Recanvas

Build and render an image using canvas, yoga-layout and react in node environment.

About

This library is built to solve a simple (and maybe common) problem, that rendering an image on server is hard.

The most common (and most probably straight-forward) solution is to render an DOM element with the usual suspects (html, css, javascript) and take a screenshot with testing libs like Puppeteer or Playwright. That is a great solution if you already have the testing library already setup.

If you do not have the E2E setup or your server does not support running it during the runtime, then this library is for you.

Recanvas uses node-canvas under the hood to render the image. This allows for server-side rendering without using browser environment. Alone, imperative canvas is very difficult to work with, so this library provides React components to abstract the canvas methods. Furthermore, it uses yoga-layout to layout the components, so the canvas can be created with same principles of a flexbox.

Installation

npm install recanvas
---
yarn add recanvas

Usage

Generate a canvas

import { View, Text, renderCanvas } from "recanvas"

function generateCanvas() {
  const canvas = renderCanvas(<SocialImage />, {
    width: 400,
    height: 300, // optional, default is equal to width
    quality: 2, // quality is 1 by default, increase it for better quality (min: 0.1)
    font: { color: "#ffffff", size: 20 }, // Override default font options
  })

  return canvas
}

function SocialImage() {
  return (
    <View style={{ backgroundColor: "red", padding: 20 }}>
      <Text style={{ color: "white" }}>Hello World</Text>
    </View>
  )
}

Return the image generated as response

  • ExpressJs / Node HTTP

    app.get("/image", (req, res) => {
  const canvas = generateCanvas()
  const buffer = canvas.toBuffer() // Node.Buffer (default mimeType: image/png)

  res.writeHead(200, {
    "Content-type": "image/png",
    "Cache-Control": "public, max-age=2592000",
    "Content-Length": Buffer.byteLength(buffer).toString(),
  })

  return res.send(buffer)
}

  • Remix-run / Native Response

    const loader = () => {
  const canvas = generateCanvas()
  const buffer = canvas.toBuffer() // Node.Buffer (default mimeType: image/png)

  return new Response(buffer, {
    headers: {
      "Content-Type": "image/png",
      "Cache-Control": "public, max-age=2592000",
      "Content-Length": Buffer.byteLength(buffer).toString(),
    },
  })
}

Example

Future

Need to add support for:

  • Images
  • Multiline URL

License

MIT © Siddhant Gupta

GitHub

View Github