skia-canvas

`bash
pnpm install skia-canvas
pnpm approve-builds
`
In non-interactive scenarios (like building via CI), you can approve the build step when you add skia-canvas to your project:

`bash
pnpm install skia-canvas --allow-build=skia-canvas
`

Alternatively, you can add a pnpm.onlyBuiltDependencies entry to your package.json file to mark the build-step as allowed:
`json
{
"pnpm": {
"onlyBuiltDependencies": ["skia-canvas"]
}
}
`

Platform Support

Skia Canvas runs on Linux, macOS, or Windows as well as serverless platforms like Vercel and AWS Lambda. Precompiled versions of the library’s native code will be automatically downloaded in the appropriate architecture (arm64 or x64) when you install it via npm.

The underlying Rust library uses [N-API][node_napi] v8 which allows it to run on all currently supported Node.js releases, and it is backward compatible with versions going back to v12.22+, v14.17+, v15.12+, and v16+.

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The library is compatible with Linux systems using glibc 2.28 or later as well as Alpine Linux and the musl C library it favors. It will make use of the system’s fontconfig settings in /etc/fonts if they exist but will otherwise fall back to using a placeholder configuration, looking for installed fonts at commonly used Linux paths.

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If you are setting up a Dockerfile that uses node as its basis, the simplest approach is to set your FROM image to one of the (Debian-derived) defaults like node:lts, node:22, node:24-bookworm, or simply:
`dockerfile
FROM node
`

If you wish to use Alpine as the underlying distribution, you can start with something along the lines of:

`dockerfile
FROM node:alpine
`

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Skia Canvas depends on libraries that aren't present in the standard Lambda runtime. You can add these to your function by uploading a ‘layer’ (a zip file containing the required libraries and node_modules directory) and configuring your function to use it.

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If you are using a framework like Next.js that bundles your server-side code with Webpack, you'll need to mark skia-canvas as an ‘external’, otherwise its platform-native binary file will be excluded from the final build. Try adding these options to your next.config.ts file:

`js
const nextConfig: NextConfig = {
serverExternalPackages: ['skia-canvas'],
webpack: (config, options) => {
if (options.isServer){
config.externals = [
...config.externals,
{'skia-canvas': 'commonjs skia-canvas'},
]
}
return config
}
};
`

Compiling from Source

If prebuilt binaries aren’t available for your system you’ll need to compile the portions of this library that directly interface with Skia.

Start by installing:

1. A recent version of git (older versions have difficulties with Skia's submodules)
2. The Rust compiler and cargo package manager using rustup
3. A C compiler toolchain (either LLVM/Clang or MSVC)
4. Python 3 (used by Skia's build process)
5. The Ninja build system
6. On Linux: Fontconfig and OpenSSL

Detailed instructions for setting up these dependencies on different operating systems can be found in the ‘Building’ section of the Rust Skia documentation. The Dockerfiles in the containers directory may also be useful for identifying needed dependencies. Once all the necessary compilers and libraries are present, running npm run build will give you a usable library (after a fairly lengthy compilation process).

Global Settings

> There are a handful of settings that can only be configured at launch and will apply to all the canvases you create in your script. The sections below describe the different [environment variables][node_env] you can set to make global changes. You can either set them as part of your command line invocation, or place them in a .env file in your project directory and use Node 20's [--env-file argument][node_env_arg] to load them all at once.

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When rendering canvases in the background (e.g., by using the asynchronous [toFile][toFile] or [toBuffer][toBuffer] methods), tasks are spawned in a thread pool managed by the [rayon][rayon] library. By default it will create up to as many threads as your CPU has cores. You can see this default value by inspecting any [Canvas][canvas] object's [engine.threads][engine] property. If you wish to override this default, you can set the SKIA_CANVAS_THREADS environment variable to your preferred value.

For example, you can limit your asynchronous processing to two simultaneous tasks by running your script with:
`bash
SKIA_CANVAS_THREADS=2 node my-canvas-script.js
`

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There are a number of situations where the browser API will react to invalid arguments by silently ignoring the method call rather than throwing an error. For example, these lines will simply have no effect:

`js
ctx.fillRect(0, 0, 100, "october")
ctx.lineTo(NaN, 0)
`


Skia Canvas does its best to emulate these quirks, but allows you to opt into a stricter mode in which it will throw TypeErrors in these situations (which can be useful for debugging).

Set the SKIA_CANVAS_STRICT environment variable to 1 or true to enable this mode.

Example Usage

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`js
import {Canvas} from 'skia-canvas'

let canvas = new Canvas(400, 400),
ctx = canvas.getContext("2d"),
{width, height} = canvas;

let sweep = ctx.createConicGradient(Math.PI * 1.2, width/2, height/2)
sweep.addColorStop(0, "red")
sweep.addColorStop(0.25, "orange")
sweep.addColorStop(0.5, "yellow")
sweep.addColorStop(0.75, "green")
sweep.addColorStop(1, "red")
ctx.strokeStyle = sweep
ctx.lineWidth = 100
ctx.strokeRect(100,100, 200,200)

// render to multiple destinations using a background thread
async function render(){
// save a ‘retina’ image...
await canvas.saveAs("rainbox.png", {density:2})
// ...or use a shorthand for canvas.toBuffer("png")
let pngData = await canvas.png
// ...or embed it in a string
let pngEmbed =
}
render()

// ...or save the file synchronously from the main thread
canvas.saveAsSync("rainbox.pdf")
`

