textstring/index.html at main · pushmatrix/textstring · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>textstring</title>
  <style>
    * { margin: 0; padding: 0; box-sizing: border-box; }
    html, body { width: 100%; height: 100%; overflow: hidden; background: #f5f0e8; touch-action: none; }
    #container {
      position: relative;
      width: 100%;
      max-width: 600px;
      margin: 0 auto;
      padding: 0 20px;
      user-select: none;
      -webkit-user-select: none;
    }
    .letter {
      position: absolute;
      top: 0; left: 0;
      will-change: transform;
      font-family: 'Georgia', serif;
      font-size: 20px;
      line-height: 1;
      color: #4a4a4a;
      pointer-events: none;
    }
    .letter.draggable {
      pointer-events: auto;
      cursor: grab;
      z-index: 10;
      touch-action: none;
    }
    .letter.dragging {
      cursor: grabbing;
    }
  </style>
</head>
<body>
  <div id="container"></div>

  <script type="module">
    import { prepareWithSegments, layoutWithLines } from './pretext.js';

    const FULL_TEXT = "Alice was beginning to get very tired of sitting by her sister on the bank, and of having nothing to do: once or twice she had peeped into the book her sister was reading, but it had no pictures or conversations in it, \u201cand what is the use of a book,\u201d thought Alice \u201cwithout pictures or conversations?\u201d So she was considering in her own mind (as well as she could, for the hot day made her feel very sleepy and stupid), whether the pleasure of making a daisy-chain would be worth the trouble of getting up and picking the daisies, when suddenly a White Rabbit with pink eyes ran close by her. There was nothing so very remarkable in that; nor did Alice think it so very much out of the way to hear the Rabbit say to itself, \u201cOh dear! Oh dear! I shall be late!\u201d";
    const SHORT_TEXT = "Alice was beginning to get very tired of sitting by her sister on the bank, and of having nothing to do: once or twice she had peeped into the book her sister was reading, but it had no pictures or conversations in it, \u201cand what is the use of a book,\u201d thought Alice \u201cwithout pictures or conversations?\u201d So she was considering in her own mind (as well as she could, for the hot day made her feel very sleepy and stupid).";
    const TEXT = window.innerWidth < 600 ? SHORT_TEXT : FULL_TEXT;
    const FONT = '20px Georgia';
    const LINE_HEIGHT = 28;
    const CONSTRAINT_DIST = 1.2;
    const UNLOCK_THRESHOLD = 1;
    const ITERATIONS = 12;
    const DAMPING = 0.97;
    const GRAVITY = 0.15;
    let gravityOn = true;
    let unraveling = false;
    let unravelIdx = -1;
    window.addEventListener('keydown', (e) => {
      if (e.key === 'f' || e.key === 'F') {
        gravityOn = !gravityOn;
        if (gravityOn && !unraveling) {
          unraveling = true;
          hint.style.opacity = '0';
          unravelIdx = letters.length - 1;
          while (unravelIdx >= 0 && !letters[unravelIdx].locked) unravelIdx--;
        }
      }
    });

    const container = document.getElementById('container');
    const measureCtx = document.createElement('canvas').getContext('2d');
    measureCtx.font = FONT;

    // Prepare text once with pretext
    const prepared = prepareWithSegments(TEXT, FONT);
    const MARGIN = 20;
    const segmenter = new Intl.Segmenter(undefined, { granularity: 'grapheme' });

    function getMaxWidth() {
      return container.getBoundingClientRect().width - MARGIN * 2;
    }

    // Measure all graphemes once — these never change
    const allGraphemes = [...segmenter.segment(TEXT)].map(s => s.segment);
    const graphemeWidths = allGraphemes.map(g => measureCtx.measureText(g).width);

