PMREMNode: Only generate PMREM with ready image data.

[Mugen87]

Related issue: #28827

Description

This PR fixes point 2. of #28827.

Sometimes when loading a page with a textured background, the texture isn't rendered at all and is black. When refreshing the page, the issue disappears. This does not happen if the code waits until the env map has been loaded (like in webgpu_loader_gltf). However, the new webgpu_materials_basic does not so it can be used as a test case.

The proposed fix is similar to how the previous automatic cube map and cube uv conversion of WebGLRenderer works. Meaning before environment maps are converted, it's important to wait until image data are ready.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
684 kB (169.4 kB)	684 kB (169.4 kB)	+0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
460.9 kB (111.2 kB)	460.9 kB (111.2 kB)	+0 B

[sunag]

pmremTexture() should contemplate this but it has not been implemented yet, if this update is done inside pmremTexture(), the solution level would be expanded.

[Mugen87]

I've updated the PR and moved the logic inside PMREMNode. This is indeed the more general solution.

[Mugen87]

The PR fixes the issue for the WebGPU backend, but not when using WebGL.

Previously, the background was black when the source textures weren't ready. Now it renders the PMREM but not with the correct mapping. This can be reproduced with webgpu_materials_basic(I've just removed the spheres for better visibility).

I wonder why the backends behave differently 🤔 .