VRDisplay: requestPresent() method
==================================

**Deprecated:** This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

**Non-standard:** This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

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

**Note:** This method was part of the old WebVR API. It has been superseded by the WebXR Device API.

Syntax
------


```js
requestPresent(layers)
```

### 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
--------


```js
if (navigator.getVRDisplays) {
  console.log("WebVR 1.1 supported");
  // Then get the displays attached to the computer
  navigator.getVRDisplays().then((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", () => {
        if (btn.textContent === "Start VR display") {
          vrDisplay.requestPresent([{ source: canvas }]).then(() => {
            console.log("Presenting to WebVR display");

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

            const leftEye = vrDisplay.getEyeParameters("left");
            const 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();
        }
      });
    }
  });
}
```


**Note:** You can see this complete code at raw-webgl-example.

Specifications
--------------

This method was part of the old WebVR API that has been superseded by the WebXR Device API. It is no longer on track to becoming a standard.

Until all browsers have implemented the new WebXR APIs, it is recommended to rely on frameworks, like A-Frame, Babylon.js, or Three.js, or a polyfill, to develop WebXR applications that will work across all browsers [1].

Browser compatibility
---------------------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

See also
--------

* WebVR API