Loading retina images from a subdirectory - macos

Question

I'm using NSDrawNinePartImage() to draw a stretchable control. Since this of course requires nine separate images to draw the parts (plus some extras that are drawn over that), I have a directory full of files like top-left.png and top-left#2x.png. I include this directory in my app bundle as a folder reference.
Unfortunately, the usual image-loading APIs like -[NSImage imageNamed:] and -[NSBundle imageForResource:] don't seem to support subdirectories, even if you put a slash in the name. Instead, I'm loading the images with this method:
- (NSImage*)popoverImage:(NSString*)name {
NSURL * url = [[NSBundle bundleForClass:self.class] URLForResource:name withExtension:#"png" subdirectory:#"popover"];
return [[NSImage alloc] initWithContentsOfURL:url];
}
This works fine for normal displays, but it ignores the 2x images for retina displays. How can I get it to load the retina images as well? Is there a better way than loading the two reps separately and combining them by hand? I'd rather not use TIFFs as my source files for these resources, because I use Acorn as my image editor and last time I checked, it doesn't really understand compound image formats like that very well.

Answer 1

The simple answer is to use TIFF's, your concern is misplaced. In Xcode set the project preference "Combine High Resolution Artwork" and continue to produce your two PNG's with Acorn as you do now. During build Xcode will combine those two PNG's into a single TIFF and store that in your bundle.

Answer 2

I ended up biting the bullet and combining the images manually at runtime. I did so by adding this method in a category on NSImage, and then using it in place of -initWithContentsOfURL::
- (id)initRetinaImageWithContentsOfURL:(NSURL *)url {
if((self = [self initWithContentsOfURL:url])) {
NSURL * baseURL = url.URLByDeletingLastPathComponent;
NSString * baseName = url.lastPathComponent.stringByDeletingPathExtension;
NSString * extension = url.lastPathComponent.pathExtension;
NSString * retinaBaseName = [NSString stringWithFormat:#"%##2x", baseName];
NSURL * retinaURL = [baseURL URLByAppendingPathComponent:[retinaBaseName stringByAppendingPathExtension:extension]];
if([retinaURL checkResourceIsReachableAndReturnError:NULL]) {
NSData * data = [[NSData alloc] initWithContentsOfURL:retinaURL];
NSBitmapImageRep * rep = [[NSBitmapImageRep alloc] initWithData:data];
rep.size = self.size;
[self addRepresentation:rep];
}
}
return self;
}

Answer 3

This is what I do:
NSArray *paths = [NSBundle.mainBundle pathsForResourcesOfType: #"icns" inDirectory: #"Collections/1"];
for (NSString *path in paths) {
NSString *fileName = [[path lastPathComponent] stringByDeletingPathExtension];
NSImage *image = [[NSImage alloc] initWithContentsOfFile: path];
image.name = fileName;
[iconCollectionController addObject: #{#"icon": image}];
}
but as CRD already pointed out you need to combine your artwork (either as tiff or icns files). But it frees you from manually selecting an image resolution (which also requires you to listen to backing store changes).