# Gradient ASCII

> A soft glow of light drawn in ASCII characters that scramble under the pointer, with a panel for every setting.

A background of light typed out in characters: a smooth gradient underneath, and over it a grid of monospaced glyphs that grows denser where the light is brighter. It drifts and wavers on its own; the pointer scrambles the characters it passes, and a click sends a ring of them out. Four shapes, five sets of characters and a Customize panel tune the rest.

A React component by Bruno Delorence: https://brunodelorence.com/components/gradient-ascii. MIT License, Copyright (c) 2026 Bruno Delorence.

Category: Motion.

## Anatomy

1. **Stage**: The framed canvas the shader draws on, 741 by 600 and never under 280 px tall. Dark areas of the light stay transparent, so its own fill shows through.
2. **Replay**: A frosted square in the corner that plays the 2.2 s intro again: the light fading in from its source while the cells decode.
3. **Customize card**: The card under the stage, with its title and Reset over the panel. `controls={false}` leaves it out, for use as a plain background.
4. **Panel**: Every setting in three columns of 40 px rows; two under 600 px of the component, one under 380 px.
5. **Colours**: A swatch per colour over a native colour input, with minus and plus to keep two to eight. It spans two rows.
6. **Menu**: Preset, Shape, Characters and Click Effect: a row that opens a listbox under it, Custom when the values match no entry.
7. **Scrubber**: The whole row is the slider: press or drag anywhere to set it, arrows to step. A fill and a handle show where the value sits.
8. **Switch**: Mouse Interaction, Intro and Light Mode: a row with a 36 by 20 track, `role="switch"`.

## When to use

- A hero or landing background that should feel alive and technical without a video: light that drifts and wavers, typed out in characters.
- A launch, coming-soon or product page where the pointer is invited to play: it scrambles the characters it passes and a click sends a ring out.
- A brand moment that needs its own palette: two to eight colours, four shapes and five sets of characters cover a wide range from one component.
- A design tool or playground where the reader tunes a generative look and copies the settings: the Customize panel exposes every one of them.

## When not to use

- Behind long reading text or a dense form. The moving characters fight the words; use a still gradient or a flat surface.
- A page that must run without WebGL, or on very weak devices. Use a CSS radial gradient or a static image of it.
- Many copies on one page, such as a card each. Every instance holds its own WebGL canvas; use one background behind the whole grid.
- Showing data. The brightness is decorative noise, not a value; use a chart or a heatmap.
- A loading state. Use a skeleton or a spinner that says something is on its way.

## Installation

Install it with the shadcn CLI, into components/gradient-ascii of any React project:

```sh
npx shadcn@latest add https://brunodelorence.com/r/gradient-ascii.json
```

Or copy all the source files below into one folder of your project. Either way it needs React 19 and a bundler with CSS Modules (Next.js, Vite).

It has a dark colour scheme. Its colours are CSS light-dark() pairs, kept inside @supports so that builds which rewrite light-dark() for older browsers leave them alone: it follows your page’s color-scheme (light unless the page sets one) or its colorScheme prop, with nothing to configure. Browsers without light-dark() show it light.

## Usage

```tsx
import { GradientAscii } from './gradient-ascii';

export function Hero() {
  return (
    <GradientAscii
      controls={false}
      autoplay={false}
      shape="eclipse"
      colors={['#78350f', '#f59e0b', '#fffbeb']}
      characters=" 01"
      cellSize={15}
    />
  );
}
```

## States

- **Horizon**: The default, Atmosphere: light glowing over a dark curve, from the sun out to the far sky, in Letters at 18 px.
- **Pinch**: The Lagoon preset: a band of light squeezed in the middle, in Classic characters at 16 px.
- **Rise**: The Rose preset: light welling up from the bottom edge, in Letters at 22 px.
- **Eclipse**: The Corona preset: a ring of light round a dark disc, in Binary at 15 px.
- **Blocks, no gradient**: `characters=" ░▒▓█"` with `gradientOpacity={0}`: only the characters are left, drawn as shapes that fill their cells.
- **Depth of field**: `depthOfField={0.8}` and `glow={0.8}`: characters away from the light go soft, as if out of focus.
- **Light**: `colorScheme="light"`, or a light page: Light Mode turns on, the light becomes a wash and the characters a darker shade of it.
- **Dark**: `colorScheme="dark"`, or a dark page: a near-black stage that the light glows out of.

## How it works

- One WebGL fragment shader draws the whole picture at the canvas’s device pixels: the light per pixel, and a character per cell over it. A slow value noise warps the light so it wavers as it drifts; the speed scales that clock, and 0 holds the shape still.
- Each shape gives three things at a point: how much light there is, how far into it the point lies, and where it sits across it. The first colour is the edge of the shadow; the rest run across the light: on the horizon from the sun out to the far sky, on pinch, rise and eclipse from the outskirts in to the heart of the light. Dark areas stay transparent, so the stage shows through.
- Cells are 0.6 as wide as they are tall and centred on the canvas. Each cell asks the light at its middle how bright it is and picks a character further along the ramp the brighter it is. A seeded noise empties the dimmer cells first (density), and now and then a cell swaps to a neighbouring brightness (flicker).
- The glyphs come from an atlas drawn once on a 2D canvas at the cell’s exact size in device pixels, so they stay crisp; a blurred twin of it gives the glow and the out-of-focus characters. Blocks and dots are drawn as shapes, so they fill their cells whatever the font.
- Scrambling is an energy per cell kept on the CPU and sent as a small texture: the pointer stamps it along its path (scrambleRadius of the height around it), and it drains in about half a second. A click’s ring is drawn by the shader itself, a band one cell wide travelling at about one height a second; a burst stamps a wide patch instead. A scrambled cell shows a random character of the ramp, changed sixteen times a second.
- The intro fades the light in from its source over 2.2 s (the planet’s edge, the band’s heart, the bottom, the disc’s rim), its far colours coming last, while the cells it reaches decode. The replay button in the corner plays it again; changing the shape plays it too.
- It draws only while on screen and the tab is visible. Under reduced motion it draws a single still frame, the light fully in, nothing drifting or scrambling.
- The Customize panel is three columns of 40 px rows (two under 600 px, one under 380 px): the colours (two to eight, each a native colour input), four menus, fourteen scrubbers you press or drag anywhere on the row, and three switches. A preset sets a palette, a shape, a set of characters and a cell size together; Reset goes back to the props.
- Every colour of the stage and the panel is a light-dark() token, so it follows the page’s color-scheme or the colorScheme prop. On a light stage Light Mode is on by default: the light becomes a wash and the characters a darker shade of it.

## API reference

- **colors** (`string[]`, default `['#1e3fd8', '#f6f8ff', '#a5d8ff', '#38bdf8']`): Two to eight colours. The first is the edge of the shadow; the rest run across the light (on a horizon from the sun to the far sky, on the other shapes from the outskirts to the heart). Dark areas stay transparent.
- **shape** (`'horizon' | 'pinch' | 'rise' | 'eclipse'`, default `'horizon'`): Horizon glows over a dark curve, pinch is a band of light squeezed in the middle, rise wells up from the bottom and eclipse rings a dark disc.
- **characters** (`string`, default `' =+xX0S8#@'`): Characters from dimmest to brightest; a space leaves a cell empty. CHARACTER_SETS has five: Letters, Classic, Binary, Blocks and Dots.
- **cellSize** (`number`, default `18`): Height of a character cell in px, 8 to 40; cells are 0.6 as wide.
- **density** (`number`, default `0.8`): Share of cells that show a character, 0 to 1. Brighter areas fill in first.
- **glyphOpacity** (`number`, default `0.85`): How strongly the characters stand out from the gradient, 0 to 1.
- **gradientOpacity** (`number`, default `0.9`): Opacity of the gradient behind the characters, 0 to 1. At 0 only the characters are left.
- **glow** (`number`, default `0.2`): Soft glow around the characters, 0 to 1.5.
- **depthOfField** (`number`, default `0`): Share of characters drawn out of focus, 0 to 1.
- **flicker** (`number`, default `0.2`): How often characters swap to a neighbouring brightness, 0 to 1.
- **softness** (`number`, default `0.5`): How soft the edges of the shape are, 0 to 1.
- **scale** (`number`, default `1`): Size of the shape, 0.4 to 2.5.
- **flow** (`number`, default `0.5`): How much the light wavers as it drifts, 0 to 2.
- **speed** (`number`, default `1`): Speed of the drift, 0 to 3. 0 holds the shape still.
- **grain** (`number`, default `0.08`): Strength of the film grain, 0 to 0.4.
- **variation** (`number`, default `0`): A seed, 0 to 10: a different drift and a different pattern of characters.
- **mouseInteraction** (`boolean`, default `true`): The pointer scrambles the characters it passes; they settle back half a second later.
- **scrambleRadius** (`number`, default `0.1`): Size of the scrambled area around the pointer, as a share of the height (0.02 to 0.4).
- **clickEffect** (`'wave' | 'burst' | 'none'`, default `'wave'`): Wave sends a ring of scrambled characters out from a click; burst scrambles a patch under it.
- **intro** (`boolean`, default `true`): Fades the light in from its source while the characters decode.
- **lightMode** (`boolean`): Draws the light as a wash for a light background, with characters a shade darker. Unset, it follows the colour scheme.
- **fontFamily** (`string`, default `'ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace'`): Font of the characters. A monospaced font keeps the grid even.
- **dpr** (`number`, default `2`): The highest device pixel ratio it draws at; never over 2.
- **controls** (`boolean`, default `true`): Shows the Customize panel under the stage. Turn it off to use it as a background.
- **onSettingsChange** (`(settings: GradientSettings) => void`): Called with all the settings after every change made on the panel.
- **autoplay** (`boolean`, default `true`): While on screen and untouched, a demo pointer wanders through the light, scrambling as it goes, and clicks every 4.2 s. Any real input hands it to the reader.
- **colorScheme** (`'light' | 'dark' | 'system'`): Forces a colour scheme; by default it follows the page.
- **className** (`string`): Extra class names for the root.

## Accessibility

- The stage is one image with a label naming the shape (role="img"); the canvas and the demo pointer are hidden from assistive technology.
- Every scrubber is a slider with its label, range and value (aria-valuetext with its unit): arrows step it, Page Up and Down take bigger steps, Home and End go to the ends.
- Menus are buttons that open a listbox: the arrows move, Enter or Space picks, Escape closes and gives the focus back. Switches are buttons with role="switch"; each colour is a native colour input with its own label.
- Picking a preset or resetting is announced in a polite live region. Every control shows a focus ring for the keyboard.
- Under reduced motion it draws one still frame: nothing drifts, decodes or scrambles, and the demo stays off. It stops drawing offscreen and in hidden tabs.

