Bit-Math Bayer8 Dither

'use client';

import { useEffect, useRef, useState } from 'react';
import { cn } from '@/lib/utils';
import { useRaf } from '@/hooks/use-raf';
import { useReducedMotion } from '@/hooks/use-reduced-motion';
import { useResizeObserver } from '@/hooks/use-resize-observer';
import { useSmoothPointer } from '@/hooks/use-smooth-pointer';
import { useVisibility } from '@/hooks/use-visibility';
import { hasWebGL, loseContext, pixelRatio } from '@/lib/webgl';
import {
  BAYER8_DITHER_FRAG,
  BAYER8_DITHER_VERT,
} from '@/components/motion/shaders/bayer8-ordered-dither';

/* ==========================================================================
   Bit-Math Bayer8 Ordered Dither
   --------------------------------------------------------------------------
   Raw WebGL2. A smooth gradient is reduced to a handful of levels through an
   8x8 ordered-dither matrix that is DERIVED from gl_FragCoord with six integer
   ops — no lookup texture, no 64-float uniform array, no branches. The full
   derivation lives at the top of the shader file.

   Uploading a 8x8 texture would mean a second texture unit, a sampler, a
   GL_NEAREST filter that some drivers still get wrong on non-power-of-two
   viewports, and a resource to dispose. Six integer instructions cost less
   than the texture fetch they replace.
   ========================================================================== */

export interface Bayer8OrderedDitherProps {
  /** Output steps per channel, both ends included. 2 is pure 1-bit. */
  levels?: number;
  /** CSS pixels per dither cell. Scaled by DPR so the texture is stable. */
  cellSize?: number;
  /** Multiplier on the sweep. */
  speed?: number;
  /** Darkest output colour, linear 0..1 RGB. */
  dark?: readonly [number, number, number];
  /** Lightest output colour, linear 0..1 RGB. */
  light?: readonly [number, number, number];
  maxDpr?: number;
  className?: string;
}

// #region critical
const TRIANGLE = new Float32Array([-1, -1, 3, -1, -1, 3]);
const LEVELS = 5;
const CELL_SIZE = 2;
const DARK: readonly [number, number, number] = [0.035, 0.038, 0.045];
const LIGHT: readonly [number, number, number] = [0.9, 0.94, 0.92];

interface Gpu {
  gl: WebGL2RenderingContext;
  program: WebGLProgram;
  vao: WebGLVertexArrayObject;
  buffer: WebGLBuffer;
  locations: Map<string, WebGLUniformLocation | null>;
}

function build(gl: WebGL2RenderingContext): Gpu | null {
  const compile = (type: number, src: string): WebGLShader | null => {
    const shader = gl.createShader(type);
    if (!shader) return null;
    gl.shaderSource(shader, src);
    gl.compileShader(shader);
    if (gl.getShaderParameter(shader, gl.COMPILE_STATUS)) return shader;
    console.error('[bayer8-ordered-dither]', gl.getShaderInfoLog(shader));
    gl.deleteShader(shader);
    return null;
  };

  const vert = compile(gl.VERTEX_SHADER, BAYER8_DITHER_VERT);
  const frag = compile(gl.FRAGMENT_SHADER, BAYER8_DITHER_FRAG);
  const program = gl.createProgram();
  const vao = gl.createVertexArray();
  const buffer = gl.createBuffer();
  if (!vert || !frag || !program || !vao || !buffer) return null;

  gl.attachShader(program, vert);
  gl.attachShader(program, frag);
  gl.linkProgram(program);
  gl.deleteShader(vert);
  gl.deleteShader(frag);
  if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
    console.error('[bayer8-ordered-dither]', gl.getProgramInfoLog(program));
    gl.deleteProgram(program);
    return null;
  }

