add WCAG 2.1 compliant alternate color

MiraAPI/Patches/Options/GameOptionsMenuPatch.cs

@@ -202,7 +202,7 @@ public static class GameOptionsMenuPatch
         {
             categoryHeaderMasked.Background.color = group.GroupColor;
             categoryHeaderMasked.Divider.color = group.GroupColor;
-            categoryHeaderMasked.Title.color = group.GroupColor.GetAlternateColor();
+            categoryHeaderMasked.Title.color = group.GroupColor.FindAlternateColor();
         }
 
         categoryHeaderMasked.Background.size = new Vector2(
@@ -232,10 +232,10 @@ public static class GameOptionsMenuPatch
             {
                 if (group.GroupColor != Color.clear)
                 {
-                    renderer.color = group.GroupColor.GetAlternateColor();
+                    renderer.color = group.GroupColor.FindAlternateColor();
                     if (renderer.transform.parent.TryGetComponent<GameOptionButton>(out var btn))
                     {
-                        btn.interactableColor = group.GroupColor.GetAlternateColor();
+                        btn.interactableColor = group.GroupColor.FindAlternateColor();
                         btn.interactableHoveredColor = Color.white;
                     }
                 }

MiraAPI/Patches/Options/LobbyViewPanePatches.cs

@@ -340,7 +340,7 @@ public static class LobbyViewPanePatches
                     viewSettingsInfoPanelRoleVariant.chanceTitle.color =
                         viewSettingsInfoPanelRoleVariant.chanceBackground.color =
                             viewSettingsInfoPanelRoleVariant.background.color =
-                                customRole.RoleColor.GetAlternateColor();
+                                customRole.RoleColor.FindAlternateColor();
                 instance.settingsInfo.Add(viewSettingsInfoPanelRoleVariant.gameObject);
                 num -= 0.664f;
             }

MiraAPI/Patches/Options/RoleSettingMenuPatches.cs

@@ -384,7 +384,7 @@ public static class RoleSettingMenuPatches
         }
 
         __instance.roleHeaderSprite.color = customRole.RoleColor;
-        __instance.roleHeaderText.color = customRole.RoleColor.GetAlternateColor();
+        __instance.roleHeaderText.color = customRole.RoleColor.FindAlternateColor();
 
         var categoryHeaderMasked = __instance.AdvancedRolesSettings.transform.Find("CategoryHeaderMasked").GetComponent<CategoryHeaderMasked>();
 
@@ -465,7 +465,7 @@ public static class RoleSettingMenuPatches
         __instance.roleChances.Add(roleOptionSetting);
 
         roleOptionSetting.titleText.transform.localPosition = new Vector3(-0.5376f, -0.2923f, 0f);
-        roleOptionSetting.titleText.color = customRole.RoleColor.GetAlternateColor();
+        roleOptionSetting.titleText.color = customRole.RoleColor.FindAlternateColor();
         roleOptionSetting.titleText.horizontalAlignment = HorizontalAlignmentOptions.Left;
 
         if (GameSettingMenuPatches.SelectedMod is null ||
@@ -483,7 +483,7 @@ public static class RoleSettingMenuPatches
 
             var passiveButton = newButton.GetComponent<GameOptionButton>();
             passiveButton.OnClick = new ButtonClickedEvent();
-            passiveButton.interactableColor = btnRend.color = customRole.RoleColor.GetAlternateColor();
+            passiveButton.interactableColor = btnRend.color = customRole.RoleColor.FindAlternateColor();
             passiveButton.interactableHoveredColor = Color.white;
 
             passiveButton.OnClick.AddListener((UnityAction)(() => { ChangeTab(role, __instance); }));

