XRWebGLLayer: framebuffer property

The read-only XRWebGLLayer property framebuffer is an opaque WebGLFramebuffer which is used to buffer the rendered image if the XR compositor is being used. Otherwise, this property's value is null. The opaque framebuffer is functionally nearly the same as a standard WebGL framebuffer, except for the differences covered in the section How opaque framebuffers are special below.

Value

A WebGLFramebuffer object representing the framebuffer into which the 3D scene is being rendered, or null if the XR compositor is disabled for the session.

Usage notes

How opaque framebuffers are special

The framebuffer represented by the framebuffer property is opaque. As such, its behavior is different in several ways from a standard WebGL context. These differences cause the opaque framebuffer to behave more like the default WebGL framebuffer:

• Opaque framebuffers may support anti-aliasing, even under WebGL 1.0, which don't normally do so.
• Opaque framebuffers' attachments (buffers and the like) can't be inspected or changed. Calling functions such as framebufferTexture2D(), framebufferRenderbuffer(), deleteFramebuffer(), or getFramebufferAttachmentParameter() on an opaque framebuffer results in the WebGL error INVALID_OPERATION (0x0502).
• Opaque framebuffers are considered incomplete and are not available for rendering other than while executing the requestAnimationFrame() callback. Attempting to clear, draw to, or read from the framebuffer results in a WebGL INVALID_FRAMEBUFFER_OPERATION error (0x0506). Calling checkFramebufferStatus() on the WebGL context from outside the animation frame callback causes the WebGL FRAMEBUFFER_UNSUPPORTED error (0x8CDD) to be reported.
• Opaque framebuffers initialized with the depth property set to false will not have a depth buffer and will rely on the coordinates alone to determine distance.
• Opaque framebuffers initialized without specifying a stencil property will not have a stencil buffer.
• Opaque framebuffers will not have an alpha channel available unless the alpha property is true when creating the layer.
• The XR compositor assumes that opaque framebuffers use colors with premultiplied alpha, regardless of whether or not the WebGL context's premultipliedAlpha context attribute is set.

The default configuration of a new framebuffer

Upon creating a new XRWebGLLayer, its new framebuffer is initialized just like the default framebuffer for any WebGL interface:

• The color buffer is configured with its clear value set to the color (0, 0, 0, 0) (meaning transparent black).
• The depth buffer's clear value is the number 1.0.
• The stencil buffer is filled with 0.

Examples

This example gets the XRWebGLLayer for a session and then passes its framebuffer into the WebGL context's bindFramebuffer() function.

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

Specifications

Browser compatibility

See also

• WebXR Device API