## Source

### gradient-ascii/gradient-ascii.tsx

```tsx
// Copyright (c) 2026 Bruno Delorence. MIT License.

'use client';

import {
  useEffect,
  useEffectEvent,
  useMemo,
  useRef,
  useState,
  type PointerEvent as ReactPointerEvent,
  type RefObject,
} from 'react';
import { Panel } from './panel';
import { DEFAULTS, presetOf, type GradientSettings, type Shape } from './presets';
import { createRenderer, type Renderer } from './renderer';
import { useAutoplay } from './use-autoplay';
import styles from './gradient-ascii.module.css';

export { CHARACTER_SETS, PRESETS, DEFAULTS } from './presets';
export type { ClickEffect, GradientSettings, Shape } from './presets';

/*
 * Gradient ASCII: a soft glow of light drawn in characters, as a background. Under it lies a
 * smooth gradient; over it, a grid of monospaced characters picks denser glyphs where the light
 * is brighter. The light drifts and wavers; the pointer scrambles the characters it passes, and a
 * click sends a ring of scrambled characters out (or bursts a patch).
 *
 * - The picture is one WebGL shader (renderer.ts): the light per pixel, a character per cell, the
 *   glyphs from an atlas drawn at the canvas's device pixels, the scramble as a small texture.
 * - The demo stage carries a Customize panel (panel.tsx) with every setting: the colours, a
 *   preset (palette, shape, characters and cell size together), the shape, the characters, the
 *   click effect, fourteen scrubbers and three switches. Props set the starting values; the
 *   panel changes them from there, and Reset goes back to the props.
 * - It draws only while on screen and the tab is visible. Under reduced motion it draws one still
 *   frame: the light fully in, nothing drifting, nothing scrambling.
 * - While on screen and untouched, a demo pointer wanders through the light, scrambling as it
 *   goes, and clicks now and then. Any real input hands the stage to the reader.
 * - Light or dark: the stage and the panel take light-dark() tokens; on a light stage the light
 *   is drawn as a wash with darker characters (Light Mode), unless the lightMode prop says
 *   otherwise.
 */

type Settable = Omit<GradientSettings, 'lightMode'> & { lightMode: boolean | undefined };

export type GradientAsciiProps = Partial<Settable> & {
  className?: string;
  /** While on screen and untouched, a demo pointer scrambles the characters and clicks. */
  autoplay?: boolean;
  colorScheme?: 'light' | 'dark' | 'system';
  /** Shows the Customize panel under the stage. Turn it off to use it as a background. */
  controls?: boolean;
  /** The highest device pixel ratio it draws at (it never goes over 2). */
  dpr?: number;
  /** Called with every change made on the panel. */
  onSettingsChange?: (settings: GradientSettings) => void;
};

const SETTING_KEYS = Object.keys(DEFAULTS) as (keyof GradientSettings)[];

/** Where the demo pointer roams for each shape, as shares of the stage: centre and reach. */
const ROAM: Record<Shape, { x: number; y: number; rx: number; ry: number }> = {
  horizon: { x: 0.5, y: 0.3, rx: 0.34, ry: 0.15 },
  pinch: { x: 0.5, y: 0.5, rx: 0.36, ry: 0.1 },
  rise: { x: 0.5, y: 0.8, rx: 0.3, ry: 0.1 },
  eclipse: { x: 0.5, y: 0.5, rx: 0.26, ry: 0.32 },
};
/** The demo clicks every CLICK_EVERY ms. */
const CLICK_EVERY = 4200;

/** The colour scheme the stage ends up with: from the prop, or the page's. */
function useLightScheme(probe: RefObject<HTMLSpanElement | null>, scheme?: string) {
  const [light, setLight] = useState(scheme !== 'dark');
  useEffect(() => {
    const read = () => {
      const element = probe.current;
      if (!element) return;
      // The probe's colour is light-dark(black, white): what it resolves to is the scheme.
      setLight(getComputedStyle(element).color.replace(/\s/g, '') === 'rgb(0,0,0)');
    };
    read();
    const media = window.matchMedia('(prefers-color-scheme: dark)');
    media.addEventListener('change', read);
    const observer = new MutationObserver(read);
    // A scheme set anywhere above (a class, a theme, a data-color-scheme) changes it.
    observer.observe(document.documentElement, {
      attributes: true,
      subtree: true,
      attributeFilter: ['class', 'data-theme', 'data-color-scheme'],
    });
    return () => {
      media.removeEventListener('change', read);
      observer.disconnect();
    };
  }, [probe, scheme]);
  return light;
}

function useReducedMotion() {
  const [reduced, setReduced] = useState(false);
  useEffect(() => {
    const media = window.matchMedia('(prefers-reduced-motion: reduce)');
    const read = () => setReduced(media.matches);
    read();
    media.addEventListener('change', read);
    return () => media.removeEventListener('change', read);
  }, []);
  return reduced;
}

export function GradientAscii({
  className,
  autoplay = true,
  colorScheme,
  controls = true,
  dpr = 2,
  onSettingsChange,
  ...props
}: GradientAsciiProps) {
  const { ref: root, take, playing } = useAutoplay<HTMLDivElement>(8000);
  const canvas = useRef<HTMLCanvasElement>(null);
  const stage = useRef<HTMLDivElement>(null);
  const pointer = useRef<HTMLSpanElement>(null);
  const probe = useRef<HTMLSpanElement>(null);
  const renderer = useRef<Renderer | null>(null);
  const [failed, setFailed] = useState(false);
  const [overrides, setOverrides] = useState<Partial<GradientSettings>>({});
  const [announcement, setAnnouncement] = useState('');
  const light = useLightScheme(probe, colorScheme);
  const reduced = useReducedMotion();

  // The props as settings, the colour scheme choosing Light Mode unless lightMode is given.
  const propKey = JSON.stringify(SETTING_KEYS.map((key) => props[key]));
  const base = useMemo(() => {
    const given: Partial<GradientSettings> = {};
    for (const key of SETTING_KEYS) {
      const value = props[key];
      if (value !== undefined) (given as Record<string, unknown>)[key] = value;
    }
    return { ...DEFAULTS, lightMode: light, ...given } as GradientSettings;
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [propKey, light]);
  const settings = useMemo(() => ({ ...base, ...overrides }), [base, overrides]);

  const change = (patch: Partial<GradientSettings>) => {
    const next = { ...overrides, ...patch };
    setOverrides(next);
    const merged = { ...base, ...next };
    onSettingsChange?.(merged);
    if ('cellSize' in patch && 'shape' in patch) {
      const name = presetOf(merged);
      if (name) setAnnouncement(`Preset ${name}`);
    }
  };

  // The renderer lives as long as the canvas.
  useEffect(() => {
    const element = canvas.current;
    if (!element) return;
    let made: Renderer | null = null;
    try {
      made = createRenderer(element);
    } catch {
      made = null;
    }
    if (!made) {
      setFailed(true);
      return;
    }
    renderer.current = made;
    // It draws only while some of it is on screen and the tab is visible.
    let onScreen = false;
    const update = () => made.active(onScreen && !document.hidden);
    const observer = new IntersectionObserver(([entry]) => {
      onScreen = entry.isIntersecting;
      update();
    });
    observer.observe(element);
    document.addEventListener('visibilitychange', update);
    return () => {
      observer.disconnect();
      document.removeEventListener('visibilitychange', update);
      made.destroy();
      renderer.current = null;
    };
  }, []);

  useEffect(() => {
    renderer.current?.set(settings, reduced, dpr);
  }, [settings, reduced, dpr]);

  // The demo: a pointer roaming the light on the renderer's own clock, clicking now and then.
  const roam = useEffectEvent((now: number, start: number) => {
    const box = stage.current;
    const arrow = pointer.current;
    if (!box || !arrow) return;
    const seconds = (now - start) / 1000;
    const area = ROAM[settings.shape];
    const w = box.clientWidth;
    const h = box.clientHeight;
    const x = (area.x + area.rx * Math.sin(seconds * 0.47 + 0.4)) * w;
    const y = (area.y + area.ry * Math.sin(seconds * 0.83 + 1.1)) * h;
    arrow.style.transform = `translate(${x}px, ${y}px)`;
    renderer.current?.pointer(x, y);
    const beat = Math.floor((now - start) / CLICK_EVERY);
    if (beat > Number(arrow.dataset.beat ?? 0)) {
      arrow.dataset.beat = String(beat);
      arrow.dataset.pressed = 'true';
      renderer.current?.click(x, y);
      window.setTimeout(() => (arrow.dataset.pressed = 'false'), 180);
    }
  });
  const demo = autoplay && playing && !failed;
  useEffect(() => {
    const made = renderer.current;
    const arrow = pointer.current;
    if (!demo || !made || !arrow) return;
    const start = performance.now();
    arrow.dataset.beat = '0';
    arrow.style.opacity = '1';
    made.onTick((now) => roam(now, start));
    return () => {
      made.onTick(null);
      made.pointer(null);
      arrow.style.opacity = '0';
    };
  }, [demo]);

  const local = (event: ReactPointerEvent) => {
    const rect = stage.current!.getBoundingClientRect();
    return { x: event.clientX - rect.left, y: event.clientY - rect.top };
  };

  return (
    <div
      ref={root}
      className={`${styles.root} ${className ?? ''}`}
      data-color-scheme={colorScheme}
      onKeyDownCapture={take}
    >
      <span ref={probe} className={styles.probe} aria-hidden="true" />
      <div className={styles.frame} data-part="frame">
        <div
          ref={stage}
          className={styles.stage}
          data-part="stage"
          data-failed={failed}
          role="img"
          aria-label={`A soft ${settings.shape} of light drawn in characters`}
          onPointerMove={(event) => {
            if (event.pointerType === 'mouse' || event.buttons) take();
            const { x, y } = local(event);
            renderer.current?.pointer(x, y);
          }}
          onPointerLeave={() => renderer.current?.pointer(null)}
          onPointerDown={(event) => {
            take();
            const { x, y } = local(event);
            renderer.current?.click(x, y);
          }}
        >
          <canvas ref={canvas} className={styles.canvas} aria-hidden="true" />
          <span className={styles.pointerLayer} aria-hidden="true">
            <span ref={pointer} className={styles.demoPointer}>
              <svg viewBox="0 0 20 20">
                <path
                  d="M3 2v14.5l3.6-3.3 2.6 5.6 2.4-1.1-2.6-5.5h5.2z"
                  strokeWidth="1.3"
                  strokeLinejoin="round"
                />
              </svg>
            </span>
          </span>
        </div>
        <button
          type="button"
          className={styles.replay}
          aria-label="Replay the intro"
          data-part="replay"
          onClick={() => {
            take();
            renderer.current?.replay();
          }}
        >
          <svg viewBox="0 0 16 16" aria-hidden="true">
            <path
              d="M13.2 6.4A5.4 5.4 0 0 0 3.1 5.3M2.8 9.6a5.4 5.4 0 0 0 10.1 1.1M3 2.6v2.9h2.9M13 13.4v-2.9h-2.9"
              fill="none"
              stroke="currentColor"
              strokeWidth="1.3"
              strokeLinecap="round"
              strokeLinejoin="round"
            />
          </svg>
        </button>
      </div>
      {controls && (
        <div onPointerDownCapture={take}>
          <Panel
            settings={settings}
            changed={Object.keys(overrides).length > 0}
            onChange={change}
            onReset={() => {
              setOverrides({});
              onSettingsChange?.(base);
              renderer.current?.replay();
              setAnnouncement('Settings reset');
            }}
          />
        </div>
      )}
      <p className={styles.hidden} aria-live="polite">
        {announcement}
      </p>
    </div>
  );
}
```

