RecipesCam/docker/frontend/shared/utils/toneShader.ts

import { BaseFilter, ColorAdjustments } from '../types';
import { HSL_BANDS, hslBandGaps, isMonochromeBase } from './colorUtils';

// Tone-domain adjustments (the four-point tonal range + Fuji-style Dynamic
// Range). SkSL runtime effect over a child image shader.
//
// TONAL RANGE — HIGHLIGHT, SHADOW, WHITE and BLACK. The four knobs are the
// four zones of the tone mapping doc, and no two of them own the same part of
// the ramp:
//
//   BLACKS     peak at 0.00, gone by 0.25
//   SHADOWS    peak at 0.25, gone by 0.50
//   HIGHLIGHTS peak at 0.75, gone by 0.50 and by 1.00
//   WHITES     peak at 1.00, gone by 0.75
//
// The four masks below are those tents — the doc's smoothsteps, one per quarter
// of the ramp — and the 0.50 midpoint is in none of them: it is the one value
// every one of the four leaves where it was.
//
// Colour: the luma takes the move and R, G, B keep their DIFFERENCES — the
// pixel lands on its new luma with the chroma it had, so the hue is untouched
// and a grey stays grey. The doc reaches the same place with a ratio
// (`R_new = R_old * Luma_new / Luma_old`), which is exact while it fits and
// moves the hue the moment a channel clips; see the note on `k` below.
//
// These four masks are ADDED in the doc's own pseudo-shader, and measured that
// way the ramp inverts: BLACK +10 against SHADOW -10 falls to a slope of -5 per
// unit luma at t = 0.87 (scratchpad tone-proto.mjs), a dark band where the ramp
// should still be climbing. Read here instead as the four ANCHORS of one ramp —
// knots at 0.00, 0.25, 0.50, 0.75 and 1.00, each moved by its own knob, each
// held inside the knot before it, drawn straight in between — the same
// measurement is monotone for every combination of the four at full deflection.
// A knob moves its anchor by a quarter of the ramp, so +10 BLACKS puts the toe
// on 0.25 and -10 WHITES rolls the head down to 0.75: the reach a tonal range
// slider has in the program this layout copies, without the inversion. SHADOW is
// the one knob held to half of that, because the knot it moves is the HEAD of
// the quarter above it and not an end of the ramp: a band cannot be lifted at
// its head and keep its slope at the same time, so the knob's travel is what has
// to give — see the measured note on a1.
//
// WHITE and BLACK are not the per-channel toe and shoulder they were on the WB
// tab any more. The doc puts the two points on the ends of the SAME ramp as the
// other two, so they are the ends this ramp is drawn through, and nothing else
// in the shader reads them.
//
// The ramp is drawn through the BASE LAYER, not through the pixel. The pixel's
// own luma, run through a knot move, is a GLOBAL curve: every pixel at luma t
// lands on the same o whatever is around it, so a knot lifted onto the band above
// it (SHADOW's a1) is a band whose whole spread is squashed to the slope left
// over — at SHADOW +100 a quarter of the ramp carries half its contrast, and on a
// real frame 0.50 of it survived: the grey sheet the knob was reported for. What
// the eye is reading there is LOCAL contrast, and a curve drawn through the pixel
// cannot see it.
//
// So the curve is drawn through what the frame holds AROUND the pixel — a coarse
// edge-aware blur of the luma, TONE_BASE_RADIUS of the frame wide (the
// fix_shadow.md decomposition, Base x Detail) — and the neighbourhood's new luma
// is added to the pixel's own difference from it: Base' + Detail. Base moves,
// detail keeps its size: the same lift, on the same pixels, with the texture
// inside the region left standing instead of drawn flat. Full deflection on the
// same frame keeps 0.78 of the band's spread where the global move kept 0.57
// (shadow-live.mjs, before and after, over the deployed pass; shadow-band.py,
// the numpy twin of this maths, put it at 0.78 to 0.80).
//
// The detail used to ride the gain instead — Base' * (Input / Base), the other
// half of the same decomposition — and that is the reconstruction a tonal knob
// must not use: the gain is a function of the neighbourhood, so the detail is
// scaled by how dark or bright the region is, and a knob that takes the base
// toward zero takes the texture with it. BLACK -100 did exactly that (see the
// note in toneRamp), and on a monochrome frame, where all three channels ARE
// the pixel's luma, it returned the blurred base outright.
//
// It costs nothing where there is no lift to make: with every knob on zero the
// ramp at base IS base, so the difference is exactly zero and the pass is the
// identity however coarse the base is. A caller that hands in no neighbourhood
// at all (a mask, which has none) hands in the pixel's own image as the base and
// gets the global move back — which is why the shared maths can take the base as
// an argument and mean the same thing in both places.
//
// Between two knots the ramp is drawn STRAIGHT, and that is deliberate: a
// smoothstep there is an S-curve through the knots, so it bends the ramp by up
// to six code values in the quarter-tones even with all four knobs on zero — and
// this pass still runs for the stock split tones and for DR alone, where nothing
// the user set asked for a contrast move. Straight segments keep a neutral
// setting the exact identity. The smoothsteps are the four ZONE masks above,
// which is where the doc's shape belongs: they weight DR and the split tones,
// and nothing but their peak positions has to be smooth.
//
// The -HL highlight recovery that used to run in LINEAR light ahead of all this
// is gone with it: HIGHLIGHT is one zone move now, in both directions. There is
// still detail at the top to move — the develop's own knee compresses the two
// stops the sensor holds above its white level into the frame (see
// highlight-knee-check.mjs), so -WHITES pulls a plateau down onto 0.75 rather
// than onto a flat 1.0.
//
// dr  - DR strength 0..1: lifts shadows slightly and rolls highlights (Fuji
//       extended DR); 0/auto/DR100 = no extra curve. It moves the same four
//       knots the knobs move, so DR and a knob cannot fight over the middle and
//       DR cannot invert the ramp either — added as its own masked terms on top
//       it could, and did: see the fold noted on the knots below.
// hl  - highlight -1..1: moves the 0.75 anchor, + up toward white, - down.
// sh  - shadow    -1..1: moves the 0.25 anchor, + up, - down.
// wh  - white point -1..1: moves the 1.00 anchor. + is free to pass 1.0 — that
//       is the move that clips a highlight toward white — and - pulls the head
//       of the ramp down under it.
// bl  - black point -1..1: moves the 0.00 anchor. + lifts the toe off the
//       floor (a faded black), - has nothing left to crush at 0.
// vib - vibrance -1..1: chroma-masked saturation. It rides along in this shader
//       (rather than the colour matrix) because it needs per-pixel chroma:
//       already-vivid pixels move least, so skins/skies deepen without the neon
//       clip a plain Saturation boost causes.
// shT/hlT - split tone (per-channel RGB bias, -1..1 each): a fixed cast applied
//       to the shadows and/or the highlights only. A 4x5 colour matrix cannot do
//       this — it is one linear map, so any cast it applies must also hit the
//       midtones and the opposite end. Classic Neg wants green/cyan shadows with
//       warm highlights at once, so the stock ships these values and the pass
//       stays active for it even when every user knob is 0. All-zero still = no
//       pass.
// hslOn/hslH/hslS/hslL - the selective-colour mixer: eight hue bands, each with
//       a hue shift, a saturation scale and a lightness offset (-1..1, from the
//       -10..10 knobs). Which pixels a band owns is decided HERE, per pixel, by
//       hue — so unlike everything else above it, the eight bands are not a
//       global move and cannot live in the colour matrix. See the band block at
//       the foot of TONE_SKSL.
// gh/gs/gl - the mixer's overall move: the same three quantities for the WHOLE
//       image, so they are simply the starting value of the per-band
//       accumulator and every hue gets them at full weight. The lightness one
//       is not gated by saturation (unlike the bands'), so a frame drained to
//       grey by -SAT still answers +LUM.
// The eight band lines of TONE_SKSL's mixer, generated from HSL_BANDS so the
// anchors and the gaps in the shader are the same numbers the chips are built
// from. Each line reads its own band's three values with a CONSTANT index —
// SkSL indexes uniform arrays by constant only, which is why this is unrolled
// rather than looped.
const BAND_BLOCK = hslBandGaps()
  .map(
    (b, i) => `    float w${i} = bandW(hd, ${b.hue.toFixed(1)}, ${b.left.toFixed(1)}, ${b.right.toFixed(1)}) * gate;
    acc += vec3(w${i} * hslH[${i}], w${i} * hslS[${i}], w${i} * hslL[${i}]);\n`
  )
  .join('');

