Sampling Explainer

"use client"

import * as React from "react"
import { SamplingExplainer, SamplingSettings } from "@/components/ui/sampling-explainer"

const reducedMotion = () => window.matchMedia("(prefers-reduced-motion: reduce)").matches

/**
 * Settings along a slow loop: temperature swings from focused to wild while top P closes
 * and opens, so the next token's chances keep reshaping. Drag either slider and the tour waits.
 */
function tour(t: number): SamplingSettings {
  const phase = (t / 4200) * Math.PI * 2
  const temperature = 1.3 - 0.75 * Math.cos(phase)
  const topP = 0.82 + 0.17 * Math.cos(phase * 0.5 + 0.6)
  return {
    temperature: Math.round(temperature * 100) / 100,
    topP: Math.round(Math.min(1, Math.max(0.3, topP)) * 100) / 100,
  }
}

const FIT_CSS = "html,body{overflow:hidden}[data-fit-small] [data-fit-hide]{display:none!important}"

/**
 * 21st shows a demo in a small frame: about 674 by 421 on a component page, 358 by 224 on a
 * phone and 245 by 139 on a profile card. A demo taller than its frame gets scrollbars, which
 * render white on dark pages. FitFrame fills the frame exactly instead.
 *
 * - "scale": the content shrinks until it fits, centered. For visuals such as orbs.
 * - "crop": the content stays at full size from the top and fades out at the bottom. For text
 *   that streams in, where a changing scale would make the page breathe.
 *
 * `minWidth` lays out a wide demo (a table, a two column panel) at that width and scales it down
 * to the frame, instead of letting it collapse to a narrow layout. The frame centers it, so it
 * shrinks evenly on both sides.
 *
 * Anything marked `data-fit-hide` (state buttons, the chatcn.dev line) drops out in frames
 * shorter than `hideBelow`, so a profile card shows the visual alone.
 */
function FitFrame({
  children,
  mode = "scale",
  hideBelow = 360,
  minWidth,
}: {
  children: React.ReactNode
  mode?: "scale" | "crop"
  hideBelow?: number
  minWidth?: string
}) {
  const content = React.useRef<HTMLDivElement>(null)
  const [cropped, setCropped] = React.useState(false)

  React.useLayoutEffect(() => {
    const el = content.current
    if (!el) return
    const measure = () => {
      const vw = window.innerWidth
      const vh = window.innerHeight
      el.toggleAttribute("data-fit-small", vh < hideBelow)
      // Layout sizes ignore the transform, so measuring never feeds back.
      const w = Math.max(el.offsetWidth, el.scrollWidth)
      const h = Math.max(el.offsetHeight, el.scrollHeight)
      const scale = mode === "scale" ? Math.min(1, vw / w, vh / h) : 1
      el.style.transform = scale < 1 ? `scale(${scale})` : ""
      setCropped(mode === "crop" && h > vh + 1)
    }
    measure()
    const observer = new ResizeObserver(measure)
    observer.observe(el)
    // Content that changes inside a fixed width box (a headline that cycles words) never resizes
    // the box itself, so changes below it measure again on the next frame.
    let frame = 0
    const mutations = new MutationObserver(() => {
      cancelAnimationFrame(frame)
      frame = requestAnimationFrame(measure)
    })
    mutations.observe(el, { subtree: true, childList: true, characterData: true })
    window.addEventListener("resize", measure)
    return () => {
      observer.disconnect()
      mutations.disconnect()
      cancelAnimationFrame(frame)
      window.removeEventListener("resize", measure)
    }
  }, [mode, hideBelow])

  const fade = "linear-gradient(to bottom, #000 calc(100% - 40px), transparent)"
  return (
    <div
      className="flex w-full justify-center overflow-hidden"
      style={{
        height: "100dvh",
        alignItems: mode === "crop" ? "flex-start" : "center",
        maskImage: cropped ? fade : undefined,
        WebkitMaskImage: cropped ? fade : undefined,
      }}
    >
      <style>{FIT_CSS}</style>
      <div
        ref={content}
        className="w-full shrink-0"
        style={{ transformOrigin: mode === "crop" ? "top center" : "center", minWidth }}
      >
        {children}
      </div>
    </div>
  )
}

const CANDIDATES = [
  { token: " Canberra", logit: 8.2 },
  { token: " Sydney", logit: 6.1 },
  { token: " Melbourne", logit: 5.3 },
  { token: " located", logit: 4.4 },
  { token: " a", logit: 3.9 },
  { token: " the", logit: 3.6 },
  { token: " not", logit: 2.7 },
  { token: " Perth", logit: 2.1 },
]

/** How long a choice holds a tour before it carries on. */
const RESUME_MS = 5000

/** The line under each 21st demo that points back to the kit. */
function MoreOn({ slug, children }: { slug: string; children: React.ReactNode }) {
  return (
    <p data-fit-hide className="text-[0.75rem]/[1rem] text-(color:--chatcn-fg-faint) text-center text-balance">
      {children}{" "}
      <a
        href={`https://chatcn.dev/docs/components/${slug}`}
        target="_blank"
        rel="noopener"
        className="text-(color:--chatcn-fg-subtle) hover:text-(color:--chatcn-fg) underline underline-offset-2"
      >
        chatcn.dev
      </a>
    </p>
  )
}

export default function SamplingExplainerPreview() {
  const [value, setValue] = React.useState<SamplingSettings>({ temperature: 1.2, topP: 0.9 })
  // Dragging a slider holds the tour for a few seconds.
  const heldUntil = React.useRef(0)
  React.useEffect(() => {
    if (reducedMotion()) return
    const began = performance.now()
    const id = window.setInterval(() => {
      if (performance.now() > heldUntil.current) setValue(tour(performance.now() - began + 1050))
    }, 50)
    return () => window.clearInterval(id)
  }, [])
  return (
    <FitFrame minWidth="46rem">
      <div className="flex w-full flex-col items-center justify-center gap-6 p-6">
        <SamplingExplainer
          className="max-w-4xl"
          context="The capital of Australia is"
          candidates={CANDIDATES}
          value={value}
          onValueChange={(next) => {
            heldUntil.current = performance.now() + RESUME_MS
            setValue(next)
          }}
        />
        <MoreOn slug="sampling-explainer">
          Temperature and top P on real logits, with draws you can sample. On
        </MoreOn>
      </div>
    </FitFrame>
  )
}