JavaScript
Next.js
Node.js
Deno

Generate Image From HTML Using Satori and Resvg

5 min read
Anas Rin

TL;DR

Generate image from HTML using github.com/vercel/satori (to convert HTML to SVG) and github.com/yisibl/resvg-js (to convert SVG to PNG) on Node.js and Deno.

Example: github.com/anasrar/satori-resvg.

Background

When Vercel Introducing OG Image Generation: Fast, dynamic social card images at the Edge, and play around with @vercel/og and realize it only work with Edge Runtime and I want to create script that generate fully static image.

Vercel explain technical details behind @vercel/og, that it using github.com/vercel/satori and github.com/RazrFalcon/resvg.

Now let's create from scratch using Node.js and Deno.

Dependencies

Satori

Satori convert HTML to SVG, automatically wrap text and using Yoga Layout under the hood.

Pros

  • Support JSX syntax.
  • Support image (URL and base64).
  • Automatically wrap text.
  • CSS Flexbox.

Cons

  • Only support JSX and React Node.
  • Explicit inline style.
  • Text baked to path.
  • CSS features not fully implemented.

Satori-html

Satori-html convert HTML to React Node, this is because Satori only support React node object at least on Node.js.

Resvg-js

Resvg-js convert SVG to PNG, Rust-Node binding for github.com/RazrFalcon/resvg.

Victor Mono

Victor mono is font that we will use because Satori need at least 1 font as default font.

Flow

HTMLSatoriResvgPNG

Node.js

Tested on node v19.0.1.

mkdir node-image
cd node-image
pnpm init
pnpm add satori@0.0.44 satori-html@0.3.2 @resvg/resvg-js@2.2.0
touch main.mjs
import { readFile, writeFile } from "node:fs/promises";
import { html } from "satori-html";
import satori from "satori";
import { Resvg } from "@resvg/resvg-js";
const template = html(`
<div style="display: flex; flex-flow: column nowrap; align-items: stretch; width: 600px; height: 400px; backgroundImage: linear-gradient(to right, #0f0c29, #302b63, #24243e); color: #000;">
<div style="display: flex; flex: 1 0; flex-flow: row nowrap; justify-content: center; align-items: center;">
<img style="border: 8px solid rgba(255, 255, 255, 0.2); border-radius: 50%;" src="https://placeimg.com/240/240/animals" alt="animals" />
</div>
<div style="display: flex; justify-content: center; align-items: center; margin: 6px; padding: 12px; border-radius: 4px; background: rgba(255, 255, 255, 0.2); color: #fff; font-size: 22px;">
The quick brown fox jumps over the lazy dog.
</div>
</div>
`);
// convert html to svg
const svg = await satori(template, {
width: 600,
height: 400,
fonts: [
{
name: "VictorMono",
data: await readFile("./VictorMono-Bold.ttf"),
weight: 700,
style: "normal",
},
],
});
// render png
const resvg = new Resvg(svg, {
background: "rgba(238, 235, 230, .9)",
});
const pngData = resvg.render();
const pngBuffer = pngData.asPng();
await writeFile("./output.png", pngBuffer);
node main.mjs

Output

node output with cat the middle and caption the quick brown fox jumps over the lazy dog

Deno

Tested on deno 1.29.1.

mkdir deno-image
cd deno-image
touch main.tsx
import React from "https://esm.sh/react@18.2.0";
import satori, { init } from "npm:satori@0.0.44/wasm";
import initYoga from "npm:yoga-wasm-web@0.2.0";
import { Resvg } from "npm:@resvg/resvg-js@2.2.0";
import cacheDir from "https://deno.land/x/cache_dir@0.2.0/mod.ts";
const wasm = await Deno.readFile(
`${cacheDir()}/deno/npm/registry.npmjs.org/yoga-wasm-web/0.2.0/dist/yoga.wasm`,
);
const yoga =
await (initYoga as unknown as (wasm: Uint8Array) => Promise<unknown>)(wasm);
init(yoga);
const template = (
<div
style={{
display: "flex",
flexFlow: "column nowrap",
alignItems: "stretch",
width: "600px",
height: "400px",
backgroundImage: "linear-gradient(to top, #7028e4 0%, #e5b2ca 100%)",
color: "#000",
}}
>
<div
style={{
display: "flex",
flex: "1 0",
flexFlow: "row nowrap",
justifyContent: "center",
alignItems: "center",
}}
>
<img
style={{
border: "8px solid rgba(255, 255, 255, 0.2)",
borderRadius: "50%",
}}
src="https://placeimg.com/240/240/animals"
alt="animals"
/>
</div>
<div
style={{
display: "flex",
justifyContent: "center",
alignItems: "center",
margin: "6px",
padding: "12px",
borderRadius: "4px",
background: "rgba(255, 255, 255, 0.2)",
color: "#fff",
fontSize: "22px",
}}
>
The quick brown fox jumps over the lazy dog.
</div>
</div>
);
// convert html to svg
const svg = await satori(
template,
{
width: 600,
height: 400,
fonts: [
{
name: "VictorMono",
data: await Deno.readFile("./VictorMono-Bold.ttf"),
weight: 700,
style: "normal",
},
],
},
);
// render png
const resvg = new Resvg(svg, {
background: "rgba(238, 235, 230, .9)",
});
const pngData = resvg.render();
const pngBuffer = pngData.asPng();
await Deno.writeFile("./output.png", pngBuffer);
// ffi block, need to force exit
Deno.exit(0);
deno run --unstable --allow-env --allow-ffi --allow-net --allow-read --allow-write main.tsx

Output

deno output with cat the middle and caption the quick brown fox jumps over the lazy dog