero,CGPointMake(0,contextRect.size.height),0);

This will get you very close to what Apple does on the tabbar but, not exact. To get there, just add two more points/colors in components and instead of NULL in CGGradientCreateWithColorComponents, use something like {0,0.5,0.6,1.0}. In fact, all you need is one background color and three alpha points (with color part being all 1s, since you just need shading while retaining a single color profile).

I will post my code if this isn't clear ... cheers.

It's been almost a year but here is the code. Add this as a category to UIImage or convert to class-wide. Remember, the image you are passing (self) has to be an alpha only image (the mask is created based on the visible parts of the image).

- (UIImage *) imageWithBackgroundColor:(UIColor *)bgColor 
                           shadeAlpha1:(CGFloat)alpha1 
                           shadeAlpha2:(CGFloat)alpha2
                           shadeAlpha3:(CGFloat)alpha3 
                           shadowColor:(UIColor *)shadowColor 
                          shadowOffset:(CGSize)shadowOffset 
                            shadowBlur:(CGFloat)shadowBlur { 

    UIImage *image = self;

    CGColorRef cgColor = [bgColor CGColor];
    CGColorRef cgShadowColor = [shadowColor CGColor];

    CGFloat components[16] = {1,1,1,alpha1,1,1,1,alpha1,1,1,1,alpha2,1,1,1,alpha3};
    CGFloat locations[4] = {0,0.5,0.6,1};

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();  

    CGGradientRef colorGradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, (size_t)4);

    CGRect contextRect;
    contextRect.origin.x = 0.0f;
    contextRect.origin.y = 0.0f;
    contextRect.size = [image size];
    //contextRect.size = CGSizeMake([image size].width+5,[image size].height+5);  
    // Retrieve source image and begin image context
    UIImage *itemImage = image;
    CGSize itemImageSize = [itemImage size];
    CGPoint itemImagePosition; 
    itemImagePosition.x = ceilf((contextRect.size.width - itemImageSize.width) / 2);
    itemImagePosition.y = ceilf((contextRect.size.height - itemImageSize.height) / 2);
    UIGraphicsBeginImageContext(contextRect.size);
    CGContextRef c = UIGraphicsGetCurrentContext();
    // Setup shadow
    CGContextSetShadowWithColor(c, shadowOffset, shadowBlur, cgShadowColor);
    // Setup transparency layer and clip to mask
    CGContextBeginTransparencyLayer(c, NULL);
    CGContextScaleCTM(c, 1.0, -1.0);
    CGContextClipToMask(c, CGRectMake(itemImagePosition.x, -itemImagePosition.y, itemImageSize.width, -itemImageSize.height), [itemImage CGImage]);
    // Fill and end the transparency layer
    CGContextSetFillColorWithColor(c, cgColor);     
    contextRect.size.height = -contextRect.size.height;
    CGContextFillRect(c, contextRect);
    CGContextDrawLinearGradient(c, colorGradient,CGPointZero,CGPointMake(contextRect.size.width*1.0/4.0,contextRect.size.height),0);
    CGContextEndTransparencyLayer(c);
    //CGPointMake(contextRect.size.width*3.0/4.0, 0)
    // Set selected image and end context
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CGColorSpaceRelease(colorSpace);
    CGGradientRelease(colorGradient);

    return resultImage;

}

For example, the following will produce an effect very similar to what the native tabbar does:

UIImage *niceImage = [[UIImage imageNamed:@"image_name"] imageWithBackgroundColor:[UIColor colorWithRed:41.0/255.0 green:147.0/255.0 blue:239.0/255.0 alpha:1.0] 
                                                                      shadeAlpha1:0.6 
                                                                      shadeAlpha2:0.0 
                                                                      shadeAlpha3:0.4 
                                                                      shadowColor:[UIColor blackColor] 
                                                                     shadowOffset:CGSizeMake(0.0f, -1.0f)  
                                                                       shadowBlur:3.0];