// The four tonal-range knobs, as the four bands the ramp in TONE_MATH_SKSL owns.
// Each band is compactly supported — a knob is exactly the identity outside its
// own — which is what makes the four independent without a guard, and a guard is
// what they used to share: one ceiling over two amplitudes, so a film stock that
// already sits on SHADOW took the BLACK knob's travel down with it (0.663 of it
// on the monochrome stock). See the head of the ramp for the whole argument.
//
// The edges are the doc's (§2.1 and §2.4): BLACKS dies on 0.18, the middle grey
// the doc anchors the toe to, and WHITES starts on 0.80, its shoulder.
export const TONE_BLACK_EDGE = 0.18;
export const TONE_WHITE_EDGE = 0.80;

// How much of its band a knob is worth at full deflection — 100 on the slider.
// BLACK's pair is the doc's own (0.7 opens the toe through the square root, 0.85
// is how hard the crush bites). HIGHLIGHT and WHITE are measured rather than
// inherited: the doc prints the shapes and leaves the rates off, and its own
// sample — a raw pow(L, 1.5) with no headroom term, and a WHITE worth 0.5 —
// either clips or does nothing on a real frame. These are the largest rates that
// keep a full +100 inside the cube on the sweep in highlight-knee-check, with the
// head rolling into the shoulder instead of onto the clamp.
export const TONE_BLACK_LIFT = 0.7;
export const TONE_BLACK_CRUSH = 0.85;
export const TONE_HIGH_GAIN = 2.5;
export const TONE_WHITE_GAIN = 1.5;

// How far out the BASE layer of `toneRamp` reads, as a fraction of the frame's
// own width — the fix_shadow.md neighbourhood (it asks for 2%..5% of the width).
// A fraction rather than a pixel count so the preview and the export look at the
// same neighbourhood, and the measurement is flat across the range anyway: full
// deflection on the sample frame keeps 0.77 of the band's spread at 0.7%, 0.80 at
// 2.5%, 0.81 at 4.8%.
//
// The caller turns this into a BLUR, and it took a bug to make that a blur in
// fact and not only in name. The base used to be nine point samples of the child
// out at plus or minus this radius, and point samples are not an average: on a
// frame with texture at the sampling scale — a waterfall, a mountainside — the
// nine-tap luma aliases, the gain o(base)/base inherits the alias, and the
// reconstruction paints it as mottle. Measured on a 1160x774 frame at
// SHADOW +100, the high-frequency (9px high-pass) part of that gain field was
// 0.063 against 0.005 for a real blur of the same radius — 13x. So the base is
// now a real gaussian blur of the child, made by the caller (Skia's own
// MakeBlur, see blurredBase() in exportEngine.ts) and read here as ONE tap. That
// is also the cheaper pass: nine child evals walk the whole exposure/matrix
// chain nine times, one eval does not.
export const TONE_BASE_RADIUS = 0.025;

// One gaussian sigma of the base blur, as a fraction of TONE_BASE_RADIUS. A box
// of the same radius and a gaussian of this sigma carry the same weight at the
// radius, so the neighbourhood is the one the radius has always named while the
// cuts are smooth instead of hard.
export const TONE_BASE_SIGMA = 0.35;

