Implement basic histogram

Closes #66

Fotografix.Core.Tests/BitmapAssert.cs

@@ -57,7 +57,7 @@ private static async Task SaveAsync(CanvasBitmap bitmap, string filename)
 
             using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
             {
-                await bitmap.SaveAsync(stream, CanvasBitmapFileFormat.Jpeg);
+                await bitmap.SaveAsync(stream, filename.EndsWith(".png") ? CanvasBitmapFileFormat.Png : CanvasBitmapFileFormat.Jpeg);
             }
 
             await CoreApplication.MainView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () => await Launcher.LaunchFolderAsync(tempFolder));

Fotografix.Core.Tests/Fotografix.Core.Tests.csproj

@@ -161,6 +161,7 @@
     <Content Include="TestData\Barn_exposure.jpg" />
     <Content Include="TestData\Barn_exposure_thumbnail.jpg" />
     <Content Include="TestData\Barn_highlights.jpg" />
+    <Content Include="TestData\Barn_histogram.png" />
     <Content Include="TestData\Barn_hue_yellow.jpg" />
     <Content Include="TestData\Barn_luminance_yellow.jpg" />
     <Content Include="TestData\Barn_saturation.jpg" />

Fotografix.Core.Tests/PhotoEditorTest.cs

@@ -1,4 +1,5 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.Graphics.Canvas;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using System.Threading.Tasks;
 using Windows.Foundation;
 using Windows.Storage;
@@ -214,6 +215,20 @@ public void ScalesSizeToFitMaxDimension()
             Assert.AreEqual(new Size(100, 50), PhotoEditor.ScaleDimensions(new Size(100, 50), 200), "originalSize < maxDimension: should not scale");
         }
 
+        [TestMethod]
+        public async Task ComputesHistogram()
+        {
+            using (var editor = await PhotoEditor.CreateAsync(photo))
+            {
+                var histogram = editor.ComputeHistogram();
+
+                using (var output = histogram.ExportToCanvasBitmap(CanvasDevice.GetSharedDevice()))
+                {
+                    await BitmapAssert.VerifyAsync(output, "Barn_histogram.png");
+                }
+            }
+        }
+
         private async Task VerifyOutputAsync(PhotoEditor editor, string filename)
         {
             using (var output = editor.ExportToCanvasBitmap())

Fotografix.Core/Fotografix.Core.csproj

@@ -121,6 +121,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="CropRect.cs" />
+    <Compile Include="Histogram.cs" />
     <Compile Include="IPhoto.cs" />
     <Compile Include="IRenderScaleProvider.cs" />
     <Compile Include="Xmp\BitmapPropertiesXmpExtensions.cs" />

Fotografix.Core/Histogram.cs

@@ -0,0 +1,65 @@
+using Microsoft.Graphics.Canvas;
+using Microsoft.Graphics.Canvas.Effects;
+using Windows.Foundation;
+using Windows.UI;
+
+namespace Fotografix
+{
+    public sealed class Histogram
+    {
+        private const int NumBins = 256;
+        private const int Height = 100;
+
+        private readonly float[] r;
+        private readonly float[] g;
+        private readonly float[] b;
+
+        public Histogram(float[] r, float[] g, float[] b)
+        {
+            this.r = r;
+            this.g = g;
+            this.b = b;
+        }
+
+        public static Histogram Compute(ICanvasImage image, Rect rect, ICanvasResourceCreator resourceCreator)
+        {
+            float[] r = CanvasImage.ComputeHistogram(image, rect, resourceCreator, EffectChannelSelect.Red, NumBins);
+            float[] g = CanvasImage.ComputeHistogram(image, rect, resourceCreator, EffectChannelSelect.Green, NumBins);
+            float[] b = CanvasImage.ComputeHistogram(image, rect, resourceCreator, EffectChannelSelect.Blue, NumBins);
+            return new Histogram(r, g, b);
+        }
+
+        public static Size RenderSize => new Size(NumBins, Height);
+
+        public void Draw(CanvasDrawingSession ds)
+        {
+            float s = Height / 0.025f;
+
+            void Draw(float[] x, Color color)
+            {
+                for (int i = 0; i < NumBins; i++)
+                {
+                    ds.DrawLine(i, Height, i, Height - s * x[i], color);
+                }
+            }
+
+            ds.Blend = CanvasBlend.Add;
+            Draw(r, Color.FromArgb(255, 255, 0, 0));
+            Draw(g, Color.FromArgb(255, 0, 255, 0));
+            Draw(b, Color.FromArgb(255, 0, 0, 255));
+        }
+
+        public CanvasBitmap ExportToCanvasBitmap(ICanvasResourceCreator resourceCreator)
+        {
+            var rt = new CanvasRenderTarget(resourceCreator, NumBins, Height, 96);
+
+            using (var ds = rt.CreateDrawingSession())
+            {
+                ds.Clear(Colors.Transparent);
+                Draw(ds);
+            }
+
+            return rt;
+        }
+    }
+}