  gl.bindVertexArray(vao);
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.bufferData(gl.ARRAY_BUFFER, TRIANGLE, gl.STATIC_DRAW);
  const attrib = gl.getAttribLocation(program, 'a_pos');
  if (attrib >= 0) {
    gl.enableVertexAttribArray(attrib);
    gl.vertexAttribPointer(attrib, 2, gl.FLOAT, false, 0, 0);
  }
  gl.bindVertexArray(null);

  return { gl, program, vao, buffer, locations: new Map() };
}

function loc(gpu: Gpu, name: string): WebGLUniformLocation | null {
  const cached = gpu.locations.get(name);
  if (cached !== undefined) return cached;
  const found = gpu.gl.getUniformLocation(gpu.program, name);
  gpu.locations.set(name, found);
  return found;
}

export function Bayer8OrderedDither({
  levels = LEVELS,
  cellSize = CELL_SIZE,
  speed = 1,
  dark = DARK,
  light = LIGHT,
  maxDpr = 2,
  className,
}: Bayer8OrderedDitherProps) {
  const host = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const gpuRef = useRef<Gpu | null>(null);
  const dprRef = useRef(1);

  const { width, height } = useResizeObserver(host);
  const reduced = useReducedMotion();
  const visible = useVisibility();
  const pointer = useSmoothPointer({ target: host, smoothing: 0.004 });
  const [supported, setSupported] = useState(true);

  const paramsRef = useRef({ levels, cellSize, speed, dark, light });
  paramsRef.current = { levels, cellSize, speed, dark, light };

  const drawRef = useRef<(elapsed: number) => void>(() => {});
  drawRef.current = (elapsed: number) => {
    const gpu = gpuRef.current;
    if (!gpu) return;
    const { gl } = gpu;
    const params = paramsRef.current;
    const p = pointer.current;

    gl.useProgram(gpu.program);
    gl.uniform2f(loc(gpu, 'u_resolution'), gl.drawingBufferWidth, gl.drawingBufferHeight);
    gl.uniform1f(loc(gpu, 'u_time'), elapsed * params.speed);
    gl.uniform2f(loc(gpu, 'u_pointer'), p.nx, 1 - p.ny);
    gl.uniform1f(loc(gpu, 'u_levels'), Math.max(2, Math.round(params.levels)));
    // Cell size is authored in CSS pixels and converted here, so the dither
    // grain is the same physical size on a 1x monitor and a 3x phone.
    gl.uniform1f(loc(gpu, 'u_cell'), Math.max(1, params.cellSize * dprRef.current));
    gl.uniform3f(loc(gpu, 'u_dark'), params.dark[0], params.dark[1], params.dark[2]);
    gl.uniform3f(loc(gpu, 'u_light'), params.light[0], params.light[1], params.light[2]);

    gl.bindVertexArray(gpu.vao);
    gl.drawArrays(gl.TRIANGLES, 0, 3);
    gl.bindVertexArray(null);
  };

  useEffect(() => {
    const canvas = canvasRef.current;
    if (!canvas) return;
    if (!hasWebGL()) {
      setSupported(false);
      return;
    }

    const gl = canvas.getContext('webgl2', {
      antialias: false,
      alpha: false,
      depth: false,
      stencil: false,
      powerPreference: 'high-performance',
    });
    if (!gl) {
      setSupported(false);
      return;
    }

    const gpu = build(gl);
    if (!gpu) {
      loseContext(gl);
      setSupported(false);
      return;
    }
    gpuRef.current = gpu;
    setSupported(true);

    return () => {
      gpuRef.current = null;
      gl.deleteVertexArray(gpu.vao);
      gl.deleteBuffer(gpu.buffer);
      gl.deleteProgram(gpu.program);
      loseContext(gl);
    };
  }, []);

  useEffect(() => {
    const canvas = canvasRef.current;
    const gpu = gpuRef.current;
    if (!canvas || !gpu || width === 0 || height === 0) return;

