Android WebXR: WebGL layer is not cleared between frames (started Aug 22)

🌵 Needle Engine
1

Hi team,

Since early Saturday Aug 22, AR sessions on Android show heavy smearing:
the WebGL layer is never cleared between frames, so everything drawn
accumulates on screen. The camera passthrough itself renders correctly —
only the rendered 3D layer piles up. The AR reticle leaves a trail of
overlapping rings as I move the phone (see screenshots).

BROKEN: https://mushroom-house.netlify.app/
WORKING: https://halloween-ar-01.netlify.app/

Both are old builds. I have not touched either project since deploying
them. The mushroom one worked fine until Saturday and then started
failing on its own.

Environment

  • Needle Engine 5.1.4 (both builds report this in the console)
  • Unity 6000.3.7f1, Universal 3D (URP) template
  • Android phone (bought one week ago), Chrome
  • iPhone via App Clip: the SAME broken build works correctly

Also reproduces with a brand-new empty scene containing only a cube,
built from a fresh project with the same template. So it is not related
to scene content or complexity.

What I have ruled out

  • Not the scene or the 3D content — iOS App Clip renders it correctly
  • Not the Needle version — both builds report 5.1.4
  • Not scene complexity — a single-cube scene reproduces it
  • Not the browser or device alone — another old build still works on the
    same phone and browser

Given that a previously working deployment broke without being rebuilt,
I suspect something changed on the device side (ARCore / Google Play
Services for AR auto-update around Aug 22), but I cannot explain why one
build is affected and another is not.

Happy to test anything or provide more builds.

image
image699×1568 90.6 KB

2

The smearing (WebGL layer not cleared) strongly points to a change in ARCore or Chrome’s WebXR compositor that now expects the app to explicitly clear the color buffer each frame.

Try this first:
In your Unity scene, open the WebXR component and make sure Transparent Background is unchecked. Also set the Camera’s Clear Flags to Solid Color (not Don’t Clear).

If that doesn’t help, add this to a script:

start() {
  this.context.renderer.autoClear = true;
}

One question: Can you share a screenshot comparing the WebXR component settings between the working (halloween-ar-01) and broken (mushroom-house) builds? Same Needle version, so the difference is likely a toggle you missed in the new scene.

If that’s not it, test by deploying the broken scene to a new URL and try disabling alpha in the WebXR session options – but the component toggle is the fastest fix.

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