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Switch to using animation request for scroll inertia dispatch #18997

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Merged
maxkatz6 merged 2 commits into from
Jun 14, 2025
Merged

Switch to using animation request for scroll inertia dispatch #18997

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935f35d
switch to using animation request for scroll inertia dispatch
emmauss Jun 2, 2025
a60f7a9
run inertia calcs in dispatcher operation
emmauss Jun 4, 2025
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126 changes: 73 additions & 53 deletions src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
using System;
using System.Diagnostics;
using System.Security.Cryptography;
using Avalonia.Media;
using Avalonia.Platform;
using Avalonia.Threading;

Expand All @@ -20,19 +22,23 @@ public class ScrollGestureRecognizer : GestureRecognizer
private bool _scrolling;
private Point _trackedRootPoint;
private IPointer? _tracking;
private Stopwatch? _stopWatch;
private int _gestureId;
private Point _pointerPressedPoint;
private VelocityTracker? _velocityTracker;

// Movement per second
private Vector _inertia;
private Vector? _inertia;
private ulong? _lastMoveTimestamp;
private TimeSpan _lastTime;
private TimeSpan _inertiaStartTime;
private int _currentInertiaGestureId;

/// <summary>
/// Defines the <see cref="CanHorizontallyScroll"/> property.
/// </summary>
public static readonly DirectProperty<ScrollGestureRecognizer, bool> CanHorizontallyScrollProperty =
AvaloniaProperty.RegisterDirect<ScrollGestureRecognizer, bool>(nameof(CanHorizontallyScroll),
AvaloniaProperty.RegisterDirect<ScrollGestureRecognizer, bool>(nameof(CanHorizontallyScroll),
o => o.CanHorizontallyScroll, (o, v) => o.CanHorizontallyScroll = v);

/// <summary>
Expand All @@ -47,7 +53,7 @@ public class ScrollGestureRecognizer : GestureRecognizer
/// </summary>
public static readonly DirectProperty<ScrollGestureRecognizer, bool> IsScrollInertiaEnabledProperty =
AvaloniaProperty.RegisterDirect<ScrollGestureRecognizer, bool>(nameof(IsScrollInertiaEnabled),
o => o.IsScrollInertiaEnabled, (o,v) => o.IsScrollInertiaEnabled = v);
o => o.IsScrollInertiaEnabled, (o, v) => o.IsScrollInertiaEnabled = v);

/// <summary>
/// Defines the <see cref="ScrollStartDistance"/> property.
Expand Down Expand Up @@ -102,6 +108,7 @@ protected override void PointerPressed(PointerPressedEventArgs e)
{
EndGesture();
_tracking = e.Pointer;
_inertia = null;
_gestureId = ScrollGestureEventArgs.GetNextFreeId();
_trackedRootPoint = _pointerPressedPoint = point.Position;
_velocityTracker = new VelocityTracker();
Expand All @@ -121,7 +128,7 @@ protected override void PointerMoved(PointerEventArgs e)
if (CanVerticallyScroll && Math.Abs(_trackedRootPoint.Y - rootPoint.Y) > ScrollStartDistance)
_scrolling = true;
if (_scrolling)
{
{
// Correct _trackedRootPoint with ScrollStartDistance, so scrolling does not start with a skip of ScrollStartDistance
_trackedRootPoint = new Point(
_trackedRootPoint.X - (_trackedRootPoint.X >= rootPoint.X ? ScrollStartDistance : -ScrollStartDistance),
Expand All @@ -147,23 +154,25 @@ protected override void PointerMoved(PointerEventArgs e)

protected override void PointerCaptureLost(IPointer pointer)
{
if (pointer == _tracking) EndGesture();
if (pointer == _tracking)
EndGesture();
}

void EndGesture()
{
_tracking = null;
if (_scrolling)
{
_stopWatch?.Stop();
_stopWatch = null;
_inertia = default;
_scrolling = false;
Target!.RaiseEvent(new ScrollGestureEndedEventArgs(_gestureId));
_gestureId = 0;
_lastMoveTimestamp = null;
}

