Add pixel difference statistics and changed region counts in image diff view

- Calculate changed pixel count and percentage in ImageDifferenceDetector
- Display pixel difference statistics in image diff toolbar
- Show total number of detected change regions when outline mode is active

Author: Marek Maślanka

src/Models/DiffResult.cs

@@ -82,10 +82,17 @@ public class ImageDiff
         public string OldImageSize => Old != null ? $"{Old.PixelSize.Width} x {Old.PixelSize.Height}" : "0 x 0";
         public string NewImageSize => New != null ? $"{New.PixelSize.Width} x {New.PixelSize.Height}" : "0 x 0";
 
-        public IReadOnlyList<Avalonia.Rect> ChangeOutlines => _changeOutlines ??= ImageDifferenceDetector.DetectChangeBoxes(Old, New);
-        public int ChangeCount => ChangeOutlines.Count;
+        public ImageDiffDetectionResult DetectionResult => _detectionResult ??= ImageDifferenceDetector.Detect(Old, New);
 
-        private IReadOnlyList<Avalonia.Rect> _changeOutlines = null;
+        public IReadOnlyList<Avalonia.Rect> ChangeOutlines => DetectionResult.ChangeBoxes;
+        public int ChangeCount => DetectionResult.ChangeBoxes.Count;
+        public long ChangedPixelCount => DetectionResult.ChangedPixels;
+        public double ChangedPixelPercentage => DetectionResult.ChangedPercentage;
+
+        public string DiffPixelStatsText => $"{ChangedPixelCount:N0} px ({ChangedPixelPercentage:F2}%)";
+        public string DiffAreaStatsText => ChangeCount == 1 ? "1 area" : $"{ChangeCount} areas";
+
+        private ImageDiffDetectionResult _detectionResult = null;
     }
 
     public class EmptyFile

src/Models/ImageDifferenceDetector.cs

@@ -7,34 +7,72 @@
 
 namespace SourceGit.Models
 {
+    public class ImageDiffDetectionResult
+    {
+        public long ChangedPixels { get; set; } = 0;
+        public long TotalPixels { get; set; } = 0;
+        public double ChangedPercentage => TotalPixels > 0 ? (double)ChangedPixels / TotalPixels * 100.0 : 0.0;
+        public List<Rect> ChangeBoxes { get; set; } = [];
+    }
+
     public static class ImageDifferenceDetector
     {
-        public static List<Rect> DetectChangeBoxes(Bitmap oldBmp, Bitmap newBmp)
+        public static ImageDiffDetectionResult Detect(Bitmap oldBmp, Bitmap newBmp)
         {
+            var result = new ImageDiffDetectionResult();
+
             if (oldBmp == null && newBmp == null)
-                return [];
+                return result;
 
             if (oldBmp == null)
-                return [new Rect(0, 0, newBmp.PixelSize.Width, newBmp.PixelSize.Height)];
+            {
+                var w = newBmp.PixelSize.Width;
+                var h = newBmp.PixelSize.Height;
+                result.TotalPixels = (long)w * h;
+                result.ChangedPixels = result.TotalPixels;
+                result.ChangeBoxes = [new Rect(0, 0, w, h)];
+                return result;
+            }
 
             if (newBmp == null)
-                return [new Rect(0, 0, oldBmp.PixelSize.Width, oldBmp.PixelSize.Height)];
+            {
+                var w = oldBmp.PixelSize.Width;
+                var h = oldBmp.PixelSize.Height;
+                result.TotalPixels = (long)w * h;
+                result.ChangedPixels = result.TotalPixels;
+                result.ChangeBoxes = [new Rect(0, 0, w, h)];
+                return result;
+            }
 
             var oldBytes = GetRgbaBytes(oldBmp, out var w1, out var h1);
             var newBytes = GetRgbaBytes(newBmp, out var w2, out var h2);
 
             if (oldBytes == null && newBytes == null)
-                return [];
+                return result;
+
             if (oldBytes == null)
-                return [new Rect(0, 0, w2, h2)];
+            {
+                result.TotalPixels = (long)w2 * h2;
+                result.ChangedPixels = result.TotalPixels;
+                result.ChangeBoxes = [new Rect(0, 0, w2, h2)];
+                return result;
+            }
+
             if (newBytes == null)
-                return [new Rect(0, 0, w1, h1)];
+            {
+                result.TotalPixels = (long)w1 * h1;
+                result.ChangedPixels = result.TotalPixels;
+                result.ChangeBoxes = [new Rect(0, 0, w1, h1)];
+                return result;
+            }
 
