Restructure folder layout for ColorAnalyzer component

Author: Avid29

components/ColorAnalyzer/samples/ColorAnalyzer.Samples.csproj

@@ -18,4 +18,7 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
   </ItemGroup>
+  <ItemGroup>
+    <Folder Include="ContrastHelper\" />
+  </ItemGroup>
 </Project>

components/ColorAnalyzer/samples/AccentAnalyzerSample.xaml renamed to components/ColorAnalyzer/samples/ColorPaletteSampler/AccentAnalyzerSample.xaml

@@ -1,4 +1,4 @@
-<!--  Licensed to the .NET Foundation under one or more agreements. The .NET Foundation licenses this file to you under the MIT license. See the LICENSE file in the project root for more information.  -->
+<!--  Licensed to the .NET Foundation under one or more agreements. The .NET Foundation licenses this file to you under the MIT license. See the LICENSE file in the project root for more information.  -->
 <Page x:Class="ColorAnalyzerExperiment.Samples.AccentAnalyzerSample"
       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
@@ -11,7 +11,7 @@
       mc:Ignorable="d">
 
     <Page.Resources>
-        <helpers:ColorPaletteSampler x:Name="ColorPaletteSample"
+        <helpers:ColorPaletteSampler x:Name="ColorPaletteSampler"
                                      Source="{x:Bind SampledImage}">
             <helpers:AccentColorPaletteSelector x:Name="AccentPalette"
                                                 MinColorCount="3" />
@@ -41,7 +41,7 @@
                 <interactivity:Interaction.Behaviors>
                     <interactivity:EventTriggerBehavior EventName="ImageOpened">
                         <interactivity:CallMethodAction MethodName="UpdatePalette"
-                                                        TargetObject="{x:Bind ColorPaletteSample}" />
+                                                        TargetObject="{x:Bind ColorPaletteSampler}" />
                     </interactivity:EventTriggerBehavior>
                 </interactivity:Interaction.Behaviors>
             </Image>

components/ColorAnalyzer/samples/AccentAnalyzerSample.xaml.cs renamed to components/ColorAnalyzer/samples/ColorPaletteSampler/AccentAnalyzerSample.xaml.cs

@@ -9,6 +9,65 @@ namespace CommunityToolkit.WinUI.Helpers;
 
 internal static class ColorExtensions
 {
+    internal static Color ToColor(this Vector3 color)
+    {
+        color *= 255;
+        return Color.FromArgb(255, (byte)(color.X), (byte)(color.Y), (byte)(color.Z));
+    }
+
+    internal static Vector3 ToVector3(this Color color)
+    {
+        var vector = new Vector3(color.R, color.G, color.B);
+        return vector / 255;
+    }
+
+    /// <summary>
+    /// Get WCAG contrast ratio between two colors.
+    /// </summary>
+    internal static double ContrastRatio(this Color color1, Color color2)
+    {
+        // Using the formula for contrast ratio
+        // Source WCAG guidelines: https://www.w3.org/TR/WCAG20/#contrast-ratiodef
+
+        // Calculate perceived luminance for both colors
+        double luminance1 = color1.PerceivedLuminance();
+        double luminance2 = color2.PerceivedLuminance();
+
+        // Determine lighter and darker luminance
+        double lighter = Math.Max(luminance1, luminance2);
+        double darker = Math.Min(luminance1, luminance2);
+
+        // Calculate contrast ratio
+        return (lighter + 0.05f) / (darker + 0.05f);
+    }
+
+    internal static double PerceivedLuminance(this Color color)
+    {
+        // Color theory is a massive iceberg. Here's a peek at the tippy top:
+
+        // There's two (main) standards for calculating luminance from RGB values.
+
+        // + ------------- + ------------------------------------ + ------------------ + ------------------------------------------------------------------------------- +
+        // | Standard      | Formula                              | Ref. Section       | Ref. Link                                                                       |
+        // + ------------- + ------------------------------------ + ------------------ + ------------------------------------------------------------------------------- +
+        // | ITU Rec. 709  | Y = 0.2126 R + 0.7152 G + 0.0722 B   | Page 4/Item 3.2    | https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-6-201506-I!!PDF-E.pdf  |
+        // + ------------- + ------------------------------------ + ------------------ + ------------------------------------------------------------------------------- +
+        // | ITU Rec. 601  | Y = 0.299 R + 0.587 G + 0.114 B      | Page 2/Item 2.5.1  | https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-7-201103-I!!PDF-E.pdf  |
+        // + ------------- + ------------------------------------ + ------------------ + ------------------------------------------------------------------------------- +
+
+        // They're based on the standard ability of the human eye to perceive brightness,
+        // from different colors, as well as the average monitor's ability to produce them.
+        // Both standards produce similar results, but Rec. 709 is more accurate for modern displays.
+
+        // NOTE: If we for whatever reason we ever need to optimize this code,
+        // we can make approximations using integer math instead of floating point math.
+        // The precise values are not critical, as long as the relative luminance is accurate.
+        // Like so: return (2 * color.R + 7 * color.G + color.B);
+
+        // TLDR: We use ITU Rec. 709 standard formula for perceived luminance.
+        return (0.2126f * color.R + 0.7152f * color.G + 0.0722 * color.B) / 255;
+    }
+
     internal static float FindColorfulness(this Color color)
     {
         var vectorColor = color.ToVector3();
@@ -37,18 +96,6 @@ internal static float FindColorfulness(this Color[] colors)
         return std + (0.3f * mean);
     }
 
-    internal static Color ToColor(this Vector3 color)
-    {
-        color *= 255;
-        return Color.FromArgb(255, (byte)(color.X), (byte)(color.Y), (byte)(color.Z));
-    }
-
-    internal static Vector3 ToVector3(this Color color)
-    {
-        var vector = new Vector3(color.R, color.G, color.B);
-        return vector / 255;
-    }
-
     private static float FindStandardDeviation(IEnumerable<float> data, out float avg)
     {
         var average = data.Average();