### gradient-ascii/renderer.ts

```tsx
// Copyright (c) 2026 Bruno Delorence. MIT License.

import type { GradientSettings, Shape } from './presets';

/*
 * The renderer: one WebGL fragment shader draws the whole picture, the soft light and the
 * characters over it, at the canvas's device pixels.
 *
 * - The light is a field worked out per pixel: each shape gives how much light there is (L), how
 *   far into it a point lies (m: the edge colour gives way to the light's own), and where it sits
 *   across the light (u, which picks among the colours after the first). A slow noise warps the
 *   field so it wavers as it drifts.
 * - The characters live on a grid of cells, each 0.6 as wide as it is tall. A cell asks the same
 *   field at its middle how bright it is and picks a character from the ramp; a seeded noise
 *   leaves the dimmer cells empty first (density), and now and then a cell swaps with a
 *   neighbouring brightness (flicker).
 * - The glyphs come from an atlas drawn once on a 2D canvas, at the cell's exact size in device
 *   px, so they stay crisp; a blurred twin of it gives the glow and the out-of-focus characters.
 *   Blocks and dots are drawn as shapes, so they fill their cells whatever the font.
 * - Scrambling is an energy per cell, kept on the CPU (a few thousand bytes) and sent as a small
 *   texture: the pointer and a click's burst raise it, and it drains in about half a second. A
 *   click's ring is drawn by the shader itself, a thin band one cell wide travelling at about one
 *   height of the canvas a second. A cell with energy shows a random character from the ramp,
 *   changed sixteen times a second.
 * - The intro fades the light in from its source over 2.2 s while the cells it reaches decode.
 * - Time stops when the canvas is offscreen or the tab hidden; under reduced motion the renderer
 *   draws one still frame, with the light fully in.
 */

const VERTEX = `
attribute vec2 aPos;
void main() { gl_Position = vec4(aPos, 0.0, 1.0); }
`;

const FRAGMENT = `
precision highp float;
uniform vec2 uRes;
uniform vec2 uCell;
uniform vec2 uGrid;
uniform vec2 uOffset;
uniform float uTime;
uniform float uClock;
uniform float uIntro;
uniform vec3 uColors[8];
uniform float uCount;
uniform float uShape;
uniform float uSoft;
uniform float uScale;
uniform float uFlow;
uniform float uGrain;
uniform float uDensity;
uniform float uGlyph;
uniform float uGrad;
uniform float uGlow;
uniform float uDof;
uniform float uFlicker;
uniform float uSeed;
uniform float uLight;
uniform float uChars;
uniform sampler2D uAtlas;
uniform sampler2D uBlur;
uniform sampler2D uEnergy;
// Up to four rings from clicks: centre (device px), radius (device px), strength.
uniform vec4 uWaves[4];
uniform float uBand;

float hash(vec2 p) {
  p = fract(p * vec2(123.34, 456.21));
  p += dot(p, p + 45.32);
  return fract(p.x * p.y);
}
float noise(vec2 p) {
  vec2 i = floor(p);
  vec2 f = fract(p);
  f = f * f * (3.0 - 2.0 * f);
  return mix(mix(hash(i), hash(i + vec2(1.0, 0.0)), f.x),
             mix(hash(i + vec2(0.0, 1.0)), hash(i + vec2(1.0, 1.0)), f.x), f.y);
}

// The colours after the first, as one ramp: u = 0 is the second colour, 1 the last.
vec3 sky(float u) {
  float n = uCount - 2.0;
  vec3 c = uColors[1];
  float pos = clamp(u, 0.0, 1.0) * n;
  for (int i = 0; i < 6; i++) {
    float fi = float(i);
    if (fi < n) {
      vec3 next = uColors[2];
      if (i == 1) next = uColors[3];
      if (i == 2) next = uColors[4];
      if (i == 3) next = uColors[5];
      if (i == 4) next = uColors[6];
      if (i == 5) next = uColors[7];
      c = mix(c, next, clamp(pos - fi, 0.0, 1.0));
    }
  }
  return c;
}

// The light at p (centred, in heights of the canvas, y down): x = L, how much light; y = m, how
// far into it; z = u, where across it; w = the intro's distance from the light's source.
vec4 field(vec2 p) {
  float t = uTime;
  float s = uSeed * 7.31;
  vec2 warp = vec2(
    noise(p * 1.7 + vec2(t * 0.13 + s, -t * 0.08)),
    noise(p * 1.7 + vec2(-t * 0.1 + 3.7, t * 0.12 + s * 1.3))
  ) - 0.5;
  vec2 p0 = p;
  p += warp * uFlow * 0.13;
  p.y += sin(p.x * 2.6 + t * 0.5 + s) * uFlow * 0.03;
  float W = 0.1 + uSoft * 0.4;
  float L = 0.0; float m = 0.0; float u = 0.0; float k = 0.0;
  if (uShape < 0.5) {
    // Horizon: a dark planet below, its edge a wide curve; the sun high in the middle.
    vec2 q = (p - vec2(0.0, 0.5)) / uScale + vec2(0.0, 0.5);
    float d = length(q - vec2(0.0, 1.4)) - 1.15;
    L = smoothstep(-0.03, W * 1.05, d);
    vec2 sun = vec2(sin(t * 0.07 + s) * 0.04, -0.62);
    u = smoothstep(0.2, 0.75, length((q - sun) * vec2(1.6, 0.8)));
    // Under the sun the edge's blue gives way slowly; out towards the far sky, sooner.
    float spread = W / 0.3;
    m = smoothstep((0.22 - 0.06 * u) * spread, (0.66 - 0.16 * u) * spread, d);
    k = max(d, 0.0) * 1.6;
  } else if (uShape < 1.5) {
    // Pinch: a band of light between two dark lobes that squeeze it in the middle, its heart a
    // long glow at the centre.
    vec2 q = p / uScale;
    vec2 a = (q - vec2(0.0, -0.68)) / vec2(0.72, 0.45);
    vec2 b = (q - vec2(0.0, 0.69)) / vec2(0.72, 0.45);
    float d = min(length(a) - 1.0, length(b) - 1.0) * 0.45;
    float core = length((q - vec2(0.0, 0.03)) * vec2(0.8, 2.4));
    L = smoothstep(-0.03, W * 0.45, d);
    m = 1.0 - smoothstep(0.1, 0.8, core);
    u = 1.0 - smoothstep(0.0, 0.5, core);
    k = core * 0.9;
  } else if (uShape < 2.5) {
    // Rise: light welling up from below the bottom edge.
    vec2 q = (p - vec2(0.0, 0.5)) / uScale;
    float r = length((q - vec2(0.0, 0.2)) * vec2(0.5, 1.0));
    float d = 0.62 - r;
    L = smoothstep(-0.02, W * 0.9, d);
    m = smoothstep(0.0, W * 0.8 + 0.06, d);
    u = 1.0 - smoothstep(0.2, 0.36, r);
    k = r * 1.4;
  } else {
    // Eclipse: a dark disc, its edge never wavering, ringed with light that fades outwards in
    // slow uneven rays.
    vec2 q0 = p0 / uScale;
    vec2 q = p / uScale;
    vec2 dir = q0 / max(length(q0), 1e-4);
    float rays = noise(dir * 1.8 + vec2(s, t * 0.22)) * 0.5 + noise(dir * 4.2 + vec2(-t * 0.27, s)) * 0.5;
    float edge = length(q0) - 0.235;
    float dr = max(length(q) - 0.235, edge * 0.6);
    float reach = (W * 0.6 + 0.24) * (0.75 + rays * 0.5);
    L = smoothstep(-0.004, 0.004, edge) * pow(1.0 - smoothstep(0.0, reach, dr), 2.6);
    m = 1.0 - smoothstep(0.0, reach * 0.25, dr);
    u = 1.0 - smoothstep(0.0, W * 0.03 + 0.012, max(edge, 0.0));
    k = abs(edge) * 2.2;
  }
  return vec4(L, m, u, k);
}

void main() {
  vec2 px = vec2(gl_FragCoord.x, uRes.y - gl_FragCoord.y);
  // The grid is centred on the canvas: uOffset is where its first cell starts (zero or less).
  vec2 cell = floor((px - uOffset) / uCell);
  vec2 local = (px - uOffset - cell * uCell) / uCell;
  vec2 p = (px - 0.5 * uRes) / uRes.y;
  vec2 pc = ((cell + 0.5) * uCell + uOffset - 0.5 * uRes) / uRes.y;

  // The intro: the light fades in and spreads out from its source (the planet's edge, the
  // band's heart, the bottom, the disc's rim), its far colours coming last.
  float front = uIntro * 1.5;
  vec4 f = field(p);
  vec4 fc = field(pc);
  float fade = smoothstep(0.0, 0.55, uIntro);
  f.x *= fade * (1.0 - smoothstep(front - 0.5, front, f.w));
  fc.x *= fade * (1.0 - smoothstep(front - 0.5, front, fc.w));
  float settle = smoothstep(0.35, 1.0, uIntro);
  f.y *= mix(0.4, 1.0, settle);
  fc.y *= mix(0.4, 1.0, settle);
  if (uShape > 0.5) {
    f.z = mix(1.0, f.z, settle);
    fc.z = mix(1.0, fc.z, settle);
  }

  vec3 base = mix(uColors[0], sky(f.z), f.y);
  vec3 cbase = mix(uColors[0], sky(fc.z), fc.y);
  // How bright a cell reads: the light, deeper in it brighter, brightest at its heart (the sun,
  // on a horizon).
  float b = uShape < 0.5
    ? pow(fc.x, 0.5) * mix(0.66, 1.0, fc.y) * (1.0 - 0.32 * fc.z)
    : uShape < 2.5 && uShape > 1.5
    ? pow(fc.x, 0.6) * (0.6 + 0.4 * fc.z)
    : pow(fc.x, 0.5) * (0.72 + 0.28 * max(fc.z, fc.y * 0.6));
  b = clamp(b, 0.0, 1.0);

  // Which character: brighter cells go further along the ramp; dimmer cells empty out first.
  float n = uChars;
  float seed = uSeed * 13.7;
  float rate = 0.8 + 2.4 * hash(cell + seed + 9.1);
  float tick = floor(uClock * rate + hash(cell + 4.2) * 7.0);
  float swap = hash(cell * 1.17 + tick * 0.371 + seed);
  float jitter = swap < uFlicker * 0.45 ? (hash(cell + tick + 2.3) < 0.5 ? -1.0 : 1.0) : 0.0;
  float idx = clamp(floor(b * (n - 1.0) + 0.5 + jitter), 0.0, n - 1.0);
  float gap = noise(cell * vec2(0.23, 0.61) + seed) * 0.6 + hash(cell + seed + 1.7) * 0.4;
  float keep = uDensity >= 0.999 ? 1.0 : step(gap, uDensity * (0.48 + 0.62 * b));
  if (b < 0.035) keep = 0.0;
  idx *= keep;

  // Scrambling: the pointer's energy, and the intro's decoding front.
  float energy = texture2D(uEnergy, (cell + 0.5) / uGrid).r;
  vec2 mid = (cell + 0.5) * uCell + uOffset;
  for (int i = 0; i < 4; i++) {
    vec4 w = uWaves[i];
    if (w.w > 0.0) {
      float off = abs(length(mid - w.xy) - w.z);
      energy = max(energy, (1.0 - smoothstep(0.0, uBand, off)) * w.w);
    }
  }
  float decode = (1.0 - smoothstep(0.0, 0.3, abs(fc.w - front + 0.3))) * (1.0 - smoothstep(0.75, 1.0, uIntro));
  float lit = energy;
  energy = max(energy, decode);
  float frame = floor(uClock * 16.0 + hash(cell) * 3.0);
  bool scrambled = energy > 0.06 + hash(cell * 0.73 + seed) * 0.6;
  if (scrambled) idx = 1.0 + floor(hash(cell * 1.31 + frame * 0.177 + seed) * (n - 1.0));

  vec2 uv = vec2((idx + local.x) / n, local.y);
  float crisp = texture2D(uAtlas, uv).a;
  float soft = texture2D(uBlur, uv).a;
  float dofCell = step(hash(cell * 0.91 + seed + 5.5), uDof);
  float cov = mix(crisp, min(soft * 1.5, 1.0) * 0.85, dofCell);
  if (idx < 0.5) { cov = 0.0; soft = 0.0; }

  float seen = smoothstep(0.02, 0.55, fc.x);
  // The pointer's scramble shows even at the light's fringe; the intro's decoding only where lit.
  if (scrambled) seen = max(seen, 0.85 * smoothstep(0.0, 0.3, lit) * smoothstep(0.0, 0.2, fc.x));
  vec3 ink = uLight > 0.5
    ? cbase * mix(0.62, 0.42, fc.z * fc.y)
    : min(cbase * 1.42 + vec3(0.03), vec3(1.0));
  if (scrambled && uLight < 0.5) ink = mix(ink, vec3(1.0), 0.3);

  vec3 wash = uLight > 0.5 ? mix(base, vec3(1.0), 0.12) : base;
  float ga = f.x * uGrad;
  float gl = cov * uGlyph * seen;
  vec3 rgb = wash * ga * (1.0 - gl) + ink * gl;
  float alpha = ga * (1.0 - gl) + gl;
  float halo = soft * uGlow * 0.6 * uGlyph * seen * (uLight > 0.5 ? 0.4 : 1.0);
  rgb += ink * halo * (1.0 - gl);
  alpha = min(alpha + halo * (1.0 - gl), 1.0);

  // Film grain, only where something is drawn.
  float g = hash(px + fract(uClock * 7.13) * vec2(91.7, 37.3)) - 0.5;
  rgb += g * uGrain * 1.1 * alpha;
  rgb = clamp(rgb, 0.0, alpha);
  gl_FragColor = vec4(rgb, alpha);
}
`;

const SHAPES: Record<Shape, number> = { horizon: 0, pinch: 1, rise: 2, eclipse: 3 };

/** How long the intro takes, in ms. */
export const INTRO_MS = 2200;
/** How fast a click's ring travels, in heights of the canvas per second; the shader draws it. */
const WAVE_SPEED = 1.05;
/** How fast scrambled cells settle: energy drained per second. */
const SETTLE = 2.1;

type Wave = { x: number; y: number; start: number };

export type Renderer = {
  /**
   * Applies new settings; `still` draws one frame and stops (reduced motion); `maxDpr` caps the
   * device pixel ratio it draws at.
   */
  set: (settings: GradientSettings, still: boolean, maxDpr?: number) => void;
  /** Whether time may run: false offscreen or in a hidden tab. */
  active: (on: boolean) => void;
  /** A pointer at x, y (css px from the canvas's top left) or gone (null). */
  pointer: (x: number | null, y?: number) => void;
  click: (x: number, y: number) => void;
  replay: () => void;
  /** Called every frame with the time, before drawing (the demo moves its pointer here). */
  onTick: (callback: ((now: number) => void) | null) => void;
  destroy: () => void;
};

function hexToRgb(hex: string): [number, number, number] {
  const value = hex.replace('#', '');
  const full =
    value.length === 3
      ? value
          .split('')
          .map((c) => c + c)
          .join('')
      : value.padEnd(6, '0').slice(0, 6);
  const n = parseInt(full, 16);
  if (Number.isNaN(n)) return [1, 1, 1];
  return [((n >> 16) & 255) / 255, ((n >> 8) & 255) / 255, (n & 255) / 255];
}

/** Draws one glyph into its cell: blocks and dots as shapes, the rest as text. */
function drawGlyph(g: CanvasRenderingContext2D, char: string, x: number, w: number, h: number) {
