PaintWorkletGlobalScope: registerPaint() method

The registerPaint() method of the PaintWorkletGlobalScope interface registers a class to programmatically generate an image where a CSS property expects a file.

Syntax

registerPaint(name, classRef)

Parameters

name

The name of the worklet class to register.

classRef

A reference to the class that implements the worklet.

Return value

None (undefined).

Exceptions

TypeError

Thrown when one of the arguments is invalid or missing.

InvalidModificationError DOMException

Thrown when the a worklet already exists with the specified name.

Examples

The following shows registering an example worklet module. This should be in a separate js file. Note that registerPaint() is called without a reference to PaintWorkletGlobalScope. The file itself is loaded through CSS.paintWorklet.addModule() (documented here on the parent class of PaintWorklet, at Worklet.addModule().

/* checkboardWorklet.js */

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);

The first step in using a paintworklet is defining the paint worklet using the registerPaint() function, as done above. To use it, you register it with the CSS.paintWorklet.addModule() method:

CSS.paintWorklet.addModule("checkboardWorklet.js");

You can then use the paint() CSS function in your CSS anywhere an <image> value is valid.

li {
  background-image: paint(checkerboard);
}

Specifications

Browser compatibility

See also

• CSS Painting API
• Houdini APIs