    // Get reading-order positions for each grapheme at a given width.
    // We do our own word-wrap using pretext's measured widths as ground truth,
    // but track every grapheme including trailing spaces so the count always
    // matches allGraphemes.length.
    function layoutPositions(maxWidth) {
      // First pass: compute line breaks to get total height
      const rawPositions = [];
      let x = 0;
      let lineY = 0;

      for (let gi = 0; gi < allGraphemes.length; gi++) {
        const g = allGraphemes[gi];
        const w = graphemeWidths[gi];

        if (g === ' ' && x > 0) {
          let wordW = 0;
          for (let j = gi + 1; j < allGraphemes.length && allGraphemes[j] !== ' '; j++) {
            wordW += graphemeWidths[j];
          }
          if (x + w + wordW > maxWidth) {
            rawPositions.push({ x: x + MARGIN, y: lineY, w });
            x = 0;
            lineY += LINE_HEIGHT;
            continue;
          }
        }

        rawPositions.push({ x: x + MARGIN, y: lineY, w });
        x += w;
      }

      // Vertical center offset
      const totalHeight = lineY + LINE_HEIGHT;
      const containerRect = container.getBoundingClientRect();
      const viewportHeight = window.innerHeight;
      const offsetY = Math.max(0, (viewportHeight - containerRect.top - totalHeight) * 0.3);

      return rawPositions.map(p => ({ x: p.x, y: p.y + offsetY, w: p.w }));
    }

    // Initial layout — compute positions and zig-zag ordering once
    let positions = layoutPositions(getMaxWidth());

    // Build zig-zag string order mapping (reading index -> string index) based on initial layout
    // This mapping is fixed — it never changes on resize
    function buildZigzagMapping(maxWidth) {
      const { lines } = layoutWithLines(prepared, maxWidth, LINE_HEIGHT);

      // Build per-line reading indices
      const lineIndices = [];
      let gi = 0;
      for (let li = 0; li < lines.length; li++) {
        const lineGraphemes = [...segmenter.segment(lines[li].text)].map(s => s.segment);
        const indices = [];
        for (let j = 0; j < lineGraphemes.length; j++) {
          indices.push(gi++);
        }
        lineIndices.push(indices);
      }

      // Zig-zag: snake so last line goes L->R
      const lastLineIdx = lineIndices.length - 1;
      const needFlip = lastLineIdx % 2 === 1;
      const stringOrder = []; // stringOrder[stringIdx] = readingIdx
      for (let li = 0; li < lineIndices.length; li++) {
        const reversed = needFlip ? (li % 2 === 0) : (li % 2 === 1);
        if (reversed) {
          stringOrder.push(...[...lineIndices[li]].reverse());
        } else {
          stringOrder.push(...lineIndices[li]);
        }
      }

      return stringOrder;
    }

    const stringOrder = buildZigzagMapping(getMaxWidth());

    // Build letters array in string order
    const letters = stringOrder.map(ri => {
      const p = positions[ri];
      return {
        ch: allGraphemes[ri],
        w: p.w,
        x: p.x, y: p.y,
        ox: p.x, oy: p.y,
        px: p.x, py: p.y,
        readingIdx: ri,
        locked: true
      };
    });

    // Compute rest lengths in string order
    function computeRestLengths() {
      const rests = [];
      for (let i = 0; i < letters.length - 1; i++) {
        const a = letters[i], b = letters[i + 1];
        const dist = Math.hypot(
          (b.ox + b.w / 2) - (a.ox + a.w / 2),
          (b.oy + LINE_HEIGHT / 2) - (a.oy + LINE_HEIGHT / 2)
        );
        rests.push(dist * CONSTRAINT_DIST);
      }
      return rests;
    }

    let restLengths = computeRestLengths();

    // DOM elements
    const els = [];
    for (const l of letters) {
      const span = document.createElement('span');
      span.className = 'letter';
      span.textContent = l.ch;
      container.appendChild(span);
      els.push(span);
    }

    // Unlock last 6
    const lastIdx = letters.length - 1;
    for (let i = lastIdx; i > lastIdx - 6; i--) {
      letters[i].locked = false;
      els[i].classList.add('draggable');
    }

    // "DRAG ME" hint
    const hint = document.createElement('img');
    hint.src = 'drag.png';
    hint.style.cssText = 'position:absolute;top:0;left:0;width:60px;pointer-events:none;opacity:0;transition:opacity 0.8s;';
    container.appendChild(hint);
    function positionHint() {
      const last = letters[lastIdx];
      hint.style.transform = `translate(${last.ox - 30}px, ${last.oy + LINE_HEIGHT + 2}px)`;
    }
    positionHint();
    setTimeout(() => { hint.style.opacity = '1'; }, 500);

