Podwójna helisa

<main class="pen" data-motion="paused"><header><div><h1>Podwójna helisa</h1><p>Zmień skręt modelu.</p></div></header><section class="scene" aria-label="Wizualizacja"><canvas id="helix" role="img" aria-label="Obracająca się przestrzenna podwójna helisa"></canvas><p class="helix-legend"><span>Nici</span><span>Wiązania</span></p></section><div class="toolbar"><button id="motion" type="button" aria-pressed="false">Uruchom</button><label for="twist">Skręt <input id="twist" type="range" min="15" max="50" value="30"><output id="twist-value">30°</output></label></div></main>

* { box-sizing: border-box; }
html, body { margin: 0; min-width: 280px; }
body { background: var(--paper); color: var(--ink); font: 16px/1.5 Arial, sans-serif; }
.pen { min-height: 100vh; padding: clamp(16px, 3vw, 30px); display: flex; flex-direction: column; gap: 16px; max-width: 1120px; margin: auto; }
header { display: flex; align-items: baseline; justify-content: space-between; gap: 20px; flex-wrap: wrap; }
h1 { font-size: clamp(26px, 4.1vw, 42px); line-height: 1.08; margin: 0 0 8px; letter-spacing: -.04em; }
p { margin: 0; max-width: 64ch; }
.scene { position: relative; min-height: 230px; flex: 1; display: grid; place-items: center; overflow: hidden; }
.scene canvas { position: absolute; inset: 0; width: 100%; height: 100%; }
.toolbar { display: flex; align-items: center; flex-wrap: wrap; gap: 12px 20px; }
.toolbar label { display: flex; align-items: center; flex-wrap: wrap; gap: 8px; min-height: 44px; }
button, select { font: inherit; color: var(--ink); background: var(--paper); border: 1px solid currentColor; border-radius: 0; min-height: 44px; padding: 8px 15px; cursor: pointer; }
button:hover { background: var(--ink); color: var(--paper); }
button:focus-visible, select:focus-visible, input:focus-visible { outline: 3px solid var(--accent); outline-offset: 4px; }
input[type=range] { width: 145px; max-width: 42vw; accent-color: var(--accent); min-height: 36px; cursor: pointer; }
output, .hint { font-size: 14px; }
[data-motion="paused"] .animated { animation-play-state: paused !important; }
@media (max-width: 500px) { header { gap: 6px; } .scene { min-height: 280px; } .toolbar { gap: 10px; } .toolbar label { font-size: 14px; } }
@media (prefers-reduced-motion: reduce) { *, *::before, *::after { transition-duration: 0s !important; scroll-behavior: auto !important; } }
body{--paper:#e9f1f8;--ink:#22364c;--accent:#ad3d60}.scene{background:#cbdfea;border:1px solid #94b3c8}.helix-legend{position:absolute;bottom:15px;left:18px;display:flex;gap:20px;font-size:13px}.helix-legend span::before{content:"";display:inline-block;width:10px;height:10px;margin-right:7px;background:#ba466b}.helix-legend span:last-child::before{background:#567992}

(() => {

const root = document.querySelector('.pen');
const preference = matchMedia('(prefers-reduced-motion: reduce)');
const motionButton = document.querySelector('#motion');
let playing = !preference.matches, elapsed = 0, paint = null;
function syncMotion() {
  root.dataset.motion = playing ? 'running' : 'paused';
  motionButton.textContent = playing ? 'Wstrzymaj' : 'Uruchom';
  motionButton.setAttribute('aria-pressed', String(playing));
}
motionButton.addEventListener('click', () => { playing = !playing; syncMotion(); });
preference.addEventListener('change', event => { playing = !event.matches; syncMotion(); });
syncMotion();
function run(draw) {
  paint = draw;
  draw(0);
  let last = performance.now(), lastPaint = 0;
  function frame(now) {
    if (playing && !document.hidden) { elapsed += Math.min(now - last, 48) / 1000; if (now - lastPaint >= 30) { draw(elapsed); lastPaint = now; } }
    last = now;
    requestAnimationFrame(frame);
  }
  requestAnimationFrame(frame);
}
function canvasSurface(selector) {
  const canvas = document.querySelector(selector), context = canvas.getContext('2d');
  if (!context) { canvas.replaceWith(document.createTextNode('Ta wizualizacja wymaga obsługi Canvas 2D.')); return null; }
  const surface = { canvas, context, width: 0, height: 0 };
  function resize() {
    const box = canvas.parentElement.getBoundingClientRect(), ratio = Math.min(devicePixelRatio || 1, 2);
    surface.width = box.width; surface.height = box.height;
    canvas.width = Math.max(1, Math.round(box.width * ratio)); canvas.height = Math.max(1, Math.round(box.height * ratio));
    context.setTransform(ratio, 0, 0, ratio, 0, 0);
    if (paint) paint(elapsed);
  }
  resize(); new ResizeObserver(resize).observe(canvas.parentElement);
  return surface;
}
const surface=canvasSurface('#helix');if(!surface)return;const ctx=surface.context,slider=document.querySelector('#twist');slider.addEventListener('input',()=>{document.querySelector('#twist-value').value=slider.value+'°';if(paint)paint(elapsed);});
function point(index,side,time){const a=index*Number(slider.value)*Math.PI/180+side*Math.PI+time*.55,z=Math.sin(a),scale=1/(1.9+z*.17);return{x:surface.width/2+Math.cos(a)*Math.min(surface.width*.3,115)*scale*1.8,y:surface.height/2+(index-8.5)*Math.min(surface.height/22,15)*scale*1.8,z,side};}
run(time=>{const {width:w,height:h}=surface;ctx.clearRect(0,0,w,h);const pairs=[];for(let i=0;i<18;i++)pairs.push([point(i,0,time),point(i,1,time)]);ctx.lineWidth=2;pairs.forEach(([a,b])=>{ctx.strokeStyle='#6c90a4';ctx.beginPath();ctx.moveTo(a.x,a.y);ctx.lineTo(b.x,b.y);ctx.stroke();});for(let side=0;side<2;side++){ctx.strokeStyle=side?'#c56e46':'#ad3d60';ctx.lineWidth=3;ctx.beginPath();pairs.forEach((pair,i)=>i?ctx.lineTo(pair[side].x,pair[side].y):ctx.moveTo(pair[side].x,pair[side].y));ctx.stroke();}pairs.flat().sort((a,b)=>a.z-b.z).forEach(p=>{ctx.fillStyle=p.side?'#d79059':'#ba466b';ctx.beginPath();ctx.arc(p.x,p.y,5+p.z,0,Math.PI*2);ctx.fill();ctx.strokeStyle='#ffffffaa';ctx.lineWidth=1;ctx.stroke();});});
})();