07Posterized Gradient Bands

<main class="stage">
<div class="pv is-demo" id="pvRoot">
  <canvas class="pv__canvas" id="pvCanvas" width="480" height="300"></canvas>
  <p class="pv__caption">A background where a band-count value cuts a smooth gradient into color stripes</p>
  <p class="pv__step"><span id="bandLabel"></span><b id="bandVal">10</b></p>
  <input class="pv__range" id="bandRange" type="range" min="3" max="24" step="1" value="10" aria-label="band count">
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-paper);

.pv {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.pv__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.pv__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 72%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 247, 230, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

.pv__step {
  position: absolute;
  right: $sp-3;
  top: $sp-3;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 247, 230, .85);
  color: $subject-ink;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
  pointer-events: none;
}

.pv__range {
  position: absolute;
  left: $sp-3;
  top: $sp-3;
  width: 44%;
  margin: 0;
  accent-color: $subject-blue;
}

@media (max-width: 340px) {
  .pv__caption, .pv__step { font-size: 10px; padding: $sp-1 $sp-2; }
  .pv__range { width: 52%; }
}

@media (prefers-reduced-motion: reduce) {
  .pv { cursor: default; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.pv {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.pv__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.pv__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 72%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

.pv__step {
  position: absolute;
  right: 12px;
  top: 12px;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.85);
  color: #17141a;
  font-weight: 700;
  font-size: 11px;
  font-variant-numeric: tabular-nums;
  pointer-events: none;
}

.pv__range {
  position: absolute;
  left: 12px;
  top: 12px;
  width: 44%;
  margin: 0;
  accent-color: #2f6df6;
}

@media (max-width: 340px) {
  .pv__caption, .pv__step {
    font-size: 10px;
    padding: 4px 8px;
  }
  .pv__range {
    width: 52%;
  }
}
@media (prefers-reduced-motion: reduce) {
  .pv {
    cursor: default;
  }
}

(function () {
  // 기법: 대각선으로 흐르는 부드러운 무지개 hue 값을 posterizeHue() 로 PLASMA_BAND_COUNT 구간에
  // 맞춰 계단화한다 — Bands 수가 늘수록 띠가 가늘어지고 부드러운 그라데이션에 가까워진다.
  // 실제 입력: range 슬라이더로 Bands 수를 3~24 사이에서 즉시 바꿀 수 있다.
  var BAND_LABEL = 'Bands ';
  var root = document.getElementById('pvRoot');
  var canvas = document.getElementById('pvCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;
  var bandValEl = document.getElementById('bandVal');
  var bandLabelEl = document.getElementById('bandLabel');
  var bandRangeEl = document.getElementById('bandRange');
  bandLabelEl.textContent = BAND_LABEL;

  var CALC_W = 160, CALC_H = 100;
  var LOOP_MS = 2000;
  var PLASMA_BAND_COUNT = 10;

  function hslToRgb(h, s, l) {
    h = ((h % 360) + 360) % 360;
    var c = (1 - Math.abs(2 * l - 1)) * s;
    var x = c * (1 - Math.abs((h / 60) % 2 - 1));
    var m = l - c / 2;
    var r, g, b;
    if (h < 60) { r = c; g = x; b = 0; }
    else if (h < 120) { r = x; g = c; b = 0; }
    else if (h < 180) { r = 0; g = c; b = x; }
    else if (h < 240) { r = 0; g = x; b = c; }
    else if (h < 300) { r = x; g = 0; b = c; }
    else { r = c; g = 0; b = x; }
    return [(r + m) * 255, (g + m) * 255, (b + m) * 255];
  }

  var off = document.createElement('canvas');
  off.width = CALC_W; off.height = CALC_H;
  var octx = off.getContext('2d');
  var offImg = octx.createImageData(CALC_W, CALC_H);
  var offBuf = offImg.data;

  function posterizeHue(raw, bands) {
    var step = 360 / bands;
    return Math.floor(raw / step) * step + step / 2;
  }

  function renderField(t) {
    var diag = t * 0.03;
    var idx = 0;
    for (var y = 0; y < CALC_H; y += 1) {
      for (var x = 0; x < CALC_W; x += 1) {
        var raw = (x * 1.4 + y * 1.1 + diag) % 360;
        var hue = posterizeHue(raw, PLASMA_BAND_COUNT);
        var rgb = hslToRgb(hue, 0.68, 0.5);
        offBuf[idx] = rgb[0]; offBuf[idx + 1] = rgb[1]; offBuf[idx + 2] = rgb[2]; offBuf[idx + 3] = 255;
        idx += 4;
      }
    }
  }

  var cw = 480, ch = 300;
  function fit() {
    var r = wrap.getBoundingClientRect();
    cw = Math.max(1, Math.round(r.width));
    ch = Math.max(1, Math.round(r.height));
    canvas.width = cw; canvas.height = ch;
    draw(lastElapsed);
  }

  var lastElapsed = 0;
  function draw(elapsed) {
    lastElapsed = elapsed;
    renderField(elapsed);
    octx.putImageData(offImg, 0, 0);
    ctx.imageSmoothingEnabled = false;
    ctx.clearRect(0, 0, cw, ch);
    ctx.drawImage(off, 0, 0, CALC_W, CALC_H, 0, 0, cw, ch);
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var playing = !reduce;
  var elapsed = reduce ? LOOP_MS * 0.5 : 0;
  if (reduce) { root.classList.remove('is-demo'); }

