UIImage+Additions

UIImage+Additions.h

//  UIImage+Additions.h
//  Copyright (c) 2012 Tobias Reiss (MIT License)

#import <UIKit/UIKit.h>

@interface UIImage (Additions)

+ (UIImage *)deviceAgnosticImageNamed:(NSString *)name;
- (UIImage *)deviceAgnosticImageFromRect:(CGRect)frame;

@end

UIImage+Additions.m

//  UIImage+Additions.h
//  Copyright (c) 2012 Tobias Reiss (MIT License)

#import "UIImage+Additions.h"

@implementation UIImage (Additions)

/*
 * deviceAgnosticImageNamed
 *
 * This method tackles a common problem where
 * devs want to use iPhone's "@2x" image on iPad's "@1x" devices
 * and a "@4x" version on iPad's "@2x" devices.
 * "@4x" means double the size of the iPhone's @2x size.
 * 
 * Example:
 * This call `[UIImage deviceAgnosticImageNamed:@"myImage.png"];`
 * would return the following images.
 *   - iPhone (1x) -> "myImage.png"
 *   - iPhone (2x) -> "myImage@2x.png"
 *   - iPad   (1x) -> "myImage@2x.png"
 *   - ipad   (2x) -> "myImage@4x.png"
 *
 * That means your bundle should contain the following images:
 *   - myImage.png
 *   - myImage@2x.png
 *   - myImage@4x.png
 * 
 */
+ (UIImage *)deviceAgnosticImageNamed:(NSString *)name
{
  // determine iPad
  BOOL isIpad = UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad;

  if (isIpad) {
    NSString *ext = ext = name.pathExtension;
    // determine resolution
    NSString *imageName = [NSString stringWithFormat:@"%@@%dx",
                           [name substringToIndex:MAX(0, name.length - ext.length - 1)],
                           ((int)[[UIScreen mainScreen] scale]) * 2];
    NSString *fileLocation = [[NSBundle mainBundle] pathForResource:imageName ofType:ext];
    return [UIImage imageWithData:[NSData dataWithContentsOfFile:fileLocation]];
  } else {
    return [UIImage imageNamed:name];
  }
}

/*
 * deviceAgnosticImageFromRect
 *
 * Returns a clipping of a "deviceAgnosticImage" (see `deviceAgnosticImageNamed`). 
 * Especially useful for Image-Sprites.
 * 
 * Example:
 * ```
 * UImage *sprite = [UIImage deviceAgnosticImageNamed:@"myImage.png"];
 * UIImage *image1 = [sprite deviceAgnosticImageFromRect:aRect];
 * UIImage *image2 = [sprite deviceAgnosticImageFromRect:anotherRect];
 * ```
 * 
 */
- (UIImage *)deviceAgnosticImageFromRect:(CGRect)frame {
    
    // determine iPad
    BOOL isIpad = UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad;
    // determine factor
    CGFloat factor = isIpad ? 2.0 : 1.0;
    // determine resolution
    uint8_t scale = [[UIScreen mainScreen] scale] * factor;
    // scale frame according to the output device
    frame.origin.x *= scale;
    frame.origin.y *= scale;
    frame.size.width *= scale;
    frame.size.height *= scale;
    // clip image
    CGImageRef imageRef = CGImageCreateWithImageInRect(self.CGImage, frame);
    // convert to UIImage
    return [UIImage imageWithCGImage:imageRef scale:scale / factor orientation:self.imageOrientation];
}

@end