Split Screen Reveal

:root {
  --bg: #040913;
  --bg-soft: #091a35;
  --text: #edf4ff;
  --muted: #b5c8e8;
  --line: rgba(178, 203, 244, 0.24);
  --accent-cyan: #86e7ff;
  --accent-blue: #4f7fff;
  --accent-gold: #ffbe78;
  --split-progress: 0;
  --split-reveal: 8%;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
}

body {
  font-family: "Sora", "Avenir Next", "Segoe UI", sans-serif;
  color: var(--text);
  background: radial-gradient(circle at 9% 8%, rgba(134, 231, 255, 0.11), transparent 34%),
    radial-gradient(circle at 88% 86%, rgba(255, 190, 120, 0.1), transparent 38%),
    linear-gradient(180deg, #061025 0%, var(--bg) 64%);
  overflow-x: clip;
}

.back {
  position: fixed;
  left: 14px;
  top: 12px;
  z-index: 35;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  border-radius: 999px;
  border: 1px solid rgba(255, 255, 255, 0.22);
  padding: 0.38rem 0.7rem;
  color: #dff0ff;
  background: rgba(7, 14, 28, 0.72);
  text-decoration: none;
  font-size: 0.78rem;
  font-weight: 600;
  backdrop-filter: blur(8px);
}

.scroll-track {
  min-height: 280vh;
}

.sticky-shell {
  position: sticky;
  top: 0;
  height: 100vh;
  display: grid;
  grid-template-columns: minmax(320px, 1fr) minmax(320px, 1fr);
}

.panel {
  min-height: 100vh;
  position: relative;
}

.left-panel {
  padding: clamp(4.2rem, 8vw, 5.6rem) clamp(1.1rem, 4vw, 3.2rem) clamp(2rem, 4vw, 3rem);
  border-right: 1px solid rgba(255, 255, 255, 0.08);
  background: linear-gradient(120deg, rgba(10, 28, 57, 0.9), rgba(6, 16, 33, 0.9)),
    linear-gradient(180deg, rgba(255, 255, 255, 0.04), transparent 58%);
  display: grid;
  align-content: start;
  gap: 1.15rem;
}

.eyebrow {
  margin: 0;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: #c5ddfc;
  font-size: 0.72rem;
}

.left-panel h1 {
  margin: 0;
  font-size: clamp(2rem, 5.6vw, 3.8rem);
  line-height: 0.95;
  letter-spacing: -0.02em;
}

.lead {
  margin: 0;
  max-width: 52ch;
  color: var(--muted);
  line-height: 1.62;
}

.progress-wrap {
  margin-top: 0.2rem;
  display: grid;
  gap: 0.52rem;
}

.progress-bar {
  width: min(480px, 100%);
  height: 9px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.11);
  border: 1px solid rgba(255, 255, 255, 0.18);
  overflow: hidden;
}

.progress-fill {
  display: block;
  height: 100%;
  width: var(--split-reveal);
  min-width: 8%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--accent-cyan), var(--accent-blue), var(--accent-gold));
  box-shadow: 0 0 16px rgba(134, 231, 255, 0.55);
  transition: width 140ms linear;
}

.progress-label {
  margin: 0;
  color: #d0e2fb;
  font-size: 0.88rem;
}

#progressLabel {
  font-weight: 700;
  color: #f7fbff;
}

.story-steps {
  list-style: none;
  padding: 0;
  margin: 0.2rem 0 0;
  display: grid;
  gap: 0.62rem;
}

.story-step {
  border-radius: 14px;
  border: 1px solid var(--line);
  background: rgba(12, 26, 50, 0.56);
  padding: 0.75rem 0.8rem;
  opacity: 0.62;
  transform: translateX(0);
  transition: opacity 260ms ease, border-color 260ms ease, transform 260ms ease, background 260ms
    ease;
}

.story-step.active {
  opacity: 1;
  border-color: rgba(134, 231, 255, 0.46);
  background: rgba(16, 33, 63, 0.86);
  transform: translateX(4px);
}