  const blocks = ' ░▒▓█';
  const dots = ' ·•●';
  if (blocks.includes(char) && char !== ' ') {
    g.globalAlpha = (blocks.indexOf(char) / 4) * 0.82 + 0.18;
    const bw = Math.max(1, Math.round(w * 0.66));
    g.fillRect(x + Math.round((w - bw) / 2), 0, bw, h);
    g.globalAlpha = 1;
    return;
  }
  if (dots.includes(char) && char !== ' ') {
    const r = [0, 0.12, 0.24, 0.37][dots.indexOf(char)] * w;
    g.beginPath();
    g.arc(x + w / 2, h / 2, Math.max(0.8, r), 0, Math.PI * 2);
    g.fill();
    return;
  }
  g.fillText(char, x + w / 2, h / 2 + h * 0.03);
}

export function createRenderer(canvas: HTMLCanvasElement): Renderer | null {
  const gl = canvas.getContext('webgl', {
    premultipliedAlpha: true,
    alpha: true,
    antialias: false,
    preserveDrawingBuffer: false,
  });
  if (!gl) return null;

  const compile = (type: number, source: string) => {
    const shader = gl.createShader(type)!;
    gl.shaderSource(shader, source);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS))
      throw new Error(gl.getShaderInfoLog(shader) ?? 'shader');
    return shader;
  };
  const program = gl.createProgram()!;
  gl.attachShader(program, compile(gl.VERTEX_SHADER, VERTEX));
  gl.attachShader(program, compile(gl.FRAGMENT_SHADER, FRAGMENT));
  gl.linkProgram(program);
  gl.useProgram(program);
  const buffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, 3, -1, -1, 3]), gl.STATIC_DRAW);
  const aPos = gl.getAttribLocation(program, 'aPos');
  gl.enableVertexAttribArray(aPos);
  gl.vertexAttribPointer(aPos, 2, gl.FLOAT, false, 0, 0);
  const uniforms = new Map<string, WebGLUniformLocation | null>();
  const u = (name: string) => {
    if (!uniforms.has(name)) uniforms.set(name, gl.getUniformLocation(program, name));
    return uniforms.get(name)!;
  };

  const makeTexture = (unit: number, filter: number) => {
    const texture = gl.createTexture()!;
    gl.activeTexture(gl.TEXTURE0 + unit);
    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, filter);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, filter);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    return texture;
  };
  const atlasTexture = makeTexture(0, gl.NEAREST);
  const blurTexture = makeTexture(1, gl.LINEAR);
  const energyTexture = makeTexture(2, gl.NEAREST);
  gl.uniform1i(u('uAtlas'), 0);
  gl.uniform1i(u('uBlur'), 1);
  gl.uniform1i(u('uEnergy'), 2);
  gl.pixelStorei(gl.UNPACK_ALIGNMENT, 1);

  let settings: GradientSettings | null = null;
  let still = false;
  let running = false;
  let isActive = false;
  let raf = 0;
  let last = 0;
  let drift = 0;
  let clock = 0;
  let introStart = -1;
  let dpr = 1;
  let maxDpr = 2;
  let cssW = 0;
  let cssH = 0;
  let cellW = 1;
  let cellH = 1;
  let cols = 1;
  let rows = 1;
  let offsetX = 0;
  let offsetY = 0;
  let energy = new Float32Array(1);
  let energyBytes = new Uint8Array(1);
  let energyLive = false;
  let atlasKey = '';
  let waves: Wave[] = [];
  let lastPointer: { x: number; y: number } | null = null;
  let tick: ((now: number) => void) | null = null;

  const buildAtlas = () => {
    if (!settings) return;
    const chars = [...settings.characters];
    const key = `${chars.join('')}|${cellW}|${cellH}|${settings.fontFamily}`;
    if (key === atlasKey) return;
    atlasKey = key;
    const make = () => {
      const c = document.createElement('canvas');
      c.width = cellW * chars.length;
      c.height = cellH;
      const g = c.getContext('2d')!;
      g.fillStyle = '#fff';
      g.textAlign = 'center';
      g.textBaseline = 'middle';
      g.font = `500 ${Math.round(cellH * 0.8)}px ${settings!.fontFamily}`;
      return { c, g };
    };
    const crisp = make();
    chars.forEach((char, i) => drawGlyph(crisp.g, char, i * cellW, cellW, cellH));
    // The blurred twin: each glyph's shadow, its glyph drawn out of the canvas.
    const blur = make();
    blur.g.shadowColor = '#fff';
    blur.g.shadowBlur = Math.max(2, cellW * 0.45);
    const away = blur.c.width + cellW * 4;
    blur.g.shadowOffsetX = away;
    blur.g.save();
    blur.g.translate(-away, 0);
    chars.forEach((char, i) => drawGlyph(blur.g, char, i * cellW, cellW, cellH));
    blur.g.restore();
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, atlasTexture);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, crisp.c);
    gl.activeTexture(gl.TEXTURE1);
    gl.bindTexture(gl.TEXTURE_2D, blurTexture);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, blur.c);
    gl.uniform1f(u('uChars'), chars.length);
  };

  const resize = () => {
    if (!settings) return;
    const rect = canvas.getBoundingClientRect();
    dpr = Math.min(window.devicePixelRatio || 1, maxDpr);
    cssW = Math.max(1, rect.width);
    cssH = Math.max(1, rect.height);
    const w = Math.max(1, Math.round(cssW * dpr));
    const h = Math.max(1, Math.round(cssH * dpr));
    if (canvas.width !== w || canvas.height !== h) {
      canvas.width = w;
      canvas.height = h;
    }
    cellH = Math.max(4, Math.round(settings.cellSize * dpr));
    cellW = Math.max(3, Math.round(settings.cellSize * 0.6 * dpr));
    const nextCols = Math.ceil(w / cellW);
    const nextRows = Math.ceil(h / cellH);
    offsetX = Math.floor((w - nextCols * cellW) / 2);
    offsetY = Math.floor((h - nextRows * cellH) / 2);
    if (nextCols !== cols || nextRows !== rows || energy.length !== nextCols * nextRows) {
      cols = nextCols;
      rows = nextRows;
      energy = new Float32Array(cols * rows);
      energyBytes = new Uint8Array(cols * rows);
      uploadEnergy();
    }
    gl.viewport(0, 0, w, h);
    buildAtlas();
  };

  const uploadEnergy = () => {
    for (let i = 0; i < energy.length; i++) energyBytes[i] = Math.round(energy[i] * 255);
    gl.activeTexture(gl.TEXTURE2);
    gl.bindTexture(gl.TEXTURE_2D, energyTexture);
    gl.texImage2D(
      gl.TEXTURE_2D,
      0,
      gl.LUMINANCE,
      cols,
      rows,
      0,
      gl.LUMINANCE,
      gl.UNSIGNED_BYTE,
      energyBytes,
    );
  };

  /** Raises the energy of the cells within `radius` css px of x, y. */
  const stamp = (x: number, y: number, radius: number, strength = 1) => {
    const cx = (x * dpr - offsetX) / cellW;
    const cy = (y * dpr - offsetY) / cellH;
    const rx = Math.max(0.6, (radius * dpr) / cellW);
    const ry = Math.max(0.6, (radius * dpr) / cellH);
    for (let row = Math.max(0, Math.floor(cy - ry)); row <= Math.min(rows - 1, cy + ry); row++) {
      for (let col = Math.max(0, Math.floor(cx - rx)); col <= Math.min(cols - 1, cx + rx); col++) {
        const dx = (col + 0.5 - cx) / rx;
        const dy = (row + 0.5 - cy) / ry;
        const d = dx * dx + dy * dy;
        if (d > 1) continue;
        const i = row * cols + col;
        energy[i] = Math.max(energy[i], strength * (1 - d * 0.6) * (0.7 + Math.random() * 0.3));
      }
    }
    energyLive = true;
  };

  /** The rings still travelling, as the shader takes them: centre, radius, strength. */
  const waveUniform = new Float32Array(16);
  const advanceWaves = (now: number) => {
    waveUniform.fill(0);
    if (!waves.length) return;
    const maxR = Math.hypot(cssW, cssH);
    waves = waves.filter((wave) => ((now - wave.start) / 1000) * WAVE_SPEED * cssH < maxR + 40);
    waves.slice(-4).forEach((wave, i) => {
      const r = ((now - wave.start) / 1000) * WAVE_SPEED * cssH;
      waveUniform.set(
        [wave.x * dpr, wave.y * dpr, r * dpr, 0.85 * (1 - Math.min(1, r / maxR))],
        i * 4,
      );
    });
  };

  const draw = (now: number) => {
    if (!settings) return;
    const s = settings;
    const colors = s.colors.slice(0, 8);
    const flat = new Float32Array(24);
    colors.forEach((hex, i) => flat.set(hexToRgb(hex), i * 3));
    gl.uniform3fv(u('uColors'), flat);
    gl.uniform1f(u('uCount'), Math.max(2, colors.length));
    gl.uniform2f(u('uRes'), canvas.width, canvas.height);
    gl.uniform2f(u('uCell'), cellW, cellH);
    gl.uniform2f(u('uGrid'), cols, rows);
    // The shader's y runs down from the top, as offsetY does.
    gl.uniform2f(u('uOffset'), offsetX, offsetY);
    gl.uniform1f(u('uTime'), drift);
    gl.uniform1f(u('uClock'), clock);
    const progress =
      still || !s.intro || introStart < 0 ? 1 : Math.min(1, (now - introStart) / INTRO_MS);
    // Eased in and out: the light gathers, then settles.
    gl.uniform1f(u('uIntro'), progress * progress * (3 - 2 * progress));
    gl.uniform1f(u('uShape'), SHAPES[s.shape]);
    gl.uniform1f(u('uSoft'), s.softness);
    gl.uniform1f(u('uScale'), s.scale);
    gl.uniform1f(u('uFlow'), s.flow);
    gl.uniform1f(u('uGrain'), s.grain);
    gl.uniform1f(u('uDensity'), s.density);
    gl.uniform1f(u('uGlyph'), s.glyphOpacity);
    gl.uniform1f(u('uGrad'), s.gradientOpacity);
    gl.uniform1f(u('uGlow'), s.glow);
    gl.uniform1f(u('uDof'), s.depthOfField);
    gl.uniform1f(u('uFlicker'), s.flicker);
    gl.uniform1f(u('uSeed'), s.variation);
    gl.uniform1f(u('uLight'), s.lightMode ? 1 : 0);
    gl.uniform4fv(u('uWaves'), waveUniform);
    gl.uniform1f(u('uBand'), cellH * 0.9);
    gl.clearColor(0, 0, 0, 0);
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.drawArrays(gl.TRIANGLES, 0, 3);
  };

  const frame = (now: number) => {
    raf = 0;
    if (!running || !settings) return;
    const dt = last ? Math.min(0.1, (now - last) / 1000) : 0;
    last = now;
    drift += dt * settings.speed;
    clock += dt;
    tick?.(now);
    advanceWaves(now);
    if (energyLive) {
      let any = false;
      for (let i = 0; i < energy.length; i++) {
        if (energy[i] > 0) {
          energy[i] = Math.max(0, energy[i] - dt * SETTLE);
          any = true;
        }
      }
      uploadEnergy();
      energyLive = any;
    }
    draw(now);
    raf = requestAnimationFrame(frame);
  };

  const update = () => {
    const shouldRun = isActive && !still && !!settings;
    if (shouldRun && !running) {
      running = true;
      last = 0;
      if (introStart < 0) introStart = performance.now();
      raf = requestAnimationFrame(frame);
    } else if (!shouldRun && running) {
      running = false;
      cancelAnimationFrame(raf);
      raf = 0;
    }
    if (!running && settings) draw(performance.now());
  };

  const observer = new ResizeObserver(() => {
    resize();
    if (!running) draw(performance.now());
  });
  observer.observe(canvas);

  return {
    set(next, nextStill, nextMaxDpr = 2) {
      maxDpr = Math.max(0.5, Math.min(2, nextMaxDpr));
      const shapeChanged = settings && settings.shape !== next.shape;
      settings = next;
      still = nextStill;
      if (still) {
        energy.fill(0);
        waves = [];
        uploadEnergy();
        drift = 0;
        clock = 0;
      }
      if (shapeChanged && next.intro && !still) introStart = performance.now();
      resize();
      update();
    },
    active(on) {
      isActive = on;
      update();
    },
    pointer(x, y = 0) {
      if (!settings || still || !settings.mouseInteraction || x === null) {
        lastPointer = null;
        return;
      }
      const radius = settings.scrambleRadius * cssH;
      // Fill in the path between two events, so a fast stroke leaves no gaps.
      if (lastPointer) {
        const dx = x - lastPointer.x;
        const dy = y - lastPointer.y;
        const steps = Math.min(24, Math.ceil(Math.hypot(dx, dy) / Math.max(4, radius * 0.4)));
        for (let i = 1; i < steps; i++)
          stamp(lastPointer.x + (dx * i) / steps, lastPointer.y + (dy * i) / steps, radius);
      }
      stamp(x, y, radius);
      lastPointer = { x, y };
    },
    click(x, y) {
      if (!settings || still) return;
      if (settings.clickEffect === 'wave') {
        waves.push({ x, y, start: performance.now() });
        stamp(x, y, settings.scrambleRadius * cssH * 0.6);
      } else if (settings.clickEffect === 'burst') {
        stamp(x, y, Math.max(settings.scrambleRadius * 2.4, 0.12) * cssH);
      }
    },
    replay() {
      introStart = performance.now();
      if (!running && settings) draw(performance.now());
    },
    onTick(callback) {
      tick = callback;
    },
    destroy() {
      running = false;
      cancelAnimationFrame(raf);
      observer.disconnect();
      // The context stays with the canvas (React may mount the same canvas again); only this
      // renderer's own objects go.
      gl.deleteTexture(atlasTexture);
      gl.deleteTexture(blurTexture);
      gl.deleteTexture(energyTexture);
      gl.deleteBuffer(buffer);
      gl.deleteProgram(program);
    },
  };
}
```

