{"$schema":"https://ui.shadcn.com/schema/registry-item.json","name":"x-walkers","type":"registry:component","title":"X walkers","description":"X marks crawl across a field of dots, reaching their arms to the next dot and dragging themselves over; they keep away from your pointer, and a click sets down a new one.","author":"Yash Bavadiya <https://xevrion.dev>","dependencies":[],"registryDependencies":["utils"],"files":[{"path":"components/x-walkers.tsx","type":"registry:component","content":"\"use client\";\n\nimport { useEffect, useRef } from \"react\";\nimport { usePreviewPlay } from \"@/lib/preview-play\";\nimport { useReducedMotion } from \"@/hooks/use-reduced-motion\";\nimport { cn } from \"@/lib/utils\";\n\n// After Okazz's X grid study (https://x.com/okazz_): on a field of dots,\n// some of the dots are X's, and the X's crawl. To move, an X reaches its\n// leading arms out to the next dot, slides its body over, and drags its\n// trailing arms after it; arms thin as they stretch, so they read as soft\n// limbs rather than sticks. Here they also keep away from your pointer,\n// and clicking an empty dot sets a new X down on it.\n\nconst TAU = Math.PI * 2;\n// Dots along each side.\nconst COUNT = 17;\n// How many X's the field starts with, and the most it will hold.\nconst START = 22;\nconst MOST = 60;\n// One step: brisk, a scurry rather than a stroll, but still long enough\n// to catch the reach and the pull.\nconst STEP = 0.48;\n// How long an X rests between steps, at least and at most, in seconds:\n// short, so the field is always busy somewhere.\nconst REST_MIN = 0.12;\nconst REST_MAX = 1.1;\n// An arm sets off this far through a step: leading arms at 0, trailing\n// arms at LAG. Each arm then takes the rest of the step to arrive.\nconst LAG = 0.3;\nconst ARM_TRAVEL = 1 - LAG;\n// The pointer's reach, in cells, inside which X's step away from it.\nconst SHY = 3.2;\n// A new X grows its arms out over this long.\nconst GROW = 0.35;\n// Points along each side of an arm's outline.\nconst TAPER = 14;\n\n// Adds one arm to the current path: a smooth outline along a curve from\n// the body (cx, cy) through a bend (bx, by) to the tip, wide at the body and\n// narrowing to the tip, with round ends. Filled, not stroked, so it has no\n// seams.\nfunction armPath(\n  ctx: CanvasRenderingContext2D,\n  cx: number,\n  cy: number,\n  bx: number,\n  by: number,\n  tx: number,\n  ty: number,\n  base: number,\n  tip: number,\n) {\n  if (base <= 0.01) return;\n  // Each arm is its own fill: an outline winds one way or the other with\n  // the arm's direction, and two opposite ones in one path would cancel\n  // where they overlap.\n  ctx.beginPath();\n  const left: number[] = [];\n  const right: number[] = [];\n  for (let s = 0; s <= TAPER; s++) {\n    const u = s / TAPER;\n    const v = 1 - u;\n    const x = v * v * cx + 2 * v * u * bx + u * u * tx;\n    const y = v * v * cy + 2 * v * u * by + u * u * ty;\n    // The curve's direction here, turned a quarter for the sides.\n    let gx = 2 * v * (bx - cx) + 2 * u * (tx - bx);\n    let gy = 2 * v * (by - cy) + 2 * u * (ty - by);\n    const g = Math.hypot(gx, gy) || 1;\n    gx /= g;\n    gy /= g;\n    const half = (base + (tip - base) * u ** 0.85) / 2;\n    left.push(x - gy * half, y + gx * half);\n    right.push(x + gy * half, y - gx * half);\n  }\n  ctx.moveTo(left[0], left[1]);\n  for (let i = 2; i < left.length; i += 2) ctx.lineTo(left[i], left[i + 1]);\n  for (let i = right.length - 2; i >= 0; i -= 2) ctx.lineTo(right[i], right[i + 1]);\n  ctx.closePath();\n  ctx.fill();\n  // Round ends: the body and the tip.\n  ctx.beginPath();\n  ctx.arc(cx, cy, base / 2, 0, TAU);\n  ctx.fill();\n  ctx.beginPath();\n  ctx.arc(tx, ty, tip / 2, 0, TAU);\n  ctx.fill();\n}\n\ntype Walker = {\n  // The dot it's on, or leaving.\n  col: number;\n  row: number;\n  // The dot it's heading for, while stepping.\n  toCol: number;\n  toRow: number;\n  // When the current step began, or -1 at rest.\n  stepAt: number;\n  // When it next sets off.\n  nextAt: number;\n  // When it appeared, for the grow-in.\n  born: number;\n};\n\n// The four arms point along the diagonals.