UniformsUtils: Check for XRRenderTarget in getUnlitUniformColorSpace

[mrxz]

Fixed #27868

Description

Adds a check to getUnlitUniformColorSpace to return the render target's texture colour space in case of the WebXR render target. With this change both fog colour and background colour remain consistent inside and outside VR sessions. This is similar to the logic in WebGLProgams.js and WebGLRenderer.js.

This contribution is funded by Fern Solutions

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
669.5 kB (166.1 kB)	669.6 kB (166.2 kB)	+55 B

🌳 Bundle size after tree-shaking

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

Filesize dev	Filesize PR	Diff
449.7 kB (108.8 kB)	449.8 kB (108.8 kB)	+55 B

[donmccurdy]

Note — I don't have access to a WebXR-compatible device at the moment. Could someone test that background and fog colors work as expected in a WebXR session before this is merged?

[mrxz]

@donmccurdy Here are some screenshots taken with a Meta Quest 3 on a test scene.

	Outside WebXR	In WebXR Session
Without this PR
With this PR