.story-step h2 {
  margin: 0;
  font-size: 0.95rem;
}

.story-step p {
  margin: 0.35rem 0 0;
  color: var(--muted);
  line-height: 1.45;
  font-size: 0.83rem;
}

.right-panel {
  background: linear-gradient(165deg, #101f3f, #0a1730 62%, #081426);
  overflow: hidden;
}

.right-mask {
  position: absolute;
  inset: 0;
  clip-path: inset(0 calc(100% - var(--split-reveal)) 0 0);
  transition: clip-path 130ms linear;
  border-left: 1px solid rgba(255, 255, 255, 0.08);
}

.right-atmosphere {
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.blob {
  position: absolute;
  border-radius: 999px;
  filter: blur(30px);
  opacity: 0.42;
}

.blob-a {
  width: 240px;
  height: 240px;
  top: 10%;
  left: 14%;
  background: rgba(134, 231, 255, 0.44);
}

.blob-b {
  width: 300px;
  height: 300px;
  top: 45%;
  left: 46%;
  background: rgba(79, 127, 255, 0.34);
}

.blob-c {
  width: 220px;
  height: 220px;
  top: 62%;
  left: 10%;
  background: rgba(255, 190, 120, 0.28);
}

.blob-d {
  width: 170px;
  height: 170px;
  top: 24%;
  left: 68%;
  background: rgba(190, 150, 255, 0.26);
}

.right-content {
  position: relative;
  z-index: 2;
  height: 100%;
  padding: clamp(4.1rem, 7vw, 5.2rem) clamp(1rem, 4vw, 2.4rem) 2.2rem;
  display: grid;
  gap: 1rem;
  align-content: start;
  opacity: calc(0.5 + (var(--split-progress) * 0.5));
  transform: translate3d(
    calc((1 - var(--split-progress)) * 30px),
    calc((1 - var(--split-progress)) * 10px),
    0
  );
  transition: transform 220ms linear, opacity 220ms linear;
}

.board-head {
  display: grid;
  gap: 0.48rem;
}

.board-kicker {
  margin: 0;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  font-size: 0.7rem;
  color: #cbe4ff;
}

.board-head h2 {
  margin: 0;
  font-size: clamp(1.35rem, 3vw, 2.2rem);
}

.board-head p {
  margin: 0;
  color: var(--muted);
  line-height: 1.55;
}

.board-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.62rem;
}

.tile {
  border-radius: 15px;
  border: 1px solid var(--line);
  background: rgba(8, 17, 34, 0.62);
  padding: 0.72rem;
  display: grid;
  gap: 0.44rem;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.04);
  transform: translateY(calc((1 - var(--split-progress)) * 12px));
  transition: transform 220ms linear, border-color 220ms linear;
}

.tile:hover {
  border-color: rgba(134, 231, 255, 0.48);
}

.tile-large {
  grid-column: 1 / -1;
}

.tile-label {
  margin: 0;
  color: #9fd5ff;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-size: 0.67rem;
}

.tile h3 {
  margin: 0;
  font-size: 1rem;
}

.tile p {
  margin: 0;
  color: var(--muted);
  font-size: 0.84rem;
  line-height: 1.48;
}

.reveal-line {
  position: absolute;
  top: 0;
  left: calc(var(--split-reveal) * 1);
  width: 2px;
  height: 100%;
  background: linear-gradient(
    180deg,
    rgba(134, 231, 255, 0),
    rgba(134, 231, 255, 0.85),
    rgba(134, 231, 255, 0)
  );
  box-shadow: 0 0 18px rgba(134, 231, 255, 0.66);
  pointer-events: none;
}

.reveal-line::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 10px;
  height: 10px;
  transform: translate(-50%, -50%);
  border-radius: 50%;
  background: #d2f6ff;
  box-shadow: 0 0 18px rgba(134, 231, 255, 0.9);
}

html.global-reduce-motion .progress-fill,
html.global-reduce-motion .right-mask,
html.global-reduce-motion .story-step,
html.global-reduce-motion .right-content,
html.global-reduce-motion .tile {
  transition: none !important;
}

