zlyfunction.github.io/cloth.html at main · zlyfunction/zlyfunction.github.io · 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>Cloth Simulation</title>
    <style>
        * { margin: 0; padding: 0; box-sizing: border-box; }
        body { background: #080810; overflow: hidden; font-family: 'SF Mono', 'Fira Code', monospace; }
        canvas { display: block; touch-action: none; cursor: crosshair; }
        #ui {
            position: fixed; top: 20px; left: 20px;
            color: rgba(255,255,255,0.4); font-size: 11px; line-height: 2;
            pointer-events: none; user-select: none;
        }
        #ui b { color: rgba(255,255,255,0.8); font-weight: normal; }
        #controls {
            position: fixed; top: 20px; right: 20px;
            display: flex; flex-direction: column; gap: 7px;
        }
        button {
            background: rgba(255,255,255,0.06); border: 1px solid rgba(255,255,255,0.12);
            color: rgba(255,255,255,0.6); padding: 6px 13px; font-size: 11px;
            font-family: inherit; cursor: pointer; border-radius: 5px; transition: all 0.12s;
            letter-spacing: 0.04em; min-width: 100px; text-align: left;
            -webkit-tap-highlight-color: transparent;
        }
        button:hover { background: rgba(255,255,255,0.11); color: rgba(255,255,255,0.9); border-color: rgba(255,255,255,0.25); }
        button.on   { background: rgba(100,160,255,0.13); border-color: rgba(100,160,255,0.35); color: rgba(130,185,255,0.9); }
        button.warn { background: rgba(255,100,80,0.1);   border-color: rgba(255,100,80,0.3);   color: rgba(255,140,120,0.9); }
        hr.sep { border: none; border-top: 1px solid rgba(255,255,255,0.08); margin: 2px 0; }
        #footer {
            position: fixed; bottom: 18px; left: 50%; transform: translateX(-50%);
            color: rgba(255,255,255,0.12); font-size: 10px; letter-spacing: 0.25em;
            text-transform: uppercase; pointer-events: none;
        }
        @media (max-width: 768px) {
            #ui { display: none; }
            button { min-width: 90px; padding: 10px 10px; font-size: 12px; }
        }
    </style>
</head>
<body>
<canvas id="c"></canvas>

<div id="ui">
    <div><b>drag</b> — grab &amp; pull cloth</div>
    <div><b>right-drag</b> — knife cut</div>
    <div><b>shift+drag</b> — blow burst</div>
</div>

<div id="controls">
    <button id="btnReset">reset</button>
    <button id="btnGravity" class="on">gravity</button>
    <button id="btnWind">wind</button>
    <button id="btnGyro">gyro</button>
    <button id="btnColor">mono</button>
    <hr class="sep">
    <button id="btnMat">linen</button>
    <hr class="sep">
    <button id="btnCoarse">coarsen −</button>
    <button id="btnFine">refine  +</button>
    <hr class="sep">
    <button id="btnTouchMode">✂ cut</button>
</div>

<div id="footer">cloth simulation</div>

<script>
'use strict';

// ─── Canvas ─────────────────────────────────────────────────────────────────
const canvas = document.getElementById('c');
const ctx = canvas.getContext('2d', { alpha: false });
let viewWidth = 1;
let viewHeight = 1;
let dpr = 1;

// ─── Resolution levels: [cols, rows] — physical cloth size stays constant ───
const LEVELS = [
    [20, 14],
    [30, 21],
    [40, 28],   // default (matches original)
    [56, 38],
];

// ─── Material presets ────────────────────────────────────────────────────────
// grav: gravity per frame, damp: velocity damping, stiff: constraint stiffness
const MATERIALS = [
    { name: 'linen',     grav: 0.65, damp: 0.981, stiff: 1.00 },
    { name: 'silk',      grav: 0.15, damp: 0.997, stiff: 0.82 },
    { name: 'cotton',    grav: 0.45, damp: 0.987, stiff: 0.95 },
    { name: 'polyester', grav: 0.32, damp: 0.993, stiff: 0.98 },
];

