UIColor+.h

//
//  UIColor+.h
//  iTest
//
//  Created by iwill on 11-03-09.
//  Copyright 2011 iwill. All rights reserved.
//

#import <Foundation/Foundation.h>


@interface UIColor (plus)


- (UIColor *) inverseColor;


@end

UIColor+.m

//
//  UIColor+.m
//  iMSC
//
//  Created by iwill on 11-03-09.
//  Copyright 2011 iwill. All rights reserved.
//

#import "UIColor+.h"


@implementation UIColor (plus)


- (UIColor *) inverseColor {
    CGColorRef oldCGColor = self.CGColor;
    int numberOfComponents = CGColorGetNumberOfComponents(oldCGColor);
    
    // can not invert - the only component is the alpha
    // e.g. self == [UIColor groupTableViewBackgroundColor]
    if (numberOfComponents <= 1) {
        return [UIColor colorWithCGColor:oldCGColor];
    }
    
    const CGFloat *oldComponentColors = CGColorGetComponents(oldCGColor);
    CGFloat newComponentColors[numberOfComponents];
    int i = - 1;
    while (++i < numberOfComponents - 1) {
        newComponentColors[i] = 1 - oldComponentColors[i];
    }
    newComponentColors[i] = oldComponentColors[i]; // alpha
    
    CGColorRef newCGColor = CGColorCreate(CGColorGetColorSpace(oldCGColor), newComponentColors);
    UIColor *newColor = [UIColor colorWithCGColor:newCGColor];
    CGColorRelease(newCGColor);
    
    return newColor;
}


@end