PositionSensorVRDevice.getImmediateState

The getImmediateState() method of the VRDevice interface returns the current instantaneous position sensor state. This is intended to only be used rarely, for certain special uses, for example sampling the immediate position of a hand orientation sensor — or at least it will be, in the future.

For most standard uses, you'll probably want to use PositionSensorVRDevice.getState instead.

Syntax

var myPositionstate = PositionSensorVRDevice.getImmediateState();

Parameters

None.

Returns

A VRPositionState object.

Examples

Our positionsensorvrdevice demo uses the WebVR API to update the view of a simple 2D canvas scene on each frame of a requestAnimationFrame loop. The main function that updates the view data is as follows:

function setView() {
  var posState = gPositionSensor.getImmediateState();
  if(posState.hasPosition) {
    posPara.textContent = 'Position: x' + roundToTwo(posState.position.x) + " y"
                                + roundToTwo(posState.position.y) + " z"
                                + roundToTwo(posState.position.z);
    xPos = -posState.position.x * WIDTH * 2;
    yPos = posState.position.y * HEIGHT * 2;
    if(-posState.position.z > 0.01) {
      zPos = -posState.position.z;
    } else {
      zPos = 0.01;
    }
  }

  if(posState.hasOrientation) {
    orientPara.textContent = 'Orientation: x' + roundToTwo(posState.orientation.x) + " y"
                                + roundToTwo(posState.orientation.y) + " z"
                                + roundToTwo(posState.orientation.z);
    xOrient = posState.orientation.x * WIDTH;
    yOrient = -posState.orientation.y * HEIGHT * 2;
    zOrient = posState.orientation.z * 180;

  }
}

Here we are grabbing a VRPositionState object using getImmediateState() and storing it in posState (the actual live demo uses getState(), but both seem to do the same thing currently.) We then check to make sure that position and orientation info is present in the current frame using VRPositionState.hasPosition and VRPositionState.hasOrientation (these return null if, for example the head mounted display is turned off or not pointing at the position sensor, which would cause an error.)

We then output the x, y and z position and orientation values for informational purposes, and use those values to update the xPos, yPos, zPos, xOrient, yOrient, and zOrient variables, which are used to update the scene rendering on each frame.

Specifications

Specification	Status	Comment
WebVR The definition of 'PositionSensorVRDevice' in that specification.	Editor's Draft	Initial definition

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.