css3d_rotate.html

<!-- vim: sw=4 ts=4 expandtab smartindent ft=javascript
-->
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>demo</title>
    <style> document, body { margin: 0px; padding: 0px; overflow: hidden; } </style>
  </head>

  <body>

    <div
        style="z-index:1;margin:1vh;position:absolute;top:0px;left:0px;display:flex;flex-direction:column;"
        id="inputs"
    >

        <div>
            <input type="text" value="3" id="size_input" style="margin:0.2vh;"/>
            <label for="size_input">size</label>
        </div>

        <div>
            <input type="text" value="60" id="count_input" style="margin:0.2vh;"/>
            <label for="count_input">count</label>
        </div>

        <div>
            <input type="text" value="360" id="perspective_input" style="margin:0.2vh;"/>
            <label for="perspective_input">perspective</label>
        </div>
    </div>

    <script>"use strict";
for (const input of document.querySelector('#inputs').querySelectorAll('input')) {
    input.oninput = init;
}

const parent = document.createElement('div');
parent.id = 'carousel-holder'
let divs;
function init() {
    parent.innerHTML = '';
    parent.style.width   = '100vw';
    parent.style.height  = '100vh';
    parent.style.perspective = parseInt(document.querySelector('input#perspective_input').value) + 'px';
    document.body.appendChild(parent);

    const size_vh = parseInt(document.querySelector('input#size_input').value);
    const count = parseInt(document.querySelector('input#count_input').value);

    divs = [];
    for (let i = 0; i < count; i++) {
        const div = document.createElement('div');
        div.style.width  = size_vh + 'vh';
        div.style.height = size_vh + 'vh';
        div.style.backgroundColor = 'gray';

        div.style.display        = 'flex';
        div.style.justifyContent = 'center';
        div.style.alignItems     = 'center';
        div.style.fontSize = size_vh*0.5 + 'vh';
        div.textContent += "🤔";

        divs.push(div);
        parent.appendChild(div);
    }
}

window.onload = () => {
    document.body.style.backgroundColor = 'white';

    init();

    requestAnimationFrame(function frame(dt) {
        requestAnimationFrame(frame);

        const size_vh = parseInt(document.querySelector('input#size_input').value);

        for (let i = 0; i < divs.length; i++) {
            const t = i / divs.length;
            const ANGLE_RANGE = Math.PI * 2;
            const angle = (t + dt*0.000025) * ANGLE_RANGE;
            let y = Math.cos(angle);
            let z = Math.sin(angle);
            /* NOTE: Math.atan2(y, z) is tempting, but you get upside down quads */
            const tan_angle = -Math.atan2(y, -z);

            y *= window.innerHeight*0.3;
            z *= window.innerHeight*0.3;
            divs[i].style.position = 'absolute';
            divs[i].style.top = (y + window.innerHeight*0.5) + 'px';
            divs[i].style.left = `calc(${window.innerWidth*0.5}px - ${size_vh*0.5}vh)`;
            divs[i].style.transform = `translateZ(${-z}px) rotateX(${tan_angle}rad)`;
            divs[i].style.zIndex = -~~z;
        }
    });
}
    </script>
  </body>
</html>