Function open_ext_session 

fn open_ext_session(
    conn: &Connection,
    queue: &mut EventQueue<CaptureState>,
    state: &mut CaptureState,
    output: &WlOutput,
    wake: RawFd,
    index: usize,
    from_main: &Receiver<ToHost>,
    paint_cursor: bool,
    generation: u64,
    free: &mut Vec<usize>,
    want: &mut Option<Want>,
) -> Result<(ExtImageCaptureSourceV1, ExtImageCopyCaptureSessionV1), ExtOutcome>

Open an ext capture session on output, with or without the host painting its cursor into the frames, and wait for its first buffer constraints: the point that decides whether this protocol works here at all. A session’s cursor option is fixed at creation, so a toggle closes the session and opens another through here.