The requestViewportScale() method of the XRView interface requests that the user agent sets the requested viewport scale for this viewport to the given value. This is used for dynamic viewport scaling which allows rendering to a subset of the WebXR viewport using a scale factor that can be changed every animation frame.

scale

A number greater than 0.0 and less than or equal to 1.0 representing the scale factor.

None (undefined).

Dynamic viewport scaling allows applications to only use a subset of the available framebuffer. The feature may not be available on all systems since it depends on driver support, so you might want to ensure that requestViewportScale() exists before calling it.

The scale parameter can be a number greater than 0.0 and less than or equal to 1.0.

Alternatively, you can use the XRView.recommendedViewportScale property which contains the user agent's recommended value based on internal heuristics. If the user agent doesn't provide a recommended viewport scale, its value is null and the call to requestViewportScale() is ignored.

The following example shows how to request and apply a new viewport scale. The call to XRWebGLLayer.getViewport() applies the change and returns the updated viewport.

for (const view of pose.views) {
  if (view.requestViewportScale) {
    view.requestViewportScale(0.8);
    // or use view.requestViewportScale(view.recommendedViewportScale);
  }
  const viewport = glLayer.getViewport(view);
}

• XRView.recommendedViewportScale