FlutterVSyncWaiter Class Reference

#import <FlutterVSyncWaiter.h>

Inheritance diagram for FlutterVSyncWaiter:

Instance Methods
(instancetype)	- initWithDisplayLink:block:
(void)	- waitForVSync:
(void)	- invalidate

Detailed Description

Definition at line 12 of file FlutterVSyncWaiter.h.

Method Documentation

initWithDisplayLink:block:

- (instancetype) initWithDisplayLink:		(FlutterDisplayLink*)	displayLink
block:		(void(^)(CFTimeInterval timestamp, CFTimeInterval targetTimestamp, uintptr_t baton))	block

Creates new waiter instance tied to provided NSView. This function must be called on the main thread.

Provided |block| will be invoked on main thread.

Definition at line 46 of file FlutterVSyncWaiter.mm.

                                   :(FlutterDisplayLink*)displayLink
                              block:(void (^)(CFTimeInterval timestamp,
                                              CFTimeInterval targetTimestamp,
                                              uintptr_t baton))block {
  FML_DCHECK([NSThread isMainThread]);
  if (self = [super init]) {
    _block = block;
 
    _displayLink = displayLink;
    _displayLink.delegate = self;
    // Get at least one callback to initialize _lastTargetTimestamp.
    _displayLink.paused = NO;
    _warmUpFrame = YES;
  }

invalidate

- (void) invalidate

Invalidates the waiter. This must be called on the main thread before the instance is deallocated.

Definition at line 46 of file FlutterVSyncWaiter.mm.

                   {
  // It is possible that there is pending vsync request while the view for which
  // this waiter belongs is being destroyed. In that case trigger the vsync
  // immediately to avoid deadlock.
  if (_pendingBaton.has_value()) {
    CFTimeInterval now = CACurrentMediaTime();
    _block(now, now, _pendingBaton.value());
    _pendingBaton = std::nullopt;
  }
 
  [_displayLink invalidate];

Referenced by TEST_F().

waitForVSync:

- (void) waitForVSync:

(uintptr_t)

baton

Schedules |baton| to be signaled on next display refresh. This function must be called on the main thread.

Definition at line 46 of file FlutterVSyncWaiter.mm.

                    :(uintptr_t)baton {
  FML_DCHECK([NSThread isMainThread]);
  // CVDisplayLink start -> callback latency is two frames, there is
  // no need to delay the warm-up frame.
  if (_warmUpFrame) {
    _warmUpFrame = NO;
    TRACE_VSYNC("WarmUpFrame", baton);
    CFTimeInterval now = CACurrentMediaTime();
    _block(now, now, baton);
    return;
  }
 
  if (_pendingBaton.has_value()) {
    [FlutterLogger logWarning:@"Engine requested vsync while another was pending"];
    _block(0, 0, *_pendingBaton);
    _pendingBaton = std::nullopt;
  }
 
  TRACE_VSYNC("VSyncRequest", _pendingBaton.value_or(0));
 
  CFTimeInterval tick_interval = _displayLink.nominalOutputRefreshPeriod;
  if (_displayLink.paused || tick_interval == 0 || _lastTargetTimestamp == 0) {
    // When starting display link the first notification will come in the middle
    // of next frame, which would incur a whole frame period of latency.
    // To avoid that, first vsync notification will be fired using a timer
    // scheduled to fire where the next frame is expected to start.
    // Also use a timer if display link does not belong to any display
    // (nominalOutputRefreshPeriod being 0)
 
    // Start of the vsync interval.
    CFTimeInterval start = CACurrentMediaTime();
 
    // Timer delay is calculated as the time to the next frame start.
    CFTimeInterval delay = 0;
 
    if (tick_interval != 0 && _lastTargetTimestamp != 0) {
      CFTimeInterval phase = fmod(_lastTargetTimestamp, tick_interval);
      CFTimeInterval now = start;
      start = now - (fmod(now, tick_interval)) + phase;
      if (start < now) {
        start += tick_interval;
      }
      delay = std::max(start - now - kTimerLatencyCompensation, 0.0);
    }
 
    [FlutterRunLoop.mainRunLoop performAfterDelay:delay
                                            block:^{
                                              CFTimeInterval targetTime = start + tick_interval;
                                              TRACE_VSYNC("SynthesizedInitialVSync", baton);
                                              _block(start, targetTime, baton);
                                            }];
    _displayLink.paused = NO;
  } else {
    _pendingBaton = baton;

Referenced by TEST_F().

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The documentation for this class was generated from the following files:

• shell/platform/darwin/macos/framework/Source/FlutterVSyncWaiter.h
• shell/platform/darwin/macos/framework/Source/FlutterVSyncWaiter.mm