PaintWorklet

The PaintWorklet interface of the CSS Painting API programmatically generates an image where a CSS property expects a file. Access this interface through CSS.paintWorklet.

Privacy concerns

To avoid leaking visited links, this feature is currently disabled in Chrome-based browsers for <a> elements with an href attribute, and for children of such elements. For details, see the following:

• The CSS Painting API Privacy Considerations section
• The CSS Painting API spec issue “CSS Paint API leaks browsing history”

Properties

PaintWorklet.devicePixelRatio

Returns the current device's ratio of physical pixels to logical pixels.

Event handlers

None.

Methods

This interface inherits methods from Worklet.

PaintWorklet.registerPaint()

Registers a class programmatically generate an image where a CSS property expects a file.

CSS.PaintWorklet.addModule()

The addModule() method, inhertied from the Worklet interface loads the module in the given JavaScript file and adds it to the current PaintWorklet.

Examples

The following three examples go together to show creating, loading, and using a PaintWorklet.

Create a PaintWorklet

The following shows an example worklet module. This should be in a separate js file. Note that registerPaint() is called without a reference to PaintWorklet.

class CheckerboardPainter {
  paint(ctx, geom, properties) {
    // Use `ctx` as if it was a normal canvas
    const colors = ['red', 'green', 'blue'];
    const size = 32;
    for(let y = 0; y < geom.height/size; y++) {
      for(let x = 0; x < geom.width/size; x++) {
        const color = colors[(x + y) % colors.length];
        ctx.beginPath();
        ctx.fillStyle = color;
        ctx.rect(x * size, y * size, size, size);
        ctx.fill();
      }
    }
  }
}

// Register our class under a specific name
registerPaint('checkerboard', CheckerboardPainter);

Load a PaintWorklet

The following example demonstrates loading the above worklet from its js file and does so by feature detection.

<script>
  if ('paintWorklet' in CSS) {
    CSS.paintWorklet.addModule('checkerboard.js');
  }
</script>

Use a PaintWorklet

This example shows how to use a PaintWorklet in a stylesheet, including the simplest way to provide a fallback if PaintWorklet isn't supported.

<style>
  textarea {
    background-image: url(checkerboard);
    background-image: paint(checkerboard);
  }
</style>
<textarea></textarea>

You can also use the @supports at-rule.

@supports (background: paint(id)) {
  background-image: paint(checkerboard);
}

Specifications

Browser compatibility

See also

• CSS Painting API
• Houdini APIs