Fotografix.Core/PhotoEditor.cs

@@ -1,5 +1,7 @@
 using Microsoft.Graphics.Canvas;
+using Microsoft.Graphics.Canvas.Effects;
 using System;
+using System.Numerics;
 using System.Threading.Tasks;
 using Windows.Foundation;
 using Windows.Graphics.Imaging;
@@ -11,17 +13,20 @@ public sealed class PhotoEditor : IRenderScaleProvider, IDisposable
     {
         private readonly IPhoto photo;
         private readonly CanvasBitmap bitmap;
+        private readonly Transform2DEffect histogramTransform;
         private PhotoAdjustment adjustment;
         private bool dirty;
 
         private PhotoEditor(IPhoto photo, CanvasBitmap bitmap)
         {
             this.photo = photo;
             this.bitmap = bitmap;
+            this.histogramTransform = new Transform2DEffect { CacheOutput = true };
         }
 
         public void Dispose()
         {
+            histogramTransform.Dispose();
             adjustment.Dispose();
             bitmap.Dispose();
         }
@@ -67,7 +72,7 @@ public void Draw(CanvasDrawingSession ds)
         public event EventHandler Invalidated;
 
         public Size OriginalSize => bitmap.Size;
-        public Size RenderSize => adjustment.GetOutputSize(resourceCreator: bitmap);
+        public Size RenderSize => adjustment.GetOutputSize(ResourceCreator);
 
         public float RenderScale
         {
@@ -145,9 +150,9 @@ public CanvasBitmap ExportToCanvasBitmap(int? maxDimension = null)
             var originalRenderScale = adjustment.RenderScale;
             adjustment.RenderScale = 1;
 
-            var bounds = adjustment.Output.GetBounds(resourceCreator: bitmap);
+            var bounds = adjustment.Output.GetBounds(ResourceCreator);
             var scaledSize = ScaleDimensions(new Size(bounds.Width, bounds.Height), maxDimension);
-            var rt = new CanvasRenderTarget(resourceCreator: bitmap, size: scaledSize);
+            var rt = new CanvasRenderTarget(ResourceCreator, size: scaledSize);
 
             using (var ds = rt.CreateDrawingSession())
             {
@@ -166,6 +171,18 @@ public async Task<SoftwareBitmap> ExportToSoftwareBitmapAsync(int? maxDimension
             }
         }
 
+        public Histogram ComputeHistogram()
+        {
+            var bounds = adjustment.Output.GetBounds(ResourceCreator);
+            var scaledSize = ScaleDimensions(new Size(bounds.Width, bounds.Height), ThumbnailSize);
+
+            histogramTransform.TransformMatrix = Matrix3x2.CreateScale((float)(scaledSize.Width / bounds.Width));
+            histogramTransform.Source = adjustment.Output;
+            return Histogram.Compute(histogramTransform, new Rect(0, 0, scaledSize.Width, scaledSize.Height), ResourceCreator);
+        }
+
+        private ICanvasResourceCreatorWithDpi ResourceCreator => bitmap;
+
         private void SetAdjustment(PhotoAdjustment value)
         {
             if (value == null)

Fotografix/EditorTemplates.xaml

@@ -121,6 +121,13 @@
 
     <DataTemplate x:Key="PhotoAdjustmentTemplate" x:DataType="local:EditorViewModel" x:DefaultBindMode="TwoWay">
         <StackPanel>
+            <!-- Histogram -->
+            <Border BorderBrush="{ThemeResource CardStrokeColorDefaultBrush}"
+                    BorderThickness="1" CornerRadius="8" Margin="-8,0,0,8">
+                <Image Source="{x:Bind HistogramSource, Mode=OneWay}" />
+            </Border>
+
+            <!-- Light -->
             <winui:Expander IsExpanded="True" Header="Light">
                 <StackPanel>
                     <Slider Header="Exposure" Value="{x:Bind Adjustment.Exposure}" />
@@ -132,6 +139,7 @@
                 </StackPanel>
             </winui:Expander>
 