\nconst ARMS = [\n  [1, 1],\n  [-1, 1],\n  [-1, -1],\n  [1, -1],\n].map(([x, y]) => [x / Math.SQRT2, y / Math.SQRT2]);\nconst NEIGHBOURS = [\n  [1, 0],\n  [-1, 0],\n  [0, 1],\n  [0, -1],\n  [1, 1],\n  [-1, 1],\n  [1, -1],\n  [-1, -1],\n];\n\n// Seeded, so the field starts the same way every time.\nfunction random(seed: number) {\n  return () => {\n    seed |= 0;\n    seed = (seed + 0x6d2b79f5) | 0;\n    let t = Math.imul(seed ^ (seed >>> 15), 1 | seed);\n    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;\n    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;\n  };\n}\n\nconst clamp = (v: number) => Math.min(1, Math.max(0, v));\nconst inOut = (t: number) => (t < 0.5 ? 4 * t * t * t : 1 - (-2 * t + 2) ** 3 / 2);\n\nexport function XWalkers({ className }: { className?: string }) {\n  const reduceMotion = useReducedMotion();\n  const play = usePreviewPlay();\n  const canvasRef = useRef<HTMLCanvasElement>(null);\n\n  useEffect(() => {\n    const canvas = canvasRef.current;\n    if (!canvas) return;\n    const ctx = canvas.getContext(\"2d\");\n    if (!ctx) return;\n\n    const rand = random(11);\n    const animate = !reduceMotion && play !== false;\n    const start = performance.now();\n    const now = () => (performance.now() - start) / 1000;\n\n    const walkers: Walker[] = [];\n    const taken = new Set<number>();\n    const key = (c: number, r: number) => r * COUNT + c;\n    const place = (col: number, row: number, born: number) => {\n      walkers.push({\n        col,\n        row,\n        toCol: col,\n        toRow: row,\n        stepAt: -1,\n        nextAt: born + REST_MIN + rand() * (REST_MAX - REST_MIN),\n        born,\n      });\n      taken.add(key(col, row));\n    };\n    while (walkers.length < START) {\n      const col = Math.floor(rand() * COUNT);\n      const row = Math.floor(rand() * COUNT);\n      // Already grown, so the first frame is a finished picture.\n      if (!taken.has(key(col, row))) place(col, row, -GROW);\n    }\n\n    let size = 0;\n    let dpr = 1;\n    let frame = 0;\n    let visible = false;\n    const pointer = { x: 0, y: 0, on: false };\n\n    const resize = () => {\n      size = canvas.clientWidth;\n      dpr = Math.min(window.devicePixelRatio || 1, 4);\n      canvas.width = Math.round(size * dpr);\n      canvas.height = Math.round(size * dpr);\n      ctx.setTransform(dpr, 0, 0, dpr, 0, 0);\n    };\n    // Grid geometry: an even margin round the dots.\n    const layout = () => {\n      const margin = size * 0.07;\n      const gap = (size - margin * 2) / (COUNT - 1);\n      return { margin, gap };\n    };\n\n    // Picks the next dot for an X: any free neighbour, or, near the\n    // pointer, the free neighbour farthest from it.\n    const choose = (w: Walker, t: number) => {\n      const { margin, gap } = layout();\n      const px = (pointer.x - margin) / gap;\n      const py = (pointer.y - margin) / gap;\n      const near = pointer.on && Math.hypot(w.col - px, w.row - py) < SHY;\n      const options = NEIGHBOURS.map(([dc, dr]) => [w.col + dc, w.row + dr]).filter(\n        ([c, r]) => c >= 0 && r >= 0 && c < COUNT && r < COUNT && !taken.has(key(c, r)),\n      );\n      if (!options.length) {\n        w.nextAt = t + 0.4;\n        return;\n      }\n      let pick = options[Math.floor(rand() * options.length)];\n      if (near) {\n        pick = options.reduce((best, o) =>\n          Math.hypot(o[0] - px, o[1] - py) > Math.hypot(best[0] - px, best[1] - py) ? o : best,\n        );\n      }\n      w.toCol = pick[0];\n      w.toRow = pick[1];\n      w.stepAt = t;\n      taken.add(key(pick[0], pick[1]));\n    };\n\n    const update = (t: number) => {\n      const { margin, gap } = layout();\n      for (const w of walkers) {\n        if (w.stepAt >= 0 && t - w.stepAt >= STEP) {\n          taken.delete(key(w.col, w.row));\n          w.col = w.toCol;\n          w.row = w.toRow;\n          w.stepAt = -1;\n          const near =\n            pointer.on &&\n            Math.hypot(w.col - (pointer.x - margin) / gap, w.row - (pointer.y - margin) / gap) < SHY;\n          // Shy ones keep going; the rest take a breather.\n          w.nextAt = t + (near ? 