The XRWebGLLayer interface's getViewport() method returns the XRViewport that should be used to render the specified XRView into the WebGL layer. For WebXR devices which use a single framebuffer for both the left and right eyes, the returned viewport represents the region of the framebuffer into which the scene should be rendered for the eye represented by the view.

view

An XRView object indicating the view for which the viewport is to be returned.

A XRViewport object representing the viewport which will restrict drawing to the portion of the layer corresponding to the specified view.

InvalidStateError DOMException

Thrown if either the specified view is not in an active XRFrame or that XRFrame and the XRWebGLLayer are not part of the same WebXR session.

This example demonstrates in part what the callback for the requestAnimationFrame() function might look like, using getViewport() to get the viewport so that drawing can be constrained to the area set aside for the eye whose viewpoint is currently being rendered.

This works because the set of views returned by an XRViewerPose each represent one eye's perspective on the scene. Since the framebuffer is split in half, one half for each eye, setting the WebGL viewport to match the WebXR layer's viewport will ensure that when rendering the scene for the current eye's pose, it is rendered into the correct half of the framebuffer.

<<<--- add link to appropriate section in the Cameras and views article --->>>

function drawFrame(time, frame) {
  const session = frame.session;

  const pose = frame.getViewerPose(mainReferenceSpace);

  if (pose) {
    const glLayer = session.renderState.baseLayer;
    gl.bindFramebuffer(gl.FRAMEBUFFER, glLayer.framebuffer);

    gl.clearColor(0, 0, 0, 1.0);
    gl.clearDepth(1.0);
    gl.clear(gl.COLOR_BUFFER_BIT, gl.DEPTH_COLOR_BIT);

    for (const view of pose.views) {
      const viewport = glLayer.getViewport(view);
      gl.viewport(viewport.x, viewport.y, viewport.width, viewport.height);

      /* Render the scene now */
    }
  }
}

• WebXR Device API