### gradient-ascii/panel.tsx

```tsx
// Copyright (c) 2026 Bruno Delorence. MIT License.

'use client';

import {
  useEffect,
  useId,
  useRef,
  useState,
  type CSSProperties,
  type KeyboardEvent as ReactKeyboardEvent,
  type PointerEvent as ReactPointerEvent,
} from 'react';
import {
  CHARACTER_SETS,
  PRESETS,
  RANGES,
  characterSetOf,
  presetOf,
  type CharacterSet,
  type ClickEffect,
  type GradientSettings,
  type NumberSetting,
  type Preset,
  type Shape,
} from './presets';
import styles from './gradient-ascii.module.css';

/*
 * The panel that tunes the gradient, in three columns of rows (two, then one, on narrow
 * stages): the colours, four menus, a scrubber for every number and three switches.
 *
 * - A scrubber is the whole row: press anywhere on it, or drag, to set the value; the arrow
 *   keys step it, Page Up and Down take ten steps, Home and End go to the ends. Its fill and its
 *   handle show where the value sits in the range.
 * - A menu is a button that opens a list under it (the listbox pattern): arrows move, Enter or
 *   Space picks, Escape closes and gives the focus back.
 * - Each colour is a native colour input under its swatch; minus and plus take the last colour
 *   away or add one (two to eight).
 */

type Change = (patch: Partial<GradientSettings>) => void;

const SHAPES: { value: Shape; label: string }[] = [
  { value: 'horizon', label: 'Horizon' },
  { value: 'pinch', label: 'Pinch' },
  { value: 'rise', label: 'Rise' },
  { value: 'eclipse', label: 'Eclipse' },
];
const CLICKS: { value: ClickEffect; label: string }[] = [
  { value: 'wave', label: 'Wave' },
  { value: 'burst', label: 'Burst' },
  { value: 'none', label: 'None' },
];

/** The order of the scrubbers, row by row across the three columns. */
const NUMBERS: NumberSetting[] = [
  'cellSize',
  'density',
  'glyphOpacity',
  'gradientOpacity',
  'glow',
  'depthOfField',
  'flicker',
  'softness',
  'scale',
  'flow',
  'speed',
  'grain',
  'variation',
  'scrambleRadius',
];

function format(key: NumberSetting, value: number) {
  const range = RANGES[key];
  const text = String(Number(value.toFixed(range.step >= 1 ? 0 : 2)));
  return range.unit ? `${text}${range.unit}` : text;
}

function Chevron({ open }: { open: boolean }) {
  return (
    <svg className={styles.chevron} data-open={open} viewBox="0 0 14 14" aria-hidden="true">
      <path
        d="M3.5 5.25 7 8.75l3.5-3.5"
        fill="none"
        stroke="currentColor"
        strokeWidth="1.3"
        strokeLinecap="round"
        strokeLinejoin="round"
      />
    </svg>
  );
}

function Select<T extends string>({
  label,
  value,
  options,
  onChange,
  part,
}: {
  label: string;
  value: T | null;
  options: { value: T; label: string }[];
  onChange: (value: T) => void;
  part: string;
}) {
  const [open, setOpen] = useState(false);
  const [active, setActive] = useState(0);
  const button = useRef<HTMLButtonElement>(null);
  const list = useRef<HTMLUListElement>(null);
  const box = useRef<HTMLDivElement>(null);
  const id = useId();
  const current = options.find((option) => option.value === value);

  useEffect(() => {
    if (!open) return;
    list.current?.focus();
    const close = (event: PointerEvent) => {
      if (!box.current?.contains(event.target as Node)) setOpen(false);
    };
    document.addEventListener('pointerdown', close);
    return () => document.removeEventListener('pointerdown', close);
  }, [open]);

  const show = () => {
    setActive(
      Math.max(
        0,
        options.findIndex((option) => option.value === value),
      ),
    );
    setOpen(true);
  };
  const pick = (index: number) => {
    onChange(options[index].value);
    setOpen(false);
    button.current?.focus();
  };
  const onListKey = (event: ReactKeyboardEvent) => {
    if (event.key === 'ArrowDown') setActive((i) => (i + 1) % options.length);
    else if (event.key === 'ArrowUp') setActive((i) => (i - 1 + options.length) % options.length);
    else if (event.key === 'Home') setActive(0);
    else if (event.key === 'End') setActive(options.length - 1);
    else if (event.key === 'Enter' || event.key === ' ') pick(active);
    else if (event.key === 'Escape' || event.key === 'Tab') {
      setOpen(false);
      if (event.key === 'Escape') button.current?.focus();
      return;
    } else return;
    event.preventDefault();
  };

  return (
    <div className={styles.selectBox} ref={box} data-part={part}>
      <button
        ref={button}
        type="button"
        className={styles.row}
        aria-haspopup="listbox"
        aria-expanded={open}
        aria-controls={open ? `${id}-list` : undefined}
        aria-label={`${label}: ${current?.label ?? 'Custom'}`}
        onClick={() => (open ? setOpen(false) : show())}
        onKeyDown={(event) => {
          if (event.key === 'ArrowDown' || event.key === 'ArrowUp') {
            event.preventDefault();
            show();
          }
        }}
      >
        <span className={styles.label}>{label}</span>
        <span className={styles.selectValue}>
          <span>{current?.label ?? 'Custom'}</span>
          <Chevron open={open} />
        </span>
      </button>
      {open && (
        <ul
          ref={list}
          id={`${id}-list`}
          className={styles.menu}
          role="listbox"
          aria-label={label}
          tabIndex={-1}
          aria-activedescendant={`${id}-${active}`}
          onKeyDown={onListKey}
        >
          {options.map((option, index) => (
            <li
              key={option.value}
              id={`${id}-${index}`}
              role="option"
              aria-selected={option.value === value}
              className={styles.option}
              data-active={index === active}
              onPointerEnter={() => setActive(index)}
              onClick={() => pick(index)}
            >
              {option.label}
            </li>
          ))}
        </ul>
      )}
    </div>
  );
}

function Scrubber({
  name,
  value,
  onChange,
}: {
  name: NumberSetting;
  value: number;
  onChange: (value: number) => void;
}) {
  const range = RANGES[name];
  const track = useRef<HTMLDivElement>(null);
  const [dragging, setDragging] = useState(false);
  const share = (value - range.min) / (range.max - range.min);
  const snap = (v: number) => {
    const stepped = Math.round((v - range.min) / range.step) * range.step + range.min;
    return Math.min(range.max, Math.max(range.min, Number(stepped.toFixed(4))));
  };
  const fromPointer = (event: ReactPointerEvent) => {
    const rect = track.current!.getBoundingClientRect();
    const x = Math.min(1, Math.max(0, (event.clientX - rect.left) / rect.width));
    onChange(snap(range.min + x * (range.max - range.min)));
  };
  const onKey = (event: ReactKeyboardEvent) => {
    const big = range.step * 10 > (range.max - range.min) / 4 ? range.step * 2 : range.step * 10;
    const moves: Record<string, number> = {
      ArrowRight: range.step,
      ArrowUp: range.step,
      ArrowLeft: -range.step,
      ArrowDown: -range.step,
      PageUp: big,
      PageDown: -big,
    };
    if (event.key in moves) onChange(snap(value + moves[event.key]));
    else if (event.key === 'Home') onChange(range.min);
    else if (event.key === 'End') onChange(range.max);
    else return;
    event.preventDefault();
  };
  return (
    <div
      ref={track}
      className={`${styles.row} ${styles.scrubber}`}
      role="slider"
      tabIndex={0}
      aria-label={range.label}
      aria-valuemin={range.min}
      aria-valuemax={range.max}
      aria-valuenow={value}
      aria-valuetext={format(name, value)}
      data-dragging={dragging}
      data-part="scrubber"
      style={{ '--share': share } as CSSProperties}
      onKeyDown={onKey}
      onPointerDown={(event) => {
        if (event.button !== 0) return;
        event.currentTarget.setPointerCapture(event.pointerId);
        setDragging(true);
        fromPointer(event);
      }}
      onPointerMove={(event) => {
        if (dragging) fromPointer(event);
      }}
      onPointerUp={() => setDragging(false)}
      onPointerCancel={() => setDragging(false)}
    >
      <span className={styles.fill} aria-hidden="true" />
      <span className={styles.ticks} aria-hidden="true">
        {Array.from({ length: 9 }, (_, i) => (
          <span key={i} className={styles.tick} style={{ left: `${(i + 1) * 10}%` }} />
        ))}
      </span>
      <span className={styles.handle} aria-hidden="true" />
      <span className={styles.label}>{range.label}</span>
      <span className={styles.value}>{format(name, value)}</span>
    </div>
  );
}

function Switch({
  label,
  checked,
  onChange,
}: {
  label: string;
  checked: boolean;
  onChange: (checked: boolean) => void;
}) {
  return (
    <button
      type="button"
      role="switch"
      aria-checked={checked}
      className={styles.row}
      data-part="switch"
      onClick={() => onChange(!checked)}
    >
      <span className={styles.label}>{label}</span>
      <span className={styles.switch} data-on={checked} aria-hidden="true">
        <span className={styles.knob} />
      </span>
    </button>
  );
}

function Colors({ colors, onChange }: { colors: string[]; onChange: (colors: string[]) => void }) {
  return (
    <div className={styles.colors} role="group" aria-label="Colors" data-part="colors">
      <div className={styles.colorsHead}>
        <span className={styles.label}>Colors</span>
        <span className={styles.colorButtons}>
          <button
            type="button"
            className={styles.iconButton}
            aria-label="Remove the last colour"
            disabled={colors.length <= 2}
            onClick={() => onChange(colors.slice(0, -1))}
          >
            <svg viewBox="0 0 14 14" aria-hidden="true">
              <path d="M2.9 7h8.2" stroke="currentColor" strokeWidth="1.3" strokeLinecap="round" />
            </svg>
          </button>
          <button
            type="button"
            className={styles.iconButton}
            aria-label="Add a colour"
            disabled={colors.length >= 8}
            onClick={() => onChange([...colors, colors[colors.length - 1]])}
          >
            <svg viewBox="0 0 14 14" aria-hidden="true">
              <path
                d="M2.9 7h8.2M7 2.9v8.2"
                stroke="currentColor"
                strokeWidth="1.3"
                strokeLinecap="round"
              />
            </svg>
          </button>
        </span>
      </div>
      <div className={styles.swatches}>
        {colors.map((color, index) => (
          <label key={index} className={styles.swatch} style={{ background: color }}>
            <input
              type="color"
              className={styles.colorInput}
              value={color}
              aria-label={`Colour ${index + 1} of ${colors.length}`}
              onChange={(event) =>
                onChange(colors.map((c, i) => (i === index ? event.target.value : c)))
              }
            />
          </label>
        ))}
      </div>
    </div>
  );
}

export function Panel({
  settings,
  onChange,
  onReset,
  changed,
}: {
  settings: GradientSettings;
  onChange: Change;
  onReset: () => void;
  /** Whether anything differs from the props: only then is there something to reset. */
  changed: boolean;
}) {
  const preset = presetOf(settings);
  const characters = characterSetOf(settings.characters);
  const number = (name: NumberSetting) => (
    <Scrubber
      key={name}
      name={name}
      value={settings[name]}
      onChange={(value) => onChange({ [name]: value })}
    />
  );
  return (
    <section className={styles.customize} aria-label="Customize" data-part="customize">
      <div className={styles.customizeHead}>
        <h2 className={styles.customizeTitle}>Customize</h2>
        <button
          type="button"
          className={styles.reset}
          data-part="reset"
          data-shown={changed}
          aria-hidden={!changed}
          tabIndex={changed ? 0 : -1}
          onClick={onReset}
        >
          <svg viewBox="0 0 14 14" aria-hidden="true">
            <path
              d="M2.6 7a4.4 4.4 0 1 0 1.3-3.1M2.6 2.4v2.3h2.3"
              fill="none"
              stroke="currentColor"
              strokeWidth="1.2"
              strokeLinecap="round"
              strokeLinejoin="round"
            />
          </svg>
          Reset
        </button>
      </div>
      <div className={styles.panel} data-part="panel">
        <Colors colors={settings.colors} onChange={(colors) => onChange({ colors })} />
        <Select<Preset>
          label="Preset"
          part="preset"
          value={preset}
          options={(Object.keys(PRESETS) as Preset[]).map((name) => ({ value: name, label: name }))}
          onChange={(name) => {
            const next = PRESETS[name];
            onChange({ ...next, colors: [...next.colors] });
          }}
        />
        <Select<Shape>
          label="Shape"
          part="shape"
          value={settings.shape}
          options={SHAPES}
          onChange={(shape) => onChange({ shape })}
        />
        <Select<CharacterSet>
          label="Characters"
          part="characters"
          value={characters}
          options={(Object.keys(CHARACTER_SETS) as CharacterSet[]).map((name) => ({
            value: name,
            label: name,
          }))}
          onChange={(name) => onChange({ characters: CHARACTER_SETS[name] })}
        />
        <Select<ClickEffect>
          label="Click Effect"
          part="click-effect"
          value={settings.clickEffect}
          options={CLICKS}
          onChange={(clickEffect) => onChange({ clickEffect })}
        />
        {NUMBERS.map(number)}
        <Switch
          label="Mouse Interaction"
          checked={settings.mouseInteraction}
          onChange={(mouseInteraction) => onChange({ mouseInteraction })}
        />
        <Switch label="Intro" checked={settings.intro} onChange={(intro) => onChange({ intro })} />
        <Switch
          label="Light Mode"
          checked={settings.lightMode}
          onChange={(lightMode) => onChange({ lightMode })}
        />
      </div>
    </section>
  );
}
```