    // Resize: relayout locked letters using their fixed reading-order index
    window.addEventListener('resize', () => {
      const newPositions = layoutPositions(getMaxWidth());
      for (let i = 0; i < letters.length; i++) {
        const np = newPositions[letters[i].readingIdx];
        if (letters[i].locked) {
          letters[i].x = np.x;
          letters[i].y = np.y;
          letters[i].ox = np.x;
          letters[i].oy = np.y;
          letters[i].px = np.x;
          letters[i].py = np.y;
        } else {
          letters[i].ox = np.x;
          letters[i].oy = np.y;
        }
      }
      // Rest lengths stay fixed — the string doesn't change length
      positionHint();
    });

    // Drag state — multitouch: map pointerId -> { idx, offsetX, offsetY }
    const drags = new Map();

    function isDragged(idx) {
      for (const d of drags.values()) if (d.idx === idx) return true;
      return false;
    }

    container.addEventListener('pointerdown', (e) => {
      const idx = els.indexOf(e.target);
      if (idx === -1 || letters[idx].locked) return;
      // Don't allow two fingers on the same letter
      if (isDragged(idx)) return;
      const rect = container.getBoundingClientRect();
      drags.set(e.pointerId, {
        idx,
        offsetX: e.clientX - rect.left - letters[idx].x,
        offsetY: e.clientY - rect.top - letters[idx].y
      });
      els[idx].classList.add('dragging');
      e.target.setPointerCapture(e.pointerId);
      e.preventDefault();
    });

    window.addEventListener('pointermove', (e) => {
      const d = drags.get(e.pointerId);
      if (!d) return;
      const rect = container.getBoundingClientRect();
      const l = letters[d.idx];
      l.x = e.clientX - rect.left - d.offsetX;
      l.y = e.clientY - rect.top - d.offsetY;
      l.px = l.x;
      l.py = l.y;
      l.locked = false;
    });

    window.addEventListener('pointerup', (e) => {
      const d = drags.get(e.pointerId);
      if (!d) return;
      els[d.idx].classList.remove('dragging');
      drags.delete(e.pointerId);
    });

    window.addEventListener('pointercancel', (e) => {
      const d = drags.get(e.pointerId);
      if (!d) return;
      els[d.idx].classList.remove('dragging');
      drags.delete(e.pointerId);
    });

    // Physics
    function simulate() {
      // Unravel step (one letter per fixed tick)
      if (unraveling) {
        if (!gravityOn || unravelIdx < 0) { unraveling = false; }
        else if (letters[unravelIdx].locked) {
          letters[unravelIdx].locked = false;
          letters[unravelIdx].px = letters[unravelIdx].x;
          letters[unravelIdx].py = letters[unravelIdx].y - 0.5;
          unravelIdx--;
        } else {
          unravelIdx--;
        }
      }

      // Unlock propagation
      for (let i = letters.length - 2; i >= 0; i--) {
        if (letters[i].locked && !letters[i + 1].locked) {
          const a = letters[i], b = letters[i + 1];
          const dx = (b.x + b.w / 2) - (a.ox + a.w / 2);
          const dy = (b.y + LINE_HEIGHT / 2) - (a.oy + LINE_HEIGHT / 2);
          const dist = Math.hypot(dx, dy);
          if (dist > restLengths[i] + UNLOCK_THRESHOLD) {
            a.locked = false;
            a.px = a.x;
            a.py = a.y;
            hint.style.opacity = '0';
          }
        }
      }

      // Verlet
      for (let i = 0; i < letters.length; i++) {
        const l = letters[i];
        if (l.locked || isDragged(i)) continue;
        const vx = (l.x - l.px) * DAMPING;
        const vy = (l.y - l.py) * DAMPING;
        l.px = l.x;
        l.py = l.y;
        l.x += vx;
        l.y += vy + (gravityOn ? GRAVITY : 0);
      }

