06Light Shaft Background Fading Layer by Layer

<main class="stage">
<div class="d3 is-demo" id="d3Root" tabindex="0">
  <canvas class="d3__canvas" id="d3Canvas" width="480" height="300"></canvas>
  <p class="d3__caption">Several light-shaft layers are drawn with their opacity multiplied down by an exponential function of depth, so the near shaft stays crisp while the far one almost dissolves into the background</p>
</div>
</main>

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

.d3 {
  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;
  background: $stage-yellow;
  outline: none;
}

.d3__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.d3__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 78%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .78);
  color: #fff;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .d3__caption { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .d3 { cursor: default; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.d3 {
  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);
  background: #ffd23f;
  outline: none;
}

.d3__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.d3__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 78%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.78);
  color: #fff;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .d3__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .d3 {
    cursor: default;
  }
}

(function () {
  // 기법: 겹마다 깊이값(거리값)이 시간에 따라 완만히 흔들리고, shaftOpacityForDepth 가 그 깊이값에
  // LIGHT_SHAFT_DECAY 를 지수(exp)로 곱해 불투명도를 구한다 — 거리가 커질수록 불투명도가 기하급수로
  // 줄어 먼 겹은 배경에 거의 스며들고 가까운 겹만 선명하게 남는다.
  var root = document.getElementById('d3Root');
  var canvas = document.getElementById('d3Canvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var CALC_W = 160, CALC_H = 100;
  var SOURCE_X = CALC_W * 0.5, SOURCE_Y = -6;
  var SHAFT_LAYER_COUNT = 7;
  var LIGHT_SHAFT_DECAY = 0.42;
  var MAX_OPACITY = 0.62;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rnd = seedRand(429061);

  var shafts = [];
  for (var i = 0; i < SHAFT_LAYER_COUNT; i += 1) {
    shafts.push({
      angleBase: -0.62 + (1.24 / (SHAFT_LAYER_COUNT - 1)) * i,
      distanceBase: 1.1 + i * 0.62,
      swayRange: 0.6 + rnd() * 0.6,
      swaySpeed: 0.0013 + rnd() * 0.0011,
      phase: rnd() * Math.PI * 2,
      width: 8 + rnd() * 6,
      hue: i % 2 === 0 ? '90,60,170' : '40,30,110'
    });
  }

  function depthFor(shaft, t) {
    return shaft.distanceBase + Math.sin(t * shaft.swaySpeed + shaft.phase) * shaft.swayRange;
  }

  function shaftOpacityForDepth(depth) {
    var v = Math.exp(-LIGHT_SHAFT_DECAY * depth) * MAX_OPACITY;
    return Math.max(0, Math.min(MAX_OPACITY, v));
  }

  var elapsed = 0;
  var cw = 480, ch = 300;

  function drawScene(t) {
    var sx = cw / CALC_W, sy = ch / CALC_H;
    ctx.clearRect(0, 0, cw, ch);

    ctx.fillStyle = 'rgba(60,40,120,.55)';
    ctx.beginPath();
    ctx.arc(SOURCE_X * sx, SOURCE_Y * sy, 10 * sx, 0, Math.PI * 2);
    ctx.fill();

    ctx.globalCompositeOperation = 'lighter';
    for (var i = 0; i < shafts.length; i += 1) {
      var shaft = shafts[i];
      var depth = depthFor(shaft, t);
      var op = shaftOpacityForDepth(depth);
      var angle = shaft.angleBase + Math.sin(t * shaft.swaySpeed * 0.7 + shaft.phase) * 0.13;
      var length = 118 + depth * 6;
      var endX = SOURCE_X + Math.sin(angle) * length;
      var endY = SOURCE_Y + Math.cos(angle) * length;

      var grad = ctx.createLinearGradient(SOURCE_X * sx, SOURCE_Y * sy, endX * sx, endY * sy);
      grad.addColorStop(0, 'rgba(' + shaft.hue + ',' + op + ')');
      grad.addColorStop(1, 'rgba(' + shaft.hue + ',0)');

      var perpX = Math.cos(angle) * shaft.width;
      var perpY = -Math.sin(angle) * shaft.width;

      ctx.fillStyle = grad;
      ctx.beginPath();
      ctx.moveTo((SOURCE_X - perpX * 0.15) * sx, (SOURCE_Y - perpY * 0.15) * sy);
      ctx.lineTo((SOURCE_X + perpX * 0.15) * sx, (SOURCE_Y + perpY * 0.15) * sy);
      ctx.lineTo((endX + perpX) * sx, (endY + perpY) * sy);
      ctx.lineTo((endX - perpX) * sx, (endY - perpY) * sy);
      ctx.closePath();
      ctx.fill();
    }
    ctx.globalCompositeOperation = 'source-over';
  }