### gradient-ascii/presets.ts

```tsx
// Copyright (c) 2026 Bruno Delorence. MIT License.

/*
 * The settings a gradient takes, their defaults and ranges, and the named starting points: four
 * presets (a palette, a shape, a set of characters and a cell size each) and five sets of
 * characters. The panel and the renderer both read from here.
 */

export type Shape = 'horizon' | 'pinch' | 'rise' | 'eclipse';
export type ClickEffect = 'wave' | 'burst' | 'none';

export type GradientSettings = {
  /**
   * Two to eight colours. The first is the edge of the shadow; the rest run across the light: on
   * a horizon from the sun out to the far sky, on the other shapes from the outskirts in to the
   * heart of the light.
   */
  colors: string[];
  shape: Shape;
  /** Characters from dimmest to brightest; a space leaves a cell empty. */
  characters: string;
  /** Height of a character cell in px; cells are 0.6 as wide. */
  cellSize: number;
  density: number;
  glyphOpacity: number;
  gradientOpacity: number;
  glow: number;
  depthOfField: number;
  flicker: number;
  softness: number;
  scale: number;
  flow: number;
  speed: number;
  grain: number;
  variation: number;
  mouseInteraction: boolean;
  scrambleRadius: number;
  clickEffect: ClickEffect;
  intro: boolean;
  lightMode: boolean;
  fontFamily: string;
};

export const CHARACTER_SETS = {
  Letters: ' =+xX0S8#@',
  Classic: ' .:-=+*#%@',
  Binary: ' 01',
  Blocks: ' ░▒▓█',
  Dots: ' ·•●',
} as const;
export type CharacterSet = keyof typeof CHARACTER_SETS;

export const PRESETS = {
  Atmosphere: {
    colors: ['#1e3fd8', '#f6f8ff', '#a5d8ff', '#38bdf8'],
    shape: 'horizon',
    characters: CHARACTER_SETS.Letters,
    cellSize: 18,
  },
  Lagoon: {
    colors: ['#0d9488', '#5eead4', '#f0fdfa'],
    shape: 'pinch',
    characters: CHARACTER_SETS.Classic,
    cellSize: 16,
  },
  Rose: {
    colors: ['#9f1239', '#f43f5e', '#fda4af', '#fff1f2'],
    shape: 'rise',
    characters: CHARACTER_SETS.Letters,
    cellSize: 22,
  },
  Corona: {
    colors: ['#78350f', '#f59e0b', '#fffbeb'],
    shape: 'eclipse',
    characters: CHARACTER_SETS.Binary,
    cellSize: 15,
  },
} satisfies Record<string, Pick<GradientSettings, 'colors' | 'shape' | 'characters' | 'cellSize'>>;
export type Preset = keyof typeof PRESETS;

export const DEFAULTS: GradientSettings = {
  ...PRESETS.Atmosphere,
  colors: [...PRESETS.Atmosphere.colors],
  shape: 'horizon',
  density: 0.8,
  glyphOpacity: 0.85,
  gradientOpacity: 0.9,
  glow: 0.2,
  depthOfField: 0,
  flicker: 0.2,
  softness: 0.5,
  scale: 1,
  flow: 0.5,
  speed: 1,
  grain: 0.08,
  variation: 0,
  mouseInteraction: true,
  scrambleRadius: 0.1,
  clickEffect: 'wave',
  intro: true,
  lightMode: false,
  fontFamily: 'ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace',
};

export type NumberSetting = {
  [K in keyof GradientSettings]: GradientSettings[K] extends number ? K : never;
}[keyof GradientSettings];

/** Each number's range, step, and how the panel writes it. */
export const RANGES: Record<
  NumberSetting,
  { label: string; min: number; max: number; step: number; unit?: string }
> = {
  cellSize: { label: 'Cell Size', min: 8, max: 40, step: 1, unit: 'px' },
  density: { label: 'Density', min: 0, max: 1, step: 0.05 },
  glyphOpacity: { label: 'Glyph Opacity', min: 0, max: 1, step: 0.05 },
  gradientOpacity: { label: 'Gradient Opacity', min: 0, max: 1, step: 0.05 },
  glow: { label: 'Glow', min: 0, max: 1.5, step: 0.05 },
  depthOfField: { label: 'Depth of Field', min: 0, max: 1, step: 0.05 },
  flicker: { label: 'Flicker', min: 0, max: 1, step: 0.05 },
  softness: { label: 'Softness', min: 0, max: 1, step: 0.05 },
  scale: { label: 'Scale', min: 0.4, max: 2.5, step: 0.05 },
  flow: { label: 'Flow', min: 0, max: 2, step: 0.05 },
  speed: { label: 'Speed', min: 0, max: 3, step: 0.05 },
  grain: { label: 'Grain', min: 0, max: 0.4, step: 0.01 },
  variation: { label: 'Variation', min: 0, max: 10, step: 1 },
  scrambleRadius: { label: 'Scramble Radius', min: 0.02, max: 0.4, step: 0.01 },
};

/** The preset whose palette, shape, characters and cell size these settings carry, if any. */
export function presetOf(settings: GradientSettings): Preset | null {
  for (const [name, preset] of Object.entries(PRESETS) as [Preset, (typeof PRESETS)[Preset]][]) {
    if (
      preset.shape === settings.shape &&
      preset.characters === settings.characters &&
      preset.cellSize === settings.cellSize &&
      preset.colors.join() === settings.colors.join()
    )
      return name;
  }
  return null;
}

/** The named set these characters are, if any. */
export function characterSetOf(characters: string): CharacterSet | null {
  for (const [name, set] of Object.entries(CHARACTER_SETS) as [CharacterSet, string][])
    if (set === characters) return name;
  return null;
}
```

