Function refresh_start 

pub fn refresh_start(trigger: u32, converges: bool) -> u32

The still frames a refresh after the region moved waits for (cleanup_due’s start): a refresh through the rate control (converges) is that rate control’s own frames, each within its budget, so it starts on the first still frame, where waiting trigger frames only left the picture as the motion did; a refresh held at the paint-over quantizer waits for the screen to stay still. A region that changed only a little (a caret, a keystroke) waits trigger either way, or a caret blinking on a clean screen would send every frame.