XRWebGLLayer - Web APIs 编辑

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The XRWebGLLayer interface of the WebXR Device API provides a linkage between the WebXR device (or simulated XR device, in the case of an inline session) and a WebGL context used to render the scene for display on the device. In particular, it provides access to the WebGL framebuffer and viewport to ease access to the context.

Although XRWebGLLayer is currently the only type of framebuffer layer supported by WebGL, it's entirely possible that future updates to the WebXR specification may allow for other layer types and corresponding image sources.

Constructor

new XRWebGLLayer()

Creates and returns a new XRWebGLLayer object for use by the specified XRSession, using a particular WebGLRenderingContext or WebGL2RenderingContext as the destination context.

Properties

antialias Read only

A Boolean value indicating whether or not the WebGL context's framebuffer supports anti-aliasing. The specific type of anti-aliasing is determined by the user agent.

framebuffer Read only

Returns a WebGLFramebuffer suitable for passing into the bindFrameBuffer() method.

framebufferWidth Read only

Returns the width of the XRWebGLLayer's framebuffer.

framebufferHeight Read only

Returns the height of the layer's framebuffer.

ignoreDepthValues Read only

A Boolean which Indicates whether or not the WebXR compositor should make use of the contents of the layer's depth buffer while compositing the scene.

Methods

getViewport()

Returns a new XRViewport instance representing the position, width, and height to which the WebGL context's viewport must be set to contain drawing to the area of the framebuffer designated for the specified view's contents. In this way, for example, the rendering of the left eye's point of view and of the right eye's point of view are each placed into the correct parts of the framebuffer.

Static methods

getNativeFramebufferScaleFactor()

Returns the scaling factor that can be used to scale the resolution of the recommended WebGL framebuffer resolution to the rendering device's native resolution.

Examples

Binding the layer to a WebGL context

This snippet, taken from Drawing a frame in Movement, orientation, and motion: A WebXR example, shows how the XRWebGLLayer is obtained from the XRSession object's rendering state and is then bound as the current rendering WebGL framebuffer by calling the WebGL bindFrameBuffer() function.

let glLayer = xrSession.renderState.baseLayer;
gl.bindFrameBuffer(gl.FRAMEBUFFER, glLayer.framebuffer);

Rendering every view in a frame

Each time the GPU is ready to render the scene to the XR device, the XR runtime calls the function you specified when you called the XRSession method requestAnimationFrame() to ask to render the frame.

That function receives as input an XRFrame which encapsulates the data needed to render the frame. This information includes the pose (an XRViewerPose object) that describes the position and facing direction of the viewer within the scene as well as a list of XRView objects, each representing one perspective on the scene. In current WebXR implementations, there will never be more than two entries in this list: one describing the position and viewing angle of the left eye and another doing the same for the right.

let pose = xrFrame.getViewerPose(xrReferenceSpace);

if (pose) {
  let glLayer = xrSession.renderState.baseLayer;
  gl.bindFrameBuffer(gl.FRAMEBUFFER, glLayer.Framebffer);

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

    /* Render the view */
  }
}

Specifications

Browser compatibility

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See also

• WebXR Device API
• Getting started with WebGL
• WebGLRenderingContext and WebGL2RenderingContext
• Drawing a frame in Movement, orientation, and motion: A WebXR example