avalonia: PanAndZoom gesture recognizer now can do single-touch panning

InABox.Avalonia/Components/ImageEditor/PanAndZoomGestureRecognizer.cs

@@ -42,6 +42,7 @@ public class PanAndZoomGestureRecognizer : GestureRecognizer
     private float _initialDistance;
     private IPointer? _firstContact;
     private Point _firstPoint;
+    private Point _initialFirstPoint;
     private IPointer? _secondContact;
     private Point _secondPoint;
     private Point _previousOrigin;
@@ -83,6 +84,14 @@ public class PanAndZoomGestureRecognizer : GestureRecognizer
                 e.Handled = pinchEventArgs.Handled;
                 e.PreventGestureRecognition();
             }
+            else if(_firstContact != null)
+            {
+                var pinchEventArgs = new PanAndZoomEventArgs(1, _firstPoint, _firstPoint - _initialFirstPoint);
+                _initialFirstPoint = _firstPoint;
+                Target?.RaiseEvent(pinchEventArgs);
+                e.Handled = pinchEventArgs.Handled;
+                e.PreventGestureRecognition();
+            }
         }
     }
 
@@ -94,8 +103,6 @@ public class PanAndZoomGestureRecognizer : GestureRecognizer
             {
                 _firstContact = e.Pointer;
                 _firstPoint = e.GetPosition(visual);
-
-                return;
             }
             else if (_secondContact == null && _firstContact != e.Pointer)
             {
@@ -117,6 +124,12 @@ public class PanAndZoomGestureRecognizer : GestureRecognizer
                 Capture(_secondContact);
                 e.PreventGestureRecognition();
             }
+            else if(_firstContact != null)
+            {
+                _initialFirstPoint = _firstPoint;
+                Capture(_firstContact);
+                e.PreventGestureRecognition();
+            }
         }
     }
 
@@ -135,11 +148,13 @@ public class PanAndZoomGestureRecognizer : GestureRecognizer
             if (_secondContact == pointer)
             {
                 _secondContact = null;
+                _initialFirstPoint = _firstPoint;
             }
 
             if (_firstContact == pointer)
             {
                 _firstContact = _secondContact;
+                _initialFirstPoint = _secondPoint;
 
                 _secondContact = null;
             }