    const dpr = pixelRatio(maxDpr);
    dprRef.current = dpr;
    const w = Math.max(1, Math.round(width * dpr));
    const h = Math.max(1, Math.round(height * dpr));
    if (canvas.width !== w || canvas.height !== h) {
      canvas.width = w;
      canvas.height = h;
    }
    gpu.gl.viewport(0, 0, w, h);
    drawRef.current(0);
  }, [width, height, maxDpr, supported, reduced]);

  const running = supported && visible && !reduced && width > 0 && height > 0;
  useRaf((_dt, elapsed) => drawRef.current(elapsed), running);
  // #endregion critical

  return (
    <div ref={host} className={cn('relative h-full w-full overflow-hidden', className)}>
      {supported ? (
        <canvas ref={canvasRef} className="block h-full w-full" />
      ) : (
        <div
          aria-hidden
          className="h-full w-full bg-bg"
          style={{
            backgroundImage:
              'radial-gradient(circle at 1px 1px, var(--k-line-strong) 1px, transparent 0), linear-gradient(180deg, var(--k-surface), var(--k-bg))',
            backgroundSize: '4px 4px, 100% 100%',
          }}
        />
      )}
    </div>
  );
}

/* ==========================================================================
   Bit-Math Bayer8 Dither — GLSL ES 3.00
   --------------------------------------------------------------------------
   The 8x8 ordered-dither matrix is DERIVED from the coordinate with six
   integer operations. No texture, no 64-entry constant array, no branches.

   Derivation. The Bayer matrix is defined recursively:

     M2   = [[0, 2], [3, 1]]
     M2n(x, y) = 4 * Mn(x mod n, y mod n) + M2(x div n, y div n)

   Write M2 in binary — 0=00, 2=10, 3=11, 1=01 — and a pattern appears:

     M2(a, b) = 2 * (a ^ b) + b

   Unrolling the recursion three times for the 8x8 case gives

     M8(x, y) = 16 * M2(x0, y0) + 4 * M2(x1, y1) + M2(x2, y2)

   where xN is bit N of x. Substituting the closed form for M2:

     M8(x, y) = 32*(x0^y0) + 16*y0
              +  8*(x1^y1) +  4*y1
              +  2*(x2^y2) +     y2

   Read as bits, that is the three-bit values of (x ^ y) and y interleaved and
   REVERSED — the least significant bit of the coordinate controls the most
   significant bit of the threshold, which is exactly what makes the pattern
   maximally dispersed rather than clustered.
   ========================================================================== */

export const BAYER8_DITHER_VERT = `#version 300 es
in vec2 a_pos;
out vec2 v_uv;

void main() {
  v_uv = a_pos * 0.5 + 0.5;
  gl_Position = vec4(a_pos, 0.0, 1.0);
}
`;

export const BAYER8_DITHER_FRAG = `#version 300 es
precision highp float;

in vec2 v_uv;
out vec4 fragColor;

uniform vec2  u_resolution;
uniform float u_time;
uniform vec2  u_pointer;
uniform float u_levels;   /* output steps per channel, including both ends */
uniform float u_cell;     /* device pixels per dither cell */
uniform vec3  u_dark;
uniform vec3  u_light;

/* Threshold in [0, 1) for this cell. See the derivation at the top of the
   file. '& 7' is the modulo — the matrix tiles every 8 cells on both axes. */
float bayer8(vec2 cellCoord) {
  ivec2 c = ivec2(floor(cellCoord));
  int x = c.x & 7;
  int y = c.y & 7;

  int v = 32 * ((x & 1) ^ (y & 1))
        + 16 * (y & 1)
        +  8 * (((x >> 1) & 1) ^ ((y >> 1) & 1))
        +  4 * ((y >> 1) & 1)
        +  2 * (((x >> 2) & 1) ^ ((y >> 2) & 1))
        +       ((y >> 2) & 1);

  /* Divide by 64, not 63. The matrix holds 0..63, and dividing by 63 would
     make the top cell land on exactly 1.0, which pushes that one cell in every
     tile a full step brighter and stamps a visible dot grid into flat areas. */
  return float(v) / 64.0;
}

