scroll-world.js

/*
 * Complide Enterprise — scroll-world engine.
 *
 * True scroll-world technique: one continuous generated camera-flight video
 * (5 Veo dive-in clips joined by first/last-frame connector clips, so every
 * seam is frame-identical — no cuts). Scroll position only drives time: the
 * video is encoded scrub-friendly and its currentTime is scrubbed by a
 * lerped scroll progress.
 *
 * If the flight video is missing or fails, the engine falls back to the
 * still-image mode: exponential zoom-through + crossfade connectors built
 * from the same diorama stills.
 */
(function () {
  "use strict";

  var scenes = Array.prototype.slice.call(document.querySelectorAll(".scene"));
  var cards = Array.prototype.slice.call(document.querySelectorAll(".card"));
  var dots = Array.prototype.slice.call(document.querySelectorAll(".rail__dots li"));
  var rail = document.querySelector(".rail");
  var railFill = document.getElementById("railFill");
  var spacer = document.getElementById("worldSpacer");
  var world = document.getElementById("world");
  var video = document.getElementById("flightVideo");

  var N = scenes.length;
  var SCENE_VH = 2.2;      // scroll length per scene, in viewport heights
  var TAIL_VH = 0.4;       // extra runway after the last scene

  // Segment layout of flight.mp4 (written by tools/assemble_flight.sh).
  // Dives carry the copy cards; connectors are the in-between flights.
  var TIMELINE = window.FLIGHT_TIMELINE || null;

  var reducedMotion = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  var LERP = reducedMotion ? 1 : 0.1;

  var scrollLen = 1;
  var target = 0;
  var current = 0;
  var videoMode = false;
  var duration = 0;

  // A scrollTo we issue ourselves (autoplay, or a nav jump) must not be read
  // back as the reader taking control — set right before the call, cleared by
  // the very next 'scroll' event it produces.
  var programmaticScroll = false;

  scenes.forEach(function (s, i) { s.style.zIndex = String(N - i); });

  /* ── shared helpers ─────────────────────────────────────────────────── */

  var clamp01 = function (v) { return Math.min(1, Math.max(0, v)); };
  var easeInCubic = function (t) { return t * t * t; };
  var easeOutCubic = function (t) { return 1 - Math.pow(1 - t, 3); };

  function layout() {
    scrollLen = Math.max(1, (N * SCENE_VH + TAIL_VH) * window.innerHeight);
    spacer.style.height = scrollLen + "px";
    readScroll();
    current = target;
    render(current);
  }

  function readScroll() {
    var max = Math.max(1, spacer.offsetTop + scrollLen - window.innerHeight);
    target = clamp01(window.scrollY / max);
  }

  /* ── video mode ─────────────────────────────────────────────────────── */

  // Maps global progress → [segment index, local t within segment].
  // Scroll is distributed over segments proportionally to their duration.
  function segmentAt(p) {
    var t = p * duration;
    for (var i = 0; i < TIMELINE.length; i++) {
      if (t <= TIMELINE[i].end || i === TIMELINE.length - 1) {
        var seg = TIMELINE[i];
        return { seg: seg, i: i, local: clamp01((t - seg.start) / (seg.end - seg.start)) };
      }
    }
  }

  function renderVideo(p) {
    var t = p * duration;
    // Never seek to the exact end (some browsers show a black frame there).
    if (video.readyState >= 1) video.currentTime = Math.min(t, duration - 0.05);

    var pos = segmentAt(p);
    var isDive = pos.seg.name.indexOf("dive_") === 0;
    var sceneIdx = isDive ? Math.floor(pos.i / 2) : Math.floor((pos.i + 1) / 2);

