inverse color

inverse Color

// UIColor+InverseColor.h
@interface UIColor(InverseColor)
- (UIColor*)inverseColor;
@end

// UIColor+InverseColor.m
@implement UIColor(InverseColor)
- (UIColor*)inverseColor {
    CGColorRef oldCGColor = self.CGColor;
    NSInteger numOfComponents = CGColorGetNumberOfComponents(oldCGColor);
    
    // can not invert - the only component is the alpha
    // e.g. self == [UIColor groupTableViewBackgroundColor]
    if (1 == numOfComponents) {
        return [UIcolor colorWithColor:oldCGColor];
    }

#if 0
    CGFloat r, g, b, a;
    [self getRed:&r green:&g blue:&b alpha:&a];
    return [UIColor colorWithRed:1.f-r green:1.-g blue:1.-b alpha:a];
#endif
    
    const CGFloat *oldCGColorComponents = CGColorGetComponents(oldCGColor);
    CGFloat newCGColorComponents[numOfComponents];
    int i = numOfComponents - 1;
    newCGColorComponents[i] = oldCGColorComponents[i]; // alpha
    while (i-- > 0) {
        newCGColorComponents[i] = 1 - oldCGColorComponents[i];
    }

    CGColorRef newCGColor = CGColorCreate(CGColorGetColorSpace(oldCGColor), newCGColorComponents);
    UIColor *newColor = [UIColor colorWithCGColor:newCGColor];
    CGColorRelease(newCGColor);

    return newColor;
}

inverse Color