             int maxW = Math.Max(w1, w2);
             int maxH = Math.Max(h1, h2);
 
             if (maxW <= 0 || maxH <= 0)
-                return [];
+                return result;
+
+            result.TotalPixels = (long)maxW * maxH;
 
             const int cellSize = 16;
             int gridW = (maxW + cellSize - 1) / cellSize;
@@ -43,6 +81,7 @@ public static List<Rect> DetectChangeBoxes(Bitmap oldBmp, Bitmap newBmp)
             var cellBounds = new Rect[gridW, gridH];
             var hasDiff = new bool[gridW, gridH];
             bool anyDiff = false;
+            long diffPixelCount = 0;
 
             for (int cy = 0; cy < gridH; cy++)
             {
@@ -107,6 +146,7 @@ public static List<Rect> DetectChangeBoxes(Bitmap oldBmp, Bitmap newBmp)
 
                             if (diffPixel)
                             {
+                                diffPixelCount++;
                                 cellHasDiff = true;
                                 if (x < minX) minX = x;
                                 if (x > maxX) maxX = x;
@@ -125,8 +165,10 @@ public static List<Rect> DetectChangeBoxes(Bitmap oldBmp, Bitmap newBmp)
                 }
             }
 
+            result.ChangedPixels = diffPixelCount;
+
             if (!anyDiff)
-                return [];
+                return result;
 
             var visited = new bool[gridW, gridH];
             var clusters = new List<Rect>();
@@ -193,7 +235,8 @@ public static List<Rect> DetectChangeBoxes(Bitmap oldBmp, Bitmap newBmp)
                 }
             }
 
-            return clusters;
+            result.ChangeBoxes = clusters;
+            return result;
         }
 
         private static byte[] GetRgbaBytes(Bitmap bitmap, out int width, out int height)

src/Views/ImageDiffView.axaml

@@ -51,8 +51,28 @@
           <StackPanel Orientation="Horizontal" Spacing="4" VerticalAlignment="Center">
             <Path Width="12" Height="12" Data="{StaticResource Icons.Eye}" Fill="{DynamicResource Brush.FG1}"/>
             <TextBlock Text="{DynamicResource Text.Diff.Image.HighlightChanges}" FontSize="10" VerticalAlignment="Center"/>
+            <Border Background="{DynamicResource Brush.Badge}"
+                    CornerRadius="6"
+                    Height="14"
+                    Padding="4,0"
+                    VerticalAlignment="Center"
+                    IsVisible="{Binding Source={x:Static vm:Preferences.Instance}, Path=HighlightImageDiffChanges}">
+              <TextBlock Text="{Binding ChangeCount}" FontSize="9" Foreground="{DynamicResource Brush.BadgeFG}" VerticalAlignment="Center"/>
+            </Border>
           </StackPanel>
         </ToggleButton>
+
+        <Rectangle Width="1" Height="14" Fill="{DynamicResource Brush.Border1}" Margin="4,0"/>
+
+        <!-- Difference statistics (pixels and changed areas) -->
+        <Border Background="{DynamicResource Brush.Badge}" CornerRadius="4" Padding="6,3" VerticalAlignment="Center">
+          <StackPanel Orientation="Horizontal" Spacing="4" VerticalAlignment="Center">
+            <Path Width="11" Height="11" Data="{StaticResource Icons.Diff}" Fill="{DynamicResource Brush.FG2}" VerticalAlignment="Center"/>
+            <TextBlock Text="{Binding DiffPixelStatsText}" FontSize="10" Foreground="{DynamicResource Brush.FG1}" VerticalAlignment="Center"/>
+            <TextBlock Text="{Binding DiffAreaStatsText}" FontSize="10" Foreground="{DynamicResource Brush.Accent}" FontWeight="Bold" VerticalAlignment="Center"
+                       IsVisible="{Binding Source={x:Static vm:Preferences.Instance}, Path=HighlightImageDiffChanges}"/>
+          </StackPanel>
+        </Border>
       </StackPanel>
     </Border>