    // Cards live inside dive segments: in after 10%, out by 80%.
    for (var i = 0; i < N; i++) {
      var card = cards[i];
      var o = 0, y = 30;
      if (isDive && Math.floor(pos.i / 2) === i) {
        var lt = pos.local;
        var fadeIn = i === 0 && p < 0.002 ? 1 : clamp01(lt / 0.12);
        var fadeOut = 1 - clamp01((lt - 0.72) / 0.16);
        o = Math.min(fadeIn, fadeOut);
        y = 30 * (1 - fadeIn) - 60 * (1 - fadeOut);
      }
      card.style.opacity = o.toFixed(4);
      card.style.transform = "translate(0, calc(-50% + " + y.toFixed(1) + "px))";
      card.classList.toggle("is-live", o > 0.5);
    }

    updateChrome(p, sceneIdx);
  }

  /* ── still-image fallback mode ──────────────────────────────────────── */

  var ZOOM_THROUGH = 3.1;
  var UNDER = 0.68;
  var CF = 0.22;

  function renderStills(p) {
    var seg = 1 / N;

    for (var i = 0; i < N; i++) {
      var scene = scenes[i];
      var img = scene.firstElementChild;
      var isLast = i === N - 1;
      var t = (p - i * seg) / seg;

      if (t <= -CF || t >= 1 + (isLast ? 1 : 0.0001)) {
        if (scene.style.opacity !== "0") scene.style.opacity = "0";
        continue;
      }

      var scale, opacity, blur = 0;
      if (t < 0) {
        var k = easeOutCubic(clamp01((t + CF) / CF));
        scale = UNDER + (1 - UNDER) * k;
        opacity = k;
      } else {
        var tt = clamp01(isLast ? Math.min(t, 0.72) : t);
        scale = Math.exp(Math.log(ZOOM_THROUGH) * easeInCubic(tt));
        if (!isLast && t > 1 - CF) {
          var k2 = clamp01((t - (1 - CF)) / CF);
          opacity = 1 - k2;
          blur = 6 * k2;
        } else {
          opacity = 1;
        }
      }

      scene.style.opacity = opacity.toFixed(4);
      img.style.transform = "scale(" + scale.toFixed(5) + ")";
      scene.style.filter = blur > 0.05 ? "blur(" + blur.toFixed(2) + "px)" : "none";
    }

    for (var j = 0; j < N; j++) {
      var card = cards[j];
      var t2 = (p - j * seg) / seg;
      var o = 0, y = 30;
      if (t2 >= -0.02 && t2 <= 0.86) {
        var fadeIn = j === 0 && p < 0.002 ? 1 : clamp01(t2 / 0.04);
        var fadeOut = 1 - clamp01((t2 - 0.72) / 0.14);
        o = Math.min(fadeIn, fadeOut);
        y = 30 * (1 - fadeIn) - 60 * (1 - fadeOut);
      }
      card.style.opacity = o.toFixed(4);
      card.style.transform = "translate(0, calc(-50% + " + y.toFixed(1) + "px))";
      card.classList.toggle("is-live", o > 0.5);
    }

    updateChrome(p, Math.min(N - 1, Math.floor(p * N)));
  }

  /* ── shared chrome (rail, visibility) ───────────────────────────────── */

  function updateChrome(p, sceneIdx) {
    railFill.style.height = (p * 100).toFixed(2) + "%";
    dots.forEach(function (d, i) { d.classList.toggle("is-active", i === sceneIdx); });
    rail.classList.toggle("is-visible", p > 0.01 && p < 0.995);
    world.style.visibility = p >= 1 && window.scrollY > scrollLen ? "hidden" : "visible";
  }

  function render(p) {
    if (videoMode) renderVideo(p); else renderStills(p);
  }

  function tick() {
    current += (target - current) * LERP;
    if (Math.abs(target - current) < 0.00005) current = target;
    render(current);
    requestAnimationFrame(tick);
  }

  /* ── boot: use the flight video when available ──────────────────────── */

  function enableVideoMode() {
    duration = TIMELINE[TIMELINE.length - 1].end;
    videoMode = true;
    world.classList.add("world--video");
    render(current);
  }

  if (video && TIMELINE) {
    // Big/hi-dpi screens get the 1440p build when the host serves it;
    // on a 404 (e.g. running from the repo, which only ships 1080p) the
    // engine drops down to flight.mp4, then to the stills fallback.
    var sources = ["assets/flight.mp4"];
    var effectiveWidth = window.screen.width * (window.devicePixelRatio || 1);
    if (effectiveWidth >= 2200) sources.unshift("assets/flight_1440.mp4");

    var tryNext = function () {
      var src = sources.shift();
      if (!src) { videoMode = false; return; }
      video.src = src;
      video.load();
    };
    video.addEventListener("loadedmetadata", enableVideoMode);
    video.addEventListener("error", tryNext);
    tryNext();
  }

