How to use a texture atlas from Zwoptex in your SpriteKit game

BPTextureCache.h

//
//  BPTextureCache.h
//  BallPuzzle
//
//  Created by Adeola Bannis on 11/2/13.
//  Copyright (c) 2013 Adeola Bannis. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <SpriteKit/SpriteKit.h>
@interface BPTextureCache : NSObject
- (void)addTextureFromPlist:(NSString *)filename;
- (SKSpriteNode *)spriteWithCacheName:(NSString *)cacheName;
+ (id)sharedInstance;
@end

BPTextureCache.m

//
//  BPTextureCache.m
//  BallPuzzle
//
//  Created by Adeola Bannis on 11/2/13.
//  Copyright (c) 2013 Adeola Bannis. All rights reserved.
//

#import "BPTextureCache.h"
@interface BPTextureCache ()
{
    NSMutableArray *_allTextures;
}
@end

static BPTextureCache *__shared;

@implementation BPTextureCache

- (id)init
{
    self = [super init];
    if (self) {
        _allTextures = [[NSMutableArray alloc] init];
    }
    return self;
}

+ (id)sharedInstance
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        __shared = [[BPTextureCache alloc] init];
    });
    return __shared;
}

- (NSString *)plistPathForBaseName:(NSString *)baseName
{
    NSString *ipadSuffix = @"";
    NSString *hdSuffix = @"";
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPad) {
        ipadSuffix = @"-ipad";
        // ipadSuffix = @"~ipad"; // use this if you named your plists following Apple's device suffixes
    }
    
    if ([[UIScreen mainScreen] scale] > 1.0)
        hdSuffix = @"-hd";
        //hdSuffix = @"@2x";
    
    
    NSString *fileName = [NSString stringWithFormat:@"%@%@%@", baseName, ipadSuffix, hdSuffix];
    NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:@"plist"];
    
    if (!path && [ipadSuffix length]) {
        fileName = [NSString stringWithFormat:@"%@%@", baseName, hdSuffix];
        path = [[NSBundle mainBundle] pathForResource:fileName ofType:@"plist"];
    }
    
    if (!path && [hdSuffix length]) {
        fileName = [NSString stringWithFormat:@"%@%@", baseName, ipadSuffix];
        path = [[NSBundle mainBundle] pathForResource:fileName ofType:@"plist"];
    }
    
    if (!path) {
        path = [[NSBundle mainBundle] pathForResource:baseName ofType:@"plist"];
    }
    
    
    return path;
}

- (void)addTextureFromPlist:(NSString *)filename
{
    NSString *fileName = [filename componentsSeparatedByString:@"."][0];
    NSString *plistPath = [self plistPathForBaseName:fileName];
    
    NSDictionary *textureInfo = [NSDictionary dictionaryWithContentsOfFile:plistPath];
    
    if (textureInfo) {
        
        NSString *imageName = [textureInfo[@"metadata"][@"textureFileName"] stringByDeletingPathExtension];
        
        NSData *imageData = [[NSData alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:imageName ofType:@"png"]];
        UIImage *texImage = [UIImage imageWithData:imageData scale:[[UIScreen mainScreen] scale]];
       
        SKTexture *bulkTexture = [SKTexture textureWithImage:texImage];
        NSDictionary *info = @{@"texture":bulkTexture, @"frames":textureInfo[@"frames"]};
        [_allTextures addObject:info];
    } else {
        NSLog(@"Could not load resource %@", fileName);
    }
}

- (SKSpriteNode *)spriteWithCacheName:(NSString *)cacheName
{
    // can be faster but w/e
    SKTexture *foundTexture = nil;
    NSString *frameRectString = nil;
    for (NSDictionary *i in _allTextures) {
        NSDictionary *frameNames = i[@"frames"];
        if ([[frameNames allKeys] containsObject:cacheName]) {
            foundTexture = i[@"texture"];
            frameRectString = frameNames[cacheName][@"textureRect"];
            break;
        }
    }
    SKSpriteNode *sprite = nil;
    if (foundTexture && frameRectString) {
        CGRect sampleRect = CGRectFromString(frameRectString);
        CGRect textureRect = sampleRect;
        
        // adjust the rect to SpriteKit's [0.0 - 1.0] range, and flip Y
        // now you can reuse your Cocos2D Zwoptex textures!
        textureRect.size.width = textureRect.size.width/foundTexture.size.width;
        textureRect.size.height = textureRect.size.height/foundTexture.size.height;
        textureRect.origin.x =  (textureRect.origin.x/foundTexture.size.width);
        textureRect.origin.y =  1 - (textureRect.origin.y/foundTexture.size.height) - textureRect.size.height;
       
        // scale this down.... dunno why I need to do this but...
        CGFloat factor = 1.0/[[UIScreen mainScreen] scale];
        sampleRect = CGRectApplyAffineTransform(sampleRect, CGAffineTransformMakeScale(factor, factor));
        SKTexture *subTex = [SKTexture textureWithRect:textureRect inTexture:foundTexture];
        sprite = [SKSpriteNode spriteNodeWithTexture:subTex size:sampleRect.size];
    }
    return sprite;
}

@end