Crossfade transition

<!doctype html><html lang="ja"><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><style>body{margin:0;min-height:330px}.sample{width:100%;height:100%;min-height:330px;padding:12px!important;display:flex!important;flex-direction:column;justify-content:center;align-items:center;gap:8px!important;background:#f0efeb;color:#232323;font-family:Arial,Meiryo,sans-serif;overflow:hidden;box-sizing:border-box}.sample *{box-sizing:border-box}.lab-scene{width:100%;max-width:430px;height:140px;position:relative;overflow:hidden;border-bottom:1px solid #ccc}.lab-scene:has(canvas){max-width:320px;height:auto;aspect-ratio:16/9;flex-shrink:0}.lab-canvas{display:block;width:100%;height:100%!important;outline-offset:-3px}.lab-canvas:focus-visible{outline:2px solid #222}.lab-controls{width:100%;max-width:390px;display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:8px 14px}.lab-controls label{display:grid;grid-template-columns:1fr auto;gap:2px;font-size:11px;min-width:0}.lab-controls input{grid-column:1/-1;width:100%;min-width:0;margin:0;accent-color:#333;height:30px}.lab-controls output{font-variant-numeric:tabular-nums}.lab-actions{display:flex;gap:8px;align-items:center;flex-wrap:wrap;justify-content:center}.sample .lab-actions button{color:inherit;font:11px Arial,Meiryo,sans-serif;border:1px solid #aaa;border-radius:99px;background:transparent;min-height:44px;padding:8px 12px;cursor:pointer}.lab-status{font-size:10px;line-height:1.4;min-height:14px;margin:0;text-align:center}.lab-note{font-size:9px;line-height:1.3;color:#666;margin:0;text-align:center}.lab-actions button:focus-visible{outline:2px solid #222;outline-offset:2px}@media(prefers-reduced-motion:reduce){.sample *{animation-play-state:paused!important;transition:none!important}}.lab-scene{perspective:700px}.scene-a,.scene-b{position:absolute;inset:4px 15px;display:flex;flex-direction:column;justify-content:center;gap:6px;padding:18px;background:#deddd5;transition:opacity var(--duration,700ms),transform var(--duration,700ms),clip-path var(--duration,700ms)}.scene-b{background:#292929;color:#f8f8f5}.scene-a span,.scene-b span{font-size:10px;letter-spacing:.15em}.scene-a b,.scene-b b{font-size:48px;letter-spacing:-3px}.scene-b{opacity:0}.next .scene-b{opacity:1}</style><div class="sample"><div class="lab-scene"><div class="scene-a"><span>01</span><b>begin.</b></div><div class="scene-b"><span>02</span><b>open.</b></div></div><div class="lab-controls"><label>切り替え時間 ms<output>750</output><input aria-label="切り替え時間 ms" type="range" min="100" max="2000" step="50" value="750" data-key="duration"></label></div><div class="lab-actions"><button data-play>停止</button><button data-reset>切り替える</button></div><p class="lab-status" role="status"></p></div><script>const lab=(function runDomLab(root,cfg,setup){
 const abort=new AbortController(),values=Object.fromEntries(cfg.controls.map(c=>[c.key,c.value])),mq=matchMedia('(prefers-reduced-motion:reduce)');let auto=!mq.matches;
 const on=(el,event,fn)=>el.addEventListener(event,fn,{signal:abort.signal});
 const api=setup({root,values,kind:cfg.kind,on,reduced:mq.matches})||{};
 for(const input of root.querySelectorAll('[data-key]'))on(input,'input',()=>{values[input.dataset.key]=Number(input.value);input.closest('label').querySelector('output').textContent=input.value;api.update?.()});
 const play=root.querySelector('[data-play]');on(play,'click',()=>{auto=!auto;api.setAuto?.(auto);for(const a of root.querySelector('.lab-scene').getAnimations({subtree:true}))auto?a.play():a.pause();play.textContent=auto?'停止':'再生';play.setAttribute('aria-pressed',String(!auto))});
 const reset=root.querySelector('[data-reset]');on(reset,'click',()=>api.action?.());
 on(document,'visibilitychange',()=>api.setAuto?.(auto&&!document.hidden));
 api.update?.();if(cfg.static)play.hidden=true;
 return {setAuto(on){auto=on&&!mq.matches;api.setAuto?.(auto);for(const a of root.querySelector('.lab-scene').getAnimations({subtree:true}))auto?a.play():a.pause();play.textContent=auto?'停止':'再生'},destroy(){abort.abort();api.destroy?.()}};
})(document,{"kind":"transition-crossfade","controls":[{"key":"duration","label":"切り替え時間 ms","min":100,"max":2000,"value":750,"step":50}],"static":true},function transition({root,values:v,kind,on,reduced}){
 const stage=root.querySelector('.lab-scene'),card=root.querySelector('.transition-card'),a=root.querySelector('.scene-a'),b=root.querySelector('.scene-b'),status=root.querySelector('.lab-status');let next=false,animations=[];
 const update=()=>stage.style.setProperty('--duration',`${v.duration}ms`);
 return {update,action(){animations.forEach(a=>a.cancel());next=!next;const before=card?.getBoundingClientRect();stage.classList.toggle('next',next);if(kind==='transition-shared'&&card){const after=card.getBoundingClientRect();if(!reduced)animations.push(card.animate([{transform:`translate(${before.x-after.x}px,${before.y-after.y}px) scale(${before.width/after.width},${before.height/after.height})`},{transform:'none'}],{duration:v.duration,easing:'cubic-bezier(.2,.8,.2,1)'}))}status.textContent=next?'02 / OPEN':'01 / BEGIN';},setAuto(auto){stage.style.setProperty('--duration',auto&&!reduced?`${v.duration}ms`:'0ms');},destroy(){animations.forEach(a=>a.cancel())}};
});addEventListener('pagehide',()=>lab.destroy(),{once:true});</script></html>