SVGMaskElement: maskUnits property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

The read-only maskUnits property of the SVGMaskElement interface reflects the maskUnits attribute of a <mask> element which defines the coordinate system to use for the mask of the element.

Note: Although this property is read-only, it is merely a container for two values you can modify, baseVal and animVal.

Value

An SVGAnimatedEnumeration representing the coordinate system. The possible values are defined in the SVGUnitTypes interface:

0 (SVG_UNIT_TYPE_UNKNOWN)

The type is not one of the predefined types.

1 (SVG_UNIT_TYPE_USERSPACEONUSE)

Corresponds to a value of userSpaceOnUse for the maskUnits attribute and means that all coordinates inside the element refer to the user coordinate system as defined when the mask was created. It is the default value.

2 (SVG_UNIT_TYPE_OBJECTBOUNDINGBOX)

Corresponds to a value of objectBoundingBox for the attribute and means that all coordinates inside the element are relative to the bounding box of the element the mask is applied to. It means that the origin of the coordinate system is the top left corner of the object bounding box and the width and height of the object bounding box are considered to have a length of 1 unit value.

Examples

html
<div>
  <svg
    viewBox="0 0 100 100"
    height="200"
    width="200"
    xmlns="http://www.w3.org/2000/svg">
    <mask
      id="mask1"
      maskUnits="userSpaceOnUse"
      x="20%"
      y="20%"
      width="60%"
      height="60%">
      <rect fill="black" x="0" y="0" width="100%" height="100%" />
      <circle fill="white" cx="50" cy="50" r="35" />
    </mask>

    <mask
      id="mask2"
      maskUnits="objectBoundingBox"
      x="20%"
      y="20%"
      width="60%"
      height="60%">
      <rect fill="black" x="0" y="0" width="100%" height="100%" />
      <circle fill="white" cx="50" cy="50" r="35" />
      <animate
        attributeName="maskUnits"
        values="objectBoundingBox;userSpaceOnUse"
        dur="1s"
        repeatCount="indefinite" />
    </mask>

    <!-- Some reference rect to materialized the mask -->
    <rect id="r1" x="0" y="0" width="45" height="45" />
    <rect id="r2" x="0" y="55" width="45" height="45" />
    <rect id="r3" x="55" y="55" width="45" height="45" />
    <rect id="r4" x="55" y="0" width="45" height="45" />

    <!-- The first 3 rect are masked with useSpaceOnUse units -->
    <use mask="url(#mask1)" href="#r1" fill="blue" />
    <use mask="url(#mask1)" href="#r2" fill="green" />
    <use mask="url(#mask1)" href="#r3" fill="yellow" />

    <!-- The last rect is masked with objectBoundingBox units -->
    <use mask="url(#mask2)" href="#r4" fill="lightblue" />
  </svg>
</div>
<pre id="log"></pre>
js
const unitType = ["unknown", "userSpaceOnUse", "objectBoundingBox"];

const mask = document.getElementById("mask2");
const log = document.getElementById("log");

function displayLog() {
  const baseValue = unitType[mask.maskUnits.baseVal];
  const animValue = unitType[mask.maskUnits.animVal];
  log.textContent = `The top-right 'maskUnits.baseVal' coord system : ${baseValue}\n`;
  log.textContent += `The top-right 'maskUnits.animVal' coord system : ${animValue}`;
  requestAnimationFrame(displayLog);
}
displayLog();

Specifications

Specification
CSS Masking Module Level 1
# dom-svgmaskelement-maskunits

Browser compatibility

BCD tables only load in the browser

See also