replace @MainActor with nonisolated

[tatsuya-ogawa]

Summary

• Mark renderer(_:updateAtTime:) as nonisolated in SCNSceneRendererDelegate.

Why

On my environment, the VRMExample crashes without this change.

Notes

My understanding: SCNSceneRendererDelegate callbacks are invoked on SceneKit’s render thread (not the main actor). If the method is @MainActor, Swift Concurrency enforces an actor hop and the runtime crashes when the renderer calls into an isolated method. Marking it nonisolated lets SceneKit call it safely; any UI work can still be dispatched back to MainActor inside the method if needed.

[gemini-code-assist]

Summary of Changes

Hello @tatsuya-ogawa, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical runtime crash in the VRMExample by adjusting the concurrency isolation of a SceneKit delegate method. By marking the renderer(_:updateAtTime:) method as nonisolated, the change ensures that SceneKit's rendering thread can invoke this callback directly and safely, preventing an actor hop that previously led to application instability. This improves the robustness and correct behavior of the rendering pipeline.

Highlights

• Concurrency Isolation: The renderer(_:updateAtTime:) method within the SCNSceneRendererDelegate extension has been explicitly marked as nonisolated. This change removes the @MainActor isolation from the method, allowing it to be called directly by SceneKit's render thread without an actor hop.
• Crash Prevention: This modification resolves a crash observed in the VRMExample, which occurred when the renderer(_:updateAtTime:) callback was implicitly or explicitly isolated to the @MainActor, leading to runtime issues when invoked from SceneKit's non-main rendering thread.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a crash related to Swift Concurrency and SceneKit delegate callbacks. Marking the renderer(_:updateAtTime:) method as nonisolated is the right approach, as this delegate method is called from SceneKit's render thread, not the main actor. The change is approved. I've also added one comment suggesting a related improvement to make the code more robust by avoiding a force cast.

[gemini-code-assist]

Adding nonisolated here is the correct fix for the concurrency issue. Great job!

As a related improvement, the force cast as! on the next line is risky and could cause a crash. To make the code more robust, please consider changing line 53 to use optional casting:

(renderer.scene as? VRMScene)?.vrmNode.update(at: time)

[tattn]

Thank you for the bugfix! It was my mistake.