Run animation on UI thread.

Perspex.Base/Perspex.Base.csproj

@@ -54,6 +54,7 @@
     <Compile Include="Threading\DispatcherPriority.cs" />
     <Compile Include="Threading\DispatcherTimer.cs" />
     <Compile Include="Threading\MainLoop.cs" />
+    <Compile Include="Threading\PerspexScheduler.cs" />
   </ItemGroup>
   <ItemGroup>
     <Reference Include="Splat">

Perspex.Base/Platform/IPlatformThreadingInterface.cs

@@ -16,6 +16,8 @@ namespace Perspex.Platform
     /// </summary>
     public interface IPlatformThreadingInterface
     {
+        bool HasMessages();
+
         /// <summary>
         /// Process a single message from the windowing system, blocking until one is available.
         /// </summary>

Perspex.Base/Threading/DispatcherTimer.cs

@@ -7,6 +7,7 @@
 namespace Perspex.Threading
 {
     using System;
+    using System.Reactive.Disposables;
     using Perspex.Platform;
     using Splat;
 
@@ -105,6 +106,24 @@ namespace Perspex.Threading
             set; 
         }
 
+        public static IDisposable Run(Func<bool> action, TimeSpan interval, DispatcherPriority priority = DispatcherPriority.Normal)
+        {
+            var timer = new DispatcherTimer(priority);
+
+            timer.Interval = interval;
+            timer.Tick += (s, e) =>
+            {
+                if (!action())
+                {
+                    timer.Stop();
+                }
+            };
+
+            timer.Start();
+
+            return Disposable.Create(() => timer.Stop());
+        }
+
         public void Start()
         {
             if (!this.IsEnabled)

Perspex.Base/Threading/MainLoop.cs

@@ -30,14 +30,21 @@ namespace Perspex.Win32.Threading
         {
             while (!cancellationToken.IsCancellationRequested)
             {
-                Job job;
+                Job job = null;
 
-                // TODO: Dispatch windows messages in preference to lower priority jobs.
-                while (this.queue.Count > 0)
+                while (job != null || this.queue.Count > 0)
                 {
-                    lock (this.queue)
+                    if (job == null)
                     {
-                        job = this.queue.Dequeue();
+                        lock (this.queue)
+                        {
+                            job = this.queue.Dequeue();
+                        }
+                    }
+
+                    if (job.Priority < DispatcherPriority.Input && platform.HasMessages())
+                    {
+                        break;
                     }
 
                     try
@@ -49,6 +56,8 @@ namespace Perspex.Win32.Threading
                     {
                         job.TaskCompletionSource.SetException(e);
                     }
+
+                    job = null;
                 }
 
                 platform.ProcessMessage();
@@ -57,7 +66,7 @@ namespace Perspex.Win32.Threading
 
         public Task InvokeAsync(Action action, DispatcherPriority priority)
         {
-            var job = new Job(action);
+            var job = new Job(action, priority);
 
             lock (this.queue)
             {
@@ -70,14 +79,17 @@ namespace Perspex.Win32.Threading
 
         private class Job
         {
-            public Job(Action action)
+            public Job(Action action, DispatcherPriority priority)
             {
                 this.Action = action;
+                this.Priority = priority;
                 this.TaskCompletionSource = new TaskCompletionSource<object>();
             }
 
             public Action Action { get; private set; }
 
+            public DispatcherPriority Priority { get; private set; }
+
             public TaskCompletionSource<object> TaskCompletionSource { get; set; }
         }
     }

Perspex.Base/Threading/PerspexScheduler.cs

@@ -0,0 +1,31 @@
+// -----------------------------------------------------------------------
+// <copyright file="PerspexScheduler.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Threading
+{
+    using System;
+    using System.Reactive.Concurrency;
+    using System.Reactive.Disposables;
+
+    public class PerspexScheduler : LocalScheduler
+    {
+        private static readonly PerspexScheduler instance = new PerspexScheduler();
+
+        public static PerspexScheduler Instance
+        {
+            get { return instance; }
+        }
+
+        public override IDisposable Schedule<TState>(TState state, TimeSpan dueTime, Func<IScheduler, TState, IDisposable> action)
+        {
+            return DispatcherTimer.Run(() => 
+            {
+                action(this, state);
+                return false;
+            }, dueTime);
+        }
+    }
+}

Perspex.Controls/Presenters/ScrollContentPresenter.cs

@@ -8,8 +8,6 @@ namespace Perspex.Controls.Presenters
 {
     using System;
     using System.Linq;
-    using System.Reactive.Disposables;
-    using Perspex.Controls.Primitives;
     using Perspex.Input;
     using Perspex.Layout;
 

TestApplication/Program.cs

@@ -8,6 +8,7 @@ using Perspex.Diagnostics;
 using Perspex.Layout;
 using Perspex.Media;
 using Perspex.Media.Imaging;
+using Perspex.Threading;
 #if PERSPEX_GTK
 using Perspex.Gtk;
 #else
@@ -462,7 +463,7 @@ namespace TestApplication
                 },
             };
 
-            Observable.Interval(TimeSpan.FromMilliseconds(10))
+            Observable.Interval(TimeSpan.FromMilliseconds(10), PerspexScheduler.Instance)
                 .Subscribe(x =>
                 {
                     ((RotateTransform)rect1.RenderTransform).Angle = x;

Windows/Perspex.Win32/Interop/UnmanagedMethods.cs

@@ -511,6 +511,9 @@ namespace Perspex.Win32.Interop
         [DllImport("user32.dll")]
         public static extern IntPtr LoadCursor(IntPtr hInstance, int lpCursorName);
 
+        [DllImport("user32.dll")]
+        public static extern bool PeekMessage(out MSG lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax, uint wRemoveMsg);
+
         [DllImport("user32.dll")]
         public static extern IntPtr PostMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);
 

Windows/Perspex.Win32/Win32Platform.cs

@@ -57,6 +57,12 @@ namespace Perspex.Win32
             locator.Register(() => instance, typeof(IPlatformThreadingInterface));
         }
 
+        public bool HasMessages()
+        {
+            UnmanagedMethods.MSG msg;
+            return UnmanagedMethods.PeekMessage(out msg, IntPtr.Zero, 0, 0, 0);
+        }
+
         public void ProcessMessage()
         {
             UnmanagedMethods.MSG msg;
@@ -88,11 +94,11 @@ namespace Perspex.Win32
 
         public void Wake()
         {
-            UnmanagedMethods.PostMessage(
-                this.hwnd,
-                (int)UnmanagedMethods.WindowsMessage.WM_DISPATCH_WORK_ITEM,
-                IntPtr.Zero,
-                IntPtr.Zero);
+            //UnmanagedMethods.PostMessage(
+            //    this.hwnd,
+            //    (int)UnmanagedMethods.WindowsMessage.WM_DISPATCH_WORK_ITEM,
+            //    IntPtr.Zero,
+            //    IntPtr.Zero);
         }
 
         [SuppressMessage("Microsoft.StyleCop.CSharp.NamingRules", "SA1305:FieldNamesMustNotUseHungarianNotation", Justification = "Using Win32 naming for consistency.")]