before method

@override void before(StageFrame frame)

Parks the motion at the frame's moment.

The scene coalesces fx notifications through a scheduler the process installs — a post-frame callback under Flutter, a microtask headless — and a stage renders in a pipeline of its own that never frames and is pumped by hand. So the flush is made synchronous for exactly the span of the apply: the view hears the change now, and the pump that follows rebuilds what moved.

Implementation

@override
void before(StageFrame frame) {
  var motion = this.motion;
  if (motion == null) return;
  var installed = sceneFlushScheduler;
  sceneFlushScheduler = (flush) => flush();
  try {
    motion.apply(frame.at);
  } finally {
    sceneFlushScheduler = installed;
  }
}