WebGPURenderer: Prevent dispose of default textures.

[Mugen87]

Related issue: #31747

Description

@Makio64's live example from #31747 (comment) was really helpful to fix an edge case in WebGPURenderer's texture management.

When you start loading a texture and call dispose() during the loading process, the backends delete the GPU texture objects of the default textures. That should not happen since these objects are cached and shared across other compatible textures. The PR fixes this issue my performing the dispose() as usual except for the deletion of the GPU texture object. That requires to delegate the isDefaultTexture flag down to the texture utils components for both backends.

[Mugen87]

@Makio64 Your live example was really helpful to discover this bug! It does not yet fix the root cause of #31747 though. That is a different issue I'll try to fix with a different PR (bindings and textures getting out of sync).

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.24 79.14	338.24 79.14	+0 B +0 B
WebGPU	579.91 160.21	579.98 160.23	+68 B +13 B
WebGPU Nodes	578.52 159.97	578.59 159.99	+68 B +14 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	469.88 113.85	469.88 113.85	+0 B +0 B
WebGPU	649.62 175.88	649.69 175.9	+68 B +14 B
WebGPU Nodes	603.73 165.04	603.8 165.05	+68 B +16 B

[Makio64]

@Mugen87 thank you, happy it helps!

[sunag]

Couldn't we put the condition here instead of taking it to the backend?

if ( isDefaultTexture === false ) {

		this.backend.destroyTexture( texture );

}

[Mugen87]

In this case, the backend does not delete the texture data which is done inside the destroyTexture() methods. Meaning:

backend.delete( texture );

That was indeed the main reason why I have introduced a new parameter.

We could move backend.delete( texture ); into Textures._destroyTexture() however WebGPUTextureUtils.destroyTexture() is used at other places as well so we would have to copy this line multiple times which seems error prone.

[sunag]

You tried to add/use a flag like isDefault through the backend method backend.createDefaultTexture() similar to the one used in WebGLBackend?

three.js/src/renderers/webgl-fallback/utils/WebGLTextureUtils.js

Lines 410 to 414 in 8c698fb

	backend.set( texture, {
	textureGPU,
	glTextureType,
	isDefault: true
	} );

[Mugen87]

I've added the same flag in WebGPUTextureUtils for testing but unfortunately this introduces a regression that textures are not destroyed anymore at all since the isDefault flag persists with the texture data. It would be necessary to remove this flag or set it to false when the real texture data are available.

This kind of management already exists in Textures and it seems error prone to duplicate it in both backends.

For consistency reasons, I have removed the isDefault flag from WebGLTextureUtils since it was not evaluated it the code base anyway.