/* Quantise to 'levels' evenly spaced values, offsetting by the cell threshold
   first. '(t - 0.5) / steps' centres the perturbation on zero and scales it to
   exactly one output step: any larger and the dither injects contrast of its
   own, any smaller and the bands survive. */
vec3 quantise(vec3 c, float threshold, float levels) {
  float steps = max(levels - 1.0, 1.0);
  vec3 shifted = clamp(c + (threshold - 0.5) / steps, 0.0, 1.0);
  return floor(shifted * steps + 0.5) / steps;
}

void main() {
  float aspect = u_resolution.x / max(u_resolution.y, 1.0);
  vec2 p = v_uv;
  p.x *= aspect;
  vec2 m = u_pointer;
  m.x *= aspect;

  /* A deliberately smooth, banding-prone field: a wide radial falloff around
     the pointer, a vertical ramp, and a slow horizontal sweep. Every one of
     these is the kind of gradient that shows 8-bit staircase edges. */
  float g = 1.0 - smoothstep(0.0, 1.15, distance(p, m));
  g = mix(g, 1.0 - v_uv.y, 0.42);
  g += 0.09 * sin(v_uv.x * 3.1 + u_time * 0.25);
  g = clamp(g, 0.0, 1.0);

  /* Gamma before quantisation. The level steps are evenly spaced in the
     encoded value, and the eye is not, so quantising the linear value alone
     puts all the visible banding in the shadows. */
  g = pow(g, 1.35);

  vec3 col = mix(u_dark, u_light, g);

  /* Dividing gl_FragCoord by the cell size is what decouples the dither
     pattern from the pixel grid, so the texture stays the same physical size
     on a 1x and a 3x display. */
  float threshold = bayer8(gl_FragCoord.xy / max(u_cell, 1.0));

  fragColor = vec4(quantise(col, threshold, u_levels), 1.0);
}
`;

/* ==========================================================================
   Frame-rate-independent interpolation.
   --------------------------------------------------------------------------
   The everywhere-idiom `x += (target - x) * 0.1` is a bug: it converges twice
   as fast on a 120 Hz display as on a 60 Hz one, so the same code feels
   different on different hardware and visibly speeds up when the browser
   drops frames. `damp` fixes it by raising the retention factor to the power
   of elapsed time, which is the exact continuous form of the same curve.
   ========================================================================== */

/**
 * Fraction of the remaining distance to close this frame.
 *
 * @param smoothing Fraction of the gap that REMAINS after one second.
 *   Smaller is snappier. 0.001 ≈ very fast, 0.01 ≈ fast, 0.1 ≈ soft,
 *   0.5 ≈ slow drift.
 * @param dt Seconds elapsed since the previous frame.
 */
export function dampFactor(smoothing: number, dt: number): number {
  return 1 - Math.pow(smoothing, dt);
}

/** Move `current` toward `target` at a rate independent of frame rate. */
export function damp(
  current: number,
  target: number,
  smoothing: number,
  dt: number,
): number {
  return current + (target - current) * dampFactor(smoothing, dt);
}

/**
 * The per-frame lerp constant an author measured at 60fps, converted into the
 * `smoothing` argument `damp` wants. Lets a source that says "0.1 per frame"
 * be ported without re-tuning by eye:
 *
 *   damp(x, t, perFrameToSmoothing(0.1), dt)
 */
export function perFrameToSmoothing(alpha: number, baseFps = 60): number {
  return Math.pow(1 - alpha, baseFps);
}

export function lerp(a: number, b: number, t: number): number {
  return a + (b - a) * t;
}

export function clamp(v: number, min: number, max: number): number {
  return v < min ? min : v > max ? max : v;
}

export function inverseLerp(a: number, b: number, v: number): number {
  return a === b ? 0 : (v - a) / (b - a);
}

export function mapRange(
  v: number,
  inMin: number,
  inMax: number,
  outMin: number,
  outMax: number,
  doClamp = true,
): number {
  const t = inverseLerp(inMin, inMax, v);
  const r = lerp(outMin, outMax, doClamp ? clamp(t, 0, 1) : t);
  return r;
}

