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import React from 'react';
import PropTypes from 'prop-types';
import Hammer from 'hammerjs';
const MIN_SCALE = 1;
const MAX_SCALE = 4;
const DOUBLE_TAP_SCALE = 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;
lastScale = null;
zoomCenter = null;
componentDidMount () {
// register pinch event handlers to the container
let hammer = new Hammer.Manager(this.container, {
// required to make container scrollable by touch
touchAction: 'pan-x pan-y',
});
hammer.add(new Hammer.Pinch());
hammer.on('pinchstart', this.handlePinchStart);
hammer.on('pinchmove', this.handlePinchMove);
this.removers.push(() => hammer.off('pinchstart pinchmove'));
// register tap event handlers
hammer = new Hammer.Manager(this.image);
// NOTE the order of adding is also the order of gesture recognition
hammer.add(new Hammer.Tap({ event: 'doubletap', taps: 2 }));
hammer.add(new Hammer.Tap());
// prevent the 'tap' event handler be fired on double tap
hammer.get('tap').requireFailure('doubletap');
// NOTE 'tap' and 'doubletap' events are fired by touch and *mouse*
hammer.on('tap', this.handleTap);
hammer.on('doubletap', this.handleDoubleTap);
this.removers.push(() => hammer.off('tap doubletap'));
}
componentWillUnmount () {
this.removeEventListeners();
}
componentDidUpdate (prevProps, prevState) {
if (!this.zoomCenter) return;
const { x: cx, y: cy } = this.zoomCenter;
const { scale: prevScale } = prevState;
const { scale: nextScale } = this.state;
const { scrollLeft, scrollTop } = this.container;
// math memo:
// x = (scrollLeft + cx) / scrollWidth
// x' = (nextScrollLeft + cx) / nextScrollWidth
// scrollWidth = clientWidth * prevScale
// scrollWidth' = clientWidth * nextScale
// Solve x = x' for nextScrollLeft
const nextScrollLeft = (scrollLeft + cx) * nextScale / prevScale - cx;
const nextScrollTop = (scrollTop + cy) * nextScale / prevScale - cy;
this.container.scrollLeft = nextScrollLeft;
this.container.scrollTop = nextScrollTop;
}
removeEventListeners () {
this.removers.forEach(listeners => listeners());
this.removers = [];
}
handleClick = e => {
// prevent the click event propagated to parent
e.stopPropagation();
// the tap event handler is executed at the same time by touch and mouse,
// so we don't need to execute the onClick handler here
}
handlePinchStart = () => {
this.lastScale = this.state.scale;
}
handlePinchMove = e => {
const scale = clamp(MIN_SCALE, MAX_SCALE, this.lastScale * e.scale);
this.zoom(scale, e.center);
}
handleTap = () => {
const handler = this.props.onClick;
if (handler) handler();
}
handleDoubleTap = e => {
if (this.state.scale === MIN_SCALE)
this.zoom(DOUBLE_TAP_SCALE, e.center);
else
this.zoom(MIN_SCALE, e.center);
}
zoom (scale, center) {
this.zoomCenter = center;
this.setState({ scale });
}
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';
const marginStyle = {
position: 'absolute',
top: 0,
bottom: 0,
left: 0,
right: 0,
display: 'flex',
alignItems: 'center',
justifyContent: 'center',
transform: `scale(${scale})`,
transformOrigin: '0 0',
};
return (
<div
className='zoomable-image'
ref={this.setContainerRef}
style={{ overflow }}
>
<div
className='zoomable-image__margin'
style={marginStyle}
>
<img
ref={this.setImageRef}
role='presentation'
alt={alt}
src={src}
onClick={this.handleClick}
/>
</div>
</div>
);
}
}
|