  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;
    drawScene(elapsed);
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (reduce) root.classList.remove('is-demo');

  var warmSteps = reduce ? 0 : 120;
  for (var w = 0; w < warmSteps; w += 1) elapsed += 20;

  var lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = Math.min(ts - lastTs, 48);
    lastTs = ts;
    if (!reduce) {
      elapsed += dt;
      drawScene(elapsed);
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  drawScene(elapsed);
  requestAnimationFrame(tick);
})();

import { useEffect, useRef } from "react";
import styles from "./Depth3dLightShaftDepth.module.scss";

type Shaft = {
  angleBase: number;
  distanceBase: number;
  swayRange: number;
  swaySpeed: number;
  phase: number;
  width: number;
  hue: string;
};

export default function Depth3dLightShaftDepth() {
  const rootRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);

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

    const CALC_W = 160, CALC_H = 100;
    const SOURCE_X = CALC_W * 0.5, SOURCE_Y = -6;
    const SHAFT_LAYER_COUNT = 7;
    const LIGHT_SHAFT_DECAY = 0.42;
    const MAX_OPACITY = 0.62;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const rnd = seedRand(429061);

    const shafts: Shaft[] = [];
    for (let i = 0; i < SHAFT_LAYER_COUNT; i += 1) {
      shafts.push({
        angleBase: -0.62 + (1.24 / (SHAFT_LAYER_COUNT - 1)) * i,
        distanceBase: 1.1 + i * 0.62,
        swayRange: 0.6 + rnd() * 0.6,
        swaySpeed: 0.0013 + rnd() * 0.0011,
        phase: rnd() * Math.PI * 2,
        width: 8 + rnd() * 6,
        hue: i % 2 === 0 ? "90,60,170" : "40,30,110"
      });
    }

    function depthFor(shaft: Shaft, t: number) {
      return shaft.distanceBase + Math.sin(t * shaft.swaySpeed + shaft.phase) * shaft.swayRange;
    }

    function shaftOpacityForDepth(depth: number) {
      const v = Math.exp(-LIGHT_SHAFT_DECAY * depth) * MAX_OPACITY;
      return Math.max(0, Math.min(MAX_OPACITY, v));
    }

    let elapsed = 0;
    let cw = 480, ch = 300;

    function drawScene(t: number) {
      const sx = cw / CALC_W, sy = ch / CALC_H;
      ctx!.clearRect(0, 0, cw, ch);

      ctx!.fillStyle = "rgba(60,40,120,.55)";
      ctx!.beginPath();
      ctx!.arc(SOURCE_X * sx, SOURCE_Y * sy, 10 * sx, 0, Math.PI * 2);
      ctx!.fill();

      ctx!.globalCompositeOperation = "lighter";
      for (let i = 0; i < shafts.length; i += 1) {
        const shaft = shafts[i];
        const depth = depthFor(shaft, t);
        const op = shaftOpacityForDepth(depth);
        const angle = shaft.angleBase + Math.sin(t * shaft.swaySpeed * 0.7 + shaft.phase) * 0.13;
        const length = 118 + depth * 6;
        const endX = SOURCE_X + Math.sin(angle) * length;
        const endY = SOURCE_Y + Math.cos(angle) * length;

        const grad = ctx!.createLinearGradient(SOURCE_X * sx, SOURCE_Y * sy, endX * sx, endY * sy);
        grad.addColorStop(0, `rgba(${shaft.hue},${op})`);
        grad.addColorStop(1, `rgba(${shaft.hue},0)`);

        const perpX = Math.cos(angle) * shaft.width;
        const perpY = -Math.sin(angle) * shaft.width;

        ctx!.fillStyle = grad;
        ctx!.beginPath();
        ctx!.moveTo((SOURCE_X - perpX * 0.15) * sx, (SOURCE_Y - perpY * 0.15) * sy);
        ctx!.lineTo((SOURCE_X + perpX * 0.15) * sx, (SOURCE_Y + perpY * 0.15) * sy);
        ctx!.lineTo((endX + perpX) * sx, (endY + perpY) * sy);
        ctx!.lineTo((endX - perpX) * sx, (endY - perpY) * sy);
        ctx!.closePath();
        ctx!.fill();
      }
      ctx!.globalCompositeOperation = "source-over";
    }

    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;
      drawScene(elapsed);
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (reduce) root.classList.remove("is-demo");

    const warmSteps = reduce ? 0 : 120;
    for (let w = 0; w < warmSteps; w += 1) elapsed += 20;

    let lastTs: number | null = null;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const dt = Math.min(ts - lastTs, 48);
      lastTs = ts;
      if (!reduce) {
        elapsed += dt;
        drawScene(elapsed);
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    drawScene(elapsed);
    raf = requestAnimationFrame(tick);

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

  return (
    <main className={styles.stage}>
      <div className={`${styles.d3} is-demo`} ref={rootRef} tabIndex={0}>
        <canvas className={styles.d3__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.d3__caption}>빛줄기 여러 겹을 그리고 각 겹의 불투명도를 거리값에 지수함수로 곱해 줄여, 가까운 겹은 선명하고 먼 겹은 배경에 거의 스며든다</p>
      </div>
    </main>
  );
}