/** GLSL `smoothstep`, same semantics, for parity between JS and shader code. */
export function smoothstep(edge0: number, edge1: number, x: number): number {
  const t = clamp(inverseLerp(edge0, edge1, x), 0, 1);
  return t * t * (3 - 2 * t);
}

/**
 * Gaussian falloff, `exp(-d²)`. Yields 1.000 / 0.368 / 0.018 / 0.0001 at
 * distances 0 / 1 / 2 / 3 — a continuous focus scalar with no thresholds and
 * no branches, which is why carousels that use it feel analogue rather than
 * stepped.
 */
export function gaussian(distance: number, falloff = 1): number {
  const d = distance * falloff;
  return Math.exp(-(d * d));
}

'use client';

import { useEffect, useRef } from 'react';

/* ==========================================================================
   One shared requestAnimationFrame loop.
   --------------------------------------------------------------------------
   Forty components each calling requestAnimationFrame means forty callbacks
   the browser schedules separately and forty chances to read layout after a
   write. One loop, one ordered pass, one place to clamp delta time.

   Delta is clamped to 100 ms. Without that, returning to a backgrounded tab
   delivers a multi-second dt and every physics integration in the page
   explodes on the first frame back.
   ========================================================================== */

export type RafCallback = (dt: number, elapsed: number) => void;

const callbacks = new Set<RafCallback>();
let frame = 0;
let last = 0;
let start = 0;

const MAX_DT = 0.1;
const DEFAULT_DT = 1 / 60;

function tick(now: number) {
  frame = requestAnimationFrame(tick);
  const dt = last === 0 ? DEFAULT_DT : Math.min((now - last) / 1000, MAX_DT);
  last = now;
  const elapsed = (now - start) / 1000;
  // Copy: a callback may unsubscribe itself (or another) mid-iteration.
  for (const cb of Array.from(callbacks)) {
    if (callbacks.has(cb)) cb(dt, elapsed);
  }
}

function subscribe(cb: RafCallback) {
  callbacks.add(cb);
  if (frame === 0) {
    start = performance.now();
    last = 0;
    frame = requestAnimationFrame(tick);
  }
  return () => {
    callbacks.delete(cb);
    if (callbacks.size === 0 && frame !== 0) {
      cancelAnimationFrame(frame);
      frame = 0;
      last = 0;
    }
  };
}

/**
 * Run `cb` every frame while `enabled`.
 *
 * The callback is held in a ref, so it does not need to be memoised and the
 * subscription is never torn down just because the closure changed identity.
 */
export function useRaf(cb: RafCallback, enabled = true): void {
  const ref = useRef(cb);
  ref.current = cb;

  useEffect(() => {
    if (!enabled) return;
    return subscribe((dt, elapsed) => ref.current(dt, elapsed));
  }, [enabled]);
}

'use client';

import { useSyncExternalStore } from 'react';

/* ==========================================================================
   prefers-reduced-motion, SSR-safe.
   --------------------------------------------------------------------------
   useSyncExternalStore rather than useState + useEffect: the server snapshot
   is an explicit `false`, so the markup React renders on the server and the
   markup it hydrates with agree, and the real value lands in the same commit
   as hydration instead of one frame later. A useEffect version flashes the
   animated variant before removing it — the exact thing the user asked not to
   see.