// The tone and exposure maths, in ONE copy, because two passes ask it: the
// whole-frame passes here and a gradient mask, which moves the same knobs on the
// shape the user drew. What "HIGHLIGHT" or "EXPOSURE" means must not depend on
// where the shape is, and it did: the frame moved the ramp's knots while a mask
// ran a smoothstep luma lift with an arbitrary 0.55..1.35 chroma clamp, and the
// frame's exposure was a linear-light stop while a mask's was a stop on
// sRGB-encoded values. That divergence is what the scratchpad compat doc §3.3
// warns the Android port about. `dr` is the whole frame's DYNAMIC RANGE; a mask
// has no such knob and hands in 0, which is what DR's terms are worth when it is
// off on the frame too.
export const TONE_MATH_SKSL = `
// THE FOUR TONAL KNOBS, as thay_doi_thong_so_giong_lightroom.md §2 asks for them:
// each one owns a COMPACT band of the ramp and is exactly ZERO outside it, and the
// four moves are applied ONE AFTER THE OTHER instead of summed.
//
// The sum came with a guard, and the guard is where the knobs touched. Two bumps
// of a half share a slope, so past a total of 1 the sum carries the curve
// backwards — a fold — and the fix was one ceiling (holdLo / holdHi) shared by
// the amplitudes of a half. A stock that already sits on SHADOW therefore took
// BLACK's lift down with it: on the monochrome stock (sh = -0.24) BLACK -100 came
// back with 0.663 of the travel the knob has on its own, which is the "kéo theo
// sự thay đổi của thông số khác" report exactly. A composition of monotone maps
// is monotone by construction, so it needs no guard, and the same knob then
// measures 1.00 of its travel on every stock. (tone-curve, the arithmetic in
// plain JS on the scratchpad, and the grid sweep in highlight-knee-check.)
//
// The windows are the doc's own, in the encoded luma this whole file works in —
// the boundaries land where the doc's diagram draws them, BLACKS on the toe up to
// the doc's 0.18, SHADOWS as a bell over the deep tones, HIGHLIGHTS as a bell over
// the bright ones, WHITES on the shoulder from 0.80.
float toneBlackW(float L) {
  float u = clamp(1.0 - L / ${TONE_BLACK_EDGE}, 0.0, 1.0);
  // Squared once more than the doc's square for the same reason the sum's kernel
  // was (1-u^2)^2: the join with the identity at L = 0.18 is a slope, not an
  // angle, and an angle on a tone curve is a Mach band.
  return u * u * u;
}
float toneShadowW(float L) {
  return smoothstep(0.02, 0.12, L) * (1.0 - smoothstep(0.25, 0.55, L));
}
float toneHighW(float L) {
  return smoothstep(0.45, 0.65, L) * (1.0 - smoothstep(0.92, 1.0, L));
}
float toneWhiteW(float L) {
  float u = clamp((L - ${TONE_WHITE_EDGE}) / (1.0 - ${TONE_WHITE_EDGE}), 0.0, 1.0);
  return u * u;
}
// The ramp the pixel is rebuilt through. Read at the BASE, so the move is the
// neighbourhood's and the pixel keeps its own difference from it (fix_shadow.md's
// Base' + Detail): the ratio Base' * (Input / Base) was the first cut and it is
// what broke BLACK — it scales the detail by the neighbourhood's gain, so the
// knob that takes the base toward zero takes the picture's texture with it (the
// blur the report named on a monochrome frame, where every channel IS the luma).
//
// Every move below is monotone for any amount in [-1, 1] and lands on L = 0 and
// L = 1 without moving either, so the composition is monotone, the black point is
// the black point, and the white point is the white point whatever the four
// sliders say. The one deliberate departure from the doc's own arithmetic is the
// (1.0 - L) on HIGHLIGHTS: the doc's raw soft-knee ADDS pow(L - 0.5, 1.5) to L,
// and above 0.94 that overshoots the cube — a measured 17% of the ramp driven to
// flat white at +100 before the clamp, the "cháy vùng Whites" the doc's own §1
// opens by calling a defect. The knee reads the headroom that is left instead, so
// the move is zero at L = 1 by construction and the head rolls instead of
// clipping.
float toneCurve(float L, float bl, float sh, float hl, float wh) {
  float q;
  // BLACKS, the toe. Lift opens the detail under the doc's square root, crush
  // deepens it by the doc's 0.85, and neither touches the anchor: sqrt(0) - 0 is
  // 0, so the black point is exactly where it was — the offset that lifted
  // (0,0,0) to a grey pedestal was a SUM adding its bump's height at L = 0, which
  // is the doc's "Milky / Foggy" failure. Past 0.18 the window is 0 and the move
  // is exactly the identity.
  q = toneBlackW(L);
  L = bl > 0.0
    ? L + ${TONE_BLACK_LIFT} * bl * q * (sqrt(L) - L)
    : L * max(1.0 + ${TONE_BLACK_CRUSH} * bl * q, 0.0);
  L = clamp(L, 0.0, 1.0);
  // SHADOWS, a gain on the light with the floor still on 0: the multiplier is
  // 1 + amount * bell * (1 - L)^1.8, so the window's own bell already keeps it
  // off the midtones the doc names and the exponent keeps it off the white end.
  q = toneShadowW(L);
  L *= 1.0 + sh * q * pow(1.0 - L, 1.8);
  L = clamp(L, 0.0, 1.0);
  // HIGHLIGHTS, the doc's soft-knee against the headroom that is left — see the
  // note above the function. max(L - 0.5, 0) because the pow is undefined under
  // the knee and the window is only wide where it is not.
  q = toneHighW(L);
  L += ${TONE_HIGH_GAIN} * hl * q * pow(max(L - 0.5, 0.0), 1.5) * (1.0 - L);
  L = clamp(L, 0.0, 1.0);
  // WHITES, the doc's Hermite on the shoulder: (1 - L) * L is zero on both ends,
  // so the white point is fixed and the move is spent inside the top of the ramp.
  q = toneWhiteW(L);
  L += ${TONE_WHITE_GAIN} * wh * q * (1.0 - L) * L;
  return clamp(L, 0.0, 1.0);
}
// Below t = 0.0004 there is no ratio worth the name: dividing by what is left of
// a pixel that has almost no light on it takes whatever cast the last code value
// of 8-bit noise left there and multiplies it by the pedestal the BLACK knob just
// lifted — colour noise, amplified to the size of the lift. The scale stays 1.0
// down there and the pixel takes the pedestal as the flat grey it is.
//
// ONE move of the light, and everything in this file that changes how bright a
// pixel is goes through it: a tone knob, a mask's tone knob, and the exposure
// knob on both. The luma lands on o and the channel differences ride along at
// one shared scale k, so a knob named "change the brightness" changes the
// brightness and nothing else — what a per-channel multiply cannot promise once
// a channel reaches the ceiling, where the three clip by different amounts and
// the hue goes with them.
vec3 lightMove(vec3 c, float t, float o) {
  float k = t > 0.0004 ? o / t : 1.0;
  float hiC = max(max(c.r, c.g), c.b);
  float loC = min(min(c.r, c.g), c.b);
  if (hiC > t) k = min(k, (1.0 - o) / (hiC - t));
  if (loC < t) k = min(k, o / (t - loC));
  return clamp(vec3(o) + (c - vec3(t)) * k, 0.0, 1.0);
}
vec3 toneRamp(vec3 c, float t, float base, float bl, float sh, float hl, float wh, float dr) {
  // DR is the whole frame's DYNAMIC RANGE, and it rides the same four moves the
  // sliders do rather than adding masked terms of its own: a recovery that lifts
  // the toe and rolls the head is a BLACK and a WHITE, and after the windows a
  // tenth of a unit lands inside the band the knob owns instead of on the whole
  // frame. A mask has no such knob and hands in 0, which is what these terms are
  // worth when DR is off on the frame too.
  float o = toneCurve(base, clamp(bl + dr * 0.12, -1.0, 1.0), clamp(sh + dr * 0.06, -1.0, 1.0),
                     clamp(hl - dr * 0.09, -1.0, 1.0), clamp(wh - dr * 0.18, -1.0, 1.0));
  // A caller with no neighbourhood of its own (a mask) hands in the pixel as its
  // base, and the difference is then exactly zero: the target is the ramp at t,
  // the global move, which is what the ratio gave it too.
  float target = o + (t - base);
  return lightMove(c, t, clamp(target, 0.0, 1.0));
}

// The accurate sRGB transfer pair (0.04045/12.92 + 2.4, and its inverse): the
// same constants colorUtils.planckianLinear uses on the WB side, and the reason
// a stop is a stop here. EXPOSURE needs it — 2^ev is a multiplier on LIGHT — and
// so does anything else that has to reach the linear domain.
vec3 toLinear(vec3 c) {
  return mix(c / 12.92, pow((c + 0.055) / 1.055, vec3(2.4)), step(vec3(0.04045), c));
}
vec3 toEncoded(vec3 c) {
  return mix(c * 12.92, 1.055 * pow(c, vec3(1.0 / 2.4)) - 0.055, step(vec3(0.0031308), c));
}
// One EXPOSURE knob, wherever it is: the frame's own pass and a mask's knob. It
// linearises, moves the LIGHT by 2^ev — a stop is a multiplier on light, and on
// an sRGB-encoded value +1 EV would take a mid-grey 0.5 straight to a blown 1.0
// where a real stop gives 0.73 (measured: 0.6858 through here, and the plain
// per-channel multiply puts the same 0.6858 on a grey, so a neutral is the knob
// it always was) — and re-encodes.
//
// The linear domain decides WHERE the luma is going; the move is then made by
// lightMove on the encoded values, where the tone ramp also works. That split is
// measured, not chosen for symmetry: carrying the chroma in the LINEAR domain
// drifts the hue of the encoded pixel by up to 12° (a saturated red at -1 EV
// came back at 12.1°, a skin tone at +1 EV at 11.5° — the encoding is
// per-channel, so equal ratios in linear are not equal ratios on screen),
// against 0.00° this way. The knob whose whole promise is brightness must not be
// the one that also moves a hue: a channel that would have clipped gives up
// saturation instead, and a pixel the move has driven all the way to 1.0 is white
// in all three channels at once.
vec3 exposureMove(vec3 rgb, float ev) {
  vec3 c = clamp(rgb, 0.0, 1.0);
  float t = clamp(dot(c, vec3(0.2126, 0.7152, 0.0722)), 0.0, 1.0);
  // The linear domain says where the luma is going; the value that lands there
  // is applied as a RATIO on the pixel's own encoded luma, not pointed at
  // directly. toEncoded(luma_lin * 2^ev) is the target, and on a grey it IS the
  // pixel's new luma (a stop on a neutral is the stop it always was) — but the
  // transfer does not commute with the luma weights, so on a colour the two
  // differ by a couple of code values, and the knob on 0 EV would brighten the
  // frame instead of leaving it alone. As a ratio it is exactly 1 at 0 EV.
  float lin = max(dot(toLinear(c), vec3(0.2126, 0.7152, 0.0722)), 1e-6);
  float stop = toEncoded(vec3(min(1.0, lin * exp2(ev)))).r / toEncoded(vec3(lin)).r;
  return lightMove(c, t, clamp(t * stop, 0.0, 1.0));
}
`;

