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QuickLook.Plugin/QuickLook.Plugin.ImageViewer/ImagePanel.xaml.cs

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+using System;
+using System.IO;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+
+namespace QuickLook.Plugin.ImageViewer
+{
+    /// <summary>
+    ///     Interaction logic for ImagePanel.xaml
+    /// </summary>
+    public partial class ImagePanel : UserControl
+    {
+        private Point? _dragInitPos;
+        private double _minZoomFactor = 1d;
+        private double _zoomFactor = 1d;
+
+        public ImagePanel(string path)
+        {
+            InitializeComponent();
+
+            var ori = ImageFileHelper.GetOrientationFromExif(path);
+
+            var bitmap = new BitmapImage();
+            using (var fs = File.OpenRead(path))
+            {
+                bitmap.BeginInit();
+                bitmap.StreamSource = fs;
+                bitmap.CacheOption = BitmapCacheOption.OnLoad;
+                bitmap.Rotation = ori == ImageFileHelper.ExifOrientation.Rotate90CW
+                    ? Rotation.Rotate90
+                    : ori == ImageFileHelper.ExifOrientation.Rotate270CW
+                        ? Rotation.Rotate270
+                        : Rotation.Rotate0;
+                bitmap.EndInit();
+            }
+            viewPanelImage.Source = bitmap;
+
+            Loaded += (sender, e) => { ZoomToFit(); };
+
+            viewPanel.PreviewMouseWheel += ViewPanel_PreviewMouseWheel;
+
+            viewPanel.PreviewMouseLeftButtonDown += ViewPanel_PreviewMouseLeftButtonDown;
+            viewPanel.PreviewMouseMove += ViewPanel_PreviewMouseMove;
+        }
+
+        private void ViewPanel_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
+        {
+            _dragInitPos = e.GetPosition(viewPanel);
+            var temp = _dragInitPos.Value; // Point is a type value
+            temp.Offset(viewPanel.HorizontalOffset, viewPanel.VerticalOffset);
+            _dragInitPos = temp;
+        }
+
+        private void ViewPanel_PreviewMouseMove(object sender, MouseEventArgs e)
+        {
+            if (!_dragInitPos.HasValue)
+                return;
+
+            if (e.LeftButton == MouseButtonState.Released)
+            {
+                _dragInitPos = null;
+                return;
+            }
+
+            e.Handled = true;
+
+            var delta = _dragInitPos.Value - e.GetPosition(viewPanel);
+
+            viewPanel.ScrollToHorizontalOffset(delta.X);
+            viewPanel.ScrollToVerticalOffset(delta.Y);
+        }
+
+        private void ViewPanel_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
+        {
+            if ((Keyboard.Modifiers & ModifierKeys.Control) == 0)
+                return;
+
+            e.Handled = true;
+
+            var newZoom = _zoomFactor + e.Delta / 120 * 0.1;
+
+            newZoom = Math.Max(newZoom, _minZoomFactor);
+            newZoom = Math.Min(newZoom, 3);
+
+            Zoom(newZoom, false);
+        }
+
+        private void ZoomToFit()
+        {
+            var factor = Math.Min(viewPanel.ActualWidth / viewPanelImage.Source.Width,
+                viewPanel.ActualHeight / viewPanelImage.Source.Height);
+
+            _minZoomFactor = factor;
+
+            Zoom(factor, true);
+        }
+
+        private void Zoom(double factor, bool fromCenter)
+        {
+            _zoomFactor = factor;
+
+            var position = fromCenter
+                ? new Point(viewPanelImage.Source.Width / 2, viewPanelImage.Source.Height / 2)
+                : Mouse.GetPosition(viewPanelImage);
+
+            viewPanelImage.LayoutTransform = new ScaleTransform(factor, factor);
+
+            viewPanel.InvalidateMeasure();
+
+            // critical for calcuating offset
+            viewPanel.ScrollToHorizontalOffset(0);
+            viewPanel.ScrollToVerticalOffset(0);
+            UpdateLayout();
+
+            var offset = viewPanelImage.TranslatePoint(position, viewPanel) - Mouse.GetPosition(viewPanel);
+            viewPanel.ScrollToHorizontalOffset(offset.X);
+            viewPanel.ScrollToVerticalOffset(offset.Y);
+            UpdateLayout();
+        }
+    }
+}