      // Distance constraints
      for (let iter = 0; iter < ITERATIONS; iter++) {
        for (let i = 0; i < letters.length - 1; i++) {
          const a = letters[i], b = letters[i + 1];
          if (a.locked && b.locked) continue;
          const ax = a.x + a.w / 2, ay = a.y + LINE_HEIGHT / 2;
          const bx = b.x + b.w / 2, by = b.y + LINE_HEIGHT / 2;
          const dx = bx - ax, dy = by - ay;
          const dist = Math.hypot(dx, dy) || 0.001;
          const diff = (dist - restLengths[i]) / dist;
          const aFixed = a.locked || isDragged(i);
          const bFixed = b.locked || isDragged(i + 1);
          if (aFixed && !bFixed) {
            b.x -= dx * diff; b.y -= dy * diff;
          } else if (!aFixed && bFixed) {
            a.x += dx * diff; a.y += dy * diff;
          } else if (!aFixed && !bFixed) {
            a.x += dx * diff * 0.5; a.y += dy * diff * 0.5;
            b.x -= dx * diff * 0.5; b.y -= dy * diff * 0.5;
          }
        }
      }

      // Letter collision
      const RADIUS = 7;
      for (let i = 0; i < letters.length; i++) {
        if (letters[i].locked) continue;
        const a = letters[i];
        const acx = a.x + a.w / 2, acy = a.y + LINE_HEIGHT / 2;
        for (let j = i + 1; j < letters.length; j++) {
          if (letters[j].locked) continue;
          if (Math.abs(i - j) === 1) continue;
          const b = letters[j];
          const bcx = b.x + b.w / 2, bcy = b.y + LINE_HEIGHT / 2;
          const dx = bcx - acx, dy = bcy - acy;
          const dist = Math.hypot(dx, dy) || 0.001;
          const minDist = RADIUS * 2;
          if (dist < minDist) {
            const overlap = (minDist - dist) / dist * 0.5;
            const aD = isDragged(i);
            const bD = isDragged(j);
            if (aD) { b.x += dx * overlap; b.y += dy * overlap; }
            else if (bD) { a.x -= dx * overlap; a.y -= dy * overlap; }
            else { a.x -= dx * overlap; a.y -= dy * overlap; b.x += dx * overlap; b.y += dy * overlap; }
          }
        }
      }

      // Boundary
      const cRect = container.getBoundingClientRect();
      const minX = -cRect.left;
      const minY = -cRect.top;
      const maxX = window.innerWidth - cRect.left;
      const maxY = window.innerHeight - cRect.top;
      const bounce = 0.4;
      for (let i = 0; i < letters.length; i++) {
        const l = letters[i];
        if (l.locked || isDragged(i)) continue;
        if (l.x < minX) { l.x = minX; l.px = l.x + (l.x - l.px) * bounce; }
        if (l.x + l.w > maxX) { l.x = maxX - l.w; l.px = l.x + (l.x - l.px) * bounce; }
        if (l.y < minY) { l.y = minY; l.py = l.y + (l.y - l.py) * bounce; }
        if (l.y + LINE_HEIGHT > maxY) { l.y = maxY - LINE_HEIGHT; l.py = l.y + (l.y - l.py) * bounce; }
      }
    }

    // Fixed-timestep loop: simulate at 60Hz regardless of display refresh rate
    const FIXED_DT = 1 / 120;
    const MAX_STEPS = 4; // cap to avoid spiral of death
    let accumulator = 0;
    let lastTime = -1;

    function render(now) {
      if (lastTime < 0) { lastTime = now; requestAnimationFrame(render); return; }
      const dt = Math.min((now - lastTime) / 1000, MAX_STEPS * FIXED_DT);
      lastTime = now;
      accumulator += dt;

      while (accumulator >= FIXED_DT) {
        simulate();
        accumulator -= FIXED_DT;
      }

      for (let i = 0; i < letters.length; i++) {
        if (!letters[i].locked) els[i].classList.add('draggable');
        els[i].style.transform = `translate(${letters[i].x}px, ${letters[i].y}px)`;
      }
      requestAnimationFrame(render);
    }

    requestAnimationFrame(render);
  </script>
</body>
</html>