export const TONE_SKSL = `
uniform shader src;
// The BASE layer's child: a blur of the image above, of TONE_BASE_RADIUS, made
// by the caller. Read for its luma alone, and read ONCE per pixel — the
// neighbourhood is the blur's, not a sampling loop's (see TONE_BASE_RADIUS).
uniform shader base;
uniform float dr;
uniform float hl;
uniform float sh;
uniform float wh;
uniform float bl;
uniform float vib;
uniform float shTr;
uniform float shTg;
uniform float shTb;
uniform float hlTr;
uniform float hlTg;
uniform float hlTb;
uniform float cc;
uniform float ccb;
uniform float hslOn;
uniform float hslH[8];
uniform float hslS[8];
uniform float hslL[8];
uniform float gh;
uniform float gs;
uniform float gl;
// sRGB <-> HSL. The mixer works in HSL because that is the space the knobs are
// named after: a hue shift must not change how light a colour is, and a
// lightness move must not change its hue, which is exactly what scaling RGB
// does wrong.
vec3 rgb2hsl(vec3 c) {
  float mx = max(max(c.r, c.g), c.b);
  float mn = min(min(c.r, c.g), c.b);
  float l = (mx + mn) * 0.5;
  float d = mx - mn;
  if (d < 0.00001) return vec3(0.0, 0.0, l);
  float s = l > 0.5 ? d / max(0.00001, 2.0 - mx - mn) : d / max(0.00001, mx + mn);
  float h;
  if (mx == c.r) h = (c.g - c.b) / d + (c.g < c.b ? 6.0 : 0.0);
  else if (mx == c.g) h = (c.b - c.r) / d + 2.0;
  else h = (c.r - c.g) / d + 4.0;
  return vec3(h / 6.0, s, l);
}
float hueChannel(float p, float q, float t) {
  t = fract(t);
  if (t < 1.0 / 6.0) return p + (q - p) * 6.0 * t;
  if (t < 0.5) return q;
  if (t < 2.0 / 3.0) return p + (q - p) * (2.0 / 3.0 - t) * 6.0;
  return p;
}
vec3 hsl2rgb(vec3 hsl) {
  if (hsl.y < 0.00001) return vec3(hsl.z);
  float q = hsl.z < 0.5 ? hsl.z * (1.0 + hsl.y) : hsl.z + hsl.y - hsl.z * hsl.y;
  float p = 2.0 * hsl.z - q;
  return vec3(
    hueChannel(p, q, hsl.x + 1.0 / 3.0),
    hueChannel(p, q, hsl.x),
    hueChannel(p, q, hsl.x - 1.0 / 3.0)
  );
}
// One band's ownership of a hue: full at the band's own anchor, falling
// linearly to 0 at each neighbour's anchor (the gaps are uneven — red sits 30°
// from orange and 40° from magenta). Linearity is the point: adjacent tents
// cross at exactly 0.5 at the midpoint, so the eight weights sum to 1 at every
// hue. No pixel is counted twice, no pixel falls between two bands, and a hue
// sitting on an anchor gets that band's full value instead of a share of it.
float bandW(float hue, float anchor, float gapL, float gapR) {
  float d = mod(hue - anchor + 180.0, 360.0) - 180.0;
  return d <= 0.0 ? max(0.0, 1.0 + d / gapL) : max(0.0, 1.0 - d / gapR);
}
${TONE_MATH_SKSL}
// The BASE layer: the light the frame carries where this pixel sits, at the
// radius the caller handed in. One tap of a real blur of the same child the
// pixel comes from, so it is an AVERAGE of the neighbourhood and not a handful
// of point samples of it — that distinction is the whole bug (see
// TONE_BASE_RADIUS). Luma, because the luma is the one quantity the ramp moves
// and the colour rides the ratio afterwards; the blur being linear, blurring the
// child and taking its luma is the same as blurring the luma.
//
// A caller with no neighbourhood to speak of hands in the child itself as the
// base (see blurredBase()): the tap then lands exactly on t and the pass falls
// back to the global move, which is what a shape with a mask's degenerate base
// wants and what it got from a bx of zero before.
float baseLuma(vec2 xy) {
  vec3 s = clamp(base.eval(xy).rgb, 0.0, 1.0);
  return clamp(dot(s, vec3(0.2126, 0.7152, 0.0722)), 0.0, 1.0);
}
vec4 main(vec2 xy) {
  vec4 c = src.eval(xy);
  vec3 rgb = clamp(c.rgb, 0.0, 1.0);
  // NOTE: never name a local 'out' — it is a reserved SkSL qualifier.
  float t = clamp(dot(rgb, vec3(0.2126, 0.7152, 0.0722)), 0.0, 1.0);
  // The four tents of the doc, one per quarter of the ramp: BLACKS peaks on
  // 0.00 and is gone by 0.25, SHADOWS peaks on 0.25 and is gone by 0.50,
  // HIGHLIGHTS peaks on 0.75 and is gone by 0.50 and 1.00, WHITES peaks on
  // 1.00 and is gone by 0.75. Each is the doc's own smoothstep, each is clipped
  // by subtracting the tent before it so the four never overlap and no luma is
  // ever counted twice, and the 0.50 midpoint is weighted by none of them: they
  // are the weights the stock split tones ride, which is why they are smooth and
  // why they stay out of the ramp below — nothing else in this shader reads them.
  float blMask = 1.0 - smoothstep(0.00, 0.25, t);
  float shMask = clamp(1.0 - smoothstep(0.25, 0.50, t) - blMask, 0.0, 1.0);
  float whMask = smoothstep(0.75, 1.00, t);
  float hlMask = clamp(smoothstep(0.50, 0.75, t) - whMask, 0.0, 1.0);
  // The four tonal-range knobs, on the shared ramp: see TONE_MATH_SKSL — the
  // same knots, the same hue-preserving rebuild, the same move a gradient mask
  // makes with the same four sliders. DR is the whole frame's, so it is spent
  // here and nowhere else.
  rgb = toneRamp(rgb, t, baseLuma(xy), bl, sh, hl, wh, dr);
  // Split tone (stock look): the shadows and the highlights may each carry
  // their own tint, so the two ends of the curve can drift opposite ways
  // (Classic Neg: green-cyan darks, warm brights) without touching mid-greys.
  rgb = clamp(rgb + vec3(shTr, shTg, shTb) * shMask + vec3(hlTr, hlTg, hlTb) * hlMask, 0.0, 1.0);
  // Color Chrome / Color Chrome FX Blue: the two stock-dialed colour effects
  // DEEPEN what is already chromatic and leave neutrals exactly where they are
  // (Fuji: "deeper tone in highly saturated colour"; FX Blue does it for the
  // blue/cyan side only). Both therefore need per-pixel chroma — a 4x5 colour
  // matrix is one linear map, so any gain it applies also moves greys, and a
  // blue-only gain drags the whole white point.
  float mxc = max(max(rgb.r, rgb.g), rgb.b);
  float mnc = min(min(rgb.r, rgb.g), rgb.b);
  // Chroma ratio with a small floor: a near-black pixel with a hair of cast
  // has ratio 1.0 but no colour to deepen, and must stay put.
  float ccChroma = (mxc - mnc) / max(mxc, 0.10);
  // Color Chrome rides the chroma itself: a muted colour barely moves, a vivid
  // one gains density. The 0.25 knee keeps skin, haze and pastels untouched.
  float ccMask = cc * smoothstep(0.25, 0.85, ccChroma);
  // FX Blue: only where blue clearly leads red AND green (so magenta/purple
  // stay out), and richest in a bright blue — a dark blue has no tonality left
  // to deepen.
  float ccbBlue = clamp((rgb.b - rgb.r) * 2.0, 0.0, 1.0) * clamp((rgb.b - 0.5 * (rgb.r + rgb.g) + 0.05) * 3.0, 0.0, 1.0);
  float ccbMask = ccb * ccbBlue * smoothstep(0.15, 0.60, ccChroma) * smoothstep(0.20, 0.70, t);
  float deep = clamp(ccMask + ccbMask, 0.0, 1.0);
  // Density = lightness down with the colour difference riding along, so hue is
  // preserved and the colour cannot collapse toward black (same reason the tone
  // curve above keeps chroma). A touch of chroma is given up as it deepens.
  float l3 = dot(rgb, vec3(0.2126, 0.7152, 0.0722));
  rgb = clamp(vec3(l3 * (1.0 - 0.28 * deep)) + (rgb - vec3(l3)) * (1.0 - 0.10 * deep), 0.0, 1.0);
  // Vibrance: push the LESS-saturated pixels harder than the vivid ones.
  float l2 = dot(rgb, vec3(0.2126, 0.7152, 0.0722));
  float mx = max(max(rgb.r, rgb.g), rgb.b);
  float mn = min(min(rgb.r, rgb.g), rgb.b);
  float chroma = mx > 0.0001 ? (mx - mn) / mx : 0.0;
  float kv = 1.0 + vib * 0.75 * (1.0 - chroma);
  rgb = clamp(mix(vec3(l2), rgb, kv), 0.0, 1.0);
  // Selective colour by hue band — the last move, so a band edit is judged
  // against the colour the user actually sampled off the render.
  //
  // A grey is dropped before the weights are read: rgb2hsl hands it hue 0, so
  // without this fade every neutral pixel in the frame would be treated as
  // pure red and slide with the red band. Below 8% saturation there is no hue
  // to move anyway.
  //
  // The three accumulators are the band values scaled by ownership, so a hue
  // landing between two anchors gets a proportional mix of the two edits —
  // the same blend the weights already sum to. Hue is a turn (±30° at full),
  // saturation is a scale (0 = grey at -10), lightness is additive (±0.25 at
  // full) so it cannot invert the ramp.
  if (hslOn > 0.5) {
    vec3 hsl = rgb2hsl(rgb);
    float gate = smoothstep(0.0, 0.08, hsl.y);
    float hd = hsl.x * 360.0;
    // The overall move is the seed: every hue gets its turn and its saturation
    // scale at full weight, and the bands add their own share on top. The
    // lightness term is added below UNGATED, so it still lifts a colour that a
    // -SAT has already drained to grey.
    vec3 acc = vec3(gh, gs, 0.0) * gate;
${BAND_BLOCK}    hsl.x = fract(hsl.x + acc.x * (30.0 / 360.0));
    hsl.y = clamp(hsl.y * (1.0 + acc.y), 0.0, 1.0);
    hsl.z = clamp(hsl.z + (acc.z + gl) * 0.25, 0.0, 1.0);
    rgb = hsl2rgb(hsl);
  }
  return vec4(clamp(rgb, 0.0, 1.0), c.a);
}
`;

