TiledView.h

@interface TiledView

- (id)initWithX:(int)tileXNum Y:(int)tileYNum;
@property (nonatomic) BOOL annotates;

@end

TiledView.m

#define TILE_SIZE 256

@implementation TiledView

- (id)initWithX:(int)tileXNum Y:(int)tileYNum
{
    self = [super init];
    if (self) {
      
        CATiledLayer *tiledLayer = (CATiledLayer *)[self layer];
        tiledLayer.contents = nil;
        tiledLayer.levelsOfDetail = 1;
        tiledLayer.levelsOfDetailBias = 0;

        // logic for retina
        float screenScale = [UIScreen mainScreen].scale;
        tiledLayer.tileSize = CGSizeMake(TILE_SIZE*screenScale, TILE_SIZE*screenScale);

        // bound is auto fit with retina
        self.bounds = CGRectMake(0, 0, TILE_SIZE*tileXNum, TILE_SIZE*tileYNum);
    }
    return self;
}

- (void)dealloc
{
    [super dealloc];
}

- (void)drawRect:(CGRect)rect {
    // for UIView implemente
    // real logic is implements on below
    // - (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context
}

- (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context {
    
    CGRect rect = CGContextGetClipBoundingBox(context);
    CGFloat scale = CGContextGetCTM(context).a;
    
    CATiledLayer *tiledLayer = (CATiledLayer *)layer;
    CGSize tileSize = tiledLayer.tileSize;
    tileSize.width  /= scale;
    tileSize.height /= scale;

    int col = floorf(CGRectGetMinX(rect) / tileSize.width);
    int row = floorf(CGRectGetMinY(rect) / tileSize.height);

    CGImageRef image = [self tileForScale:scale row:row col:col];

    CGContextScaleCTM(context, 1, -1);
    rect = CGContextGetClipBoundingBox(context);
    
    if(NULL != image) {
        CGContextDrawImage(context, rect, image);
        CGImageRelease(image);
    }
    
    // draw line for debug
    if (self.annotates) {
        CGContextSetRGBStrokeColor(context, 0, 1, 0, 1);
        CGContextSetLineWidth(context, 6.0 / scale);
        CGContextStrokeRect(context, rect);
    }

}

- (CGImageRef)tileForScale:(CGFloat)scale row:(int)y col:(int)x
{
    
    NSString *path;
    {
        // path for tile
        path = xxxx/x/y;
    }

    CGDataProviderRef provider;
    if(path != nil) {
        NSURL *imageURL = [NSURL fileURLWithPath:path];
        provider = CGDataProviderCreateWithURL((CFURLRef)imageURL);
    }

    CGImageRef image = nil;
    if(provider != nil) {
        image = CGImageCreateWithJPEGDataProvider(provider, NULL, FALSE, kCGRenderingIntentDefault);
        CFRelease(provider);
    }
    
    return image;
}

@end