   Reduced motion is not "duration: 0". For most components here it means a
   different render: the final state, a static poster, or a paused frame.
   ========================================================================== */

const QUERY = '(prefers-reduced-motion: reduce)';

function subscribe(onChange: () => void) {
  if (typeof window === 'undefined' || !window.matchMedia) return () => {};
  const mql = window.matchMedia(QUERY);
  mql.addEventListener('change', onChange);
  return () => mql.removeEventListener('change', onChange);
}

function getSnapshot() {
  if (typeof window === 'undefined' || !window.matchMedia) return false;
  return window.matchMedia(QUERY).matches;
}

function getServerSnapshot() {
  return false;
}

export function useReducedMotion(): boolean {
  return useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
}

/** Generic media-query hook, same SSR guarantees. */
export function useMediaQuery(query: string): boolean {
  return useSyncExternalStore(
    (onChange) => {
      if (typeof window === 'undefined' || !window.matchMedia) return () => {};
      const mql = window.matchMedia(query);
      mql.addEventListener('change', onChange);
      return () => mql.removeEventListener('change', onChange);
    },
    () => {
      if (typeof window === 'undefined' || !window.matchMedia) return false;
      return window.matchMedia(query).matches;
    },
    () => false,
  );
}

'use client';

import { useEffect, useState, type RefObject } from 'react';

/* ==========================================================================
   Element size, from one shared ResizeObserver.
   --------------------------------------------------------------------------
   Sized from the element rather than the window because a preview in a grid
   cell resizes when the grid reflows, not when the viewport does. Reading
   `window.innerWidth` is the reason so many canvas components are correct on
   load and wrong after a sidebar opens.
   ========================================================================== */

export interface Size {
  width: number;
  height: number;
}

type Handler = (size: Size) => void;

let observer: ResizeObserver | null = null;
const handlers = new Map<Element, Handler>();

function ensureObserver(): ResizeObserver | null {
  if (typeof ResizeObserver === 'undefined') return null;
  observer ??= new ResizeObserver((entries) => {
    for (const entry of entries) {
      const box = entry.contentBoxSize?.[0];
      const size: Size = box
        ? { width: box.inlineSize, height: box.blockSize }
        : { width: entry.contentRect.width, height: entry.contentRect.height };
      handlers.get(entry.target)?.(size);
    }
  });
  return observer;
}

export function useResizeObserver(ref: RefObject<Element | null>): Size {
  const [size, setSize] = useState<Size>({ width: 0, height: 0 });

  useEffect(() => {
    const el = ref.current;
    const ro = ensureObserver();
    if (!el || !ro) return;

    // Seed synchronously: waiting for the first observer callback leaves one
    // frame where a canvas is sized 0x0, which some drivers log as an error.
    const rect = el.getBoundingClientRect();
    setSize({ width: rect.width, height: rect.height });

    handlers.set(el, (next) =>
      setSize((prev) =>
        prev.width === next.width && prev.height === next.height ? prev : next,
      ),
    );
    ro.observe(el);

    return () => {
      handlers.delete(el);
      ro.unobserve(el);
    };
  }, [ref]);

  return size;
}

'use client';

import { useEffect, useRef, type RefObject } from 'react';
import { useRaf } from '@/hooks/use-raf';
import { damp } from '@/lib/damp';

/* ==========================================================================
   Pointer position, smoothed, in several coordinate spaces at once.
   --------------------------------------------------------------------------
   Almost every cursor effect wants the same four things and computes them
   slightly differently each time: client pixels, element-local pixels, 0..1
   normalised, and -1..1 NDC for shaders. Producing all four from one damped
   source keeps a cursor dot and the shader it drives exactly in step.

   Exposed via ref for the same reason as scroll velocity: per-frame values
   must not re-render.
   ========================================================================== */

export interface PointerState {
  /** Viewport pixels. */
  clientX: number;
  clientY: number;
  /** Pixels relative to the target element's top-left. */
  x: number;
  y: number;
  /** 0..1 across the element. */
  nx: number;
  ny: number;
  /** -1..1, y up. Feed straight into a shader uniform. */
  ndcX: number;
  ndcY: number;
  /** Whether the pointer has been seen. Nothing should render before. */
  active: boolean;
}

