[webgpu migration] scene background broke (`PMREMGenerator` issue?) after swapping from WebGLRenderer to WebGPURenderer

Questions
1

I made a small patch to replace WebGLRenderer with WebGPURenderer in Lume (the patch is shown here).

I noticed that PMREMGenerator has a fix coming out in r169 thanks for @Mugen87, which I manually patched into node_modules for now, to try migrating to WebGPU.

Here is my test case scene, which is written with Lume HTML elements (powered by Three.js rendering), showing the expected result:

https://raw.githack.com/lume/lume/b5242eb39d1f3613c1071f6db40d954ca559faf6/examples/gltf-model.html

Video:

After applying that patch from the PR PMREMGenerator in node_modules, and the patch for Lume I linked above (very simple), the new outcome is this:

I’m wondering if there may be a bug, or if the background has to be handled differently with WebGPURenderer.

Here’s the piece of code that uses PMREMGenerator to make the background, fairly simple (specifically the lines marked with // HERE):

	enableBackground(
		scene: Scene,
		isEquirectangular: boolean,
		blurAmount: number,
		cb: (tex: Texture | undefined) => void,
	): void {
		const state = this.sceneStates.get(scene)
		if (!state) throw new ReferenceError('Internal error: Scene not registered with WebGLRendererThree.')

		this.#bgVersion += 1
		state.bgIsEquirectangular = isEquirectangular

		if (isEquirectangular) {
			// Load the PMREM machinery only if needed.
			if (!state.pmremgen) {
				state.pmremgen = new PMREMGenerator(state.renderer) // HERE
				// @ts-expect-error no type yet
				state.pmremgen.compileCubemapShader() // HERE (fixed with the mentioned patch)
			}
		}

		state.hasBg = true
		this.#loadBackgroundTexture(scene, blurAmount, cb)
	}

	#loadBackgroundTexture(scene: Scene, blurAmount: number, cb: (texture: Texture) => void): void {
		const state = this.sceneStates.get(scene)
		if (!state) throw new ReferenceError('Internal error: Scene not registered with WebGLRendererThree.')

		const version = this.#bgVersion

		new TextureLoader().load(scene.background ?? '', tex => {
			// In case state changed during load, ignore a loaded texture that
			// corresponds to previous state:
			if (version !== this.#bgVersion) return

			if (blurAmount > 0) {
				// TODO port to WebGPURenderer
				// // state.bgTexture = blurTexture(state.renderer, tex, 5) // Faster, but quality is not as good, has a pixelated effect. Perhaps we should provide a Scene attribute to easily pick which blur to use.
				// state.bgTexture = triangleBlurTexture(state.renderer, tex, blurAmount, 2)
				// tex.dispose()
				// tex = state.bgTexture
			}

			if (state.bgIsEquirectangular) {
				// @ts-expect-error no type yet
				state.bgTexture = state.pmremgen!.fromEquirectangular(tex).texture // HERE
				tex.dispose() // might not be needed, but just in case.
			} else {
				state.bgTexture = tex
			}

			cb(state.bgTexture!)
		})
	}

Basically the three lines marked with // HERE use the PMREMGenerator if the conditions are true that will cause pmrem generator to be used.

Is there anything obviously wrong that needs to be changed for WebGPURenderer? Or should the API usage be the same, and this might be a bug?