### gradient-ascii/use-autoplay.ts

```tsx
// Copyright (c) 2026 Bruno Delorence. MIT License.

'use client';

import { useCallback, useEffect, useRef, useState } from 'react';

/*
 * When a demo may play on its own: while part of it is on screen and the tab is visible, never
 * under reduced motion, and not while the reader is using it. `take()` hands it to the reader; it
 * takes back over `idle` ms after their last input.
 */
export function useAutoplay<T extends HTMLElement>(idle = 6000) {
  const ref = useRef<T>(null);
  const [visible, setVisible] = useState(false);
  const [reduced, setReduced] = useState(true);
  const [taken, setTaken] = useState(false);
  const timer = useRef(0);

  useEffect(() => {
    const element = ref.current;
    if (!element) return;
    let onScreen = false;
    const update = () => setVisible(onScreen && !document.hidden);
    const observer = new IntersectionObserver(
      ([entry]) => {
        onScreen = entry.isIntersecting;
        update();
      },
      { threshold: 0.3 },
    );
    observer.observe(element);
    document.addEventListener('visibilitychange', update);
    const motion = window.matchMedia('(prefers-reduced-motion: reduce)');
    const readMotion = () => setReduced(motion.matches);
    readMotion();
    motion.addEventListener('change', readMotion);
    return () => {
      observer.disconnect();
      document.removeEventListener('visibilitychange', update);
      motion.removeEventListener('change', readMotion);
    };
  }, []);

  const take = useCallback(() => {
    setTaken(true);
    window.clearTimeout(timer.current);
    timer.current = window.setTimeout(() => setTaken(false), idle);
  }, [idle]);
  useEffect(() => () => window.clearTimeout(timer.current), []);

  return { ref, take, playing: visible && !reduced && !taken };
}
```