@media (max-width: 1000px) {
  .sticky-shell {
    grid-template-columns: 1fr;
    position: relative;
    height: auto;
  }

  .scroll-track {
    min-height: 100%;
  }

  .panel {
    min-height: auto;
  }

  .left-panel {
    border-right: 0;
    min-height: 68vh;
    padding-top: 4.8rem;
  }

  .right-panel {
    min-height: 74vh;
  }

  .right-mask {
    clip-path: none;
    border-left: 0;
  }

  .reveal-line {
    display: none;
  }

  .right-content,
  .tile {
    opacity: 1;
    transform: none;
  }
}

@media (max-width: 640px) {
  .board-grid {
    grid-template-columns: 1fr;
  }

  .tile-large {
    grid-column: auto;
  }
}

if (!window.MotionPreference) {
  const __mql = window.matchMedia("(prefers-reduced-motion: reduce)");
  const __listeners = new Set();

  const MotionPreference = {
    prefersReducedMotion() {
      return __mql.matches;
    },
    setOverride(value) {
      const reduced = Boolean(value);
      document.documentElement.classList.toggle("reduced-motion", reduced);
      window.dispatchEvent(new CustomEvent("motion-preference", { detail: { reduced } }));
      for (const listener of __listeners) {
        try {
          listener({ reduced, override: reduced, systemReduced: __mql.matches });
        } catch {}
      }
    },
    onChange(listener) {
      __listeners.add(listener);
      try {
        listener({
          reduced: __mql.matches,
          override: null,
          systemReduced: __mql.matches,
        });
      } catch {}
      return () => __listeners.delete(listener);
    },
    getState() {
      return { reduced: __mql.matches, override: null, systemReduced: __mql.matches };
    },
  };

  window.MotionPreference = MotionPreference;
}

const root = document.documentElement;
const track = document.getElementById("track");
const progressBar = document.getElementById("progressBar");
const progressLabel = document.getElementById("progressLabel");
const storySteps = Array.from(document.querySelectorAll(".story-step"));
const mobileQuery = window.matchMedia("(max-width: 1000px)");

const state = {
  reduced: Boolean(window.MotionPreference && window.MotionPreference.prefersReducedMotion()),
  mobile: mobileQuery.matches,
  raf: 0,
};

const thresholds = [0, 0.36, 0.72];

function clamp(value, min, max) {
  return Math.min(max, Math.max(min, value));
}

function getScrollProgress() {
  const rect = track.getBoundingClientRect();
  const distance = rect.height - window.innerHeight;
  if (distance <= 0) return 1;
  return clamp(-rect.top / distance, 0, 1);
}

function applyStepState(progress) {
  let activeIndex = 0;
  if (progress >= thresholds[2]) {
    activeIndex = 2;
  } else if (progress >= thresholds[1]) {
    activeIndex = 1;
  }

  storySteps.forEach((step, index) => {
    step.classList.toggle("active", index <= activeIndex);
  });
}

function render() {
  state.raf = 0;
  const progress = state.reduced || state.mobile ? 1 : getScrollProgress();
  const reveal = 8 + progress * 92;
  const revealText = `${Math.round(reveal)}%`;

  root.style.setProperty("--split-progress", progress.toFixed(4));
  root.style.setProperty("--split-reveal", `${reveal.toFixed(2)}%`);

  progressLabel.textContent = revealText;
  progressBar.setAttribute("aria-valuenow", String(Math.round(reveal)));
  progressBar.setAttribute("aria-valuetext", `Reveal progress ${Math.round(reveal)} percent`);

  applyStepState(progress);
}

function scheduleRender() {
  if (state.raf) return;
  state.raf = window.requestAnimationFrame(render);
}

