Text knockout

<!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{background:repeating-linear-gradient(45deg,#ddd 0 8px,#f8f7f3 8px 16px)}.mask-art{position:absolute;inset:0;background:linear-gradient(110deg,#333,#999);color:white;display:grid;place-content:center;text-align:center;gap:5px}.mask-art b{font-size:44px;letter-spacing:-3px}.mask-art span{font-size:10px}.inverted{filter:invert(1)}.mask-art{background:none;color:#333}.mask-art b{font-size:60px;background:repeating-linear-gradient(110deg,#111 0 18px,#aaa 18px 36px);background-position:var(--p) center;background-size:200% 100%;background-clip:text;-webkit-background-clip:text;color:transparent}</style><div class="sample"><div class="lab-scene"><div class="mask-art"><b>REVEAL</b><span>what is behind?</span></div></div><div class="lab-controls"><label>背景の位置 %<output>50</output><input aria-label="背景の位置 %" type="range" min="0" max="100" step="1" value="50" data-key="progress"></label></div><div class="lab-actions"><button data-play>停止</button><button data-reset>背景を反転</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":"mask-type","controls":[{"key":"progress","label":"背景の位置 %","min":0,"max":100,"value":50,"step":1}],"static":true,"action":"背景を反転"},function masks({root,values:v,kind}){const stage=root.querySelector('.lab-scene'),status=root.querySelector('.lab-status');let inverted=false;return{update(){stage.style.setProperty('--p',v.progress+'%');stage.style.setProperty('--soft',v.soft+'%');stage.style.setProperty('--gap',v.gap+'px');stage.style.setProperty('--opening',(v.gap*v.progress/100)+'px');},action(){inverted=!inverted;stage.classList.toggle('inverted',inverted);status.textContent=inverted?'背景を反転':'元の背景';}}});addEventListener('pagehide',()=>lab.destroy(),{once:true});</script></html>