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import React, { useCallback, useEffect, useState } from 'react' |
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import type { CSSProperties } from 'react' |
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|
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interface Rect { |
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top: number |
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left: number |
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width: number |
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height: number |
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} |
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|
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export interface DemoSpotlightProps { |
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/** CSS selector for the element to leave uncovered. */ |
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target?: string |
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/** Breathing room left around the target, in pixels. */ |
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padding?: number |
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} |
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|
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const DEFAULT_PADDING = 8 |
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|
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/** Padding is applied to both sides of each axis. */ |
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const BOTH_SIDES = 2 |
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|
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const measure = (target: string, padding: number): Rect | undefined => { |
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const element = document.querySelector(target) |
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|
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if (!element) { |
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return undefined |
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} |
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|
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const { top, left, width, height } = element.getBoundingClientRect() |
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|
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return { |
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top: top - padding, |
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left: left - padding, |
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width: width + BOTH_SIDES * padding, |
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height: height + BOTH_SIDES * padding |
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} |
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} |
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|
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/** |
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* Dims and blurs the page around one element, so the commentary has something |
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* unambiguous to point at. |
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* |
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* The cutout is made from four panels around the target rather than a masked |
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* overlay: the gap between them is the hole, which keeps the blur honest and |
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* avoids masking support becoming a rendering variable. |
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*/ |
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export const DemoSpotlight: React.FC<DemoSpotlightProps> = ({ target, padding = DEFAULT_PADDING }) => { |
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const [rect, setRect] = useState<Rect>() |
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|
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const remeasure = useCallback(() => { |
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setRect(target ? measure(target, padding) : undefined) |
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}, [padding, target]) |
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|
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useEffect(() => { |
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remeasure() |
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|
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if (!target) { |
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return |
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} |
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|
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// The page scrolls and reflows underneath the spotlight, so the cutout |
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// is re-measured rather than positioned once. |
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const observer = new ResizeObserver(remeasure) |
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observer.observe(document.body) |
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window.addEventListener('scroll', remeasure, { passive: true }) |
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window.addEventListener('resize', remeasure) |
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|
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return () => { |
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observer.disconnect() |
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window.removeEventListener('scroll', remeasure) |
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window.removeEventListener('resize', remeasure) |
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} |
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}, [remeasure, target]) |
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|
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if (!rect) { |
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return null |
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} |
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|
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const { top, left, width, height } = rect |
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|
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const panels: CSSProperties[] = [ |
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{ insetBlockStart: 0, insetInlineStart: 0, inlineSize: '100%', blockSize: `${Math.max(0, top)}px` }, |
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{ insetBlockStart: `${top + height}px`, insetInlineStart: 0, inlineSize: '100%', insetBlockEnd: 0 }, |
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{ insetBlockStart: `${top}px`, insetInlineStart: 0, inlineSize: `${Math.max(0, left)}px`, blockSize: `${height}px` }, |
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{ insetBlockStart: `${top}px`, insetInlineStart: `${left + width}px`, insetInlineEnd: 0, blockSize: `${height}px` } |
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] |
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|
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const ring: CSSProperties = { |
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insetBlockStart: `${top}px`, |
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insetInlineStart: `${left}px`, |
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inlineSize: `${width}px`, |
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blockSize: `${height}px` |
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} |
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|
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return ( |
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<div className="demo-spotlight" aria-hidden="true"> |
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{panels.map((style, index) => |
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<div key={index} className="demo-spotlight__panel" style={style} />)} |
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|
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<div className="demo-spotlight__ring" style={ring} /> |
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</div> |
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) |
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} |
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