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