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`js
import {Canvas} from 'skia-canvas'

let canvas = new Canvas(400, 400),
ctx = canvas.getContext("2d"),
{width, height} = canvas

for (const color of ['orange', 'yellow', 'green', 'skyblue', 'purple']){
ctx = canvas.newPage()
ctx.fillStyle = color
ctx.fillRect(0,0, width, height)
ctx.fillStyle = 'white'
ctx.arc(width/2, height/2, 40, 0, 2 * Math.PI)
ctx.fill()
}

async function render(){
// save to a multi-page PDF file
await canvas.saveAs("all-pages.pdf")

// save to files named page-01.png, page-02.png, etc.
await canvas.saveAs("page-{2}.png")
}
render()
`

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`js
import {Window} from 'skia-canvas'

let win = new Window(300, 300)
win.title = "Canvas Window"
win.on("draw", e => {
let ctx = e.target.canvas.getContext("2d")
ctx.lineWidth = 25 + 25 * Math.cos(e.frame / 10)
ctx.beginPath()
ctx.arc(150, 150, 50, 0, 2 * Math.PI)
ctx.stroke()

ctx.beginPath()
ctx.arc(150, 150, 10, 0, 2 * Math.PI)
ctx.stroke()
ctx.fill()
})
`

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`js
import sharp from 'sharp'
import {Canvas, loadImage} from 'skia-canvas'

let canvas = new Canvas(400, 400),
ctx = canvas.getContext("2d"),
{width, height} = canvas,
[x, y] = [width/2, height/2]

ctx.fillStyle = 'red'
ctx.fillRect(0, 0, x, y)
ctx.fillStyle = 'orange'
ctx.fillRect(x, y, x, y)

// Render the canvas to a Sharp object on a background thread then desaturate
await canvas.toSharp().modulate({saturation:.25}).jpeg().toFile("faded.jpg")

// Convert an ImageData to a Sharp object and save a grayscale version
let imgData = ctx.getImageData(0, 0, width, height, {matte:'white', density:2})
await imgData.toSharp().grayscale().png().toFile("black-and-white.png")

// Create an image using Sharp then draw it to the canvas as an Image object
let sharpImage = sharp({create:{ width:x, height:y, channels:4, background:"skyblue" }})
let canvasImage = await loadImage(sharpImage)
ctx.drawImage(canvasImage, x, 0)
await canvas.saveAs('mosaic.png')
`

Benchmarks

Acknowledgements

This project is deeply indebted to the work of the Rust Skia project whose Skia bindings provide a safe and idiomatic interface to the mess of C++ that lies underneath. Many thanks to the developers of node-canvas for their terrific set of unit tests. In the absence of an Acid Test for canvas, these routines were invaluable.

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- @mpaparno contributed support for SVG rendering, raw image-buffer handling, WEBP import/export and numerous bug fixes
- @Salmondx developed the initial Raw image loading & rendering routines
- @lucasmerlin helped get GPU rendering working on Vulkan
- @cprecioso & @saantonandre corrected and expanded upon the TypeScript type definitions
- @meihuanyu contributed filter & path rendering fixes

Copyright

[bool-ops]: https://skia-canvas.org/api/path2d#complement-difference-intersect-union-and-xor
[c2d_font]: https://skia-canvas.org/api/context#font
[c2d_measuretext]: https://skia-canvas.org/api/context#measuretext
[canvas]: https://skia-canvas.org/api/canvas
[createProjection()]: https://skia-canvas.org/api/context#createprojection
[createTexture()]: https://skia-canvas.org/api/context#createtexture
[engine]: https://skia-canvas.org/api/canvas#engine
[fontlibrary-use]: https://skia-canvas.org/api/font-library#use
[fontvariant]: https://skia-canvas.org/api/context#fontvariant
[lineDashMarker]: https://skia-canvas.org/api/context#linedashmarker
[newPage]: https://skia-canvas.org/api/canvas#newpage
[p2d_interpolate]: https://skia-canvas.org/api/path2d#interpolate
[p2d_points]: https://skia-canvas.org/api/path2d#points
[p2d_round]: https://skia-canvas.org/api/path2d#round
[p2d_simplify]: https://skia-canvas.org/api/path2d#simplify
[p2d_trim]: https://skia-canvas.org/api/path2d#trim
[toFile]: https://skia-canvas.org/api/canvas#tofile
[textwrap]: https://skia-canvas.org/api/context#textwrap
[toBuffer]: https://skia-canvas.org/api/canvas#tobuffer
[toURL]: https://skia-canvas.org/api/canvas#tourl
[win_bind]: https://skia-canvas.org/api/window#on--off--once
[window]: https://skia-canvas.org/api/window
[multithreading]: https://skia-canvas.org/getting-started#multithreading
[node_napi]: https://nodejs.org/api/n-api.html#node-api-version-matrix
[node_env]: https://nodejs.org/en/learn/command-line/how-to-read-environment-variables-from-nodejs
[node_env_arg]: https://nodejs.org/dist/latest-v22.x/docs/api/cli.html#--env-fileconfig
[rayon]: https://crates.io/crates/rayon
[sharp]: https://sharp.pixelplumbing.com
[VariableFonts]: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Fonts/Variable_Fonts_Guide
[filter]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/filter
[letterSpacing]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/letterSpacing
[wordSpacing]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/wordSpacing
[createPattern()]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/createPattern
[rotate()]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/rotate
[scale()]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/scale
[translate()]: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/translate