Add feature FitToScreen

RichCanvas/Gestures/RichCanvasGestures.cs

@@ -40,6 +40,11 @@ public class RichCanvasGestures
         /// </summary>
         public static InputGesture Pan { get; set; } = new MouseKeyGesture(new MouseGesture(MouseAction.LeftClick), new KeyGesture(Key.Space));
 
+        /// <summary>
+        /// Gets or sets the <see cref="InputGesture"/> used to match the <see cref="RichCanvasCommands.FitToScreen"/>.
+        /// </summary>
+        public static InputGesture FitToScreen { get; set; } = new KeyGesture(Key.Home);
+
         /// <summary>
         /// Gets or sets the <see cref="ModifierKeys"/> used together with MouseWheel for zooming.
         /// <br/>

RichCanvas/RichCanvas.Fitting.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Windows;
+
+namespace RichCanvas
+{
+    public partial class RichCanvas
+    {
+        private void FitViewToChildren(double marginX, double marginY)
+        {
+            if (ItemsHost.Children.Count == 0)
+            {
+                return;
+            }
+
+            Rect overallBounds = new(0, 0, 0, 0);
+
+            for (int i = 0; i < ItemsHost.Children.Count; i++)
+            {
+                var child = ContainerFromElement(ItemsHost.Children[i]);
+                if (child is RichCanvasContainer container)
+                {
+                    overallBounds.Union(container.BoundingBox);
+                }
+            }
+            overallBounds.Inflate(marginX, marginY);
+
+            FitViewToRect(overallBounds);
+        }
+
+        private void FitViewToRect(Rect newView)
+        {
+            // Size / Size
+            Vector zoomAmounts = new Vector(ActualWidth / newView.Size.Width, ActualHeight / newView.Size.Height);
+            double zoomAmount = Math.Min(zoomAmounts.X, zoomAmounts.Y);
+
+            // Set viewport zoom
+            ViewportZoom = zoomAmount;
+
+            // If the canvas has a ScrollViewer and the scrollbars are visible,
+            // the offset will be off by a tad. Calling this command immediately again will fix it.
+            // We can check if there are scrollbars present by doing:
+            //      if (ExtentHeight != ViewportSize.Height) => VerticalScrollBar present
+            //      if (ExtentWidth != ViewportSize.Width) => HorizontalScrollBar present
+            // You can then try to use SystemParameters.ScrollWidth to try and account for it,
+            // but I could not get the offset perfect. Additionally, if the ScrollBar is ever styled,
+            // then we would have to go find the ScrollBar and get its width. But that opens up another whole
+            // can: we would want to cache it so we don't traverse the tree everytime, but then we need to
+            // add handling for if/when the styling changes.
+
+            // Thus I have decided that being 10 pixels off is not the end of the world, and if anyone is
+            // bothered they can hit the FitToScreen button again.
+
+            // Set viewport location
+            double offsetLeft = (ViewportSize.Width - newView.Size.Width) / 2;
+            double offsetTop = (ViewportSize.Height - newView.Size.Height) / 2;
+            Point topLeft = new Point(newView.TopLeft.X - offsetLeft, newView.TopLeft.Y - offsetTop);
+            ViewportLocation = topLeft;
+        }
+
+        /// <summary>
+        /// Change the viewport location and zoom to fit as many items as possible on screen,
+        /// using a default margin of 0.
+        /// </summary>
+        public void FitToScreen() => FitViewToChildren(0, 0);
+    }
+}
+

RichCanvas/RichCanvasCommands.cs

@@ -26,10 +26,19 @@ public class RichCanvasCommands
             RichCanvasGestures.ZoomOut
         });
 
+        /// <summary>
+        /// Change the viewport location and zoom to fit as many items as possible on screen.
+        /// </summary>
+        public static RoutedUICommand FitToScreen { get; } = new RoutedUICommand("Fit to screen", nameof(FitToScreen), typeof(RichCanvasCommands), new InputGestureCollection
+        {
+           RichCanvasGestures.FitToScreen
+        });
+
         internal static void Register(Type type)
         {
             CommandManager.RegisterClassCommandBinding(type, new CommandBinding(ZoomIn, OnZoomIn));
             CommandManager.RegisterClassCommandBinding(type, new CommandBinding(ZoomOut, OnZoomOut));
+            CommandManager.RegisterClassCommandBinding(type, new CommandBinding(FitToScreen, OnFitToScreen));
         }
 
         private static void OnZoomOut(object sender, ExecutedRoutedEventArgs e)
@@ -47,5 +56,13 @@ private static void OnZoomIn(object sender, ExecutedRoutedEventArgs e)
                 richItemsControl.ZoomIn();
             }
         }
+
+        private static void OnFitToScreen(object sender, ExecutedRoutedEventArgs e)
+        {
+            if (sender is RichCanvas richItemsControl)
+            {
+                richItemsControl.FitToScreen();
+            }
+        }
     }
 }