// EXPOSURE / EV — the one pass that has to run in LINEAR light.
//
// A stop is a multiplier on LIGHT, and the old EV row multiplied sRGB-ENCODED
// values: +1 EV took a mid-grey 0.5 straight to a blown 1.0 where a real stop
// gives 0.73. exposureMove linearises, moves the light by 2^ev, and re-encodes —
// and it spends that stop on the LUMA, not on the three channels one at a time,
// so this knob only ever changes how bright a pixel is: a channel that would
// have clipped gives up saturation instead of dragging the hue (a gradient
// mask's own EXPOSURE runs through the same function, on the mask's pixels).
//
// It sits between the graded image and the tone shader (see exportEngine step 3),
// so `ev` carries the EXPOSURE knob, the stock's own bias and the EV knob added
// up in stops — the caller hands in one number.
export const EXPOSURE_SKSL = `
uniform shader src;
uniform float ev;
${TONE_MATH_SKSL}
vec4 main(vec2 xy) {
  vec4 c = src.eval(xy);
  return vec4(exposureMove(clamp(c.rgb, 0.0, 1.0), ev), c.a);
}
`;

// Bright Pass Filter for the HDF EFFECT pass (HDF), SkSL over a child image
// shader — the pattern TONE_SKSL above already proved on device.
//
// Per channel the old 2.5*in-1.5 curve only zeroed a channel that was dark
// *itself*: a saturated blue (B = 1.0) came out of it fully lit, so a dark blue
// shadow bloomed and a dark saturated colour smeared its hue into the darks.
// Photoshop's Bright Pass filters on the LUMINANCE instead: one knee decides how
// much light a pixel carries, and one gain scales all three channels, so below
// the knee the output is exactly 0.0 (Screen against black = no-op, the shadows
// are untouched) and above it every channel keeps its ratio — the hue cannot
// drift, only the brightness blooms.
//
// Knee t0..t1 = 0.45..0.75. The web demo plays the effect up, so the knee sits
// lower and wider than the phone's 0.55..0.85: the bloom now catches the bright
// end of the midtones (a lit face, a window) instead of only true speculars,
// which is what makes it read on a photo that has no blown white.
export const GLOW_T0 = 0.45;
export const GLOW_T1 = 0.75;

export const GLOW_SKSL = `
uniform shader src;
uniform float t0;
uniform float t1;
vec4 main(vec2 xy) {
  vec4 c = src.eval(xy);
  float luma = dot(clamp(c.rgb, 0.0, 1.0), vec3(0.2126, 0.7152, 0.0722));
  return vec4(c.rgb * smoothstep(t0, t1, luma), c.a);
}
`;

// Flat uniform buffer for `makeShaderWithChildren` — same order as GLOW_SKSL's
// declarations (t0, t1).
export function glowUniformArray(): number[] {
  'worklet';
  return [GLOW_T0, GLOW_T1];
}

// Same values for the declarative <Shader> path, which indexes uniforms by
// NAME (a flat array is only valid for the JS makeShaderWithChildren API).
export const GLOW_UNIFORMS = { t0: GLOW_T0, t1: GLOW_T1 };

// SHARPENING — thay_doi_thong_so_giong_lightroom.md §4.2, all four of its
// parameters in the one knob the panel has. The doc's SHARPENING is not an
// unsharp mask: it is an unsharp mask MASKED BY AN EDGE DETECTOR, which is what
// keeps a flat sky and a cheek from gaining grain, and CORED, which is what
// keeps a noise speckle from being amplified into a white dot.
//
//   Image_sharp = Image + Amount x HighPass x Mask
//
// EDGE DETECTION is the doc's Sobel magnitude G = sqrt(Gx² + Gy²) on luminance,
// put through its soft threshold Mask = smoothstep(T, T + 0.1, G). This pass was
// the same 3x3 kernel with Mask = 1 everywhere and no coring, so every
// low-contrast pixel — every pixel of a flat sky, every pore of a face — took
// the same gain an eyelash did, and a rising SHARPENING raised the frame's noise
// with it. That is the doc's §1 complaint word for word ("khi Sharpen, ảnh nổi
// đầy sạn hạt cát").
//
// The HIGH-PASS is the doc's Radius, held at one image pixel (its 0.7-0.9px for
// a Retina panel), and it is a LUMINANCE high-pass carried by all three channels
// rather than a per-channel one: a per-channel kernel sharpens a red edge
// against a green one and draws a colour fringe down every contour.
//
// SHARPEN_CORE is the doc's Detail. Coring is SOFT (a ramp over the threshold,
// not a cliff), so a detail crossing it is not switched on and off from one
// pixel to the next.
//
// `amount` is signed the way the knob is: the negative side is the caller's
// blur and never reaches this shader. `px` is one ORIGINAL image pixel in the
// caller's canvas units, so the preview, the camera worklet and the file all
// sharpen at the same radius. The three constants are the doc's own shape; the
// doc leaves their value to the panel, and this panel has one SHARPENING knob,
// so they are fixed here. No frame has yet asked for a second one.
export const SHARPEN_CORE = 0.02;
export const SHARPEN_MASK_LO = 0.1;
export const SHARPEN_MASK_HI = SHARPEN_MASK_LO + 0.1;