  bandRangeEl.addEventListener('input', function () {
    PLASMA_BAND_COUNT = parseInt(bandRangeEl.value, 10);
    bandValEl.textContent = String(PLASMA_BAND_COUNT);
    draw(lastElapsed);
  });

  var lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = ts - lastTs;
    lastTs = ts;
    if (playing) {
      elapsed += dt;
      if (elapsed >= LOOP_MS) elapsed -= LOOP_MS;
    }
    draw(elapsed);
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  draw(elapsed);
  requestAnimationFrame(tick);
})();

import { useEffect, useRef } from "react";
import styles from "./PlasmaGradientBandPosterize.module.scss";

export default function PlasmaGradientBandPosterize() {
  const rootRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const bandLabelRef = useRef<HTMLSpanElement>(null);
  const bandValRef = useRef<HTMLElement>(null);
  const bandRangeRef = useRef<HTMLInputElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    const bandLabelEl = bandLabelRef.current;
    const bandValEl = bandValRef.current;
    const bandRangeEl = bandRangeRef.current;
    if (!root || !canvas || !bandLabelEl || !bandValEl || !bandRangeEl) return;
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
    const wrap = canvas.parentElement as HTMLElement;

    const BAND_LABEL = "구간 ";
    bandLabelEl.textContent = BAND_LABEL;

    const CALC_W = 160, CALC_H = 100;
    const LOOP_MS = 2000;
    let PLASMA_BAND_COUNT = 10;

    function hslToRgb(h: number, s: number, l: number): [number, number, number] {
      h = ((h % 360) + 360) % 360;
      const c = (1 - Math.abs(2 * l - 1)) * s;
      const x = c * (1 - Math.abs(((h / 60) % 2) - 1));
      const m = l - c / 2;
      let r = 0, g = 0, b = 0;
      if (h < 60) { r = c; g = x; b = 0; }
      else if (h < 120) { r = x; g = c; b = 0; }
      else if (h < 180) { r = 0; g = c; b = x; }
      else if (h < 240) { r = 0; g = x; b = c; }
      else if (h < 300) { r = x; g = 0; b = c; }
      else { r = c; g = 0; b = x; }
      return [(r + m) * 255, (g + m) * 255, (b + m) * 255];
    }

    const off = document.createElement("canvas");
    off.width = CALC_W; off.height = CALC_H;
    const octx = off.getContext("2d") as CanvasRenderingContext2D;
    const offImg = octx.createImageData(CALC_W, CALC_H);
    const offBuf = offImg.data;

    function posterizeHue(raw: number, bands: number) {
      const step = 360 / bands;
      return Math.floor(raw / step) * step + step / 2;
    }

    function renderField(t: number) {
      const diag = t * 0.03;
      let idx = 0;
      for (let y = 0; y < CALC_H; y += 1) {
        for (let x = 0; x < CALC_W; x += 1) {
          const raw = (x * 1.4 + y * 1.1 + diag) % 360;
          const hue = posterizeHue(raw, PLASMA_BAND_COUNT);
          const rgb = hslToRgb(hue, 0.68, 0.5);
          offBuf[idx] = rgb[0]; offBuf[idx + 1] = rgb[1]; offBuf[idx + 2] = rgb[2]; offBuf[idx + 3] = 255;
          idx += 4;
        }
      }
    }

    let cw = 480, ch = 300;
    function fit() {
      const r = wrap.getBoundingClientRect();
      cw = Math.max(1, Math.round(r.width));
      ch = Math.max(1, Math.round(r.height));
      canvas!.width = cw; canvas!.height = ch;
      draw(lastElapsed);
    }

    let lastElapsed = 0;
    function draw(elapsed: number) {
      lastElapsed = elapsed;
      renderField(elapsed);
      octx.putImageData(offImg, 0, 0);
      ctx!.imageSmoothingEnabled = false;
      ctx!.clearRect(0, 0, cw, ch);
      ctx!.drawImage(off, 0, 0, CALC_W, CALC_H, 0, 0, cw, ch);
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let playing = !reduce;
    let elapsed = reduce ? LOOP_MS * 0.5 : 0;
    if (reduce) { root.classList.remove("is-demo"); }

    function onRangeInput() {
      PLASMA_BAND_COUNT = parseInt(bandRangeEl!.value, 10);
      bandValEl!.textContent = String(PLASMA_BAND_COUNT);
      draw(lastElapsed);
    }
    bandRangeEl.addEventListener("input", onRangeInput);

    let lastTs: number | null = null;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const dt = ts - lastTs;
      lastTs = ts;
      if (playing) {
        elapsed += dt;
        if (elapsed >= LOOP_MS) elapsed -= LOOP_MS;
      }
      draw(elapsed);
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    draw(elapsed);
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
      bandRangeEl.removeEventListener("input", onRangeInput);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.pv} is-demo`} ref={rootRef}>
        <canvas className={styles.pv__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.pv__caption}>구간 수 값이 부드러운 색을 띠 모양으로 끊어내는 배경</p>
        <p className={styles.pv__step}>
          <span ref={bandLabelRef} />
          <b ref={bandValRef}>10</b>
        </p>
        <input
          className={styles.pv__range}
          ref={bandRangeRef}
          type="range"
          min={3}
          max={24}
          step={1}
          defaultValue={10}
          aria-label="band count"
        />
      </div>
    </main>
  );
}