// ─── Config ──────────────────────────────────────────────────────────────────
const CUT_R    = 20;
const GRAB_R   = 50;
const PIN_STEP = 4;
const CLOTH_W  = 0.75;   // fraction of screen width
const FIXED_DT = 1 / 60;
const MAX_STEPS = 4;
const COLOR_BUCKETS = 24;

// ─── State ───────────────────────────────────────────────────────────────────
let COLS, ROWS, SPACING, ITERS;
let px, py, ppx, ppy, pinned;
let cp1, cp2, clen, cactive;
let nP = 0, nC = 0;

let level     = 2;     // index into LEVELS
let matIdx    = 0;     // index into MATERIALS
let gravOn    = true;
let windOn    = false;
let colorMode = 0;
let touchMode = 0;     // 0=grab, 1=cut
let time      = 0;

// ─── Gyroscope / motion (mobile tilt-to-tip, shake-to-gust) ──────────────────
let gyroOn       = false;
let gyroBaseline = null;   // { beta, gamma } captured when gyro is enabled
let gravDirX     = 0;      // smoothed gravity direction, unit-ish vector
let gravDirY     = 1;      // default: straight down
let gravTargetX  = 0;
let gravTargetY  = 1;
let lastAccel    = null;
let shakeImpulseX = 0;
let shakeImpulseY = 0;
const GYRO_MAX_TILT   = 40;   // degrees of tilt for full gravity redirect
const GYRO_SMOOTH     = 0.12; // per-frame lerp toward target (damps sensor jitter)
const SHAKE_THRESHOLD = 12;   // m/s^2 of jerk that counts as a shake
const SHAKE_GAIN      = 2.2;  // px of impulse per m/s^2 of jerk
const SHAKE_MAX       = 40;   // px, impulse cap
const SHAKE_DECAY     = 0.85; // per physics step

// ─── Mouse / touch ───────────────────────────────────────────────────────────
const mouse = { x: 0, y: 0, lx: 0, ly: 0, down: false, right: false, shift: false };
let grabbed = -1;
let grabPrevX = 0;
let grabPrevY = 0;
let activePointer = -1;
let multiTouch = false;
const pointers = new Map();

// ─── Build cloth ─────────────────────────────────────────────────────────────
function buildCloth() {
    [COLS, ROWS] = LEVELS[level];
    const maxWidthByHeight = viewHeight * 0.82 * (COLS - 1) / (ROWS - 1);
    const clothPx = Math.min(viewWidth * CLOTH_W, maxWidthByHeight, 820);
    SPACING = clothPx / (COLS - 1);
    // Enough passes for tension propagation without overspending on dense meshes.
    ITERS = Math.max(16, Math.ceil(ROWS * 0.8));

    const startX = (viewWidth - (COLS - 1) * SPACING) / 2;
    const startY = Math.max(18, viewHeight * 0.07);
    const pinStep = Math.max(1, Math.round(PIN_STEP * (COLS - 1) / (LEVELS[2][0] - 1)));
    nP = COLS * ROWS;

    px      = new Float32Array(nP);
    py      = new Float32Array(nP);
    ppx     = new Float32Array(nP);
    ppy     = new Float32Array(nP);
    pinned  = new Uint8Array(nP);

    for (let r = 0; r < ROWS; r++) {
        for (let c = 0; c < COLS; c++) {
            const i = r * COLS + c;
            px[i] = ppx[i] = startX + c * SPACING;
            py[i] = ppy[i] = startY + r * SPACING;
            pinned[i] = (r === 0 && (c % pinStep === 0 || c === COLS - 1)) ? 1 : 0;
        }
    }

    const maxC = (COLS - 1) * ROWS + COLS * (ROWS - 1);
    cp1     = new Int32Array(maxC);
    cp2     = new Int32Array(maxC);
    clen    = new Float32Array(maxC);
    cactive = new Uint8Array(maxC);
    nC = 0;

    for (let r = 0; r < ROWS; r++) {
        for (let c = 0; c < COLS; c++) {
            const i = r * COLS + c;
            if (c < COLS - 1) { cp1[nC]=i; cp2[nC]=i+1;     clen[nC]=SPACING; cactive[nC]=1; nC++; }
            if (r < ROWS - 1) { cp1[nC]=i; cp2[nC]=i+COLS;  clen[nC]=SPACING; cactive[nC]=1; nC++; }
        }
    }
    grabbed = -1;
}

