WebGLRenderer/WebGPURenderer: Improve Physical Accuracy

[mrdoob]

Description

This PR improves the physical accuracy of the MeshPhysicalMaterial shader (WebGL) and PhysicalLightingModel (WebGPU) by updating the visibility term and diffuse energy conservation logic.

Changes

• Improved Diffuse Energy Conservation (GLSL & TSL): Changed the diffuse term calculation to conserve energy per-channel (1.0 - totalScatteringDielectric) rather than using the maximum component. This is more physically correct, particularly when interacting with colored specular effects like Iridescence.
• Removed Redundant Saturation (GLSL & TSL): Removed saturate() from V_GGX_SmithCorrelated_Anisotropic as the visibility term is mathematically bounded.

These changes align the shader more closely with ground-truth physical models and improve visual fidelity across both renderers.

(Made using https://jules.google/ and https://antigravity.google/)

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	356.97 86.61	356.88 86.59	-91 B -14 B
WebGPU	618.8 173.75	618.77 173.73	-31 B -13 B
WebGPU Nodes	617.41 173.49	617.38 173.48	-31 B -12 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	488.7 121.39	488.61 121.38	-91 B -14 B
WebGPU	690.85 189.59	690.82 189.58	-31 B -10 B
WebGPU Nodes	632.26 172.76	632.26 172.76	+0 B +0 B

[donmccurdy]

It doesn't seem like this function's implementation has changed, and the previous link gave a specific location in the paper, where the new link is a 60-page document. Perhaps the old link could be kept, or a more specific section of the new paper referenced?

[mrdoob]

Done! 53e7451