The coating's patches were drawn by varying the clump CELL with position:
cell = u * (1 + (grainZone(p * ZONE_FREQ) - 0.5) * ZONE_SWING), the same slow
value noise that picks the patch. A lattice whose cell varies with position
smears instead of resizing: its phase accumulates as
d(phase)/ds = 1/cell - s*cell'/cell^2, and c' is read along the radius from the
picture's own origin, so the second term grows with the distance s from it and
the clumps are drawn out wherever the patch's own cell runs. Measured on one
classic-neg paint (1024px, cell 1.09, the app's own Overlay at alpha 0.5, 64
tiles): with the swing on, the tiles' lag-1 correlation of the raw frame spans
-0.065..0.747 — clumps stretched into smooth blotches beside grain. The design's
+-20% swing cannot do that: the SAME field with the swing forced to 0 spans
-0.057..0.045 across its tiles, and the two-lattice field spans -0.055..0.052
(leica: -0.049..0.523 with the swing on, -0.068..0.024 at swing 0).
The zone now MIXES two FIXED lattices, 0.8x and 1.2x the stock's own cell,
weighted by that same patch noise. A fixed lattice's phase is linear in the
picture, so a patch can only choose how much of each is printed, never how
either is shaped — and the two lattices' beat falls at
1/(1/fine - 1/coarse) = 2.4 cells, 2.6px at the 35mm cell: the pixel scale, not
a line the eye reads. The mix is renormalised by sqrt(w^2 + (1-w)^2), the share
of one field's spread a two-field blend carries, so neither the mean nor the
spread follows the patch: the same classic-neg field reads sd 24.85 against
24.91 and leica 23.74 against 23.74, tile by tile.
The zone still reads what it is for. At preview scale (1600px, cell 1.70, 8x8
tiles of 200px) the mixed field's tiles span rho1 0.082..0.265, ratio 3.233,
against 0.169..0.193, ratio 1.141, with the swing forced to 0 — classic-neg;
leica 0.026..0.188, ratio 7.361, against 0.085..0.105, ratio 1.237. A coarser
patch still prints coarser clumps; it just never prints a stretched one.
Both copies carry it: docker/frontend/shared/utils/grainShader.ts and
src/utils/grainShader.ts (the phone's, which the root web harness imports too).
The field is evaluated once per lattice now, so the grain pass costs 1.94x what
one lattice did — the ratio, not the absolute.
Measured:
_grain-zone2.cjs — the 64-tile lag-1 correlation spread above, three modules
on one paint and one seed: swing 0.4 vs swing 0 vs the mix.
_grain-zone-ck.cjs — the zone's own contribution at preview scale, zone on
against the same module with the swing forced to 0, nothing else differing:
classic-neg tile sd 24.21..24.86 (ratio 1.027), hf 0.769..0.937 (1.219),
rho1 0.082..0.265 (3.233) against sd 29.04..32.95 (1.135), hf 0.834..0.858
(1.028), rho1 0.169..0.193 (1.141); leica rho1 0.026..0.188 (7.361) against
0.085..0.105 (1.237). The swing-off row's higher sd is the renormalisation
of a blend with itself (a and b are one field at swing 0), not a contrast
change in the shipped field.
_grain-fft.cjs — same paint, same seeds, three rolls, 1024px: the mix's top
spectral peak sits at 2.6px (classic-neg, cell 1.09) and 2.8..2.9px (leica,
cell 1.00) against the warped field's 3.0/4.3/6.2px and 2.7/3.8/4.5px — both
within a pixel of the clump cell, neither a coarse lattice.
_grain-bench.cjs — 12.68s per 700px field (one lattice) against 24.60s (two),
1.94x on software CanvasKit.
grain-size-test.cjs 17/0 — the SIZE rule and the readout on the module, both
lattices floored at the target's own pixel, file rho1 0.673, preview rho1
0.003.
grain-stock-test.cjs 53/0 on the deployed build — the stock table, the
halation chain and its ordering, no page errors.
grain-controls-test.cjs 20/0 on the deployed build — the patch claim still
holds there: tile sd 56.58..65.48 (mean 61.9, max/min 1.157), tile mean
spread 0.65, so a coarser patch is still not a brighter one.
_grain-spectrum.cjs (app, deployed, 1600px) — residual autocorrelation peak
0.020..0.021, top peaks at 2.0px@20/110 and 2.5px@51.
tsc: web `--noEmit` clean (the docker build runs it); the phone's scoped
config reports its pre-change baseline, nothing in grainShader.ts.
One honest number: the app-level spectral peak/median rises 4.6..6.1 to 10.2
(classic-neg, sim-classic-neg-g6/g10) because two fixed lattices beat where one
warped lattice spread. It is 20x below the value-noise field this work replaced
(29..35, tiling) and 5x below a lattice (50+), and it sits at 2px, the cell
itself.
ponytail: the field is evaluated once per lattice, so the grain pass costs
1.94x. One evaluation cannot hold two cell sizes; revisit only if a preview
budget asks for the pass back. The 0.8/1.2 rungs (ZONE_SWING/2 either side) are
one working set, not a search.
Verified: `grain-stock-test.cjs` 53/0, `grain-controls-test.cjs` 20/0 and
`_grain-spectrum.cjs` against the deployed build at localhost:8090;
`grain-size-test.cjs` 17/0; `_grain-zone2.cjs`, `_grain-zone-ck.cjs`,
`_grain-fft.cjs`, `_grain-bench.cjs` against the module built from HEAD,
`inversesqrt` still the one call the shader needed to renormalise; web
`tsc --noEmit` clean, phone scoped tsc down to its pre-existing errors.
3dtours
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