Fix: Godot ResourceLoader Threaded Progress Stuck

A loading screen uses ResourceLoader.load_threaded_request to fetch a big scene. The progress bar stays at 0%. Status checks return IN_PROGRESS indefinitely. The load eventually completes but progress never updates.

Two Common Issues

1. Progress not requested: load_threaded_get_status takes an optional Array parameter. Without it, you get status but no percentage.

2. Tight polling loop: if you call get_status in a while loop without yielding, the main thread blocks; the load thread can’t make progress, status stays IN_PROGRESS forever, your bar stays at 0%.

The Fix

func load_scene_threaded(path: String) -> Resource:
    var err = ResourceLoader.load_threaded_request(path)
    if err != OK:
        push_error("load_threaded_request failed: %d" % err)
        return null

    var progress: Array = []
    while true:
        var status = ResourceLoader.load_threaded_get_status(path, progress)
        $LoadingBar.value = progress[0] * 100

        match status:
            ResourceLoader.THREAD_LOAD_LOADED:
                return ResourceLoader.load_threaded_get(path)
            ResourceLoader.THREAD_LOAD_FAILED:
                push_error("Load failed")
                return null
            ResourceLoader.THREAD_LOAD_INVALID_RESOURCE:
                push_error("Invalid resource")
                return null

        await get_tree().process_frame   # critical: yield to engine

The progress Array receives [0.0..1.0]. The await yields back to the engine each frame, letting the load thread make progress and the UI refresh.

Status Codes to Handle

• THREAD_LOAD_IN_PROGRESS: still loading.
• THREAD_LOAD_LOADED: done. Call load_threaded_get to retrieve.
• THREAD_LOAD_FAILED: load failed mid-stream (corrupted file, missing dependency).
• THREAD_LOAD_INVALID_RESOURCE: the request was never accepted (bad path).

Always branch on all four. Ignoring FAILED produces infinite spinners on bad inputs.

Sub-Resource Progress

For large scenes that reference many sub-resources, the progress reflects sub-resource discovery in stages, not strictly linear. Expect the bar to jump (e.g., 0.1 to 0.7 in a moment) as the load resolves child resources.

Verifying

Load a known-good scene. The progress bar should climb smoothly to 1.0 over the load duration. Loading a known-corrupt resource should produce THREAD_LOAD_FAILED quickly with your error path firing.

“Pass the progress array. Yield between polls. Handle all four status codes. Threaded loading just works.”

For scene transitions, run threaded loads while a fade-out animation plays — player perceives zero wait when timed right.