// ─── Physics update ───────────────────────────────────────────────────────────
function update(dt) {
    time += dt;
    const mat   = MATERIALS[matIdx];
    const stepScale = dt / FIXED_DT;
    const grav  = gravOn ? mat.grav * stepScale * stepScale : 0;
    const damp  = Math.pow(mat.damp, stepScale);
    // Preset stiffness describes one complete solve, not every iteration.
    const stiff = mat.stiff >= 1 ? 1 : 1 - Math.pow(1 - mat.stiff, 1 / ITERS);
    const held = grabbed >= 0 && mouse.down && !mouse.right && !mouse.shift ? grabbed : -1;

    // Wind
    let wx = 0;
    if (windOn) {
        const W = 1.6;
        wx = (Math.sin(time*0.42)*W + Math.sin(time*0.78)*W*0.4 +
              Math.sin(time*1.86)*W*0.15) * stepScale * stepScale;
    }

    // Smooth the sensor-driven gravity direction to damp raw sensor jitter.
    gravDirX += (gravTargetX - gravDirX) * GYRO_SMOOTH;
    gravDirY += (gravTargetY - gravDirY) * GYRO_SMOOTH;

    // Shake impulse (devicemotion) decays each physics step after a spike.
    const shakeX = shakeImpulseX * stepScale;
    const shakeY = shakeImpulseY * stepScale;
    shakeImpulseX *= SHAKE_DECAY;
    shakeImpulseY *= SHAKE_DECAY;

    // 1. Verlet integrate
    for (let i = 0; i < nP; i++) {
        if (pinned[i] || i === held) continue;
        const vx = (px[i] - ppx[i]) * damp;
        const vy = (py[i] - ppy[i]) * damp;
        ppx[i] = px[i];
        ppy[i] = py[i];
        px[i] += vx + wx + grav * gravDirX + shakeX;
        py[i] += vy + grav * gravDirY + shakeY;
    }

    // 2. Pin the grabbed particle before solving so its pull propagates now.
    if (held >= 0) {
        px[held] = mouse.x;
        py[held] = mouse.y;
        ppx[held] = grabPrevX;
        ppy[held] = grabPrevY;
        grabPrevX = mouse.x;
        grabPrevY = mouse.y;
    }

    // 3. Blow burst (shift+drag)
    if (mouse.down && mouse.shift && !mouse.right) {
        const R = 90;
        for (let i = 0; i < nP; i++) {
            if (pinned[i]) continue;
            const dx = px[i] - mouse.x, dy = py[i] - mouse.y;
            const d2 = dx*dx + dy*dy;
            if (d2 < R*R && d2 > 0.01) {
                const d = Math.sqrt(d2), f = (1 - d/R) * 3.5 * stepScale;
                px[i] += dx/d * f; py[i] += dy/d * f;
            }
        }
    }

    // 4. Satisfy constraints
    for (let iter = 0; iter < ITERS; iter++) {
        for (let k = 0; k < nC; k++) {
            if (!cactive[k]) continue;
            const a = cp1[k], b = cp2[k];
            const wa = pinned[a] || a === held ? 0 : 1;
            const wb = pinned[b] || b === held ? 0 : 1;
            const wsum = wa + wb;
            if (wsum === 0) continue;
            const dx = px[b] - px[a];
            const dy = py[b] - py[a];
            const d2 = dx*dx + dy*dy;
            if (d2 < 1e-8) continue;
            const d    = Math.sqrt(d2);
            const diff = (d - clen[k]) / d * stiff / wsum;
            const ox   = dx * diff, oy = dy * diff;
            if (wa) { px[a] += ox; py[a] += oy; }
            if (wb) { px[b] -= ox; py[b] -= oy; }
        }
    }

