Avalonia multi-touch handling

MapControl/Avalonia/Map.Avalonia.cs

@@ -3,6 +3,7 @@
 // Licensed under the Microsoft Public License (Ms-PL)
 
 using Avalonia.Input;
+using System;
 
 namespace MapControl
 {
@@ -14,7 +15,10 @@ namespace MapControl
         public static readonly StyledProperty<double> MouseWheelZoomDeltaProperty =
             DependencyPropertyHelper.Register<Map, double>(nameof(MouseWheelZoomDelta), 0.25);
 
-        private Point? mousePosition;
+        private IPointer pointer1;
+        private IPointer pointer2;
+        private Point position1;
+        private Point position2;
 
         /// <summary>
         /// Gets or sets the amount by which the ZoomLevel property changes by a MouseWheel event.
@@ -39,10 +43,21 @@ namespace MapControl
 
             var point = e.GetCurrentPoint(this);
 
-            if (point.Properties.IsLeftButtonPressed)
+            if (pointer2 == null &&
+                (point.Properties.IsLeftButtonPressed || point.Pointer.Type == PointerType.Touch))
             {
-                e.Pointer.Capture(this);
-                mousePosition = point.Position;
+                point.Pointer.Capture(this);
+
+                if (pointer1 == null)
+                {
+                    pointer1 = point.Pointer;
+                    position1 = point.Position;
+                }
+                else
+                {
+                    pointer2 = point.Pointer;
+                    position2 = point.Position;
+                }
             }
         }
 
@@ -50,10 +65,17 @@ namespace MapControl
         {
             base.OnPointerReleased(e);
 
-            if (mousePosition.HasValue)
+            if (e.Pointer == pointer1 || e.Pointer == pointer2)
             {
                 e.Pointer.Capture(null);
-                mousePosition = null;
+
+                if (e.Pointer == pointer1)
+                {
+                    pointer1 = pointer2;
+                    position1 = position2;
+                }
+
+                pointer2 = null;
             }
         }
 
@@ -61,11 +83,38 @@ namespace MapControl
         {
             base.OnPointerMoved(e);
 
-            if (mousePosition.HasValue)
+            if (e.Pointer == pointer1 || e.Pointer == pointer2)
             {
                 var position = e.GetPosition(this);
-                TranslateMap(position - mousePosition.Value);
-                mousePosition = position;
+
+                if (pointer2 == null)
+                {
+                    TranslateMap(position - position1);
+                    position1 = position;
+                }
+                else
+                {
+                    Point oldOrigin = new((position1.X + position2.X) / 2d, (position1.Y + position2.Y) / 2d);
+                    Vector oldDistance = position2 - position1;
+
+                    if (e.Pointer == pointer1)
+                    {
+                        position1 = position;
+                    }
+                    else
+                    {
+                        position2 = position;
+                    }
+
+                    Point newOrigin = new((position1.X + position2.X) / 2d, (position1.Y + position2.Y) / 2d);
+                    Vector newDistance = position2 - position1;
+
+                    var oldAngle = Math.Atan2(oldDistance.Y, oldDistance.X) * 180d / Math.PI;
+                    var newAngle = Math.Atan2(newDistance.Y, newDistance.X) * 180d / Math.PI;
+                    var scale = newDistance.Length / oldDistance.Length;
+
+                    TransformMap(newOrigin, newOrigin - oldOrigin, newAngle - oldAngle, scale);
+                }
             }
         }
     }

MapControl/Shared/Timer.cs

@@ -4,18 +4,20 @@
 
 using System;
 #if WPF
+using System.Windows;
 using System.Windows.Threading;
 #elif UWP
 using Windows.UI.Xaml;
 #elif AVALONIA
 using Avalonia.Threading;
+using DependencyObject = Avalonia.AvaloniaObject;
 #endif
 
 namespace MapControl
 {
     internal static class Timer
     {
-        public static DispatcherTimer CreateTimer(this object _, TimeSpan interval)
+        public static DispatcherTimer CreateTimer(this DependencyObject _, TimeSpan interval)
         {
             return new DispatcherTimer { Interval = interval };
         }