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import css from './image-comparison.element.css'
import { calculateDiff, fallbackAAColor, fallbackDiffColor } from '../utils/color-diff.js'
import { colorOrFallbackColorToRGBA } from '../utils/html-color-to-rgba.js'
let loadTemplate = () => {
const templateElement = document.createElement('template')
templateElement.innerHTML = html
loadTemplate = () => templateElement
return templateElement
}
let loadStyles = () => {
const sheet = new CSSStyleSheet()
sheet.replaceSync(css)
loadStyles = () => sheet
return sheet
}
const leftImgSelector = 'img.left-side'
const rightImgSelector = 'img.right-side'
const intersectionObserver = new IntersectionObserver((entries) => {
for (const entry of entries) {
updateSliderDimensions(entry.target)
}
})
const canvasIntersectionObserver = new IntersectionObserver((entries) => {
for (const entry of entries) {
const rootNode = entry.target.getRootNode()
if (!(rootNode instanceof ShadowRoot)) { return }
const { host } = rootNode
if (!(host instanceof ImageComparisonElement)) { return }
updateDiffColors(host)
}
})
const resizeObserver = new ResizeObserver((entries) => {
for (const entry of entries) {
updateSliderDimensions(entry.target)
}
})
const componentData = new WeakMap()
export class ImageComparisonElement extends HTMLElement {
constructor () {
super()
const shadowRoot = this.attachShadow({ mode: 'open' })
shadowRoot.adoptedStyleSheets = [loadStyles()]
const template = loadTemplate()
shadowRoot.append(document.importNode(template.content, true))
const slider = shadowRoot.querySelector('.comparison-slider')
if (!slider) { return }
addSliderDragBehavior(slider)
intersectionObserver.observe(slider)
resizeObserver.observe(slider)
shadowRoot.querySelector(leftImgSelector)?.addEventListener('load', () => this.updateCanvas())
shadowRoot.querySelector(rightImgSelector)?.addEventListener('load', () => this.updateCanvas())
componentData.set(this, {})
this.addEventListener('transitionstart', transitionstartEventHandler)
}
connectedCallback () {
const shadowRoot = this.shadowRoot
if (!shadowRoot) {
return
}
const imgsLightDom = this.querySelectorAll(':scope > img, :scope > figure > img')
if (imgsLightDom.length > 0) {
const leftImg = imgsLightDom[0]
if (leftImg.parentElement?.matches('figure')) {
const text = leftImg.parentElement?.querySelector(':scope > figcaption')?.textContent
shadowRoot.querySelectorAll('.caption--left-side').forEach((element) => { element.textContent = text ?? '' })
}
shadowRoot.querySelectorAll(leftImgSelector).forEach(img => { img.src = leftImg.src })
}
if (imgsLightDom.length > 1) {
const leftImg = imgsLightDom[1]
if (leftImg.parentElement?.matches('figure')) {
const text = leftImg.parentElement?.querySelector(':scope > figcaption')?.textContent
shadowRoot.querySelectorAll('.caption--right-side').forEach((element) => { element.textContent = text ?? '' })
}
shadowRoot.querySelectorAll(rightImgSelector).forEach(img => { img.src = leftImg.src })
}
}
updateCanvas () {
const { shadowRoot } = this
if (!shadowRoot) { return }
const leftImage = shadowRoot.querySelector(leftImgSelector)
const rightImage = shadowRoot.querySelector(rightImgSelector)
if (!isLoadedImg(leftImage) || !isLoadedImg(rightImage)) {
return
}
shadowRoot.querySelectorAll('div.comparison-slider').forEach(slider => {
slider.style.width = `${leftImage.naturalWidth}px`
})
shadowRoot.querySelectorAll('canvas.diff-image').forEach(canvas => {
const width = leftImage.naturalWidth
const height = leftImage.naturalHeight
canvas.width = width
canvas.height = height
const offCanvas1 = new OffscreenCanvas(width, height)
const context1 = offCanvas1.getContext('2d')
const offCanvas2 = new OffscreenCanvas(width, height)
const context2 = offCanvas2.getContext('2d')
const context3 = canvas.getContext('2d')
if (!context1 || !context2 || !context3) { return }
context1?.drawImage(leftImage, 0, 0)
context2?.drawImage(rightImage, 0, 0)
const img1 = context1.getImageData(0, 0, width, height)
const img2 = context2.getImageData(0, 0, width, height)
const diff = context3.createImageData(width, height, { colorSpace: 'srgb' })
const diffMap = new Uint8ClampedArray(width * height)
const data = componentData.get(this)
data.diffMap = diffMap
data.appliedAAColor = null
data.appliedDiffColor = null
data.diffs = calculateDiff({
img1: img1.data,
img2: img2.data,
output: diff.data,
diffMapOutput: diffMap,
width,
height,
antialias: this.antialias
})
this.setAttribute('data-diff-pixels', data.diffs.diffPixelAmount.toString())
if (this.antialias) {
this.setAttribute('data-diff-antialias', data.diffs.aaPixelAmount.toString())
}
context3.putImageData(diff, 0, 0)
updateDiffColors(this)
canvasIntersectionObserver.observe(canvas)