    // 5. Constraints can push particles outside, so collide after the solve.
    const maxX = viewWidth;
    const maxY = viewHeight - 1;
    for (let i = 0; i < nP; i++) {
        if (pinned[i] || i === held) continue;
        const vx = px[i] - ppx[i];
        const vy = py[i] - ppy[i];
        if (px[i] < 0)    { px[i] = 0;    ppx[i] = px[i] + vx * 0.3; }
        if (px[i] > maxX) { px[i] = maxX; ppx[i] = px[i] + vx * 0.3; }
        if (py[i] < 0)    { py[i] = 0;    ppy[i] = py[i] + vy * 0.3; }
        if (py[i] > maxY) { py[i] = maxY; ppy[i] = py[i] + vy * 0.3; }
    }
}

function pointSegmentDist2(px0, py0, ax, ay, bx, by) {
    const dx = bx - ax, dy = by - ay;
    const len2 = dx*dx + dy*dy;
    if (len2 < 1e-8) {
        const ex = px0 - ax, ey = py0 - ay;
        return ex*ex + ey*ey;
    }
    const t = Math.max(0, Math.min(1, ((px0-ax)*dx + (py0-ay)*dy) / len2));
    const ex = px0 - (ax + t*dx), ey = py0 - (ay + t*dy);
    return ex*ex + ey*ey;
}

function segmentDist2(ax, ay, bx, by, cx, cy, dx, dy) {
    const rx = bx - ax, ry = by - ay;
    const sx = dx - cx, sy = dy - cy;
    const den = rx*sy - ry*sx;
    if (Math.abs(den) > 1e-8) {
        const qx = cx - ax, qy = cy - ay;
        const t = (qx*sy - qy*sx) / den;
        const u = (qx*ry - qy*rx) / den;
        if (t >= 0 && t <= 1 && u >= 0 && u <= 1) return 0;
    }
    return Math.min(
        pointSegmentDist2(ax, ay, cx, cy, dx, dy),
        pointSegmentDist2(bx, by, cx, cy, dx, dy),
        pointSegmentDist2(cx, cy, ax, ay, bx, by),
        pointSegmentDist2(dx, dy, ax, ay, bx, by)
    );
}

function cutAlongPath(ax, ay, bx, by) {
    for (let k = 0; k < nC; k++) {
        if (!cactive[k]) continue;
        const a = cp1[k], b = cp2[k];
        if (segmentDist2(ax, ay, bx, by, px[a], py[a], px[b], py[b]) < CUT_R*CUT_R) {
            cactive[k] = 0;
        }
    }
}

// ─── Grab helpers ─────────────────────────────────────────────────────────────
function findNearest(mx, my) {
    let best = -1, bestD2 = GRAB_R * GRAB_R;
    for (let i = 0; i < nP; i++) {
        if (pinned[i]) continue;
        const dx = px[i]-mx, dy = py[i]-my;
        const d2 = dx*dx + dy*dy;
        if (d2 < bestD2) { bestD2 = d2; best = i; }
    }
    return best;
}

// ─── Rendering ────────────────────────────────────────────────────────────────
function stressColor(s) {
    return `rgb(${Math.round(60+s*195)},${Math.round(150-s*130)},${Math.round(220-s*120)})`;
}

function depthColor(t) {
    return `rgb(${Math.round(80+t*160)},${Math.round(60+Math.sin(t*Math.PI)*170)},${Math.round(230-t*130)})`;
}

function draw() {
    ctx.fillStyle = '#080810';
    ctx.fillRect(0, 0, viewWidth, viewHeight);