export interface UseSmoothPointerOptions {
  /** Fraction of the gap remaining after one second. Lower = tighter. */
  smoothing?: number;
  /** Listen on this element rather than the window. */
  target?: RefObject<HTMLElement | null>;
  /** Follow touch drags as well as mouse moves. */
  touch?: boolean;
}

function makeInitialState(): PointerState {
  return {
    clientX: 0,
    clientY: 0,
    x: 0,
    y: 0,
    nx: 0.5,
    ny: 0.5,
    ndcX: 0,
    ndcY: 0,
    active: false,
  };
}

export function useSmoothPointer(
  options: UseSmoothPointerOptions = {},
): { current: PointerState } {
  const { smoothing = 0.001, target, touch = true } = options;

  const state = useRef<PointerState>(makeInitialState());
  // `null` means "no real pointer yet", which is distinct from a legitimate
  // pointer at (0, 0) in the top-left corner.
  const targetPos = useRef<{ clientX: number; clientY: number } | null>(null);
  const seeded = useRef(false);

  // Options the listener needs but that must not re-subscribe it on change.
  const touchRef = useRef(touch);
  touchRef.current = touch;

  useEffect(() => {
    const el = target?.current ?? null;
    const node: HTMLElement | Window = el ?? window;

    const onMove = (event: Event) => {
      const e = event as PointerEvent;
      if (!touchRef.current && e.pointerType === 'touch') return;
      targetPos.current = { clientX: e.clientX, clientY: e.clientY };
    };

    node.addEventListener('pointermove', onMove, { passive: true });
    return () => node.removeEventListener('pointermove', onMove);
    // `target` is a ref object; its identity is stable for the component's
    // lifetime, so this subscribes once.
  }, [target]);

  useRaf((dt) => {
    const el = target?.current ?? null;
    const rect = el
      ? el.getBoundingClientRect()
      : {
          left: 0,
          top: 0,
          width: window.innerWidth,
          height: window.innerHeight,
        };

    const pointer = targetPos.current;

    if (pointer === null) {
      // Park at the centre until a real pointer arrives, so the first move
      // eases out from the middle rather than snapping in from (0, 0). Done
      // once — re-centring every frame would fight a slow first movement.
      if (!seeded.current && rect.width > 0 && rect.height > 0) {
        seeded.current = true;
        const cx = rect.left + rect.width / 2;
        const cy = rect.top + rect.height / 2;
        state.current = {
          ...state.current,
          clientX: cx,
          clientY: cy,
          x: cx - rect.left,
          y: cy - rect.top,
        };
      }
      return;
    }

    const clientX = damp(state.current.clientX, pointer.clientX, smoothing, dt);
    const clientY = damp(state.current.clientY, pointer.clientY, smoothing, dt);

    const x = clientX - rect.left;
    const y = clientY - rect.top;
    const nx = rect.width > 0 ? x / rect.width : 0.5;
    const ny = rect.height > 0 ? y / rect.height : 0.5;

    state.current = {
      clientX,
      clientY,
      x,
      y,
      nx,
      ny,
      ndcX: nx * 2 - 1,
      ndcY: -(ny * 2 - 1),
      active: true,
    };
  });

  return state;
}

'use client';

import { useSyncExternalStore } from 'react';

/* ==========================================================================
   Document visibility, shared.
   --------------------------------------------------------------------------
   A backgrounded tab still runs `setInterval`, still holds WebGL contexts,
   and — on some platforms — still gets throttled rAF ticks with multi-second
   deltas. Anything expensive should stop when the tab is hidden and resume
   when it comes back, rather than trying to catch up.

