VRPositionState.linearVelocity

The linearVelocity read-only property of the VRPositionState interface returns the current linear velocity of the sensor.

This is the current velocity at which the sensor is moving, along the x, y, and z axes. If the sensor is incapable of providing linear velocity, the method will return null.

Syntax

var myLinearVelocity = VRPositionState.linearVelocity;

Value

A DOMPoint.

Examples

The following example is taken from our velocity-acceleration demo, which uses the WebVR API to update the view of a simple 2D canvas scene on each frame of a requestAnimationFrame loop, while ouputting the linearVelocity, VRPositionState.linearAcceleration, VRPositionState.angularVelocity, and VRPositionState.angularAcceleration values to the UI on each frame for information purposes.

function setView() {
  var posState = gPositionSensor.getState();
  
    ...

  linVelPara.textContent = 'Linear velocity: x' + formatNumber(posState.linearVelocity.x) + " y"
                                + formatNumber(posState.linearVelocity.y) + " z"
                                + formatNumber(posState.linearVelocity.z);

  linAccPara.textContent = 'Linear acceleration: x' + formatNumber(posState.linearAcceleration.x) + " y"
                                + formatNumber(posState.linearAcceleration.y) + " z"
                                + formatNumber(posState.linearAcceleration.z);
 
  angVelPara.textContent = 'Angular velocity: x' + formatNumber(posState.angularVelocity.x) + " y"
                                + formatNumber(posState.angularVelocity.y) + " z"
                                + formatNumber(posState.angularVelocity.z);

  angAccPara.textContent = 'Angular acceleration: x' + formatNumber(posState.angularVelocity.x) + " y"
                                + formatNumber(posState.angularVelocity.y) + " z"
                                + formatNumber(posState.angularVelocity.z);
}

function formatNumber(number) {
  number = number.toFixed(2);
  if(number => 0) {
    number = Math.abs(number);
    number = number.toFixed(2);
    number = "+" + number;
  }
  return number;
}

This allows you to get an idea of how these values change as the VR headset is moved and rotated.

Specifications

Browser compatibility

• [1] The support in Chrome is currently experimental. To find information on Chrome's WebVR implementation status including supporting builds, check out Bringing VR to Chrome by Brandon Jones.
• [2] The support for this feature is currently disabled by default in Firefox. To enable WebVR support in Firefox Nightly/Developer Edition, you can go to about:config and enable the dom.vr* prefs. A better option however is to install the WebVR Enabler Add-on, which does this for you and sets up other necessary parts of the environment.
• [3] The dom.vr* prefs are enabled by default at this point, in Nightly/Aurora editions.

See also

• WebVR API homepage.
• MozVr.com — demos, downloads, and other resources from the Mozilla VR team.