    if (colorMode === 0) {
        ctx.beginPath();
        for (let k = 0; k < nC; k++) {
            if (!cactive[k]) continue;
            ctx.moveTo(px[cp1[k]], py[cp1[k]]);
            ctx.lineTo(px[cp2[k]], py[cp2[k]]);
        }
        ctx.strokeStyle = 'rgba(210,218,240,0.5)';
        ctx.lineWidth = 1;
        ctx.stroke();
    } else {
        ctx.lineWidth = 1;
        const buckets = Array.from({ length: COLOR_BUCKETS }, () => new Path2D());
        for (let k = 0; k < nC; k++) {
            if (!cactive[k]) continue;
            const a = cp1[k], b = cp2[k];
            let t;
            if (colorMode === 1) {
                const dx = px[b]-px[a], dy = py[b]-py[a];
                const d = Math.sqrt(dx*dx + dy*dy);
                t = Math.min(1, Math.max(0, (d - clen[k]) / (clen[k] * 0.6)));
            } else {
                t = Math.min(1, Math.max(0, ((py[a]+py[b]) * 0.5) / viewHeight));
            }
            const bucket = Math.min(COLOR_BUCKETS - 1, Math.floor(t * COLOR_BUCKETS));
            buckets[bucket].moveTo(px[a], py[a]);
            buckets[bucket].lineTo(px[b], py[b]);
        }
        for (let i = 0; i < COLOR_BUCKETS; i++) {
            const t = (i + 0.5) / COLOR_BUCKETS;
            ctx.strokeStyle = colorMode === 1 ? stressColor(t) : depthColor(t);
            ctx.stroke(buckets[i]);
        }
    }

    // Pinned anchors
    ctx.fillStyle = 'rgba(110,175,255,0.75)';
    for (let i = 0; i < nP; i++) {
        if (!pinned[i]) continue;
        ctx.beginPath();
        ctx.arc(px[i], py[i], 3.5, 0, Math.PI*2);
        ctx.fill();
    }

    // Grabbed particle highlight
    if (grabbed >= 0 && mouse.down && !mouse.right && !mouse.shift) {
        ctx.beginPath();
        ctx.arc(px[grabbed], py[grabbed], 6, 0, Math.PI*2);
        ctx.fillStyle = 'rgba(255,255,255,0.9)';
        ctx.fill();
    }

    // Cursor indicator
    const R     = mouse.right ? 14 : mouse.shift ? 80 : 40;
    const alpha = mouse.down ? 0.18 : 0.07;
    const col   = mouse.right ? `rgba(255,70,70,${alpha})` :
                  mouse.shift ? `rgba(60,210,255,${alpha})` :
                                `rgba(180,200,255,${alpha})`;
    ctx.beginPath();
    ctx.arc(mouse.x, mouse.y, R, 0, Math.PI*2);
    ctx.fillStyle   = col;
    ctx.fill();
    ctx.strokeStyle = col.replace(/[\d.]+\)$/, '0.4)');
    ctx.lineWidth   = 1;
    ctx.stroke();
}

// ─── Loop ─────────────────────────────────────────────────────────────────────
let lastFrame = null;
let accumulator = 0;
function loop(now) {
    if (lastFrame === null) lastFrame = now;
    const elapsed = Math.min((now - lastFrame) / 1000, FIXED_DT * MAX_STEPS);
    lastFrame = now;
    accumulator = Math.min(accumulator + elapsed, FIXED_DT * MAX_STEPS);
    while (accumulator >= FIXED_DT) {
        update(FIXED_DT);
        accumulator -= FIXED_DT;
    }
    draw();
    requestAnimationFrame(loop);
}

// ─── Resize ───────────────────────────────────────────────────────────────────
function resize() {
    viewWidth = window.innerWidth;
    viewHeight = window.innerHeight;
    dpr = Math.min(window.devicePixelRatio || 1, 2);
    canvas.style.width = `${viewWidth}px`;
    canvas.style.height = `${viewHeight}px`;
    canvas.width = Math.round(viewWidth * dpr);
    canvas.height = Math.round(viewHeight * dpr);
    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    buildCloth();
}