0.05 : REST_MIN + rand() * (REST_MAX - REST_MIN));\n        }\n        if (w.stepAt < 0 && t >= w.nextAt) choose(w, t);\n      }\n    };\n\n    const draw = (t: number) => {\n      if (!size) return;\n      const { margin, gap } = layout();\n      const ink = getComputedStyle(canvas).color;\n      ctx.clearRect(0, 0, size, size);\n      ctx.fillStyle = ink;\n      ctx.strokeStyle = ink;\n      ctx.lineCap = \"round\";\n\n      // Every dot, always: an X sits over its dot, and the dot is simply\n      // there again once it walks off.\n      const dot = gap * 0.13;\n      ctx.beginPath();\n      for (let r = 0; r < COUNT; r++) {\n        for (let c = 0; c < COUNT; c++) {\n          const x = margin + c * gap;\n          const y = margin + r * gap;\n          ctx.moveTo(x + dot, y);\n          ctx.arc(x, y, dot, 0, TAU);\n        }\n      }\n      ctx.fill();\n\n      // An X a little wider than the gap between dots, so it reads as a mark\n      // sitting on the grid rather than a dot that grew.\n      const arm = gap * 0.5;\n      const thick = gap * 0.36;\n      for (const w of walkers) {\n        const fx = margin + w.col * gap;\n        const fy = margin + w.row * gap;\n        const tx = margin + w.toCol * gap;\n        const ty = margin + w.toRow * gap;\n        const p = w.stepAt >= 0 ? clamp((t - w.stepAt) / STEP) : 0;\n        const dx = tx - fx;\n        const dy = ty - fy;\n        const len = Math.hypot(dx, dy) || 1;\n        // The body slides in the middle of the step.\n        const body = inOut(clamp((p - 0.2) / 0.6));\n        const cx = fx + dx * body;\n        const cy = fy + dy * body;\n        const grow = inOut(clamp((t - w.born) / GROW));\n\n        for (const [ax, ay] of ARMS) {\n          // Arms facing the way it's going set off first.\n          const lead = (ax * dx + ay * dy) / len;\n          const leave = ((1 - lead) / 2) * LAG;\n          const k = inOut(clamp((p - leave) / ARM_TRAVEL));\n          const tipX = fx + dx * k + ax * arm * grow;\n          const tipY = fy + dy * k + ay * arm * grow;\n          const reach = Math.hypot(tipX - cx, tipY - cy);\n          // Stretched arms thin out, as if the same ink were pulled longer,\n          // and thin most at the tip, so a reaching arm tapers to a point\n          // while a resting one is an even bar.\n          const stretch = Math.min(1, arm / Math.max(reach, 0.01));\n          const base = thick * (0.7 + 0.3 * stretch);\n          const tip = Math.max(gap * 0.05, thick * stretch ** 2);\n          // A gentle bow off the straight line towards the way the arm\n          // rests, so a pulled arm curves like a limb without hooking back\n          // on itself; at rest it lies on the line and the arm is straight.\n          const bx = (cx + tipX) / 2 + ax * arm * 0.2 * (1 - stretch) * grow;\n          const by = (cy + tipY) / 2 + ay * arm * 0.2 * (1 - stretch) * grow;\n          armPath(ctx, cx, cy, bx, by, tipX, tipY, base * grow, tip * grow);\n        }\n      }\n    };\n\n    const loop = () => {\n      const t = now();\n      update(t);\n      draw(t);\n      frame = visible ? requestAnimationFrame(loop) : 0;\n    };\n    const paint = () => {\n      if (!frame) draw(animate ? now() : 0);\n    };\n\n    resize();\n    paint();\n\n    const io = new IntersectionObserver(([entry]) => {\n      visible = entry.isIntersecting;\n      if (visible && animate && !frame) frame = requestAnimationFrame(loop);\n    });\n    if (animate) io.observe(canvas);\n    const ro = new ResizeObserver(() => {\n      resize();\n      paint();\n    });\n    ro.observe(canvas);\n    const mo = new MutationObserver(paint);\n    mo.observe(document.documentElement, { attributes: true, attributeFilter: [\"data-theme\", \"class\"] });\n    const media = matchMedia(\"(prefers-color-scheme: dark)\");\n    media.addEventListener(\"change\", paint);\n\n    const toLocal = (e: PointerEvent) => {\n      const rect = canvas.getBoundingClientRect();\n      // Layout size over drawn size, in case the field is shown scaled.