@artcom/react-pixel-overlay

A PerfectPixel-style design overlay as a React component. It renders a semi-transparent design image (e.g. an exported Figma artboard) on top of your live page so you can verify a pixel-perfect implementation — without a browser extension, checked into the project so the whole team and CI screenshots get the same tool.

Framework-agnostic within React: no styling-library dependency (plain CSS modules), rendered through a portal on document.body, SSR-safe.

Features

• Overlay images — pass a list of sources (or point the bundled Vite plugin at an image folder) and pick one from a dropdown in the panel; or drop / paste any PNG, JPG or SVG onto the page at runtime
• Opacity — slider, or keys 1–9 (10–90 %) and 0 (100 %)
• Blend modes — normal, difference (identical pixels go black, deviations light up), multiply, overlay — plus color invert
• Pixel-level positioning — drag the image, or nudge with arrow keys (Shift = 10 px), plus numeric X/Y/scale inputs
• Click-through lock — locked, the overlay ignores the mouse so you can use and inspect the page beneath; unlocked, you can drag it
• Persistence — all settings and the dropped image survive reloads via localStorage, namespaced per storageKey
• Collapsible control panel

Install

npm install @artcom/react-pixel-overlay --save-dev

(Or as a file:/git dependency while unpublished.)

Usage

import { PixelOverlay } from "@artcom/react-pixel-overlay"
import "@artcom/react-pixel-overlay/styles.css"

// QA tooling only — mount in dev builds, or anywhere via `?overlay` in the URL.
const overlayEnabled =
  import.meta.env.DEV || new URLSearchParams(window.location.search).has("overlay")

function App() {
  return (
    <>
      <YourApp />
      {overlayEnabled && <PixelOverlay src="/design-overlay.png" />}
    </>
  )
}

The image is rendered at its natural size from the top-left corner of the page, so export your design at the exact target resolution (e.g. a 3840×2160 artboard for a 4K screen) and use the scale input only as a fallback.

Multiple images from a folder

A browser can't list a server directory, so the package ships a tiny Vite plugin that scans an image folder inside public/ at dev/build time and exposes the file list as a virtual module (in dev, adding/removing images reloads automatically):

// vite.config.js
import { pixelOverlaySources } from "@artcom/react-pixel-overlay/vite"

export default defineConfig({
  plugins: [react(), pixelOverlaySources("design-overlays")], // public/design-overlays/
})

import overlaySources from "virtual:pixel-overlay-sources"

<PixelOverlay sources={overlaySources} />

Every image in the folder shows up in the panel's dropdown, labeled by filename. Not using Vite? Pass any string[] (or { label, src }[]) to sources instead — e.g. from a hand-written manifest. TypeScript users can type the virtual module by referencing @artcom/react-pixel-overlay/virtual.

Props

Prop	Type	Default	Description
sources	Array<string | { label, src }>	[]	Overlay images, selectable from a dropdown. String entries are labeled by filename.
src	string	–	Shorthand for a single image; prepended to sources.
storageKey	string	"pixel-overlay"	localStorage key for settings; the dropped image is stored under <storageKey>:image. Use distinct keys for apps sharing an origin.
zIndex	number	2147482000	z-index of the image; the panel uses zIndex + 1.

A dropped/pasted image appears in the dropdown as "Dropped image" and is selected automatically. The selection is persisted; if the selected file disappears, the first entry is used.

Keyboard shortcuts

Active while no form field is focused:

Key	Action
O	Show / hide overlay
L	Toggle click-through lock / movable
B	Cycle blend mode
I	Invert colors
↑ ↓ ← →	Move by 1 px (Shift: 10 px)
1–9, 0	Opacity 10–90 %, 100 %

Notes

• Dropped images are persisted as data URLs; very large images can exceed the ~5 MB localStorage quota — the overlay still works, it just won't survive a reload (a warning is logged).
• Don't ship it to production users: gate the mount as in the example above.

Development

npm install
npm run dev     # demo playground with a sample "design"
npm run build   # builds dist/ (ESM + CJS + style.css, exported as "@artcom/react-pixel-overlay/styles.css")