Hi! I know I cannot use multiple images as trackers in AR at once on iOS. The good thing is, I donât need them at the same time or in the same AR session.
My idea was: I let the user choose in the HTML UI which mural (mural #1 or mural #2) should be animated in AR. Shortly before switching to AR modeâbefore my scene is converted into USDZâI enable or disable the correct object with the ImageTracking component.
So, I have two WebXR Image Tracking components in my scene, but only one is set to active. I also have a custom script that sets the correct object I want to export to USDZ (it switches between the two objects depending on whether the user selected mural #1 or mural #2).
I noticed that Quick Look seems to ignore which WebXR Image Tracking component is active and which isnât, and it starts mixing up the image trackers. (It feels like it always picks the one that was active when I exported my needle project)
Do you have any workaround ideas? I was thinking of using only one WebXR Image Tracking component with two images in an array, and then removing one shortly before entering AR. But iOS doesnât open scenes at all if there are two images in the array.
This is a known limitation when exporting scenes with multiple image tracking components for use in AR Quick Look on iOS. Quick Look essentially âbakes inâ the initial scene state, meaning that even though you disable one of the WebXR Image Tracking components before export, iOS still âseesâ the tracker active at the time of export. This can result in the behavior youâre describing, where Quick Look mixes up the image trackers and always uses the one that was active during export.
A reliable workaround is to only include a single active image tracker in the scene at export time. In other words, you can generate two separate USDZ files â one for mural #1 and one for mural #2 â each containing only the relevant WebXR Image Tracking component. This way, iOS Quick Look loads a USDZ file with only one image tracker, avoiding the conflict youâre seeing.
If generating separate USDZ files isnât practical for your workflow, another approach is to completely remove the inactive image tracker from the scene (instead of simply disabling it) just before export. However, given that USDZ export captures a static snapshot of the scene, any state that isnât fully removed may still be incorporated during the conversion process.
It might also be worthwhile to double-check that youâre using the latest version of Needle Engine, as improvements and workarounds for platform-specific AR behavior (see the WebXR Image Tracking docs at WebXRImageTracking.d.ts.md and (docs/xr.html)) may have been introduced.
I hope this helps clarify your options. Let me know if you need further details or assistance with your workflow!
4 replies left thread_5DCraH4veuSfK0L60WjXJ8mB Reply to this post directly if you need further help (bottom right button)
Instead of multiple WebXRImageTracking components you should have one ImageTrackingComponent with all your images and just move the image you want to become active in iOS AR to the first entry in the trackedImages list.
That being said: I think this should also work as you described. Going to look into it right now
Hi @Marcel_Wiessler1 thank you for the reply!
In my experience, when I try to export a WebXRImageTracking Component with a longer array (2 items), Quicklook will not open the USDZ file at all, writing "you need a newer iOS versionâ
2 separate active WebXRTracking Components with 1 image each in 1 Scene â> âNewer iOS errorâ
1 active WebXRTracking Components with 2 images in 1 Scene â> âNewer iOS errorâ
2 separate WebXRTracking Components with 1 image each, (1 is active, the secons is disabled) â> Scene will open.
Right now I am trying to understand why turning the image-tracking âgroupsâ on/off in runtime before exporting do not behave as they should (they always pick the same image-tracker, even when this image is not in the exported group). Will keep you in the loop
Here is what I tried in my simplified test:turn the group i do not want to export off, say to the usdzExporter which object-group to export.But I get the same ânewer iOS versionâ error this time.
```import { Behaviour, GameObject, Renderer, USDZExporter, serializable } from "@needle-tools/engine";
import { Material, Object3D } from "three";
export class SwitchARGroups extends Behaviour {
@serializable(GameObject)
group1: GameObject | undefined;
@serializable(GameObject)
group2: GameObject | undefined;
@serializable()
group1On: boolean = true;
private originalMaterial?: Material;
private usdzExporter!: USDZExporter;
onEnable() {
this.usdzExporter = GameObject.findObjectOfType(USDZExporter)!;
this.subscribeToBeforeExportEvent();
}
onDisable() {
this.unsubscribeFromBeforeExportEvent();
}
private subscribeToBeforeExportEvent() {
this.usdzExporter.addEventListener("before-export", this.onBeforeExport);
this.usdzExporter.addEventListener("after-export", this.onAfterExport);
}
private unsubscribeFromBeforeExportEvent() {
this.usdzExporter.removeEventListener("before-export", this.onBeforeExport);
this.usdzExporter.removeEventListener("after-export", this.onAfterExport);
}
onBeforeExport = () => {
console.log("onBeforeExport");
if (this.group1 && this.group2) {
this.group1.activeSelf = this.group1On;
this.group2.activeSelf = !this.group1On;
}
// check which group is active and set the exporter to that group
const groupToExport = this.group1On ? this.group1 : this.group2;
this.usdzExporter!.objectToExport = groupToExport;
}
onAfterExport = () => {
console.log("onAfterExport");
this.group1On = !this.group1On;
//
}
}
Hi Katja, Iâm currently testing my changes to improve reliability of Image Tracking for USDZ. Been just successfully testing with the project you sent (no error on export and I get the different object/image tracked depending on what i turn on/off in Unity). It will then work both with multiple ImageTracking components (first component / first image will be tracked as before)
Will test a bit more but most likely itâll just work as you have it right now without any hacks on your side with the next version
What you can do right now to test is open your web projectâs package.json and force the pre-release needle engine version. Just remember to remove this syntax later when you update your Unity package again to let the version be managed by Unity
Thank you, Marcel! We are getting further.
I used the pre-released version, and I do not get ânew iOSâ-error anymore!
But what is still strange, in my scene with two groups (the last one I described and shared code of here in forum):
switching objects bevore exporting them ist working
BUT both groups (wether I export group 1 or group 2 (each with the richt image-tracking component) they both are recognizing my first image tracker (the one with the cactus)
@Marcel_Wiessler1 , can it be, that Quicklook/USDZExporter somehow caches the setting of the object I export as USDZ first? and when I exit ar, select another group to export, it exports the right object to place, but takes the cached Image Tracker information?
I made a test which somehow proves that. I will write it down
Each time I press AR-Button, i toggle between the groups and export only 1 group
If in the first group i export is Group 1 (with WebXRImageTracking ), I go back, click âenter ARâ, export the second group â the second group will have ImageTracking behaviour (even though there is no WebXRImageTracking conponent)
**
BUT
**
if the first group i export is Group 2 (the one without WebXRImageTracking ), I go back, click âenter ARâ, export the Group 1 â the Group 1 will have no ImageTracking behaviour (even though there is a WebXRImageTracking component inside this group)
