In this post, we’ll dive into the CSS Paint API, understand how it works, and explore how it can be used to make your web designs more creative and efficient.
What Is the CSS Paint API?
The CSS Paint API is part of the Houdini suite of APIs, which aim to give developers more control over how browsers render web pages. Specifically, the Paint API allows you to write JavaScript code to generate images (or patterns) that can be used as CSS backgrounds, borders, masks, or other properties requiring an image.
Consider it like a canvas drawing function, but directly integrated into CSS. Instead of using static image files or repeating patterns, you can dynamically generate visuals based on logic and parameters.
How Does It Work?
The Paint API works by letting you define a “paint worklet” — a lightweight JavaScript module that handles the drawing logic. The browser then uses this logic to generate the image whenever it’s needed.
Here’s a high-level overview of how it works:
Register a Paint Worklet
Use JavaScript to register a custom paint worklet, which defines how your image or pattern should be drawn.Use the Worklet in CSS
Once registered, the worklet can be used in CSS via thepaint()function, much like referencing a CSS variable or an image.Browser Generates the Visual
The browser dynamically generates the visual on the fly using the worklet’s logic.
Key Features of the CSS Paint API
Dynamic and Procedural Graphics
Unlike static images, visuals created with the Paint API can adapt to changes in size, resolution, or other factors.Reusable Worklets
Once a paint worklet is defined, it can be reused across multiple elements and even shared between projects.Lightweight and Efficient
No need for large image files or external libraries — the Paint API uses minimal JavaScript to achieve stunning results.
HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>CSS Painting API Demo</title>
<link rel="stylesheet" data-wphbdelayedstyle="style.css">
<script type="wphb-delay-type" src="cssPainting.js" defer></script>
</head>
<body>
<h1>CSS Painting API Demo</h1>
<div class="element-with-checkerboard"></div>
<script type="text/javascript" id="wphb-delayed-styles-js">
(function () {
const events = ["keydown", "mousemove", "wheel", "touchmove", "touchstart", "touchend"];
function wphb_load_delayed_stylesheets() {
document.querySelectorAll("link[data-wphbdelayedstyle]").forEach(function (element) {
element.setAttribute("href", element.getAttribute("data-wphbdelayedstyle"));
}),
events.forEach(function (event) {
window.removeEventListener(event, wphb_load_delayed_stylesheets, { passive: true });
});
}
events.forEach(function (event) {
window.addEventListener(event, wphb_load_delayed_stylesheets, { passive: true });
});
})();
</script></body>
</html>
CSS
.element-with-checkerboard {
width: 190px;
height: 190px;
--checkerboard-spacing: 10px;
background-image: paint(checkerboard);
}
Getting Started With the CSS Paint API
Let’s walk through an example to see how the CSS Paint API works in practice.
Enable the Paint API in Your Browser
As of now, the CSS Paint API is supported in most major browsers, but it might still be behind a flag in some cases. Check compatibility here.
Create a Paint Worklet
A Paint Worklet is a JavaScript module that defines the logic for your custom paint. Here’s an example of a simple worklet that creates a checkerboard…
Checkerboard JS
// Define a class for our checkerboard worklet
class CheckerboardPainter {
static get inputProperties() {
return ['--checkerboard-spacing'];
}
paint(ctx, size, properties) {
// Get the custom property '--checkerboard-spacing' or use a default value
const spacing = properties.get('--checkerboard-spacing').value || 32;
for (let y = 0; y < size.height; y += spacing) {
for (let x = 0; x < size.width; x += spacing) {
ctx.fillStyle = (x / spacing + y / spacing) % 2 ? 'black' : 'white';
ctx.fillRect(x, y, spacing, spacing);
}
}
}
}
// Register our class under the 'checkerboard' name
registerPaint('checkerboard', CheckerboardPainter);
Register the Paint Worklet
To use this worklet, you need to load it in your webpage. Add the following script to your HTML…
// Register the paint worklet
if ('paintWorklet' in CSS) {
CSS.paintWorklet
.addModule('paintWorklet.js')
.then(() => {
console.log('Paint worklet registered successfully!');
})
.catch((error) => {
console.error('Failed to register paint worklet:', error);
});
} else {
console.error('CSS Paint API is not supported in this browser.');
}
Real-World Use Cases
The CSS Paint API opens up a world of possibilities for web designers and developers. Here are a few practical examples:
1. Custom Patterns and Textures
Generate patterns like polka dots, stripes, or grids dynamically without relying on image files.
2. Dynamic Styling
Create visuals that respond to CSS variables or media queries, such as a background pattern that changes based on the viewport size.
3. Unique Borders and Masks
Use the Paint API to create custom border styles or clipping masks for images and elements.
4. Performance Optimization
Replace multiple image assets with a single reusable worklet, reducing page load times and maintenance.
Limitations and Considerations
While the CSS Paint API is powerful, it’s not without some limitations:
Browser Support
Not all browsers fully support the Paint API yet. Always check compatibility for your target audience.Complexity
For simple graphics, using a static image or a CSS gradient may still be easier and more maintainable.Performance
Although efficient, complex worklets can still impact performance, especially if applied to many elements.
Conclusion
The CSS Paint API is a game-changer for web design, empowering developers to create dynamic and customizable visuals directly in CSS. While it’s still an emerging technology, its potential for creativity and performance optimization is immense.
If you’re looking to push the boundaries of what’s possible with CSS, the Paint API is worth exploring. Start small, experiment with patterns, and see how it can enhance your projects!
