The OES_fbo_render_mipmap
extension is part of the WebGL API and makes it possible to attach any level of a texture to a framebuffer object.
WebGL extensions are available using the WebGLRenderingContext.getExtension()
method. For more information, see also Using Extensions in the WebGL tutorial.
Note: This extension is only available to WebGL 1. In WebGL2, the functionality of this extension is available in the WebGL 2 context by default.