canvas kaleidoscope

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>kaleidoscope</title>

.ui-label{
            display: inline-block;
            width: 100px;
        }

.state-ui{
            max-width:500px;
            width:100%;
        }

.input-value{
            display: inline-block;
            width: 100px;
        }
    </style>
</head>
<body>
    <ul>
        <li>
            <span class="ui-label">offsetX</span>
            <input class="state-ui" data-targetprop="offsetX" type="range" min="0" max="1500">
            <span data-targetprop="offsetX" class="input-value"></span>
        </li>
        <li>
            <span class="ui-label">offsetY</span>
            <input class="state-ui" data-targetprop="offsetY" type="range" min="0" max="3000">
            <span data-targetprop="offsetY" class="input-value"></span>
        </li>
        <li>
            <span class="ui-label">offsetRotation</span>
            <input class="state-ui" data-targetprop="offsetRotation" type="range" min="0" max="6.28" step="0.001">
            <span data-targetprop="offsetRotation" class="input-value"></span>
        </li>
        <li>
            <span class="ui-label">slices</span>
            <input class="state-ui" data-targetprop="slices" type="range" min="2" max="30" step="2">
            <span data-targetprop="slices" class="input-value"></span>
        </li>
        <li>
            <span class="ui-label">zoom</span>
            <input class="state-ui" data-targetprop="zoom" type="range" min="0.01" max="2" step="0.01">
            <span data-targetprop="zoom" class="input-value"></span>
        </li>
    </ul>
    <canvas></canvas>
</body>
<script>
const HALF_PI = Math.PI/2;
const TWO_PI = Math.PI*2;

const state = {
    offsetRotation: 0.0,
    offsetScale: 1.0,
    offsetX: 0.0,
    offsetY: 0.0,
    radius: 300,
    slices: 8,  //should be divisible by 2
    zoom: 0.5,
    imageURL: 'https://assets.vogue.international.s3.amazonaws.com/projects/trends-2017/fullimages/oscar-de-la-renta-animales-fullsize.jpg'
};

const canvas = document.querySelector('canvas');
canvas.width = state.radius * 2;
canvas.height = state.radius * 2;

const initUI = (props)=>{
    Object.keys(props)
        .forEach((key)=>{
            try{
                document.querySelector('span[data-targetprop="'+key+'"]' )
                    .textContent = props[key];

document.querySelector('input[data-targetprop="'+key+'"]' )
                    .value = props[key];
            }catch(e){

}
        });
}

const draw = (props)=>{
    const context = document.querySelector('canvas').getContext('2d');
    context.fillStyle = context.createPattern(props.image, 'repeat');
    
    const scale = props.zoom * (props.radius / Math.min(props.image.width, props.image.height));
    const step = TWO_PI/state.slices;
    const cx = props.image.width/2;
    for(let i=0; i<props.slices; i++){
        context.save();
        context.translate(props.radius, props.radius);
        context.rotate(i * step)

context.beginPath();
        context.moveTo(-0.5, -0.5);
        context.arc( 0, 0, props.radius, step * -0.51, step * 0.51)
        context.lineTo(0.5, 0.5)
        context.closePath()

context.rotate(HALF_PI)
        context.scale(scale, scale)
        context.scale([-1,1][i % 2], 1)
        context.translate(props.offsetX - cx, props.offsetY)
        context.rotate(props.offsetRotation)
        context.scale(props.offsetScale, props.offsetScale)

context.fill()
        context.restore()
    }
}

initUI(state);
var img = new Image();
state.image = img;
img.onload = () => { 
    draw(state);
    document.querySelectorAll('.state-ui')
        .forEach((node)=>{
            node.oninput = (e)=>{
                state[node.dataset.targetprop] = e.target.value;
                draw(state);
                document.querySelector('span[data-targetprop="'+node.dataset.targetprop+'"]' )
                    .textContent = e.target.value;
            };
        })
        
};
img.src = state.imageURL;

</script>
</html>