export const SHARPEN_SKSL = `
uniform shader src;
uniform float a;
uniform float2 px;
const float3 SHARPEN_LUM = vec3(0.2126, 0.7152, 0.0722);
const float SHARPEN_CORE = ${SHARPEN_CORE};
const float SHARPEN_MASK_LO = ${SHARPEN_MASK_LO};
const float SHARPEN_MASK_HI = ${SHARPEN_MASK_HI};
float sharpenLum(vec2 p) {
  return dot(clamp(src.eval(p).rgb, 0.0, 1.0), SHARPEN_LUM);
}
vec4 main(vec2 xy) {
  vec2 dx = float2(px.x, 0.0);
  vec2 dy = float2(0.0, px.y);
  float yc = sharpenLum(xy);
  float yl = sharpenLum(xy - dx);
  float yr = sharpenLum(xy + dx);
  float yt = sharpenLum(xy - dy);
  float yb = sharpenLum(xy + dy);
  float ytl = sharpenLum(xy - dx - dy);
  float ytr = sharpenLum(xy + dx - dy);
  float ybl = sharpenLum(xy - dx + dy);
  float ybr = sharpenLum(xy + dx + dy);
  float gx = (ytl + 2.0 * yl + ybl) - (ytr + 2.0 * yr + ybr);
  float gy = (ytl + 2.0 * yt + ytr) - (ybl + 2.0 * yb + ybr);
  float mask = smoothstep(SHARPEN_MASK_LO, SHARPEN_MASK_HI, sqrt(gx * gx + gy * gy));
  float hp = yc - 0.25 * (yl + yr + yt + yb);
  hp *= smoothstep(SHARPEN_CORE, 2.0 * SHARPEN_CORE, abs(hp));
  vec4 c = clamp(src.eval(xy), 0.0, 1.0);
  return vec4(clamp(c.rgb + a * hp * mask, 0.0, 1.0), c.a);
}
`;

// Named uniforms for <Shader uniforms>, same names as SHARPEN_SKSL declares.
export function sharpenUniforms(a: number, pxX: number, pxY: number) {
  return { a, px: [pxX, pxY] };
}

// CLARITY's reference image B, one axis at a time — the multiple-pass
// architecture of ki_n_tr_c_multiple_passes_cho_webgpu.md: a single 15x15 kernel
// reads 225 pixels per pixel, a separable pair (1x15 then 15x1) reads 30. The
// kernel is the doc's bilateral filter: the gaussian weight falls off along the
// axis, and a range weight kills a tap whose colour is nothing like the centre's,
// so an edge is not blurred across and the reference does not ghost it.
// `dir` is one tap's step in the caller's units (px along ONE axis, the other
// component 0), so a preview and the file blur the same fraction of the frame.
// SkSL has no dynamic loop bound here, so the 15 taps are the doc's own count.
//
// The range weight reads LUMINANCE, not the colour difference the black-halo
// trade first used. A colour difference is loose on any coloured edge — two
// sides of it can share a red and differ in green — so the reference blurred
// across hair, branches and every rail, and that reference is exactly what the
// blend subtracts: the wider the reference reaches, the more a contour reads as
// detail, and clarity drew a light stroke down each one. On luminance the weight
// is one decision per tap, at the doc's own scale CLARITY_RANGE_SIGMA, and an
// edge of any hue stops the blur dead. (A four-times downsample of the source,
// md section D, is not worth it at 15 taps: measure the cost of the full-res
// pair first — ponytail: add the 4x pyramid only if a phone profile shows the
// two 1x15 passes as the frame's cost.)
export const CLARITY_BLUR_SKSL = `
uniform shader src;
uniform float2 dir;
const float3 CLARITY_LUM = vec3(0.2126, 0.7152, 0.0722);
// One tap's luminance may sit this far from the centre's and still be counted:
// a tenth of the range. Loose enough that a smooth gradient still averages,
// tight enough that a contour one pixel wide is a wall to the blur.
const float CLARITY_RANGE_SIGMA = 0.04;
vec4 main(vec2 xy) {
  vec4 c = src.eval(xy);
  float lc = dot(c.rgb, CLARITY_LUM);
  vec3 sum = c.rgb;
  float total = 1.0;
  for (int i = 1; i <= 15; i++) {
    float fi = float(i);
    float g = exp(-0.5 * (fi / 5.0) * (fi / 5.0));
    vec4 a1 = src.eval(xy + dir * fi);
    vec4 a2 = src.eval(xy - dir * fi);
    float d1 = (dot(a1.rgb, CLARITY_LUM) - lc) / CLARITY_RANGE_SIGMA;
    float d2 = (dot(a2.rgb, CLARITY_LUM) - lc) / CLARITY_RANGE_SIGMA;
    float r1 = exp(-d1 * d1);
    float r2 = exp(-d2 * d2);
    sum += g * (r1 * a1.rgb + r2 * a2.rgb);
    total += g * (r1 + r2);
  }
  return vec4(sum / total, c.a);
}
`;

// CLARITY, pass 3 of the doc's architecture: the frame's detail against its own
// blurred reference. Base is the reference B, Detail is the frame minus B, and
// the pass returns B + Detail * (1 + amount * gain * midtone). Above zero the
// detail comes back amplified; below it the knob is the mix back toward B, so
// NEGATIVE CLARITY is the positive one's soften and not a second blur picked for
// the sign (that mist had another radius than the reference the positive side
// reads, so -10 and +10 were two different neighbourhoods and a MASK's CLARITY
// could not be the frame's own move). Clamped because a file cannot hold more
// than white. Runs on the ENCODED pixels like every other grade here (only
// EXPOSURE_SKSL is linear light, see colorUtils.exposureStops) — the doc's
// formula is written for linear light, and moving the whole renderer there is a
// bigger change than this pass.
//
// The move is made ON LUMINANCE and then handed back to all three channels by
// one scale, which is the trade's own rule C. Detail is what the eye reads as
// structure, but it is not per-channel: sharpen red against a red-and-green edge
// and red alone overshoots, which is what coloured fringing along every contour
// was. One luminance value carries the whole pixel back with it, so hue is
// untouchable — skin does not go sallow at the top of the knob, and a saturated
// red or a cyan shadow keeps its ratio. The midtone weight is the doc's
// M(L) = 4L(1-L): 0 at black and at white, 1 in the middle, so the knob deepens
// the greys a picture is made of and leaves the burnt ends and the deepest
// shadows where they are, which is also where a halo would otherwise show worst.
export const CLARITY_BLEND_SKSL = `
uniform shader original;
uniform shader blurred;
uniform float strength;
const float3 CLARITY_LUM = vec3(0.2126, 0.7152, 0.0722);
// md section 5's 1.8, raised to 4.5: the range weight above now stops the blur
// at a real edge, so the reference reaches less far and carries less detail than
// the loose one did — the same knob has to be turned further to land where
// CLARITY 10 sat before. The gain was picked by clarity-halo.mjs, whose stroke
// is the pass pushing a pixel outside its own neighbourhood's range: at +10 this
// lands 55/255 (lightroom_shadow.jpg) and 54/255 (DSCF1701.JPG) against the old
// pass's 145 and 127 at the same knob, and 8.0 already reads 98 — the knob does
// not need to go further to keep the flat areas moving.
const float CLARITY_DETAIL_GAIN = 4.5;
// The same 1e-4 the doc uses under both luminance terms: an epsilon in the
// division that keeps a black pixel's ratio finite without moving any pixel a
// full step.
const float CLARITY_EPS = 0.0001;
vec4 main(vec2 xy) {
  vec4 c = original.eval(xy);
  vec3 b = blurred.eval(xy).rgb;
  // Below zero there is no detail to amplify, only the reference to move toward.
  if (strength < 0.0) {
    return vec4(clamp(mix(c.rgb, b, clamp(-strength, 0.0, 1.0)), 0.0, 1.0), c.a);
  }
  float lo = dot(c.rgb, CLARITY_LUM);
  float lb = dot(b, CLARITY_LUM);
  float mid = clamp(4.0 * lb * (1.0 - lb), 0.0, 1.0);
  float nl = clamp(lb + (lo - lb) * (1.0 + strength * CLARITY_DETAIL_GAIN * mid), 0.0, 1.0);
  float scale = (nl + CLARITY_EPS) / (lo + CLARITY_EPS);
  return vec4(clamp(c.rgb * scale, 0.0, 1.0), c.a);
}
`;

