canvg

What is canvg?

The canvg npm package is a versatile library that allows users to parse and render SVG (Scalable Vector Graphics) to a Canvas element in a browser or on the server-side using Node.js. It is particularly useful for converting SVGs into Canvas for manipulation, rendering, or exporting purposes.

What are canvg's main functionalities?

Rendering SVG to Canvas

This code sample demonstrates how to load an SVG file, render it onto a Canvas, and then save the Canvas output as a PNG file. This is useful for server-side generation of images from SVG files.

const canvg = require('canvg');
const Canvas = require('canvas');
const fs = require('fs');

const canvas = Canvas.createCanvas(800, 600);
const ctx = canvas.getContext('2d');
const svg = fs.readFileSync('path/to/your/svgfile.svg', 'utf-8');
canvg(ctx, svg);

const out = fs.createWriteStream('path/to/output.png');
const stream = canvas.createPNGStream();
stream.pipe(out);

Manipulating SVG before rendering

This example shows how to manipulate SVG data by changing its color before rendering it to a Canvas. This is useful for dynamically altering the appearance of SVGs based on runtime conditions.

const canvg = require('canvg');
const Canvas = require('canvas');
const fs = require('fs');

const canvas = Canvas.createCanvas(800, 600);
const ctx = canvas.getContext('2d');
let svg = fs.readFileSync('path/to/your/svgfile.svg', 'utf-8');

// Modify SVG data
svg = svg.replace('fill:#000000', 'fill:#123456');

// Render modified SVG to canvas
canvg(ctx, svg);

Other packages similar to canvg

fabric

Fabric.js is a powerful and rich graphics library, allowing you to manipulate and render both SVG and Canvas elements. Compared to canvg, Fabric.js offers a broader set of features for interactive object model on canvas, including a full suite of interactive capabilities such as drag and drop, object manipulation, and events.

svg2canvas

svg2canvas is another library that focuses on converting SVG documents into Canvas elements. While similar in purpose to canvg, svg2canvas might have different implementation details or performance characteristics, making it a viable alternative depending on specific project requirements.

README

canvg

JavaScript SVG parser and renderer on Canvas. It takes the URL to the SVG file or the text of the SVG file, parses it in JavaScript and renders the result on Canvas.

Quickstart   •   Examples   •   Options   •   Demo   •   Playground

---

Quickstart

Install this library using your favorite package manager:

pnpm add canvg
# or
yarn add canvg
# or
npm i canvg

Then, just import Canvg and use it:

import { Canvg } from 'canvg';

let v = null;

window.onload = async () => {
  const canvas = document.querySelector('canvas');
  const ctx = canvas.getContext('2d');

  v = await Canvg.from(ctx, './svgs/1.svg');

  // Start SVG rendering with animations and mouse handling.
  v.start();
};

window.onbeforeunload = () => {
  v.stop();
};

Description of all exports you can find in Documentation.

Examples

OffscreenCanvas

import {
  Canvg,
  presets
} from 'canvg';

self.onmessage = async (event) => {
  const {
    width,
    height,
    svg
  } = event.data;
  const canvas = new OffscreenCanvas(width, height);
  const ctx = canvas.getContext('2d');
  const v = await Canvg.from(ctx, svg, presets.offscreen());

  // Render only first frame, ignoring animations and mouse.
  await v.render();

  const blob = await canvas.convertToBlob();
  const pngUrl = URL.createObjectURL(blob);

  self.postMessage({
    pngUrl
  });
};

OffscreenCanvas browsers compatibility.

NodeJS

import {
  promises as fs
} from 'fs';
import {
  DOMParser
} from 'xmldom';
import * as canvas from 'canvas';
import fetch from 'node-fetch';
import {
  Canvg,
  presets
} from 'canvg';

const preset = presets.node({
  DOMParser,
  canvas,
  fetch
});

(async (output, input) => {
  const svg = await fs.readFile(input, 'utf8');
  const canvas = preset.createCanvas(800, 600);
  const ctx = canvas.getContext('2d');
  const v = Canvg.fromString(ctx, svg, preset);

  // Render only first frame, ignoring animations.
  await v.render();

  const png = canvas.toBuffer();

  await fs.writeFile(output, png);

})(
  process.argv.pop(),
  process.argv.pop()
);

Resize

import {
  Canvg,
  presets
} from 'canvg';

self.onmessage = async (event) => {
  const {
    width,
    height,
    svg
  } = event.data;
  const canvas = new OffscreenCanvas(width, height);
  const ctx = canvas.getContext('2d');
  const v = await Canvg.from(ctx, svg, presets.offscreen());

  /**
   * Resize SVG to fit in given size.
   * @param width
   * @param height
   * @param preserveAspectRatio
   */
  v.resize(width, height, 'xMidYMid meet');

  // Render only first frame, ignoring animations and mouse.
  await v.render();

  const blob = await canvas.convertToBlob();
  const pngUrl = URL.createObjectURL(blob);

  self.postMessage({
    pngUrl
  });
};

Browser

<script type="module">
import { Canvg } from 'https://cdn.skypack.dev/canvg';

let v = null;

window.onload = () => {
  const canvas = document.querySelector('canvas');
  const ctx = canvas.getContext('2d');

  v = Canvg.fromString(ctx, '<svg width="600" height="600"><text x="50" y="50">Hello World!</text></svg>');

  // Start SVG rendering with animations and mouse handling.
  v.start();

};
</script>
<canvas />

Options

The third parameter of new Canvg(...), Canvg.from(...) and Canvg.fromString(...) is options:

interface IOptions {
  /**
   * WHATWG-compatible `fetch` function.
   */
  fetch?: typeof fetch;
  /**
   * XML/HTML parser from string into DOM Document.
   */
  DOMParser?: typeof DOMParser;
  /**
   * Window object.
   */
  window?: Window;
  /**
   * Whether enable the redraw.
   */
  enableRedraw?: boolean;
  /**
   * Ignore mouse events.
   */
  ignoreMouse?: boolean;
  /**
   * Ignore animations.
   */
  ignoreAnimation?: boolean;
  /**
   * Does not try to resize canvas.
   */
  ignoreDimensions?: boolean;
  /**
   * Does not clear canvas.
   */
  ignoreClear?: boolean;
  /**
   * Scales horizontally to width.
   */
  scaleWidth?: number;
  /**
   * Scales vertically to height.
   */
  scaleHeight?: number;
  /**
   * Draws at a x offset.
   */
  offsetX?: number;
  /**
   * Draws at a y offset.
   */
  offsetY?: number;
  /**
   * Will call the function on every frame, if it returns true, will redraw.
   */
  forceRedraw?(): boolean;
  /**
   * Default `rem` size.
   */
  rootEmSize?: number;
  /**
   * Default `em` size.
   */
  emSize?: number;
  /**
   * Function to create new canvas.
   */
  createCanvas?: (width: number, height: number) => HTMLCanvasElement | OffscreenCanvas;
  /**
   * Function to create new image.
   */
  createImage?: (src: string, anonymousCrossOrigin?: boolean) => Promise<CanvasImageSource>;
  /**
   * Load images anonymously.
   */
  anonymousCrossOrigin?: boolean;
}

Options presets

There are two options presets:

• presets.offscreen(): options for OffscreenCanvas;
• presets.node({ DOMParser, canvas, fetch }): options for NodeJS with node-canvas.

What's implemented?

The end goal is everything from the SVG spec. The majority of the rendering and animation is working. If you would like to see a feature implemented, don't hesitate to add it to the issues list, or better is to create pull request 😎