if (mobileQuery.addEventListener) {
  mobileQuery.addEventListener("change", (event) => {
    state.mobile = event.matches;
    scheduleRender();
  });
} else if (mobileQuery.addListener) {
  mobileQuery.addListener((event) => {
    state.mobile = event.matches;
    scheduleRender();
  });
}

if (window.MotionPreference && window.MotionPreference.onChange) {
  window.MotionPreference.onChange((next) => {
    state.reduced = Boolean(next.reduced);
    scheduleRender();
  });
}

window.addEventListener("scroll", scheduleRender, { passive: true });
window.addEventListener("resize", scheduleRender);
scheduleRender();

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Demo 08 - Split Screen Reveal</title>
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <a class="back" href="../">Back to Demos</a>

    <main class="scroll-track" id="track">
      <section class="sticky-shell" aria-label="Split screen reveal stage">
        <article class="panel left-panel">
          <p class="eyebrow">Demo 08 · Scroll + Clip Path</p>
          <h1>Split Screen Reveal</h1>
          <p class="lead">
            Scroll through the timeline to expose the concept panel on the right. This version is designed as a
            presentation-ready layout, not just a raw clip-path test.
          </p>

          <div class="progress-wrap" aria-label="Reveal progress">
            <div
              class="progress-bar"
              role="progressbar"
              aria-valuemin="0"
              aria-valuemax="100"
              aria-valuenow="8"
              aria-valuetext="Reveal progress 8 percent"
              id="progressBar"
            >
              <span class="progress-fill" id="progressFill"></span>
            </div>
            <p class="progress-label"><span id="progressLabel">8%</span> exposed</p>
          </div>

          <ol class="story-steps">
            <li class="story-step active" data-step="0">
              <h2>Stage 1 · Framing</h2>
              <p>Introduce context with a stable reading zone while the visual side stays partially hidden.</p>
            </li>
            <li class="story-step" data-step="1">
              <h2>Stage 2 · Reveal</h2>
              <p>Mid-scroll opens the composition grid and spotlight cards to build momentum.</p>
            </li>
            <li class="story-step" data-step="2">
              <h2>Stage 3 · Full Composition</h2>
              <p>End state exposes the full board and callout stack for final messaging.</p>
            </li>
          </ol>
        </article>

        <article class="panel right-panel">
          <div class="right-mask" id="rightMask">
            <div class="right-atmosphere" aria-hidden="true">
              <span class="blob blob-a"></span>
              <span class="blob blob-b"></span>
              <span class="blob blob-c"></span>
              <span class="blob blob-d"></span>
            </div>

            <div class="right-content">
              <header class="board-head">
                <p class="board-kicker">Concept Board</p>
                <h2>Original Concepts Only</h2>
                <p>Modular sections, motion-safe defaults, and clear hierarchy for showcase presentations.</p>
              </header>

              <section class="board-grid" aria-label="Concept modules">
                <article class="tile tile-large">
                  <p class="tile-label">Hero Module</p>
                  <h3>Cinematic Intro Block</h3>
                  <p>Headline rhythm, ambient backdrop, and CTA choreography tuned for fast comprehension.</p>
                </article>
                <article class="tile">
                  <p class="tile-label">Feature A</p>
                  <h3>Split Narrative</h3>
                  <p>Copy and visuals remain legible while reveal transitions continue.</p>
                </article>
                <article class="tile">
                  <p class="tile-label">Feature B</p>
                  <h3>Motion Safe</h3>
                  <p>Reduced-motion users receive static composition without losing content.</p>
                </article>
                <article class="tile">
                  <p class="tile-label">Feature C</p>
                  <h3>Presentation Mode</h3>
                  <p>Large contrast-safe blocks and compact card metadata for live demos.</p>
                </article>
              </section>
            </div>
          </div>
          <span class="reveal-line" id="revealLine" aria-hidden="true"></span>
        </article>
      </section>
    </main>

    <script src="script.js"></script>
    </body>
</html>