// Strength that keeps CLARITY 10 where the 3x3 kernel had it: that kernel was
// `c*(1+4a) - a*sum` with a = 0.8, i.e. `c + 3.2*(c - mean4)`, so the same 3.2
// lands the same local contrast through the wider bilateral reference. The gain
// is for the POSITIVE side only: below zero the knob reads as its own fraction
// of the reference (0..1, the same units MASK's CLARITY uses on it).
export const CLARITY_GAIN = 3.2;

// NOISE REDUCTION — thay_doi_thong_so_giong_lightroom.md §4.1, the colour half.
// The eye is sensitive to a change in brightness and nearly blind to one in hue
// at the same scale, so the knob is spent where it costs no detail: the CHROMA
// comes from a blurred copy of the frame and the LUMA from the frame itself, and
// a strand of hair comes back exactly where it was. The split is this file's own
// lightness/chroma one, `rgb - luma`, the same the tone ramp's header describes.
//
// Until now the whole frame was blurred instead — `MakeBlur` on the draw, one
// sigma over all three channels — which is the doc's own §4 warning ("Noise
// Reduction sẽ làm nhòe toàn bộ chi tiết sợi tóc và vân da") written into the
// engine: the knob could not take a colour speckle out without taking the
// picture's edges with it.
//
// `amount` is the share of the blurred chroma: 0 leaves the pixel exactly as it
// was and 1 hands it the neighbourhood's hue with its own brightness still on
// it, so the two ends of the knob are the identity and the blur and nothing in
// between moves a pixel's luma at all.
//
// The LUMA half of §4.1 (its bilateral filter) is deliberately not here: it is
// the half that costs detail, and no frame has yet shown grain the chroma half
// left behind. ponytail: add it as a second child of this same pass if one does.
export const NR_SKSL = `
uniform shader sharp;
uniform shader blurred;
uniform float amount;
const float3 NR_LUM = vec3(0.2126, 0.7152, 0.0722);
vec4 main(vec2 xy) {
  vec3 s = clamp(sharp.eval(xy).rgb, 0.0, 1.0);
  vec3 b = clamp(blurred.eval(xy).rgb, 0.0, 1.0);
  float ys = dot(s, NR_LUM);
  float yb = dot(b, NR_LUM);
  return vec4(clamp(vec3(ys) + mix(s - vec3(ys), b - vec3(yb), amount), 0.0, 1.0), 1.0);
}
`;

// How far the chroma filter reaches, as a fraction of the frame's width — the
// doc's 3..5 pixels of a full-resolution frame, which is 0.4% of it, so a
// preview and a file average the same share of the picture. The knob's own blur
// was 0.6 of a pixel at NOISE REDUCTION 100, which is under the doc's patch and
// under a colour speckle as well.
export const NR_CHROMA_SPAN = 0.004;

// DEHAZE — raw_parameter_processing_gradient_mask_algorithms.md, section 3.2.
// Haze is scattered light: it lifts the DARKEST channel of every patch, which is
// the Dark Channel Prior. The dark channel is the MINIMUM of min(r,g,b)/A over
// the patch, and that minimum is the whole prior: a patch holding anything
// genuinely dark — a shadow, a black frame line — reads 0 and is left alone,
// while only a patch with no dark pixel in it at all is haze and gets corrected.
// The patch AVERAGE this pass used to read instead (the bilateral reference)
// called every patch hazy, so the positive end ground the frame down instead of
// taking haze out. `air` is the atmospheric light the caller estimated from the
// frame — brightest dark-channel pixel of a copy of it, the doc's 0.1% answer in
// one readback (exportEngine's atmosphericLight).
//
// The pass itself is now only the doc's last line, `J = (I - A)/t + A`, on a
// transmission the caller has already solved for. `dark` is what the caller
// hands in as an image: the dark channel itself, read off a small copy of the
// frame and interpolated back up, which is the smoothing the prior wants — see
// the caller's dehazeDarkChannel for why it cannot be had from a patch read out
// per pixel. Its cell is the patch, so a value per cell is a value per patch.
//
// What travels as an image is the dark channel and not t on purpose. A channel is
// eight bits, so it can only carry 0..1 — and t is 1 + 0.95 at the negative end
// of the knob, which would arrive here clipped to 1 and turn "put the scattered
// light back" into a pass that does nothing. The dark channel is 0..1 by
// construction, and the signed amount stays a uniform where it costs no range.
//
// Signedness is then in the expression. Positive folds t below 1 and takes the
// scattered light out; negative folds it above 1 and the same expression scatters
// it back in, which is what a negative DEHAZE is for. The floor keeps a flat sky
// from dividing by zero, and the ceiling is the largest amount the knob can ask
// for either way.
export const DEHAZE_FLOOR_T = 0.1;
export const DEHAZE_MAX_OMEGA = 0.95;

// The patch the MASK's DEHAZE reads out of its own frame (gradientMask.ts) —
// `taps` samples out at `step` each, two taps at 0.625% of the frame's width, a
// 2.5%-wide neighbourhood: the DCP's own 15-pixel patch on a 600-pixel frame and
// the same fraction of a 4000-pixel export. Five by five samples rather than
// fifteen by fifteen because the doc's 225 reads per pixel is what
// CLARITY_BLUR_SKSL above already refused, and the prior only needs a patch the
// haze is flat over. The frame-wide pass reads no patch at all any more.
export const DEHAZE_PATCH_TAPS = 2;
export const DEHAZE_PATCH_STEP = 0.00625;

export const DEHAZE_SKSL = `
uniform shader img;
uniform shader dark;
uniform float3 air;
uniform float floorT;
uniform float maxT;
uniform float amount;
vec4 main(vec2 xy) {
  vec3 c = clamp(img.eval(xy).rgb, 0.0, 1.0);
  vec3 a = max(air, vec3(0.05));
  float d = clamp(dark.eval(xy).r, 0.0, 1.0);
  float t = clamp(1.0 - amount * ${DEHAZE_MAX_OMEGA} * d, floorT, maxT);
  return vec4(clamp((c - a) / t + a, 0.0, 1.0), 1.0);
}
`;

export function dehazeUniformArray(
  air: [number, number, number],
  amount: number
): number[] {
  'worklet';
  return [air[0], air[1], air[2], DEHAZE_FLOOR_T, 1 + DEHAZE_MAX_OMEGA, amount];
}

export interface ToneUniforms {
  // All zero → no tone adjustment needed (caller can skip the shader pass).
  dr: number; // 0..1
  hl: number; // -1..1 (adjustments.highlight / 10)
  sh: number; // -1..1 (adjustments.shadow / 10)
  wh: number; // -1..1 (adjustments.whites / 10 — moves the 1.00 end of the ramp)
  bl: number; // -1..1 (adjustments.blacks / 10 — moves the 0.00 end of the ramp)
  vib: number; // -1..1 (adjustments.vibrance / 10)
  shT: [number, number, number]; // shadow split-tone RGB bias, -1..1
  hlT: [number, number, number]; // highlight split-tone RGB bias, -1..1
  cc: number; // 0..1 Color Chrome depth (0 = 'none')
  ccb: number; // 0..1 Color Chrome FX Blue depth (0 = 'none')
  hslOn: number; // 1 when any band or the overall move is set (0 skips the mixer)
  hslH: number[]; // 8 × -1..1 per band, in HSL_BANDS order (±30° of hue at full)
  hslS: number[]; // 8 × -1..1 per band (saturation scale, -1 = grey)
  hslL: number[]; // 8 × -1..1 per band (additive lightness, ±0.25 at full)
  gh: number; // -1..1 whole-image hue turn (±30° at full)
  gs: number; // -1..1 whole-image saturation scale
  gl: number; // -1..1 whole-image lightness offset (±0.25 at full, ungated)
}

