1 files changed, 100 insertions, 0 deletions
diff --git a/Views/Image/ImageControl.xaml.cs b/Views/Image/ImageControl.xaml.cs
new file mode 100644
index 0000000..2189bb0
--- /dev/null
+++ b/Views/Image/ImageControl.xaml.cs
@@ -0,0 +1,100 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Markup.Xaml;
+using Avalonia.Media;
+using System;
+
+namespace Avalar.Views.Image
+{
+    public class ImageControl : UserControl
+    {
+        private const double ZoomTick = 0.1;
+        private double CurrentZoom { get; set; } = 1.0;
+
+        private double InvCurrentZoom => 1 / CurrentZoom;
+
+        private ImageBrush Image { get; }
+
+        private Canvas ImageCanvas { get; }
+        public ImageControl()
+        {
+            InitializeComponent();
+
+            Image = this.FindResource("ImageBrush") as ImageBrush ?? throw new System.ArgumentException("ImageBrush");
+            ImageCanvas = this.FindControl<Canvas>("ImageCanvas");
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+
+        private Point MousePointerInImageSpace(Point mouseCoordinates)
+        {
+            var imageSize = Image.Source.Size;
+            var canvasSize = new Size(ImageCanvas.Bounds.Width, ImageCanvas.Bounds.Height);
+
+            double focalPointX;
+            double focalPointY;
+
+            if (canvasSize.AspectRatio > imageSize.AspectRatio)
+            {
+                focalPointY = mouseCoordinates.Y / canvasSize.Height;
+
+                var halfUnusedX = (canvasSize.AspectRatio - imageSize.AspectRatio) * canvasSize.Width / 2;
+                var clampedX = Math.Clamp(mouseCoordinates.X - halfUnusedX, 0, imageSize.Width);
+
+                focalPointX = clampedX / imageSize.Width;
+            }
+            else
+            {
+                focalPointX = mouseCoordinates.X / canvasSize.Width;
+
+                var halfUnusedY = 1 / (canvasSize.AspectRatio - imageSize.AspectRatio) * canvasSize.Height / 2;
+                var clampedY = Math.Clamp(mouseCoordinates.Y - halfUnusedY, 0, imageSize.Height);
+
+                focalPointY = clampedY / imageSize.Height;
+            }
+
+            return new Point(focalPointX, focalPointY);
+        }
+
+        private Point TransformToSourceRectSpace(Point from)
+        {
+            var sourceRectPosition = Image.SourceRect.Rect.Position;
+            var sourceRectSize = Image.SourceRect.Rect.Size;
+            return new Point(
+                from.X * sourceRectSize.Width + sourceRectPosition.X,
+                from.Y * sourceRectSize.Height + sourceRectPosition.Y
+            );
+        }
+
+        public void OnPointerWheelChanged(object sender, PointerWheelEventArgs e)
+        {
+            var invOldZoom = InvCurrentZoom;
+            var zoomFactor = e.Delta.Y * ZoomTick + 1.0;
+            CurrentZoom = Math.Clamp(CurrentZoom * zoomFactor, 1, double.PositiveInfinity);
+
+            var sourceRect = Image.SourceRect.Rect;
+
+            var canvasMouseCoordinates = e.GetPosition(ImageCanvas);
+            
+            var currentCenter = sourceRect.Center;
+            var desiredCenterInImageCoords = MousePointerInImageSpace(canvasMouseCoordinates);
+            if(e.Delta.Y < 0)
+            {
+                desiredCenterInImageCoords = new Point(1 - desiredCenterInImageCoords.X, 1 - desiredCenterInImageCoords.Y);
+            }
+            var desiredCenter = TransformToSourceRectSpace(desiredCenterInImageCoords);
+
+            var maxTravelDistance = Math.Abs(invOldZoom - InvCurrentZoom);
+
+            var newCenterX = Math.Clamp(desiredCenter.X, currentCenter.X - maxTravelDistance, currentCenter.X + maxTravelDistance);
+            var newCenterY = Math.Clamp(desiredCenter.Y, currentCenter.Y - maxTravelDistance, currentCenter.Y + maxTravelDistance);
+
+            var sourceRectNewTopLeft = new Point(newCenterX - InvCurrentZoom / 2, newCenterY - InvCurrentZoom / 2);
+            Image.SourceRect = new RelativeRect(sourceRectNewTopLeft, new Size(InvCurrentZoom, InvCurrentZoom), RelativeUnit.Relative);
+        }
+    }
+}