Merge pull request #11637 from AvaloniaUI/feature/request-animation-frame

Added TopLevel.RequestAnimationFrame

src/Avalonia.Base/Media/MediaContext.Clock.cs

@@ -4,6 +4,7 @@ using System.Diagnostics;
 using Avalonia.Animation;
 using Avalonia.Reactive;
 using Avalonia.Threading;
+using Avalonia.Utilities;
 
 namespace Avalonia.Media;
 
@@ -17,8 +18,12 @@ internal partial class MediaContext
     {
         private readonly MediaContext _parent;
         private List<IObserver<TimeSpan>> _observers = new();
-        public bool HasNewSubscriptions { get; set; }
-        public bool HasSubscriptions => _observers.Count > 0;
+        private List<IObserver<TimeSpan>> _newObservers = new();
+        private Queue<Action<TimeSpan>> _queuedAnimationFrames = new();
+        private Queue<Action<TimeSpan>> _queuedAnimationFramesNext = new();
+        private TimeSpan _currentAnimationTimestamp;
+        public bool HasNewSubscriptions => _newObservers.Count > 0;
+        public bool HasSubscriptions => _observers.Count > 0 || _queuedAnimationFrames.Count > 0;
 
         public MediaContextClock(MediaContext parent)
         {
@@ -29,19 +34,41 @@ internal partial class MediaContext
         {
             _parent.ScheduleRender(false);
             Dispatcher.UIThread.VerifyAccess();
-            HasNewSubscriptions = true;
             _observers.Add(observer);
+            _newObservers.Add(observer);
             return Disposable.Create(() =>
             {
                 Dispatcher.UIThread.VerifyAccess();
                 _observers.Remove(observer);
             });
         }
+        
+        public void RequestAnimationFrame(Action<TimeSpan> action)
+        {
+            _parent.ScheduleRender(false);
+            _queuedAnimationFrames.Enqueue(action);
+        }
 
         public void Pulse(TimeSpan now)
         {
+            _newObservers.Clear();
+            _currentAnimationTimestamp = now;
+            
+            // We are swapping the queues before enumeration
+            (_queuedAnimationFrames, _queuedAnimationFramesNext) = (_queuedAnimationFramesNext, _queuedAnimationFrames);
+            var animationFrames = _queuedAnimationFramesNext;
+            while (animationFrames.TryDequeue(out var callback))
+                callback(now);
+            
             foreach (var observer in _observers.ToArray())
-                observer.OnNext(now);
+                observer.OnNext(_currentAnimationTimestamp);
+        }
+        
+        public void PulseNewSubscriptions()
+        {
+            foreach (var observer in _newObservers.ToArray())
+                observer.OnNext(_currentAnimationTimestamp);
+            _newObservers.Clear();
         }
 
         public PlayState PlayState
@@ -50,4 +77,6 @@ internal partial class MediaContext
             set => throw new InvalidOperationException();
         }
     }
+
+    public void RequestAnimationFrame(Action<TimeSpan> action) => _clock.RequestAnimationFrame(action);
 }

src/Avalonia.Base/Media/MediaContext.cs

@@ -131,12 +131,11 @@ internal partial class MediaContext : ICompositorScheduler
         // We are doing several iterations when it happens
         for (var c = 0; c < 10; c++)
         {
-            _clock.HasNewSubscriptions = false;
             FireInvokeOnRenderCallbacks();
             
             if (_clock.HasNewSubscriptions)
             {
-                _clock.Pulse(now);
+                _clock.PulseNewSubscriptions();
                 continue;
             }
 

src/Avalonia.Controls/TopLevel.cs

@@ -25,6 +25,7 @@ using System.Linq;
 using System.Threading.Tasks;
 using Avalonia.Metadata;
 using Avalonia.Rendering.Composition;
+using Avalonia.Threading;
 
 namespace Avalonia.Controls
 {
@@ -535,7 +536,16 @@ namespace Avalonia.Controls
                     return Disposable.Create(() => { });
             }
         }
-
+        
+        /// <summary>
+        /// Enqueues a callback to be called on the next animation tick
+        /// </summary>
+        public void RequestAnimationFrame(Action<TimeSpan> action)
+        {
+            Dispatcher.UIThread.VerifyAccess();
+            MediaContext.Instance.RequestAnimationFrame(action);
+        }
+        
         protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);