@ -1,10 +1,16 @@
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 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 ) ) ;
@ -31,95 +37,81 @@ export default class ZoomableImage extends React.PureComponent {
removers = [ ] ;
container = null ;
image = null ;
last Scale = null ;
zoomCenter = null ;
last TouchEndTime = 0 ;
lastDistance = 0 ;
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' ) ) ;
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 ( ) ;
}
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 ( ) ;
handleTouchStart = e => {
if ( e . touches . length !== 2 ) return ;
// 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
this . lastDistance = getDistance ( ... e . touches ) ;
}
handlePinchStart = ( ) => {
this . lastScale = this . state . scale ;
}
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 ;
handlePinchMove = e => {
const scale = clamp ( MIN _SCALE , MAX _SCALE , this . lastScale * e . scale ) ;
this . zoom ( scale , e . center ) ;
}
e . preventDefault ( ) ;
e . stopPropagation ( ) ;
handleTap = ( ) => {
const handler = this . props . onClick ;
if ( handler ) handler ( ) ;
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 ;
}
handleDoubleTap = e => {
if ( this . state . scale === MIN _SCALE )
this . zoom ( DOUBLE _TAP _SCALE , e . center ) ;
else
this . zoom ( MIN _SCALE , e . center ) ;
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 ;
} ) ;
}
zoom ( scale , center ) {
this . zoomCenter = center ;
this . setState ( { scale } ) ;
handleClick = e => {
// don't propagate event to MediaModal
e . stopPropagation ( ) ;
const handler = this . props . onClick ;
if ( handler ) handler ( ) ;
}
setContainerRef = c => {
@ -134,18 +126,6 @@ export default class ZoomableImage extends React.PureComponent {
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
@ -153,18 +133,17 @@ export default class ZoomableImage extends React.PureComponent {
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 }
/ >
< / d i v >
< img
role = 'presentation'
ref = { this . setImageRef }
alt = { alt }
src = { src }
style = { {
transform : ` scale( ${ scale } ) ` ,
transformOrigin : '0 0' ,
} }
onClick = { this . handleClick }
/ >
< / d i v >
) ;
}
David Yip
7 years ago