})
}
get diffPixelsAmount () {
return componentData.get(this).diffPixelAmount ?? NaN
}
get antialiasedPixelsAmount () {
return componentData.get(this).aaPixelAmount ?? NaN
}
get antialias () {
return this.hasAttribute('data-antialias')
}
set antialias (val) {
this.toggleAttribute('data-antialias', !!val)
}
}
/**
*
* @param {Event} event - transition Event
*/
function transitionstartEventHandler (event) {
const { target } = event
if (target instanceof ImageComparisonElement) {
updateDiffColors(target)
}
}
/**
*
* @param {ImageComparisonElement} component - component
*/
function updateDiffColors (component) {
const data = componentData.get(component)
const { diffMap, appliedAAColor, appliedDiffColor } = data
if (!diffMap) { return }
const aaColorToApply = getComputedStyle(component).getPropertyValue('--antialias-diff-color') || fallbackAAColor
const diffColorToApply = getComputedStyle(component).getPropertyValue('--diff-color') || fallbackDiffColor
if (aaColorToApply === appliedAAColor && diffColorToApply === appliedDiffColor) { return }
const { shadowRoot } = component
if (!shadowRoot) { return }
shadowRoot.querySelectorAll('canvas.diff-image').forEach(canvas => {
const context = canvas.getContext('2d')
if (!context) { return }
const diff = context.getImageData(0, 0, canvas.width, canvas.height, { colorSpace: 'srgb' })
if (aaColorToApply !== appliedAAColor) {
const aaRGBAColor = colorOrFallbackColorToRGBA(aaColorToApply, fallbackAAColor)
for (let pos = 0, e = diffMap.length; pos < e; pos++) {
if (diffMap[pos] === 0b0011) {
const colorPos = pos * 4
const { data } = diff
data[colorPos] = aaRGBAColor[0]
data[colorPos + 1] = aaRGBAColor[1]
data[colorPos + 2] = aaRGBAColor[2]
data[colorPos + 3] = aaRGBAColor[3]
}
}
data.appliedAAColor = aaColorToApply
}
if (diffColorToApply !== appliedDiffColor) {
const diffRGBAColor = colorOrFallbackColorToRGBA(diffColorToApply, fallbackDiffColor)
for (let pos = 0, e = diffMap.length; pos < e; pos++) {
if (diffMap[pos] === 0b0001) {
const colorPos = pos * 4
const { data } = diff
data[colorPos] = diffRGBAColor[0]
data[colorPos + 1] = diffRGBAColor[1]
data[colorPos + 2] = diffRGBAColor[2]
data[colorPos + 3] = diffRGBAColor[3]
}
}
data.appliedDiffColor = diffColorToApply
}
context.putImageData(diff, 0, 0)
})
}
/**
* @param { HTMLImageElement | null} img - target object
* @returns {img is HTMLImageElement} true if img is a loaded HTMLImageElement, false otherwise
*/
function isLoadedImg (img) {
return img != null && img.complete && img.naturalWidth !== 0
}
/**
* Ensures both images in slider have the same width
* @param {Element} slider - slider element container
*/
function updateSliderDimensions (slider) {
const rightSideImage = slider.querySelector(':scope > img')
const leftSideImage = slider.querySelector('.resize img')
if (!leftSideImage || !rightSideImage) { return }
const imgWidth = rightSideImage.getBoundingClientRect().width + 'px'
leftSideImage.style.width = imgWidth
}
/**
* Add slider behavior
* @param {Element} slider - slider element container
*/
function addSliderDragBehavior (slider) {
const dragElement = slider.querySelector('div.divider')
const resizeElement = slider.querySelector('div.resize')
if (!dragElement || !resizeElement) { return }
let dragWidth = 0
let containerOffset = 0
let containerWidth = 0
let minLeft = 0
let maxLeft = 0
/**
* @param {PointerEvent} event - pointer move event
*/
const pointerMoveHandler = function (event) {
// if the user is using mouse, use preventDefault to prevent the user from
// selecting the images as he moves the slider around.
if (event.pointerType === 'mouse') {
event.preventDefault()
}
const moveX = event.clientX
let leftValue = moveX - dragWidth
// stop the divider from going over the limits of the container
if (leftValue < minLeft) {
leftValue = minLeft
} else if (leftValue > maxLeft) {
leftValue = maxLeft
}
const widthValue = (leftValue + dragWidth / 2 - containerOffset) * 100 / containerWidth + '%'
dragElement.style.left = widthValue
resizeElement.style.width = widthValue
}
dragElement.addEventListener('pointerdown', () => {
dragElement.classList.add('dragging')
dragWidth = dragElement.getBoundingClientRect().width
containerOffset = slider.getBoundingClientRect().left
containerWidth = slider.getBoundingClientRect().width
minLeft = containerOffset + 10
maxLeft = containerOffset + containerWidth - dragWidth - 10
window.addEventListener('pointermove', pointerMoveHandler)
window.addEventListener('pointerup', () => {
// stop clicking the image and move the slider
dragElement.classList.remove('dragging')
window.removeEventListener('pointermove', pointerMoveHandler)
}, { once: true })
})
}
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