Add MapBorderPanel

MapControl/Shared/MapBorderPanel.cs

@@ -0,0 +1,94 @@
+// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
+// Copyright © 2023 Clemens Fischer
+// Licensed under the Microsoft Public License (Ms-PL)
+
+#if WINUI
+using Microsoft.UI.Xaml;
+#elif UWP
+using Windows.UI.Xaml;
+#else
+using System.Windows;
+#endif
+
+namespace MapControl
+{
+    /// <summary>
+    /// A MapPanel that adjusts the ViewPosition property of its child elements so that
+    /// elements that would be outside the current viewport are arranged on a border area.
+    /// Such elements are arranged at a distance of BorderWidth/2 from the edges of the
+    /// MapBorderPanel in direction of their original azimuth from the map center.
+    /// </summary>
+    public class MapBorderPanel : MapPanel
+    {
+        public static readonly DependencyProperty BorderWidthProperty = DependencyProperty.Register(
+            nameof(BorderWidth), typeof(double), typeof(MapBorderPanel), null);
+
+        public static readonly DependencyProperty OnBorderProperty = DependencyProperty.Register(
+            "OnBorder", typeof(bool), typeof(MapBorderPanel), null);
+
+        public double BorderWidth
+        {
+            get => (double)GetValue(BorderWidthProperty);
+            set => SetValue(BorderWidthProperty, value);
+        }
+
+        public static bool GetOnBorder(FrameworkElement element)
+        {
+            return (bool)element.GetValue(OnBorderProperty);
+        }
+
+        protected override void SetViewPosition(FrameworkElement element, ref Point? position)
+        {
+            var onBorder = false;
+            var w = ParentMap.RenderSize.Width;
+            var h = ParentMap.RenderSize.Height;
+            var minX = BorderWidth / 2d;
+            var minY = BorderWidth / 2d;
+            var maxX = w - BorderWidth / 2d;
+            var maxY = h - BorderWidth / 2d;
+
+            if (position.HasValue &&
+                (position.Value.X < minX || position.Value.X > maxX ||
+                 position.Value.Y < minY || position.Value.Y > maxY))
+            {
+                var dx = position.Value.X - w / 2d;
+                var dy = position.Value.Y - h / 2d;
+                var cx = (maxX - minX) / 2d;
+                var cy = (maxY - minY) / 2d;
+                double x, y;
+
+                if (dx < 0d)
+                {
+                    x = minX;
+                    y = minY + cy - cx * dy / dx;
+                }
+                else
+                {
+                    x = maxX;
+                    y = minY + cy + cx * dy / dx;
+                }
+
+                if (y < minY || y > maxY)
+                {
+                    if (dy < 0d)
+                    {
+                        x = minX + cx - cy * dx / dy;
+                        y = minY;
+                    }
+                    else
+                    {
+                        x = minX + cx + cy * dx / dy;
+                        y = maxY;
+                    }
+                }
+
+                position = new Point(x, y);
+                onBorder = true;
+            }
+
+            element.SetValue(OnBorderProperty, onBorder);
+
+            base.SetViewPosition(element, ref position);
+        }
+    }
+}

MapControl/Shared/MapPanel.cs

@@ -105,8 +105,7 @@ namespace MapControl
         }
 
         /// <summary>
-        /// Gets the view position of an element with Location
+        /// Gets the view position of an element with Location.
-        /// or null when the element has no Location.
         /// </summary>
         public static Point? GetViewPosition(FrameworkElement element)
         {
@@ -161,7 +160,7 @@ namespace MapControl
                     var location = GetLocation(element);
                     var position = location != null ? GetViewPosition(location) : null;
 
-                    SetViewPosition(element, position);
+                    SetViewPosition(element, ref position);
 
                     if (GetAutoCollapse(element))
                     {
@@ -203,7 +202,7 @@ namespace MapControl
             return finalSize;
         }
 
-        protected virtual Point? GetViewPosition(Location location)
+        protected Point? GetViewPosition(Location location)
         {
             var position = parentMap.LocationToView(location);
 

MapControl/UWP/MapControl.UWP.csproj

@@ -104,6 +104,9 @@
     <Compile Include="..\Shared\MapBase.cs">
       <Link>MapBase.cs</Link>
     </Compile>
+    <Compile Include="..\Shared\MapBorderPanel.cs">
+      <Link>MapBorderPanel.cs</Link>
+    </Compile>
     <Compile Include="..\Shared\MapGraticule.cs">
       <Link>MapGraticule.cs</Link>
     </Compile>

MapControl/WPF/MapPanel.WPF.cs

@@ -39,7 +39,12 @@ namespace MapControl
             return (MapBase)element.GetValue(ParentMapProperty);
         }
 
-        private static void SetViewPosition(FrameworkElement element, Point? position)
+        /// <summary>
+        /// Sets the attached ViewPosition property of an element. The method is called during
+        /// ArrangeOverride and may be overridden to modify the actual view position value.
+        /// An overridden method should call this method to set the attached property.
+        /// </summary>
+        protected virtual void SetViewPosition(FrameworkElement element, ref Point? position)
         {
             element.SetValue(ViewPositionPropertyKey, position);
         }

MapControl/WinUI/MapPanel.WinUI.cs

@@ -67,7 +67,12 @@ namespace MapControl
             return parentMap;
         }
 
-        private static void SetViewPosition(FrameworkElement element, Point? position)
+        /// <summary>
+        /// Sets the attached ViewPosition property of an element. The method is called during
+        /// ArrangeOverride and may be overridden to modify the actual view position value.
+        /// An overridden method should call this method to set the attached property.
+        /// </summary>
+        protected virtual void SetViewPosition(FrameworkElement element, ref Point? position)
         {
             element.SetValue(ViewPositionProperty, position);
         }