handleDrawFrame method Null safety

void handleDrawFrame()

Called by the engine to produce a new frame.

This method is called immediately after handleBeginFrame. It calls all the callbacks registered by addPersistentFrameCallback, which typically drive the rendering pipeline, and then calls the callbacks registered by addPostFrameCallback.

See handleBeginFrame for a discussion about debugging hooks that may be useful when working with frame callbacks.

Implementation

void handleDrawFrame() {
  assert(_schedulerPhase == SchedulerPhase.midFrameMicrotasks);
  Timeline.finishSync(); // end the "Animate" phase
  try {
    // PERSISTENT FRAME CALLBACKS
    _schedulerPhase = SchedulerPhase.persistentCallbacks;
    for (final FrameCallback callback in _persistentCallbacks)
      _invokeFrameCallback(callback, _currentFrameTimeStamp!);

    // POST-FRAME CALLBACKS
    _schedulerPhase = SchedulerPhase.postFrameCallbacks;
    final List<FrameCallback> localPostFrameCallbacks =
        List<FrameCallback>.from(_postFrameCallbacks);
    _postFrameCallbacks.clear();
    for (final FrameCallback callback in localPostFrameCallbacks)
      _invokeFrameCallback(callback, _currentFrameTimeStamp!);
  } finally {
    _schedulerPhase = SchedulerPhase.idle;
    Timeline.finishSync(); // end the Frame
    assert(() {
      if (debugPrintEndFrameBanner)
        debugPrint('▀' * _debugBanner!.length);
      _debugBanner = null;
      return true;
    }());
    _currentFrameTimeStamp = null;
  }
}