\n      const k = size / rect.width;\n      return { x: (e.clientX - rect.left) * k, y: (e.clientY - rect.top) * k };\n    };\n    const onMove = (e: PointerEvent) => {\n      if (e.pointerType === \"touch\") return;\n      Object.assign(pointer, toLocal(e), { on: true });\n    };\n    const onLeave = () => {\n      pointer.on = false;\n    };\n    const onDown = (e: PointerEvent) => {\n      const p = toLocal(e);\n      const { margin, gap } = layout();\n      const col = Math.round((p.x - margin) / gap);\n      const row = Math.round((p.y - margin) / gap);\n      if (col < 0 || row < 0 || col >= COUNT || row >= COUNT) return;\n      const t = animate ? now() : -GROW;\n      if (!taken.has(key(col, row))) {\n        if (walkers.length >= MOST) {\n          // Full: the oldest one makes room.\n          const old = walkers.shift();\n          if (old) {\n            taken.delete(key(old.col, old.row));\n            if (old.stepAt >= 0) taken.delete(key(old.toCol, old.toRow));\n          }\n        }\n        place(col, row, t);\n      } else if (animate) {\n        // Poked: whoever is there scurries off at once.\n        const w = walkers.find((v) => v.col === col && v.row === row && v.stepAt < 0);\n        if (w) w.nextAt = t;\n      }\n      if (!animate) draw(0);\n    };\n\n    if (play === null) {\n      canvas.addEventListener(\"pointermove\", onMove);\n      canvas.addEventListener(\"pointerleave\", onLeave);\n      canvas.addEventListener(\"pointerdown\", onDown);\n    }\n    // The card's show is just the crawl; a hovered card animates, an idle\n    // one is a still picture.\n\n    return () => {\n      cancelAnimationFrame(frame);\n      io.disconnect();\n      ro.disconnect();\n      mo.disconnect();\n      media.removeEventListener(\"change\", paint);\n      canvas.removeEventListener(\"pointermove\", onMove);\n      canvas.removeEventListener(\"pointerleave\", onLeave);\n      canvas.removeEventListener(\"pointerdown\", onDown);\n    };\n  }, [play, reduceMotion]);\n\n  return (\n    <canvas\n      ref={canvasRef}\n      role=\"img\"\n      aria-label=\"A grid of dots where some dots are X's that crawl from dot to dot. They keep away from your pointer; click an empty dot to place a new one.\"\n      className={cn(\n        \"block aspect-square w-[420px] max-w-full touch-manipulation rounded-[28px] bg-muted text-foreground select-none\",\n        className,\n      )}\n    />\n  );\n}\n\nexport default function XWalkersDemo() {\n  return <XWalkers />;\n}\n"},{"path":"lib/preview-play.ts","type":"registry:lib","target":"lib/preview-play.ts","content":"\"use client\";\n\nimport { createContext, useContext } from \"react\";\n\n// Lets a demo know whether it's showing in an index card, and whether that\n// card is hovered or focused. Demos use it to act themselves out on hover:\n// a star button stars itself, a checkbox scribbles, and so on.\n//\n// null: not in a preview (the component's own page, or real use).\n// false: in a preview, at rest.\n// true: in a preview, being hovered or focused: play the show.\nexport const PreviewPlayContext = createContext<boolean | null>(null);\n\nexport function usePreviewPlay() {\n  return useContext(PreviewPlayContext);\n}\n"},{"path":"hooks/use-reduced-motion.ts","type":"registry:hook","target":"hooks/use-reduced-motion.ts","content":"\"use client\";\n\nimport { useSyncExternalStore } from \"react\";\n\n// Motion's useReducedMotion reads the media query on the very first client\n// render, but the server can't know it, so every component that renders\n// differently under reduced motion broke hydration for those users. This\n// reports false during hydration, matching the server HTML, then the real\n// preference straight after, and follows it if it changes.\nconst query = \"(prefers-reduced-motion: reduce)\";\n\nfunction subscribe(onChange: () => void) {\n  const media = window.matchMedia(query);\n  media.addEventListener(\"change\", onChange);\n  return () => media.removeEventListener(\"change\", onChange);\n}\n\nexport function useReducedMotion() {\n  return useSyncExternalStore(\n    subscribe,\n    () => window.matchMedia(query).matches,\n    () => false,\n  );\n}\n"}],"categories":["playground"],"docs":"From ui lab: https://lab.xevrion.dev/lab/x-walkers"}