How do I load a Data object into a SCNScene? - swift

Question

I want to load a 3d usdz blob into a view, but since I only have the data object, I'm trying to initialize the scene with that with no luck.
To that, I initialize the SCNSceneSource() and then open it using .scene().
Now what I don't understand:
If I use a URL and load the scene directly - it works.
If I use a Data object on the same URL it doesn't.
Apple docs says, the data should be of type NSData but that seems wrong.
import SceneKit
let url = URL(string: "file:///Users/thilo/Desktop/Input/UU2.usdz")!
// working
let src_ok = SCNSceneSource(url: url)
let scn_ok = src_ok?.scene(options: nil, statusHandler: {
a,b,c,d in print("OK: \(a) \(b) \(String(describing: c)) \(d) ")
})
print("Ok: \(scn_ok)")
// Not working?
let data = try! Data(contentsOf: url)
let src_bad = SCNSceneSource(data: data)
let scn_bad = src_bad?.scene(options: nil, status handler: {
a,b,c,d in print("BAD: \(a) \(b) \(String(describing: c)) \(d) ")
})
print("Failed: \(scn_bad)")
running on Playground says:
Ok: Optional(<SCNScene: 0x6000038e1200>)
BAD: 0.0 SCNSceneSourceStatus(rawValue: 4) nil 0x000000016fa948bf
BAD: 0.0 SCNSceneSourceStatus(rawValue: 4) nil 0x000000016fa942af
BAD: 0.0 SCNSceneSourceStatus(rawValue: -1) Optional(Error Domain=NSCocoaErrorDomain Code=260 "Could not load the scene" UserInfo={NSLocalizedDescription=Could not load the scene, NSLocalizedRecoverySuggestion=An error occurred while parsing the COLLADA file. Please check that it has not been corrupted.}) 0x000000016fa942af
Failed: nil
What am I missing?

Answer 1

SCNSceneSource doesn't support .usdz in Data context
Official documentation says that SCNSceneSource object supports only .scn, .dae and .abc file formats. But it turns out that SceneKit doesn't support URL-loading of .usdz only in the context of working with Data. Thus, when working with Data, use files in the .scn format.
import SceneKit
import Cocoa
class GameViewController : NSViewController {
override func viewDidLoad() {
super.viewDidLoad()
if let url = URL(string: "file:///Users/swift/Desktop/ship.scn") {
let data = try! Data(contentsOf: url)
let source = SCNSceneSource(data: data)
let sceneView = self.view as! SCNView
sceneView.scene = source?.scene()
}
}
}
To load .usdz using URL, try SCNSceneSource.init?(url: URL)
class GameViewController : NSViewController {
override func viewDidLoad() {
super.viewDidLoad()
if let url = URL(string: "file:///Users/swift/Desktop/ship.usdz") {
let source = SCNSceneSource(url: url)
let sceneView = self.view as! SCNView
sceneView.scene = source?.scene()
}
}
}
Or use SCNScene object to load .usdz model
class GameViewController : NSViewController {
override func viewDidLoad() {
super.viewDidLoad()
let url = URL(fileURLWithPath: "/Users/swift/Desktop/ship.usdz")
do {
let scene = try SCNScene(url: url)
let sceneView = self.view as! SCNView
sceneView.scene = scene
sceneView.autoenablesDefaultLighting = true
} catch {
print(error.localizedDescription)
}
}
}

Answer 2

Gathering from the comment "does not support usdz" my solution is:
to create a temporary file ( .usdz) seems to be required by the API...
and then manually remove the temporary file after loading.
First extend FileManager with the below code:
public extension FileManager {
func temporaryFileURL(fileName: String = UUID().uuidString,ext: String) -> URL? {
return URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true)
.appendingPathComponent(fileName + ext)
}
}
For a limited hard-coded use case:
let fm = FileManager.default
let tempusdz = fm.temporaryFileURL(ext:".usdz")!
fm.createFile(atPath: tempusdz.path(), contents: sceneData)
let src = SCNSceneSource(url: tempusdz)
if let scene = src?.scene(options: nil) {
....
}
try? fm.removeItem(at: tempusdz)
of course this is a hack, because it will only work if the data is in usdz format.
Since usdz is a ZIP archive, maybe testing for a zip and then just doing the below is a better option:
let sceneData:Data? = data
var sceneSrc: SCNSceneSource? = nil
var tempURL:URL? = nil
if let dataStart = sceneData?.subdata(in: 0..<4),
let dataMagic = String(data: dataStart, encoding: String.Encoding.utf8) as String?,
dataMagic == "PK\u{3}\u{4}" {
let fm = FileManager.default
tempURL = fm.temporaryFileURL(ext: ".usdz")
if let tempURL {
fm.createFile(atPath: tempURL.path(), contents: sceneData)
sceneSrc = SCNSceneSource(url: tempURL)
}
} else {
sceneSrc = SCNSceneSource(data: sceneData!)
}
let scene = sceneSrc?.scene()
if let tempURL {
try? FileManager.default.removeItem(at: tempURL)
}
Does anyone knows a better solution?
Is there an easy way to check the type of the Data ?

Answer 3

potential solution could be to verify the format of the data object and ensure that it is a valid COLLADA file.
import Foundation
let url = URL(string: "file:///Users/thilo/Desktop/Input/UU2.usdz")!
let data = try! Data(contentsOf: url)
print("Data size: \(data.count)")
print("Data format: \(data.description)")
you usually get these types of errors when the data wasn't properly formatted