WebGPUBackend: Align frontFace and cullMode values to WebGL backend.

[Mugen87]

Fixed #31764.

Description

The PR makes sure the WebGPU backend implements the render pipeline values for frontFace and cullMode like in WebGL backend.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.91 79.11	338.91 79.11	+0 B +0 B
WebGPU	579.39 159.66	579.32 159.68	-71 B +19 B
WebGPU Nodes	578 159.42	577.93 159.44	-71 B +20 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	470.78 113.9	470.78 113.9	+0 B +0 B
WebGPU	649.54 175.53	649.47 175.55	-70 B +23 B
WebGPU Nodes	603.64 164.67	603.57 164.69	-70 B +24 B

[WestLangley]

/ping @sunag

This PR causes breakage, and I would advise against changing the winding order convention at this late hour prior to a release.

TBH, I would prefer to continue with the convention @sunag established with WebGPURenderer, wherein front face winding order is always CCW. In that way, the front face is not ambiguous.

//

For example, consider the following color node when rendering transparent, double-sided materials:

material.colorNode = select( frontFacing, color( 0xff0000 ), color( 0x0000ff ) );

With this PR, the back faces will have the same color as the front faces. Transparent, double-sided materials render in two passes, with front faces and back faces rendered separately.

[sunag]

Yes, the PR brings other implications. We can revert it and bring a more robust solution in the next release.

[Mugen87]

Agreed! Thanks for reverting.

But should when then consider to align the WebGL backend to the WebGPU one? Using negative scaling is currently broken as highlighted in #31764. Having at least a consistent response of both backends seems preferable to me.

[WestLangley]

align the WebGL backend to the WebGPU one?

@Mugen87 Yes, that sounds like a very good idea.

But be particularly careful in testing bump mapping, which uses FrontFacingNode, which I expect will need to be modified. If front faces are extruded, back faces should be indented. Currently, I believe both backends are rendering bump maps correctly.