// ─── Input ────────────────────────────────────────────────────────────────────
function updateMousePos(x, y) {
    mouse.lx = mouse.x;
    mouse.ly = mouse.y;
    mouse.x = Math.max(0, Math.min(viewWidth, x));
    mouse.y = Math.max(0, Math.min(viewHeight, y));
}

function resetPointerState() {
    pointers.clear();
    activePointer = -1;
    multiTouch = false;
    mouse.down = false;
    mouse.right = false;
    mouse.shift = false;
    grabbed = -1;
}

function touchCentroid() {
    const touches = [...pointers.values()].filter(p => p.type === 'touch').slice(0, 2);
    if (touches.length < 2) return null;
    return {
        x: (touches[0].x + touches[1].x) * 0.5,
        y: (touches[0].y + touches[1].y) * 0.5,
    };
}

canvas.addEventListener('pointerdown', e => {
    e.preventDefault();
    canvas.setPointerCapture(e.pointerId);
    pointers.set(e.pointerId, { x: e.clientX, y: e.clientY, type: e.pointerType });

    const center = touchCentroid();
    if (center) {
        multiTouch = true;
        grabbed = -1;
        updateMousePos(center.x, center.y);
        mouse.down = true;
        mouse.right = false;
        mouse.shift = true;
        return;
    }

    if (activePointer !== -1 || multiTouch) return;
    activePointer = e.pointerId;
    updateMousePos(e.clientX, e.clientY);
    mouse.down = true;
    mouse.right = e.pointerType === 'touch' ? touchMode === 1 : e.button === 2;
    mouse.shift = !mouse.right && e.shiftKey;
    if (!mouse.right && !mouse.shift) {
        grabbed = findNearest(mouse.x, mouse.y);
        grabPrevX = mouse.x;
        grabPrevY = mouse.y;
    }
    if (mouse.right) cutAlongPath(mouse.x, mouse.y, mouse.x, mouse.y);
});

canvas.addEventListener('pointermove', e => {
    if (pointers.has(e.pointerId)) {
        pointers.set(e.pointerId, { x: e.clientX, y: e.clientY, type: e.pointerType });
    }
    const center = touchCentroid();
    if (center) {
        updateMousePos(center.x, center.y);
        return;
    }
    if (e.pointerId !== activePointer) {
        if (!mouse.down && e.pointerType !== 'touch') {
            updateMousePos(e.clientX, e.clientY);
            mouse.shift = e.shiftKey;
        }
        return;
    }
    updateMousePos(e.clientX, e.clientY);
    mouse.shift = !mouse.right && e.shiftKey;
    if (mouse.down && mouse.right) cutAlongPath(mouse.lx, mouse.ly, mouse.x, mouse.y);
});

function endPointer(e) {
    pointers.delete(e.pointerId);
    if (multiTouch) {
        const center = touchCentroid();
        if (center) {
            updateMousePos(center.x, center.y);
            mouse.down = true;
            mouse.right = false;
            mouse.shift = true;
            return;
        }
        // Do not unexpectedly switch from a two-finger burst to a one-finger grab.
        if (pointers.size === 0) resetPointerState();
        else {
            mouse.down = false;
            mouse.shift = false;
            grabbed = -1;
        }
        return;
    }
    if (e.pointerId === activePointer) resetPointerState();
}

canvas.addEventListener('pointerup', endPointer);
canvas.addEventListener('pointercancel', endPointer);
canvas.addEventListener('contextmenu', e => e.preventDefault());
window.addEventListener('blur', resetPointerState);

// ─── Buttons ──────────────────────────────────────────────────────────────────
document.getElementById('btnReset').addEventListener('click', buildCloth);

document.getElementById('btnGravity').addEventListener('click', function() {
    gravOn = !gravOn; this.classList.toggle('on', gravOn);
});
document.getElementById('btnWind').addEventListener('click', function() {
    windOn = !windOn; this.classList.toggle('on', windOn);
});

const colorLabels = ['mono', 'stress', 'depth'];
document.getElementById('btnColor').addEventListener('click', function() {
    colorMode = (colorMode + 1) % 3; this.textContent = colorLabels[colorMode];
});

document.getElementById('btnMat').addEventListener('click', function() {
    matIdx = (matIdx + 1) % MATERIALS.length;
    this.textContent = MATERIALS[matIdx].name;
    buildCloth();
});

document.getElementById('btnCoarse').addEventListener('click', function() {
    if (level <= 0) { this.classList.add('warn'); setTimeout(() => this.classList.remove('warn'), 300); return; }
    level--;
    buildCloth();
    document.getElementById('btnFine').classList.remove('warn');
});
document.getElementById('btnFine').addEventListener('click', function() {
    if (level >= LEVELS.length - 1) { this.classList.add('warn'); setTimeout(() => this.classList.remove('warn'), 300); return; }
    level++;
    buildCloth();
    document.getElementById('btnCoarse').classList.remove('warn');
});

document.getElementById('btnTouchMode').addEventListener('click', function() {
    touchMode = (touchMode + 1) % 2;
    this.textContent = touchMode === 0 ? '✂ cut' : '✋ grab';
    this.classList.toggle('warn', touchMode === 1);
    mouse.down = false; grabbed = -1;
});