   `useSyncExternalStore` with an explicit server snapshot so SSR markup and
   the first client render agree.
   ========================================================================== */

function subscribe(onChange: () => void): () => void {
  document.addEventListener('visibilitychange', onChange);
  return () => document.removeEventListener('visibilitychange', onChange);
}

function getSnapshot(): boolean {
  return document.visibilityState === 'visible';
}

/** Assume visible on the server: the alternative flashes a paused state. */
function getServerSnapshot(): boolean {
  return true;
}

export function useVisibility(): boolean {
  return useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
}

import type * as THREE from 'three';

/* ==========================================================================
   WebGL context lifecycle.
   --------------------------------------------------------------------------
   Chromium allows roughly 16 live WebGL contexts per RENDERER PROCESS (8 on
   low-end devices). Creating the 17th does not fail — it fires
   `webglcontextlost` on the OLDEST one, so an unrelated component elsewhere
   on the page goes black. Same-origin iframes share the renderer process, so
   isolating previews in iframes does not raise the ceiling.

   The only real fix is to release contexts on unmount, and `renderer.dispose()`
   ALONE DOES NOT DO THAT. It frees GPU objects but leaves the context itself
   alive until GC decides otherwise, which may be never. `forceContextLoss()`
   is the call that actually hands it back.
   ========================================================================== */

/**
 * Fully release a three.js renderer. Call this in the `useEffect` cleanup of
 * any component that constructs a `WebGLRenderer` — the preview host drives
 * unmount via `<Activity mode="hidden">`, so ordinary cleanup IS the disposal
 * path and nothing component-specific is required.
 */
export function disposeRenderer(renderer: THREE.WebGLRenderer | null | undefined): void {
  if (!renderer) return;

  // Stop the loop first: a queued frame that renders into a lost context
  // throws, and the throw escapes the cleanup function.
  renderer.setAnimationLoop(null);
  renderer.dispose();
  renderer.forceContextLoss();

  const canvas = renderer.domElement;
  if (canvas) {
    // Zeroing the backing store releases the drawing buffer immediately
    // instead of holding width×height×4 bytes until the node is collected.
    canvas.width = 0;
    canvas.height = 0;
  }
}

/**
 * Release a raw WebGL context (ogl, or hand-written GL). The extension is the
 * only portable way to do it; it is absent in some headless configurations,
 * hence the optional call.
 */
export function loseContext(gl: WebGLRenderingContext | WebGL2RenderingContext | null | undefined): void {
  if (!gl) return;
  gl.getExtension('WEBGL_lose_context')?.loseContext();
}

/** Recursively dispose geometries, materials and textures under a root. */
export function disposeObject(root: THREE.Object3D | null | undefined): void {
  if (!root) return;
  root.traverse((obj) => {
    const mesh = obj as THREE.Mesh;
    mesh.geometry?.dispose?.();
    const material = mesh.material;
    if (!material) return;
    const materials = Array.isArray(material) ? material : [material];
    for (const m of materials) {
      for (const value of Object.values(m as unknown as Record<string, unknown>)) {
        if (value && typeof value === 'object' && 'isTexture' in value) {
          (value as THREE.Texture).dispose();
        }
      }
      m.dispose?.();
    }
  });
}

/**
 * Device pixel ratio capped for fill-rate. Above 2 the visual gain is nil and
 * the cost is quadratic; on a 3x phone an uncapped full-screen shader is the
 * single most common cause of a janky first paint.
 */
export function pixelRatio(max = 2): number {
  if (typeof window === 'undefined') return 1;
  return Math.min(window.devicePixelRatio || 1, max);
}

/**
 * Whether WebGL is actually available. Some browsers expose the constructor
 * but fail to create a context (blocklisted GPU, no hardware acceleration);
 * a component that assumes success renders a permanently blank box.
 */
export function hasWebGL(): boolean {
  if (typeof document === 'undefined') return false;
  try {
    const canvas = document.createElement('canvas');
    const gl =
      canvas.getContext('webgl2') ??
      canvas.getContext('webgl') ??
      canvas.getContext('experimental-webgl');
    if (!gl) return false;
    (gl as WebGLRenderingContext).getExtension('WEBGL_lose_context')?.loseContext();
    return true;
  } catch {
    return false;
  }
}