MiraAPI/Utilities/ColorExtensions.cs

@@ -0,0 +1,89 @@
+using UnityEngine;
+
+namespace MiraAPI.Utilities;
+
+/// <summary>
+/// Extension methods for the Color struct.
+/// </summary>
+public static class ColorExtensions
+{
+    /// <summary>
+    /// Gets the relative luminance of a color (WCAG 2.1 specification).
+    /// </summary>
+    /// <param name="color">Color to calculate luminance for.</param>
+    /// <returns>Relative luminance value.</returns>
+    public static float GetRelativeLuminance(this Color color)
+    {
+        var r = color.r <= 0.03928f ? color.r / 12.92f : Mathf.Pow((color.r + 0.055f) / 1.055f, 2.4f);
+        var g = color.g <= 0.03928f ? color.g / 12.92f : Mathf.Pow((color.g + 0.055f) / 1.055f, 2.4f);
+        var b = color.b <= 0.03928f ? color.b / 12.92f : Mathf.Pow((color.b + 0.055f) / 1.055f, 2.4f);
+        return 0.2126f * r + 0.7152f * g + 0.0722f * b;
+    }
+
+    /// <summary>
+    /// Calculates the contrast ratio between two colors (WCAG 2.1 specification).
+    /// </summary>
+    /// <param name="colorA">First color.</param>
+    /// <param name="colorB">Second color.</param>
+    /// <returns>Contrast ratio between the two colors.</returns>
+    public static float GetContrastRatio(this Color colorA, Color colorB)
+    {
+        var luminanceA = colorA.GetRelativeLuminance();
+        var luminanceB = colorB.GetRelativeLuminance();
+        return (Mathf.Max(luminanceA, luminanceB) + 0.05f) / (Mathf.Min(luminanceA, luminanceB) + 0.05f);
+    }
+
+    /// <summary>
+    /// Generates an accessible alternate color with sufficient contrast.
+    /// </summary>
+    /// <param name="color">Base color.</param>
+    /// <param name="desiredRatio">Target contrast ratio (default 4.5f for AA).</param>
+    /// <returns>Alternate color with sufficient contrast.</returns>
+    public static Color FindAlternateColor(this Color color, float desiredRatio = 4.5f)
+    {
+        var lightColor = FindMinimumContrastColor(color, Color.white, desiredRatio);
+        var darkColor = FindMinimumContrastColor(color, Color.black, desiredRatio);
+
+        return lightColor.GetContrastRatio(color) >= darkColor.GetContrastRatio(color) ? lightColor : darkColor;
+    }
+
+    /// <summary>
+    /// Finds the color with the minimum contrast ratio to the target color.
+    /// </summary>
+    /// <param name="baseColor">The base color to start from.</param>
+    /// <param name="targetColor">The target color to compare against.</param>
+    /// <param name="desiredRatio">The desired contrast ratio.</param>
+    /// <returns>The color with the minimum contrast ratio to the target color.</returns>
+    public static Color FindMinimumContrastColor(Color baseColor, Color targetColor, float desiredRatio)
+    {
+        var baseLuminance = baseColor.GetRelativeLuminance();
+        var isLightening = targetColor == Color.white;
+
+        var targetLuminance = isLightening
+            ? desiredRatio * (baseLuminance + 0.05f) - 0.05f
+            : (baseLuminance + 0.05f) / desiredRatio - 0.05f;
+
+        if (isLightening && targetLuminance > 1f) return Color.white;
+        if (!isLightening && targetLuminance < 0f) return Color.black;
+
+        float low = 0f, high = 1f;
+        var bestColor = targetColor;
+        for (var i = 0; i < 10; i++)
+        {
+            var t = (low + high) / 2f;
+            var testColor = Color.Lerp(baseColor, targetColor, t);
+            var testLuminance = testColor.GetRelativeLuminance();
+
+            if ((isLightening && testLuminance >= targetLuminance) || (!isLightening && testLuminance <= targetLuminance))
+            {
+                high = t;
+                bestColor = testColor;
+            }
+            else
+            {
+                low = t;
+            }
+        }
+        return bestColor;
+    }
+}

MiraAPI/Utilities/Extensions.cs

@@ -245,6 +245,7 @@ public static class Extensions
     /// <param name="color">The original color.</param>
     /// <param name="amount">The amount to darken or lighten the original color by between 0.0 and 1.0.</param>
     /// <returns>An alternate color that has been darkened or lightened.</returns>
+    [Obsolete("Use FindAlternateColor for WACG compliance.")]
     public static Color GetAlternateColor(this Color color, float amount = 0.45f)
     {
         return color.IsColorDark() ? LightenColor(color, amount) : DarkenColor(color, amount);