+            <!-- Color -->
             <winui:Expander Header="Color">
                 <StackPanel>
                     <ToggleSwitch Margin="0,0,0,8" Header="Black &amp; white" IsOn="{x:Bind Adjustment.BlackAndWhite}" />
@@ -142,6 +150,7 @@
                 </StackPanel>
             </winui:Expander>
 
+            <!-- HSL -->
             <winui:Expander x:DefaultBindMode="OneWay" Header="HSL" Visibility="{x:Bind Adjustment.BlackAndWhite, Converter={StaticResource InvertedBoolToVisibilityConverter}}">
                 <Pivot Margin="4,-16,4,0">
                     <Pivot.HeaderTemplate>
@@ -156,12 +165,14 @@
                 </Pivot>
             </winui:Expander>
 
+            <!-- B&W Mix -->
             <winui:Expander x:DefaultBindMode="OneWay" Header="B&amp;W Mix"
                             Visibility="{x:Bind Adjustment.BlackAndWhite}"
                             IsExpanded="{x:Bind Adjustment.BlackAndWhite}"
                             Content="{x:Bind Adjustment.ColorRanges.LuminanceView}"
                             ContentTemplate="{StaticResource ColorRangeViewTemplate}" />
 
+            <!-- Detail -->
             <winui:Expander Header="Detail">
                 <StackPanel>
                     <!-- Preview accuracy warning -->
@@ -219,6 +230,7 @@
                 </StackPanel>
             </winui:Expander>
 
+            <!-- Crop -->
             <winui:Expander Header="Crop" IsExpanded="{x:Bind CropMode}">
                 <StackPanel>
                     <TextBlock Margin="2,0,0,8" FontWeight="SemiBold" Text="Aspect ratio" />

Fotografix/EditorViewModel.cs

@@ -1,13 +1,15 @@
 using Fotografix.Input;
 using Microsoft.Graphics.Canvas;
+using Microsoft.Graphics.Canvas.UI.Xaml;
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 using Windows.Foundation;
 using Windows.Storage;
 using Windows.System;
+using Windows.UI;
 using Windows.UI.Core;
+using Windows.UI.Xaml.Media;
 
 namespace Fotografix
 {
@@ -16,6 +18,7 @@ public sealed class EditorViewModel : NotifyPropertyChangedBase, IPointerInputHa
         public const int CropHandleSize = 6;
 
         private readonly PhotoEditor editor;
+        private readonly ICanvasResourceCreatorWithDpi resourceCreator;
         private readonly ScalingHelper scalingHelper;
         private readonly CropTracker cropTracker;
         private readonly CropOverlay cropOverlay;
@@ -31,6 +34,7 @@ public EditorViewModel(PhotoEditor editor, ICanvasResourceCreatorWithDpi resourc
             this.editor = editor;
             editor.Invalidated += (s, e) => Invalidate();
 
+            this.resourceCreator = resourceCreator;
             this.scalingHelper = new ScalingHelper(resourceCreator, editor);
             this.cropTracker = cropTracker;
             cropTracker.RectChanged += (s, e) => Invalidate();
@@ -345,6 +349,36 @@ public async Task ExportAsync(bool launchFolderAfterExport = true)
 
         #endregion
 
+        #region Histogram
+
+        private CanvasImageSource histogramSource;
+
+        public ImageSource HistogramSource
+        {
+            get
+            {
+                if (histogramSource == null)
+                {
+                    this.histogramSource = new CanvasImageSource(resourceCreator, Histogram.RenderSize);
+                    editor.Invalidated += (s, e) => UpdateHistogram();
+                    UpdateHistogram();
+                }
+
+                return histogramSource;
+            }
+        }
+
+        private void UpdateHistogram()
+        {
+            var histogram = editor.ComputeHistogram();
+            using (var ds = histogramSource.CreateDrawingSession(Color.FromArgb(192, 48, 48, 48)))
+            {
+                histogram.Draw(ds);
+            }
+        }
+
+        #endregion
+
         private void Invalidate()
         {
             Invalidated?.Invoke(this, EventArgs.Empty);