// ─── Gyroscope / motion ───────────────────────────────────────────────────────
function flashWarn(el) {
    el.classList.add('warn');
    setTimeout(() => el.classList.remove('warn'), 300);
}

function onDeviceOrientation(e) {
    if (e.beta === null || e.gamma === null) return;
    if (!gyroBaseline) gyroBaseline = { beta: e.beta, gamma: e.gamma };
    const dGamma = e.gamma - gyroBaseline.gamma;
    const dBeta  = e.beta  - gyroBaseline.beta;
    const gx = dGamma / GYRO_MAX_TILT;
    const gy = 1 - dBeta / GYRO_MAX_TILT;
    const len = Math.sqrt(gx*gx + gy*gy) || 1;
    gravTargetX = gx / len;
    gravTargetY = gy / len;
}

function onDeviceMotion(e) {
    const acc = e.accelerationIncludingGravity;
    if (!acc || acc.x === null) return;
    if (lastAccel) {
        const dx = acc.x - lastAccel.x;
        const dy = acc.y - lastAccel.y;
        const dz = acc.z - lastAccel.z;
        const jerk = Math.sqrt(dx*dx + dy*dy + dz*dz);
        if (jerk > SHAKE_THRESHOLD) {
            shakeImpulseX = Math.max(-SHAKE_MAX, Math.min(SHAKE_MAX, shakeImpulseX - dx * SHAKE_GAIN));
            shakeImpulseY = Math.max(-SHAKE_MAX, Math.min(SHAKE_MAX, shakeImpulseY + dy * SHAKE_GAIN));
        }
    }
    lastAccel = { x: acc.x, y: acc.y, z: acc.z };
}

const btnGyro = document.getElementById('btnGyro');

async function enableGyro() {
    const hasOrientation = typeof DeviceOrientationEvent !== 'undefined';
    const hasMotion = typeof DeviceMotionEvent !== 'undefined';
    if (!hasOrientation && !hasMotion) { flashWarn(btnGyro); return; }
    try {
        if (hasOrientation && typeof DeviceOrientationEvent.requestPermission === 'function') {
            if (await DeviceOrientationEvent.requestPermission() !== 'granted') { flashWarn(btnGyro); return; }
        }
        if (hasMotion && typeof DeviceMotionEvent.requestPermission === 'function') {
            if (await DeviceMotionEvent.requestPermission() !== 'granted') { flashWarn(btnGyro); return; }
        }
    } catch (err) {
        flashWarn(btnGyro);
        return;
    }
    gyroOn = true;
    gyroBaseline = null;
    lastAccel = null;
    shakeImpulseX = 0; shakeImpulseY = 0;
    window.addEventListener('deviceorientation', onDeviceOrientation);
    window.addEventListener('devicemotion', onDeviceMotion);
    btnGyro.classList.add('on');
    btnGyro.textContent = 'gyro on';
}

function disableGyro() {
    gyroOn = false;
    gravTargetX = 0; gravTargetY = 1;
    shakeImpulseX = 0; shakeImpulseY = 0;
    window.removeEventListener('deviceorientation', onDeviceOrientation);
    window.removeEventListener('devicemotion', onDeviceMotion);
    btnGyro.classList.remove('on');
    btnGyro.textContent = 'gyro';
}

btnGyro.addEventListener('click', () => { gyroOn ? disableGyro() : enableGyro(); });

// ─── Boot ─────────────────────────────────────────────────────────────────────
window.addEventListener('resize', resize);
resize();
requestAnimationFrame(loop);
</script>
</body>
</html>