// Per-stock tone pass. Fuji's Classic stocks are not a plain colour matrix:
// Classic Neg splits its tone (green-cyan darks / warm brights) and Classic
// Chrome crushes the shadows hard while muting colour. Those two parts live
// here instead of in the 4x5 matrix, which cannot move one end of the curve
// without also moving the other.
//
// The `sh` and `hl` here are written in the KNOB's unit, not the look's: a stock
// that wants its toe on 0.18 asks the SHADOW knob for whatever the window is
// worth there (1.0 at 0.25) times (1 - 0.25)^1.8, which is -0.47 on this ramp.
// The numbers moved when the ramp did — the four knobs are windows now, not
// summed bumps, and the doc's own rates (§2) replaced the quarter-anchor ones —
// so the knots below are re-solved against the new curve rather than tuned by
// eye: 0.18 / 0.22 / 0.17 on the toe and 0.7375 / 0.815 on the head, the values
// the stocks were written against, land where they always did, which is what
// highlight-knee-check pins.
const FILM_TONE: Partial<Record<BaseFilter, Partial<ToneUniforms>>> = {
  'classic-chrome': { sh: -0.47 },
  // Classic Vivid is Classic Chrome's sibling — the shadow crush belongs to the
  // stock, not to the matrix rows, so it comes along.
  'classic-vivid': { sh: -0.47 },
  'classic-neg': { shT: [-0.018, 0.009, 0.013], hlT: [0.024, 0.008, -0.012] },
  // Acros. A black-and-white stock IS its grey ramp, so this entry only shapes
  // the two ENDS and leaves the middle an identity: a smooth shadow toe that
  // reaches a true black (no film-base lift, no flat grey wash) and a highlight
  // shoulder that stops just short of white instead of clipping a cloud to
  // paper. Mid-tones are between the 0.25 and the 0.75 knots, so they keep
  // every step the matrix handed over — which is what 'deep black' costs in a
  // colour stock and does not have to cost here.
  // The values move the two end bands of the ramp: -0.20 puts the toe on 0.22
  // and -0.16 rolls the head to 0.7375 (both solved against the window's own
  // height at 0.25 and 0.75, see the note above FILM_TONE).
  monochrome: { sh: -0.20, hl: -0.16 },
  // B&W HIGH CONTRAST. Acros' ramp with both ends pushed hard: a deeper toe
  // (-0.54 against Acros' -0.20, so 0.17 against 0.22) so the darks reach true
  // black, and a shoulder that LIFTS instead of rolling (-0.16 → +0.83, the
  // head going to 0.815), which is the whites step of the brief. The stretch
  // between the two inner knots (0.25 and 0.75) is still the identity, so the
  // long smooth stretch of the greys survives — that is what keeps a hard push
  // off the posterised look, and the strength the stock needs on the greys is
  // its matrix slope (SIM_CONTRAST_BIAS in colorUtils), not another move here.
  'mono-high-contrast': { sh: -0.54, hl: 0.83 },
};

// The base layer's neighbourhood is the caller's business, not this function's:
// it is a blurred CHILD of the shader (see TONE_SKSL), so only the caller knows
// how big the frame is or whether there is a frame at all. A shape with a mask
// has no frame to look at and hands in the image it is already shading, which
// lands the base on the pixel and keeps the global ramp (see baseLuma).
export function getToneUniforms(
  adj: ColorAdjustments,
  baseFilter?: BaseFilter
): ToneUniforms {
  const drRaw = adj.dynamicRange ?? 'auto';
  const dr = drRaw === 'auto' || drRaw === 100 ? 0 : (drRaw - 100) / 300;
  const hl = Math.max(-1, Math.min(1, (adj.highlight ?? 0) / 10));
  const sh = Math.max(-1, Math.min(1, (adj.shadow ?? 0) / 10));
  const wh = Math.max(-1, Math.min(1, (adj.whites ?? 0) / 10));
  const bl = Math.max(-1, Math.min(1, (adj.blacks ?? 0) / 10));
  const vib = Math.max(-1, Math.min(1, (adj.vibrance ?? 0) / 10));
  // WHITE and BLACK ride this pass with the other two, each as the end knot of
  // the same ramp (see TONE_SKSL). They are no longer a white-balance move and
  // are read by nothing else in the pipeline.
  const film = (baseFilter && FILM_TONE[baseFilter]) || {};
  const shT: [number, number, number] = film.shT ?? [0, 0, 0];
  const hlT: [number, number, number] = film.hlT ?? [0, 0, 0];
  // Color Chrome depth per stop of the UI's none/weak/strong. A chrome set is a
  // monochrome look, so both are forced off there: the effect is colour-only
  // (the preview/export matrix skips them for monochrome for the same reason).
  const colour = !isMonochromeBase(baseFilter);
  const chromeDepth = (v: ColorAdjustments['colorChrome'] | undefined) =>
    !colour || v === 'none' || v == null ? 0 : v === 'strong' ? 0.9 : 0.45;
  const blueDepth = (v: ColorAdjustments['colorChromeBlue'] | undefined) =>
    !colour || v === 'none' || v == null ? 0 : v === 'strong' ? 1.0 : 0.5;
  // Selective colour: one slot per band, in HSL_BANDS order, so the flat buffer
  // lines up with the shader's arrays. A band the user has not moved holds
  // three zeroes and costs nothing but its slot.
  const bands = adj.hslBands ?? {};
  const tenth = (v: unknown) =>
    typeof v === 'number' && Number.isFinite(v) ? Math.max(-1, Math.min(1, v / 10)) : 0;
  const hslH: number[] = [];
  const hslS: number[] = [];
  const hslL: number[] = [];
  let hslOn = 0;
  for (const band of HSL_BANDS) {
    const v = bands[band.id];
    const [h, s, l] = v ? [tenth(v[0]), tenth(v[1]), tenth(v[2])] : [0, 0, 0];
    hslH.push(h);
    hslS.push(s);
    hslL.push(l);
    if (h || s || l) hslOn = 1;
  }
  // A monochrome stock has no hue to be selective about.
  if (!colour) hslOn = 0;
  // The mixer's overall move, which every hue receives at full weight.
  const gh = tenth(adj.hslHue);
  const gs = tenth(adj.hslSat);
  const gl = tenth(adj.hslLum);
  if (colour && (gh || gs || gl)) hslOn = 1;
  return {
    dr,
    hl: hl + (film.hl ?? 0),
    sh: sh + (film.sh ?? 0),
    wh,
    bl,
    vib,
    shT,
    hlT,
    cc: chromeDepth(adj.colorChrome),
    ccb: blueDepth(adj.colorChromeBlue),
    hslOn,
    hslH,
    hslS,
    hslL,
    gh,
    gs,
    gl,
  };
}

// Flat uniform buffer for `makeShaderWithChildren` / `<Shader uniforms>` — the
// order must match TONE_SKSL's declarations.
export function toneUniformArray(u: ToneUniforms): number[] {
  return [
    u.dr, u.hl, u.sh, u.wh, u.bl, u.vib,
    u.shT[0], u.shT[1], u.shT[2], u.hlT[0], u.hlT[1], u.hlT[2], u.cc, u.ccb,
    u.hslOn, ...u.hslH, ...u.hslS, ...u.hslL, u.gh, u.gs, u.gl,
  ];
}

export function toneIsActive(u: ToneUniforms): boolean {
  return (
    u.hslOn !== 0 ||
    u.dr !== 0 ||
    u.hl !== 0 ||
    u.sh !== 0 ||
    u.wh !== 0 ||
    u.bl !== 0 ||
    u.vib !== 0 ||
    u.shT[0] !== 0 ||
    u.shT[1] !== 0 ||
    u.shT[2] !== 0 ||
    u.hlT[0] !== 0 ||
    u.hlT[1] !== 0 ||
    u.hlT[2] !== 0 ||
    u.cc !== 0 ||
    u.ccb !== 0
  );
}