OptionalcancelCancel a handle returned by requestFrame.
OptionalgetThe renderer's current (resting) pixel ratio — read at each gesture start.
OptionalrequestSchedule cb for the next animation frame with a millisecond timestamp; returns a handle.
What the controller needs from its owner: set a pixel ratio and request a render. The optional members default sensibly:
getPixelRatio→ 1,requestFrame/cancelFrame→ the globalrequestAnimationFrame/cancelAnimationFrame. With no frame scheduler available the factor stays at its proactive value for the whole gesture (no adaptation). A suppliedrequestFrameis only ever cancelled throughcancelFrame(never the global one — its handles are foreign); withoutcancelFrame, a late tick from a stopped sampler is ignored (it carries a stale generation).