Function request 

pub fn request(
    scene: Scene,
    width: u32,
    height: u32,
    background: AlphaColor<Srgb>,
) -> PixelsRequest

Ask for the pixels of scene, width x height (at least one each), over background.

Answered at once where the thread can wait for the GPU and no frame loop renders requests; otherwise the thread’s PixelsHost answers it a few frames later, and with no host either it is answered PixelsError::Unavailable.