Fix anisotropic ibl bend factor#24515
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olukowski
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Seems the original code assumed pow(a, b) computes b^a, which isn't the case. I was briefly thinking about whether something like:
let bendFactor = 1.0 - anisotropy * (1.0 - roughness);
bent_normal = normalize(mix(bent_normal, N, pow(bendFactor, 4.0)));would make more sense, but then I realized plain multiplication is probably faster.
So looks good!
IceSentry
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Objective
Fix incorrect anisotropic IBL normal bending for
KHR_materials_anisotropy.The previous formula computed
2^(2^x)instead of thex^4bend factor described by the glTF anisotropy reference implementation. This caused anisotropy to affect areas where the anisotropy texture strength should be zero, visibly producing square texture bounds in assets such as KhronosAnisotropyDiscTest.Solution
Replace the incorrect nested
powexpression with the explicit fourth-power bend factor used by the Khronos glTF Sample ViewerTesting
Reviewers can visually test this with the Khronos
AnisotropyDiscTestandCompareAnisotropy.Showcase
Before this PR
After
Ref Khronos
Before
After
Ref Khronos
(In this asset, KHR_texture_transform is applied to the normal map, so the normal detail may not line up exactly with the Khronos viewer even after the anisotropy bend factor is fixed)