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import React from 'react';
import PropTypes from 'prop-types';
const MIN_SCALE = 1;
const MAX_SCALE = 4;
const getMidpoint = (p1, p2) => ({
x: (p1.clientX + p2.clientX) / 2,
y: (p1.clientY + p2.clientY) / 2,
});
const getDistance = (p1, p2) =>
Math.sqrt(Math.pow(p1.clientX - p2.clientX, 2) + Math.pow(p1.clientY - p2.clientY, 2));
const clamp = (min, max, value) => Math.min(max, Math.max(min, value));
export default class ZoomableImage extends React.PureComponent {
static propTypes = {
alt: PropTypes.string,
src: PropTypes.string.isRequired,
width: PropTypes.number,
height: PropTypes.number,
onClick: PropTypes.func,
}
static defaultProps = {
alt: '',
width: null,
height: null,
};
state = {
scale: MIN_SCALE,
}
removers = [];
container = null;
image = null;
lastTouchEndTime = 0;
lastDistance = 0;
componentDidMount () {
let handler = this.handleTouchStart;
this.container.addEventListener('touchstart', handler);
this.removers.push(() => this.container.removeEventListener('touchstart', handler));
handler = this.handleTouchMove;
// on Chrome 56+, touch event listeners will default to passive
// https://www.chromestatus.com/features/5093566007214080
this.container.addEventListener('touchmove', handler, { passive: false });
this.removers.push(() => this.container.removeEventListener('touchend', handler));
}
componentWillUnmount () {
this.removeEventListeners();
}
removeEventListeners () {
this.removers.forEach(listeners => listeners());
this.removers = [];
}
handleTouchStart = e => {
if (e.touches.length !== 2) return;
this.lastDistance = getDistance(...e.touches);
}
handleTouchMove = e => {
const { scrollTop, scrollHeight, clientHeight } = this.container;
if (e.touches.length === 1 && scrollTop !== scrollHeight - clientHeight) {
// prevent propagating event to MediaModal
e.stopPropagation();
return;
}
if (e.touches.length !== 2) return;
e.preventDefault();
e.stopPropagation();
const distance = getDistance(...e.touches);
const midpoint = getMidpoint(...e.touches);
const scale = clamp(MIN_SCALE, MAX_SCALE, this.state.scale * distance / this.lastDistance);
this.zoom(scale, midpoint);
this.lastMidpoint = midpoint;
this.lastDistance = distance;
}
zoom(nextScale, midpoint) {
const { scale } = this.state;
const { scrollLeft, scrollTop } = this.container;
// math memo:
// x = (scrollLeft + midpoint.x) / scrollWidth
// x' = (nextScrollLeft + midpoint.x) / nextScrollWidth
// scrollWidth = clientWidth * scale
// scrollWidth' = clientWidth * nextScale
// Solve x = x' for nextScrollLeft
const nextScrollLeft = (scrollLeft + midpoint.x) * nextScale / scale - midpoint.x;
const nextScrollTop = (scrollTop + midpoint.y) * nextScale / scale - midpoint.y;
this.setState({ scale: nextScale }, () => {
this.container.scrollLeft = nextScrollLeft;
this.container.scrollTop = nextScrollTop;
});
}
handleClick = e => {
// don't propagate event to MediaModal
e.stopPropagation();
const handler = this.props.onClick;
if (handler) handler();
}
setContainerRef = c => {
this.container = c;
}
setImageRef = c => {
this.image = c;
}
render () {
const { alt, src } = this.props;
const { scale } = this.state;
const overflow = scale === 1 ? 'hidden' : 'scroll';
return (
<div
className='zoomable-image'
ref={this.setContainerRef}
style={{ overflow }}
>
<img
role='presentation'
ref={this.setImageRef}
alt={alt}
title={alt}
src={src}
style={{
transform: `scale(${scale})`,
transformOrigin: '0 0',
}}
onClick={this.handleClick}
/>
</div>
);
}
}
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