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Document the snoise tie order in design.md and THIRD-PARTY-NOTICES

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Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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Meta Vens 2026-10-04 03:26:10 +02:00
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4
packages/cultmath/THIRD-PARTY-NOTICES.md
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@ -9,7 +9,9 @@ Gustavson's `webgl-noise` project and Unity Mathematics.
`math.snoise(float3)` and `cultmath_snoise(float3)` follow `src/noise3D.glsl` and
`math.snoise(float2)` follows `src/noise2D.glsl` of stegu/webgl-noise at commit
`22434e04d7753f7e949e8d724ab3da2864c17a0f` (the simplex-boundary fix is
`21d9fe23d7`, scale `ff3b5d34ea`, permutation `a3e6d57095`).
`21d9fe23d7`, scale `ff3b5d34ea`, permutation `a3e6d57095`). Modified from upstream:
the 3D corner tie order follows Gustavson's `simplexnoise1234`, because the
upstream `step` compares are cyclic where the offset's components are equal.
`math.snoise_grad`/`cultmath_snoise_grad` (and the `fbm_grad`/`ridged_grad`
octave sums built on them) follow the analytic-gradient differentiation from

7
packages/cultmath/docs/design.md
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@ -356,7 +356,12 @@ together, laid out as `float4(gradient.xyz, value.w)`, with no value-only twin
that permutation helper, so its values changed too, while its own kernel
(`0.5`) and scale (`130`) already matched upstream.
`NoiseGradTests.SnoiseAndItsGradientAreContinuousAcrossSimplexCellBoundaries`
pins the continuity.
pins the continuity. Ties in the offset `x0` resolve in Gustavson's
`simplexnoise1234` order (x over y, y over z, x over z), a total order, so the
four corners are always a simplex. Upstream's `step` compares are cyclic: where
the three components are equal, which includes the origin and every
`(t, t, t)`, the corners repeat the origin vertex and the value jumps by up to
0.77. `NoiseGradTests.SnoiseIsContinuousOnTheSimplexDiagonal` pins the order.
- `snoise_grad(float3 p)` carries `snoise(float3)` to value-and-gradient form,
following the differentiation in webgl-noise `src/noise3Dgrad.glsl` (Ashima
Arts / Ian McEwan, MIT), which uses the same radius, permutation and scale as

4
packages/cultmath/unity/org.gamecult.cultmath/THIRD-PARTY-NOTICES.md
View file

@ -9,7 +9,9 @@ Gustavson's `webgl-noise` project and Unity Mathematics.
`math.snoise(float3)` and `cultmath_snoise(float3)` follow `src/noise3D.glsl` and
`math.snoise(float2)` follows `src/noise2D.glsl` of stegu/webgl-noise at commit
`22434e04d7753f7e949e8d724ab3da2864c17a0f` (the simplex-boundary fix is
`21d9fe23d7`, scale `ff3b5d34ea`, permutation `a3e6d57095`).
`21d9fe23d7`, scale `ff3b5d34ea`, permutation `a3e6d57095`). Modified from upstream:
the 3D corner tie order follows Gustavson's `simplexnoise1234`, because the
upstream `step` compares are cyclic where the offset's components are equal.
`math.snoise_grad`/`cultmath_snoise_grad` (and the `fbm_grad`/`ridged_grad`
octave sums built on them) follow the analytic-gradient differentiation from