calculate fps in flutter app

main.dart

var orginalCallback;

void main() {
  runApp(...);
  orginalCallback = window.onReportTimings;
  window.onReportTimings = onReportTimings;
}

const maxframes = 60;
final lastFrames = ListQueue<FrameTiming>(maxframes);
void onReportTimings(List<FrameTiming> timings) {
  for (FrameTiming timing in timings) {
    lastFrames.addFirst(timing);
  }

  while (lastFrames.length >= maxframes) {
    lastFrames.removeLast();
  }
  if (orginalCallback != null) {
    orginalCallback(timings);
  }
  print("fps : $fps");
}
const frameInterval = const Duration(microseconds: Duration.microsecondsPerSecond ~/ 60);

double get fps {

  var lastFramesSet = <FrameTiming>[];
  for (FrameTiming timing in lastFrames) {
    if (lastFramesSet.isEmpty) {
      lastFramesSet.add(timing);
    } else {
      var lastStart = lastFramesSet.last.timestampInMicroseconds(FramePhase.buildStart);
      if (lastStart - timing.timestampInMicroseconds(FramePhase.rasterFinish) > ( frameInterval.inMicroseconds * 2)) {
        // in different set
        break;
      }
      lastFramesSet.add(timing);
    }
  }
  var frameCount = lastFramesSet.length;
  var costCount = lastFramesSet.map((t) {
    return (t.totalSpan.inMicroseconds ~/ frameInterval.inMicroseconds) + 1;
  }).fold(0, (a, b)=> a + b);
  return frameCount * 60 / costCount;
}