### gradient-ascii/gradient-ascii.module.css

```css
/* Gradient ASCII (gradient-ascii.tsx): a framed stage with the light drawn in characters, and
   under it the Customize card with its panel of rows in three columns (two under 600px, one
   under 380px: a container query on the component's own width).

   Colours are the tokens below, light-dark(light, dark) where the two differ: the component takes
   the color-scheme it inherits from the page (light unless the page says otherwise), or the one
   its colorScheme prop sets (data-color-scheme). The light itself is drawn by the shader in
   renderer.ts from its own colours; only the stage behind it comes from here.

   Memory. The canvas is one layer, sized by its frame; the panel's fills, handles and knobs move
   by width and transform on rows of fixed height, so a change never lays out the page around. */

.root {
  /* The stage behind the light, and its frame's edge. */
  --stage: #f6f5f8;
  --stage-edge: #e3e1e8;
  /* The Customize card (the dark one is a white veil of 4% over the stage), the panel inside it
     and its edge. */
  --card: #efeef2;
  --panel: #fff;
  --panel-edge: rgb(0 0 0 / 0.07);
  /* A row, a scrubber's fill, its ticks and its handle. */
  --row: rgb(0 0 0 / 0.035);
  --fill: rgb(0 0 0 / 0.05);
  --tick: #d9d6df;
  --handle: rgb(0 0 0 / 0.8);
  /* Labels, values, the card's title. */
  --label: #6a6772;
  --value: #17151b;
  --title: #17151b;
  /* An open menu, its edge, a hovered option, its shadow. */
  --menu: #fff;
  --menu-edge: #e3e1e8;
  --menu-hover: #efedf3;
  --menu-shadow: rgb(0 0 0 / 0.12);
  /* A switch on and off, and its knob. */
  --switch-on: #27222e;
  --switch-off: rgb(0 0 0 / 0.1);
  --knob-on: #fff;
  --knob-off: #fff;
  --switch-edge: rgb(0 0 0 / 0.06);
  /* The ring round a swatch, the replay button and its icon, the focus ring. */
  --swatch-ring: rgb(0 0 0 / 0.08);
  --replay: rgb(255 255 255 / 0.62);
  --replay-ink: rgb(23 21 27 / 0.6);
  --focus: #4b4655;
  /* What the probe reads to know the scheme (gradient-ascii.tsx). */
  --probe: #000;
  /* The same on both: the demo's pointer, as the system draws it. */
  --pointer: #1c1c1e;
  --pointer-edge: #fff;
  --pointer-shadow: rgb(0 0 0 / 0.3);
  position: relative;
  container-type: inline-size;
  display: grid;
  gap: 16px;
  width: 100%;
  color: var(--value);
  font:
    400 13px/19.5px Inter,
    -apple-system,
    BlinkMacSystemFont,
    'Segoe UI',
    sans-serif;
  -webkit-font-smoothing: antialiased;
  -webkit-tap-highlight-color: transparent;
}
@supports (color: light-dark(#fff, #000)) {
  .root {
    --stage: light-dark(#f6f5f8, #120f17);
    --stage-edge: light-dark(#e3e1e8, #2f293a);
    --card: light-dark(#efeef2, #1c1920);
    --panel: light-dark(#fff, #120f17);
    --panel-edge: light-dark(rgb(0 0 0 / 0.07), rgb(255 255 255 / 0.055));
    --row: light-dark(rgb(0 0 0 / 0.035), rgb(255 255 255 / 0.04));
    --fill: light-dark(rgb(0 0 0 / 0.05), rgb(255 255 255 / 0.06));
    --tick: light-dark(#d9d6df, #2f293a);
    --handle: light-dark(rgb(0 0 0 / 0.8), rgb(255 255 255 / 0.9));
    --label: light-dark(#6a6772, #aaa);
    --value: light-dark(#17151b, #fff);
    --title: light-dark(#17151b, #f4f4f5);
    --menu: light-dark(#fff, #1b1722);
    --menu-edge: light-dark(#e3e1e8, #2f293a);
    --menu-hover: light-dark(#efedf3, #373044);
    --menu-shadow: light-dark(rgb(0 0 0 / 0.12), rgb(0 0 0 / 0.4));
    --switch-on: light-dark(#27222e, #d4d4d8);
    --switch-off: light-dark(rgb(0 0 0 / 0.1), rgb(255 255 255 / 0.08));
    --knob-on: light-dark(#fff, #27222e);
    --knob-off: light-dark(#fff, #8b8794);
    --switch-edge: light-dark(rgb(0 0 0 / 0.06), rgb(255 255 255 / 0.1));
    --swatch-ring: light-dark(rgb(0 0 0 / 0.08), rgb(255 255 255 / 0.08));
    --replay: light-dark(rgb(255 255 255 / 0.62), rgb(38 33 46 / 0.62));
    --replay-ink: light-dark(rgb(23 21 27 / 0.6), rgb(244 244 245 / 0.58));
    --focus: light-dark(#4b4655, #d9d4e4);
    --probe: light-dark(#000, #fff);
  }
}
.root[data-color-scheme='light'] {
  color-scheme: light;
}
.root[data-color-scheme='dark'] {
  color-scheme: dark;
}
.root[data-color-scheme='system'] {
  color-scheme: light dark;
}

.probe {
  position: absolute;
  width: 0;
  height: 0;
  overflow: hidden;
  color: var(--probe);
}

/* The stage: a frame with the canvas filling it, and the replay button in its corner. */
.frame {
  position: relative;
  overflow: hidden;
  aspect-ratio: 741 / 600;
  min-height: 280px;
  border: 1px solid var(--stage-edge);
  border-radius: 14px;
  background: var(--stage);
}
.stage {
  position: absolute;
  inset: 0;
  cursor: crosshair;
}
.stage[data-failed='true'] {
  background: radial-gradient(
    120% 75% at 50% 0%,
    #a5d8ff 0%,
    #38bdf8 30%,
    #1e3fd8 55%,
    transparent 75%
  );
}
.canvas {
  position: absolute;
  inset: 0;
  display: block;
  width: 100%;
  height: 100%;
}
.replay {
  position: absolute;
  top: 6px;
  right: 6px;
  display: grid;
  place-items: center;
  width: 36px;
  height: 36px;
  padding: 0;
  border: 0;
  border-radius: 8px;
  background: var(--replay);
  color: var(--replay-ink);
  cursor: pointer;
  -webkit-backdrop-filter: blur(16px) saturate(1.4);
  backdrop-filter: blur(16px) saturate(1.4);
  transition: color 0.15s ease;
}
.replay svg {
  width: 16px;
  height: 16px;
}
.replay:hover {
  color: var(--value);
}

/* The demo's pointer: it moves by a transform set every frame; a click presses it a little. */
.pointerLayer {
  position: absolute;
  inset: 0;
  overflow: hidden;
  pointer-events: none;
}
.demoPointer {
  position: absolute;
  top: -2px;
  left: -3px;
  display: block;
  width: 22px;
  height: 22px;
  opacity: 0;
  filter: drop-shadow(0 1px 1.5px var(--pointer-shadow));
  transition: opacity 0.3s ease;
  will-change: transform;
}
.demoPointer svg {
  display: block;
  width: 22px;
  height: 22px;
  overflow: visible;
  fill: var(--pointer);
  stroke: var(--pointer-edge);
  transform-origin: 15% 10%;
  transition: transform 0.12s ease;
}
.demoPointer[data-pressed='true'] svg {
  transform: scale(0.86);
}

/* The Customize card: its head, then the panel. */
.customize {
  padding: 4px;
  border: 1px solid transparent;
  border-radius: 14px;
  background: var(--card);
}
.customizeHead {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 48px;
  padding: 8px 12px 10.4px 14.4px;
}
.customizeTitle {
  margin: 0;
  color: var(--title);
  font-size: 14px;
  font-weight: 600;
  line-height: 21px;
  letter-spacing: -0.01em;
}
.reset {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  height: 30px;
  padding: 0 9px;
  border: 1px solid transparent;
  border-radius: 7px;
  background: none;
  color: var(--label);
  font: inherit;
  font-size: 12px;
  font-weight: 500;
  line-height: 18px;
  cursor: pointer;
  transition:
    background-color 0.15s ease,
    color 0.15s ease;
}
.reset svg {
  width: 14px;
  height: 14px;
}
.reset[data-shown='false'] {
  visibility: hidden;
}
.reset:hover {
  background: var(--row);
  color: var(--value);
}

.panel {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 8px;
  padding: 14px 12px;
  border: 1px solid var(--panel-edge);
  border-radius: 9px;
  background: var(--panel);
}
@container (max-width: 600px) {
  .panel {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}
@container (max-width: 380px) {
  .panel {
    grid-template-columns: minmax(0, 1fr);
  }
  .colors {
    grid-row: span 1;
  }
}

/* A row: a label on the left, its value on the right. */
.row {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  width: 100%;
  min-width: 0;
  height: 40px;
  padding: 0 12px;
  overflow: hidden;
  border: 1px solid transparent;
  border-radius: 7px;
  background: var(--row);
  color: var(--value);
  font: inherit;
  text-align: left;
  cursor: pointer;
  touch-action: pan-y;
  user-select: none;
}
.row:focus-visible,
.reset:focus-visible,
.replay:focus-visible,
.iconButton:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 1px;
}
.label {
  position: relative;
  overflow: hidden;
  color: var(--label);
  font-weight: 500;
  white-space: nowrap;
  text-overflow: ellipsis;
}
.value {
  position: relative;
  flex: none;
  color: var(--value);
  font-weight: 500;
  font-variant-numeric: tabular-nums;
}

/* A scrubber: the fill up to the value, nine ticks, and the handle at the fill's end. */
.scrubber {
  --share: 0;
}
.fill {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: calc(var(--share) * 100%);
  border-radius: 7px;
  background: var(--fill);
}
.ticks {
  position: absolute;
  inset: 0;
}
.tick {
  position: absolute;
  top: 50%;
  width: 1px;
  height: 8px;
  border-radius: 999px;
  background: var(--tick);
  transform: translate(-50%, -50%);
}
.handle {
  position: absolute;
  top: 50%;
  left: calc(var(--share) * 100% - 7.75px);
  width: 3.5px;
  height: 18px;
  border-radius: 999px;
  background: var(--handle);
  opacity: 0.32;
  transform: translateY(-50%);
  transition:
    height 0.15s ease,
    opacity 0.15s ease;
}
.scrubber:hover .handle,
.scrubber:focus-visible .handle,
.scrubber[data-dragging='true'] .handle {
  height: 26px;
  opacity: 0.9;
}
.scrubber[data-dragging='true'] {
  cursor: grabbing;
}

/* A menu: its button shows the value and a chevron; the list opens under it. */
.selectBox {
  position: relative;
  min-width: 0;
}
.selectValue {
  display: inline-flex;
  flex: none;
  align-items: center;
  gap: 6px;
}
.chevron {
  width: 14px;
  height: 14px;
  color: var(--label);
  transition: transform 0.15s ease;
}
.chevron[data-open='true'] {
  transform: rotate(180deg);
}
.menu {
  position: absolute;
  top: calc(100% + 4px);
  right: 0;
  left: 0;
  z-index: 5;
  margin: 0;
  padding: 4px;
  list-style: none;
  border: 1px solid var(--menu-edge);
  border-radius: 10px;
  background: var(--menu);
  box-shadow: 0 8px 32px var(--menu-shadow);
  outline: none;
  animation: menuIn 0.14s ease-out;
}
@keyframes menuIn {
  from {
    opacity: 0;
    transform: translateY(-4px);
  }
}
.option {
  padding: 8px 12px;
  border-radius: 6px;
  color: var(--label);
  cursor: pointer;
}
.option[aria-selected='true'] {
  color: var(--value);
}
.option[data-active='true'] {
  background: var(--menu-hover);
  color: var(--value);
}

/* A switch. */
.switch {
  position: relative;
  flex: none;
  width: 36px;
  height: 20px;
  border: 1px solid var(--switch-edge);
  border-radius: 999px;
  background: var(--switch-off);
  transition: background-color 0.16s ease;
}
.switch[data-on='true'] {
  background: var(--switch-on);
}
.knob {
  position: absolute;
  top: 2px;
  left: 2px;
  width: 14px;
  height: 14px;
  border-radius: 999px;
  background: var(--knob-off);
  box-shadow: 0 1px 2px rgb(0 0 0 / 0.24);
  transition:
    transform 0.16s ease,
    background-color 0.16s ease;
}
.switch[data-on='true'] .knob {
  background: var(--knob-on);
  transform: translateX(16px);
}

/* The colours: a head with minus and plus, then the swatches in a row. */
.colors {
  grid-row: span 2;
  display: flex;
  flex-direction: column;
  gap: 8px;
  min-width: 0;
  padding: 7px 8px 8px;
  border-radius: 10px;
  background: var(--row);
}
.colorsHead {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 26px;
  padding-left: 4px;
}
.colorButtons {
  display: flex;
  gap: 2px;
}
.iconButton {
  display: grid;
  place-items: center;
  width: 26px;
  height: 26px;
  padding: 0;
  border: 0;
  border-radius: 7px;
  background: none;
  color: var(--label);
  cursor: pointer;
}
.iconButton svg {
  width: 14px;
  height: 14px;
}
.iconButton:hover:not(:disabled) {
  background: var(--fill);
  color: var(--value);
}
.iconButton:disabled {
  opacity: 0.4;
  cursor: default;
}
.swatches {
  display: flex;
  flex: 1;
  gap: 3px;
  min-height: 39px;
}
.swatch {
  position: relative;
  flex: 1;
  min-width: 0;
  border-radius: 4px;
  box-shadow: inset 0 0 0 1px var(--swatch-ring);
  cursor: pointer;
}
.swatch:first-child {
  border-radius: 9px 4px 4px 9px;
}
.swatch:last-child {
  border-radius: 4px 9px 9px 4px;
}
.swatch:has(:focus-visible) {
  outline: 2px solid var(--focus);
  outline-offset: 1px;
}
.colorInput {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  padding: 0;
  border: 0;
  opacity: 0;
  cursor: pointer;
}

.hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

@media (prefers-reduced-motion: reduce) {
  .handle,
  .knob,
  .switch,
  .chevron,
  .demoPointer,
  .demoPointer svg {
    transition: none;
  }
  .menu {
    animation: none;
  }
}
```