  /* ── nav deep-links into the flight ─────────────────────────────────── */

  var jumpMap = { "#world-gate": 1, "#world-vault": 2, "#world-bunker": 3, "#world-command": 4 };
  document.querySelectorAll('a[href^="#world-"]').forEach(function (a) {
    a.addEventListener("click", function (e) {
      var idx = jumpMap[a.getAttribute("href")];
      if (idx === undefined) return;
      e.preventDefault();
      var frac;
      if (videoMode) {
        // Aim at 25% into the scene's dive segment.
        var seg = TIMELINE[idx * 2];
        frac = (seg.start + (seg.end - seg.start) * 0.25) / duration;
      } else {
        frac = idx / N + 0.35 / N;
      }
      programmaticScroll = true;
      window.scrollTo({ top: frac * scrollLen, behavior: reducedMotion ? "auto" : "smooth" });
    });
  });

  /* ── auto-play ─────────────────────────────────────────────────────────
   * On load, arm a 7-second idle timer; if the reader hasn't touched the
   * page by then, the flight scrolls itself at a natural reading pace. Any
   * real scroll input — wheel, touch, keys, or dragging the scrollbar —
   * cancels it immediately and switches the toggle off, so autoplay never
   * fights a reader who has taken the wheel. The toggle both cancels a
   * pending auto-start and stops or restarts it once running.
   */

  var AUTOPLAY_IDLE_MS = 7000;
  var AUTOPLAY_VH_PER_SEC = 0.28;   // ~3.6s of scroll per viewport height

  var autoplayToggle = document.getElementById("autoplayToggle");
  var autoplayOn = false;       // the toggle's on/off state — true through both
                                 // the idle countdown and the active scroll
  var autoplayActive = false;   // animating scroll right now, this instant
  var autoplayTimer = null;     // pending 7s idle timeout
  var autoplayLastTs = null;

  function updateAutoplayUI() {
    if (!autoplayToggle) return;
    autoplayToggle.classList.toggle("is-playing", autoplayOn);
    autoplayToggle.setAttribute("aria-pressed", autoplayOn ? "true" : "false");
    autoplayToggle.title = autoplayOn
      ? "Auto-play is on — click to stop"
      : "Auto-play is off — click to fly through";
  }

  function stopScrolling() {
    autoplayActive = false;
    autoplayLastTs = null;
  }

  function turnAutoplayOff() {
    stopScrolling();
    if (autoplayTimer) { clearTimeout(autoplayTimer); autoplayTimer = null; }
    autoplayOn = false;
    updateAutoplayUI();
    // autoplayOn is already false here, so the fullscreenchange handler
    // above won't loop back into this function when the exit completes.
    exitFullscreenIfNeeded();
  }

  function armAutoplayTimer() {
    if (autoplayTimer) clearTimeout(autoplayTimer);
    autoplayTimer = setTimeout(function () {
      autoplayTimer = null;
      if (autoplayOn && !autoplayActive) beginScrolling();
    }, AUTOPLAY_IDLE_MS);
  }

  function autoplayStep(ts) {
    if (!autoplayActive) { autoplayLastTs = null; return; }
    if (autoplayLastTs === null) autoplayLastTs = ts;
    var dt = (ts - autoplayLastTs) / 1000;
    autoplayLastTs = ts;

    var max = Math.max(1, spacer.offsetTop + scrollLen - window.innerHeight);
    var next = window.scrollY + AUTOPLAY_VH_PER_SEC * window.innerHeight * dt;

