VRDisplay.requestPresent

The requestPresent() method of the VRDisplay interface starts the VRDisplay presenting a scene.

Syntax

vrDisplayInstance.requestPresent(layers).then(function() {
  // Do something after the presentation has begun
});

Parameters

layers

An array of VRLayerInit objects representing the scene you want to present. At the moment, this can be a minimum of 0 and a maximum of 1.

Return value

A promise that resolves once the presentation has begun. there are a number of rules surrounding the promise's fulfillment or rejection:

• If VRDisplayCapabilities.canPresent is false, or if the VRLayer array contains more than VRDisplayCapabilities.maxLayers layers, the promise will be rejected.
• If the VRDisplay is already presenting when requestPresent() is called, the VRDisplay will update the VRLayer array being presented.
• If a call to requestPresent() is rejected while the VRDisplay is already presenting it will end its presentation.
• If requestPresent() is called outside of an engagement gesture the promise will be rejected unless the VRDisplay was already presenting. This engagement gesture is also sufficient to allow requestPointerLock() calls until presentation has ended.

Examples

if(navigator.getVRDisplays) {
  console.log('WebVR 1.1 supported');
  // Then get the displays attached to the computer
  navigator.getVRDisplays().then(function(displays) {
    // If a display is available, use it to present the scene
    if(displays.length > 0) {
      vrDisplay = displays[0];
      console.log('Display found');
      // Starting the presentation when the button is clicked: It can only be called in response to a user gesture
      btn.addEventListener('click', function() {
        if(btn.textContent === 'Start VR display') {
          vrDisplay.requestPresent([{ source: canvas }]).then(function() {
            console.log('Presenting to WebVR display');

            // Set the canvas size to the size of the vrDisplay viewport

            var leftEye = vrDisplay.getEyeParameters('left');
            var rightEye = vrDisplay.getEyeParameters('right');

            canvas.width = Math.max(leftEye.renderWidth, rightEye.renderWidth) * 2;
            canvas.height = Math.max(leftEye.renderHeight, rightEye.renderHeight);

            // stop the normal presentation, and start the vr presentation
            window.cancelAnimationFrame(normalSceneFrame);
            drawVRScene();

            btn.textContent = 'Exit VR display';
          });
        } else {
          vrDisplay.exitPresent();
          console.log('Stopped presenting to WebVR display');

          btn.textContent = 'Start VR display';

          // Stop the VR presentation, and start the normal presentation
          vrDisplay.cancelAnimationFrame(vrSceneFrame);
          drawScene();
        }
      });
    }
  });
}

Specifications

Browser compatibility

See also

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