How to load sprite sheets from web API in SpriteKit - ios

Question

I'm new to SpriteKit, and my question is how to load sprite sheets from web API.
Currently, I have an API returns a big PNG image, which contains all sprite sheets, and a json about individual frame information. (file and json are generated by TexturePacker) The API looks like this:
The format just likes a .atlasc folder, which contains a big image and a plist (XML) file.
I was thinking about downloading image and plist file and save it in the disk to load. However, SKTextureAtlas.init(named: String) can only load from app bundle.
In one word, I want to load a sprite animation from the web at runtime.
I have control of the API, so I can update the API to accomplish my goal.

Answer 1

The way I've figured out is downloading image, create a sourceTexture, like: let sourceTexture = SKTexture(image: image)
Then use the frame information in json to create individual textures with method init(rect rect: CGRect, inTexture texture: SKTexture)
Sample code is:
var textures: [SKTexture] = []
let sourceTexture = SKTexture(image: image)
for frame in spriteSheet.frames {
let rect = CGRect(
x: frame.frame.origin.x / spriteSheet.size.width,
y: 1.0 - (frame.frame.size.height / spriteSheet.size.height) - (frame.frame.origin.y / spriteSheet.size.height),
width: frame.frame.size.width / spriteSheet.size.width,
height: frame.frame.size.height / spriteSheet.size.height
)
let texture = SKTexture(rect: rect, inTexture: sourceTexture)
textures.append(texture)
}

Answer 2

basically same way with #Honghao Zhang 's answer, but I was little bit confused about the whole structure at first glance.
so I share my code snippet for later readers.
Happy coding :)
func getSpriteTextures() -> [SKTexture]? {
guard let spriteSheet = loadSpriteJson(name: "sprite_json_file", codable: SpriteJson.self) else { return nil }
let sourceImage = UIImage(named: "sprite_img_file.png")!
let sourceTexture = SKTexture(image: sourceImage)
var textures: [SKTexture] = []
let sourceWidth = spriteSheet.meta.size.w
let sourceHeight = spriteSheet.meta.size.h
let orderedFrameImgNames = spriteSheet.frames.keys.sorted()
for frameImgName in orderedFrameImgNames {
let frameMeta = spriteSheet.frames[frameImgName]!
let rect = CGRect(x: frameMeta.frame.x / sourceWidth,
y: 1.0
- (frameMeta.sourceSize.h / sourceHeight)
- (frameMeta.frame.y / sourceHeight),
width: frameMeta.frame.w / sourceWidth,
height: frameMeta.frame.h / sourceHeight)
let texture = SKTexture(rect: rect, in: sourceTexture)
textures.append(texture)
}
return textures
}