    // Reached the end of the flight: loop back to the top and keep playing,
    // rather than stopping — autoplay is meant to run as a continuous demo
    // reel, not a one-shot.
    if (next >= max - 0.5) {
      programmaticScroll = true;
      window.scrollTo(0, 0);
      autoplayLastTs = null;   // restart the dt clock cleanly after the jump
      requestAnimationFrame(autoplayStep);
      return;
    }

    programmaticScroll = true;
    window.scrollTo(0, next);
    requestAnimationFrame(autoplayStep);
  }

  function enterFullscreen() {
    var el = document.documentElement;
    if (document.fullscreenElement || !el.requestFullscreen) return;
    // Succeeds when this call chain started from a real click (the toggle);
    // browsers silently reject it when the 7s idle timer fires with no
    // gesture behind it at all — nothing to catch that isn't already a
    // no-op for the reader.
    var p = el.requestFullscreen();
    if (p && p.catch) p.catch(function () {});
  }

  function exitFullscreenIfNeeded() {
    if (document.fullscreenElement && document.exitFullscreen) {
      document.exitFullscreen().catch(function () {});
    }
  }

  // If the reader exits fullscreen themselves (Esc, or the browser's own
  // exit control), treat it the same as taking the wheel: stop autoplay
  // rather than leaving it silently running behind the browser chrome again.
  document.addEventListener("fullscreenchange", function () {
    if (!document.fullscreenElement && autoplayOn) turnAutoplayOff();
  });

  function beginScrolling() {
    if (reducedMotion) return;
    // Already past the flight (deep in the regular page content below it) —
    // nothing left to play, and jumping backward to the boundary would just
    // be a surprising side effect of a stray click.
    var max = Math.max(1, spacer.offsetTop + scrollLen - window.innerHeight);
    if (window.scrollY >= max - 0.5) return;
    enterFullscreen();
    autoplayActive = true;
    requestAnimationFrame(autoplayStep);
  }

  if (autoplayToggle && !reducedMotion) {
    autoplayOn = true;
    autoplayToggle.classList.add("is-ready");
    updateAutoplayUI();
    armAutoplayTimer();
    autoplayToggle.addEventListener("click", function () {
      if (autoplayOn) {
        turnAutoplayOff();
      } else {
        autoplayOn = true;
        updateAutoplayUI();
        beginScrolling();   // explicit request: start now, no delay
      }
    });
  }

  // Autoplay scrolls every animation frame, so a "flag it just before our own
  // scrollTo, clear it on the next scroll event" test cannot tell a real wheel
  // input apart from our own once it is running — the flag is essentially
  // always true by the time any scroll event fires. So real input is caught
  // directly instead: wheel, touch and the scroll-relevant keys all mean the
  // reader took the wheel, immediately, regardless of what autoplay is doing.
  // Interactive targets (the toggle itself, nav links) are excluded so
  // operating them is never misread as "stop autoplay".
  function isInteractive(el) {
    return !!(el && el.closest && el.closest("a, button, input, select, textarea"));
  }

  function onUserScrollIntent(e) {
    if (isInteractive(e && e.target)) return;
    if (autoplayOn) turnAutoplayOff();
  }

  var SCROLL_KEYS = ["ArrowUp", "ArrowDown", "PageUp", "PageDown", "Home", "End", " "];
  window.addEventListener("wheel", onUserScrollIntent, { passive: true });
  window.addEventListener("touchstart", onUserScrollIntent, { passive: true });
  window.addEventListener("keydown", function (e) {
    if (SCROLL_KEYS.indexOf(e.key) !== -1) onUserScrollIntent(e);
  });

  // Backup path for sources that trigger neither (chiefly dragging the
  // scrollbar thumb): the flag technique still works here specifically
  // because it only has to catch scrolls that happen while autoplay is NOT
  // itself mid-step, i.e. during the idle countdown, when there is no
  // competing programmatic scroll to race against.
  function onScroll() {
    readScroll();
    if (programmaticScroll) {
      programmaticScroll = false;
    } else if (autoplayOn && !autoplayActive) {
      turnAutoplayOff();
    }
  }

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

  layout();
  requestAnimationFrame(tick);
})();