}

}

protected override void PointerReleased(PointerReleasedEventArgs e)
{
Expand All @@ -172,7 +181,8 @@ protected override void PointerReleased(PointerReleasedEventArgs e)
_inertia = _velocityTracker?.GetFlingVelocity().PixelsPerSecond ?? Vector.Zero;

e.Handled = true;
if (_inertia == default
if (_inertia == null
|| _inertia == Vector.Zero
|| e.Timestamp == 0
|| _lastMoveTimestamp == 0
|| e.Timestamp - _lastMoveTimestamp > 200
Expand All @@ -181,53 +191,63 @@ protected override void PointerReleased(PointerReleasedEventArgs e)
else
{
_tracking = null;
var savedGestureId = _gestureId;
var st = Stopwatch.StartNew();
var lastTime = TimeSpan.Zero;
Target!.RaiseEvent(new ScrollGestureInertiaStartingEventArgs(_gestureId, _inertia));
DispatcherTimer.Run(() =>
{
// Another gesture has started, finish the current one
if (_gestureId != savedGestureId)
{
return false;
}

var elapsedSinceLastTick = st.Elapsed - lastTime;
lastTime = st.Elapsed;

var speed = _inertia * Math.Pow(InertialResistance, st.Elapsed.TotalSeconds);
var distance = speed * elapsedSinceLastTick.TotalSeconds;
var scrollGestureEventArgs = new ScrollGestureEventArgs(_gestureId, distance);
Target!.RaiseEvent(scrollGestureEventArgs);

if (!scrollGestureEventArgs.Handled || scrollGestureEventArgs.ShouldEndScrollGesture)
{
EndGesture();
return false;
}

// EndGesture using InertialScrollSpeedEnd only in the direction of scrolling
if (CanVerticallyScroll && CanHorizontallyScroll && Math.Abs(speed.X) < InertialScrollSpeedEnd && Math.Abs(speed.Y) <= InertialScrollSpeedEnd)
{
EndGesture();
return false;
}
else if (CanVerticallyScroll && Math.Abs(speed.Y) <= InertialScrollSpeedEnd)
{
EndGesture();
return false;
}
else if (CanHorizontallyScroll && Math.Abs(speed.X) < InertialScrollSpeedEnd)
{
EndGesture();
return false;
}

return true;
}, TimeSpan.FromMilliseconds(16), DispatcherPriority.Background);
_stopWatch = Stopwatch.StartNew();
_lastTime = _stopWatch.Elapsed;
_inertiaStartTime = _lastTime;
_currentInertiaGestureId = _gestureId;
Target!.RaiseEvent(new ScrollGestureInertiaStartingEventArgs(_gestureId, _inertia.Value));
MediaContext.Instance.RequestAnimationFrame(OnAnimationRequested);
}
}
}

private void OnAnimationRequested(TimeSpan _)
{
// Calculate the current speed and dispatch the next inertia event. This is done asynchronously so we have run the events
// with Input priority
Dispatcher.UIThread.InvokeAsync(() =>
{
// Another gesture has started, finish the current one
if (_gestureId != _currentInertiaGestureId || _stopWatch == null || _inertia is not Vector inertia)
{
return;
}

var timeSpan = _stopWatch.Elapsed;
var elapsedSinceLastTick = timeSpan - _lastTime;
_lastTime = timeSpan;

var speed = inertia * Math.Pow(InertialResistance, (_lastTime - _inertiaStartTime).TotalSeconds);
var distance = speed * elapsedSinceLastTick.TotalSeconds;
var scrollGestureEventArgs = new ScrollGestureEventArgs(_gestureId, distance);
Target!.RaiseEvent(scrollGestureEventArgs);

if (!scrollGestureEventArgs.Handled || scrollGestureEventArgs.ShouldEndScrollGesture)
{
EndGesture();
return;
}

// EndGesture using InertialScrollSpeedEnd only in the direction of scrolling
if (CanVerticallyScroll && CanHorizontallyScroll && Math.Abs(speed.X) < InertialScrollSpeedEnd && Math.Abs(speed.Y) <= InertialScrollSpeedEnd)
{
// NO-OP
}
else if (CanVerticallyScroll && Math.Abs(speed.Y) <= InertialScrollSpeedEnd)
{
EndGesture();
return;
}
else if (CanHorizontallyScroll && Math.Abs(speed.X) < InertialScrollSpeedEnd)
{
EndGesture();
return;
}

// Reschedule on the next animation frame. TopLevel.RequestAnimationFrame isn't available on the Base project, so we use the global MediaContext
MediaContext.Instance.RequestAnimationFrame(OnAnimationRequested);
}, DispatcherPriority.Input);

}
}
}
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