<p>buffer - Uint8Array is the only destination type supported in all cases, other types are renderTarget and platform dependent. See [link:https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.12 WebGL spec] for details.</p>
<p>For reading out a [page:WebGLCubeRenderTarget WebGLCubeRenderTarget] use the optional parameter activeCubeFaceIndex to determine which face should be read.</p>