Function wait_for_frame 

fn wait_for_frame(
    conn: &RustConnection,
    damage: Option<&RootDamage>,
    pace: &FramePace,
    period: Duration,
) -> TickTrigger

Block until the capture is due a frame and say what asked for it: a change the server reported, brought forward by as much as the pacing budget allows, or the frame timer.

Without DAMAGE the wait is the timer’s alone, which is the cadence a capture keeps when nothing else can say the screen moved.