Fixes #2800 - Color picker (supporting hsl, hsv and rgb)

Terminal.Gui/Drawing/Color.cs

@@ -1,6 +1,7 @@
 #nullable enable
 using System.Collections.Frozen;
 using System.Diagnostics.Contracts;
+using System.Drawing;
 using System.Globalization;
 using System.Numerics;
 using System.Runtime.CompilerServices;
@@ -331,4 +332,4 @@ public Color GetDarkerColor ()
     public const ColorName White = ColorName.White;
 
     #endregion
-}
+}

Terminal.Gui/Drawing/ColorEventArgs.cs

@@ -0,0 +1,11 @@
+#nullable enable
+
+namespace Terminal.Gui;
+
+/// <summary>Event arguments for the <see cref="Color"/> events.</summary>
+public class ColorEventArgs : EventArgs<Color>
+{
+    /// <summary>Initializes a new instance of <see cref="ColorEventArgs"/>
+    /// <paramref name="newColor"/>The value that is being changed to.</summary>
+    public ColorEventArgs (Color newColor) :base(newColor) { }
+}

Terminal.Gui/Drawing/ColorModel.cs

@@ -0,0 +1,25 @@
+#nullable enable
+
+namespace Terminal.Gui;
+
+/// <summary>
+/// Describes away of modelling color e.g. Hue
+/// Saturation Lightness.
+/// </summary>
+public enum ColorModel
+{
+    /// <summary>
+    /// Color modelled by storing Red, Green and Blue as (0-255) ints
+    /// </summary>
+    RGB,
+
+    /// <summary>
+    /// Color modelled by storing Hue (360 degrees), Saturation (100%) and Value (100%)
+    /// </summary>
+    HSV,
+
+    /// <summary>
+    /// Color modelled by storing Hue (360 degrees), Saturation (100%) and Lightness (100%)
+    /// </summary>
+    HSL
+}

Terminal.Gui/Drawing/ColorStrings.cs

@@ -0,0 +1,78 @@
+#nullable enable
+using System.Collections;
+using System.Globalization;
+using System.Resources;
+using Terminal.Gui.Resources;
+
+namespace Terminal.Gui;
+
+/// <summary>
+///     Provides a mapping between <see cref="Color"/> and the W3C standard color name strings.
+/// </summary>
+public static class ColorStrings
+{
+    private static readonly ResourceManager _resourceManager = new (typeof (Strings));
+
+    /// <summary>
+    ///     Gets the W3C standard string for <paramref name="color"/>.
+    /// </summary>
+    /// <param name="color">The color.</param>
+    /// <returns><see langword="null"/> if there is no standard color name for the specified color.</returns>
+    public static string? GetW3CColorName (Color color)
+    {
+        // Fetch the color name from the resource file
+        return _resourceManager.GetString ($"#{color.R:X2}{color.G:X2}{color.B:X2}", CultureInfo.CurrentCulture);
+    }
+
+    /// <summary>
+    ///     Returns the list of W3C standard color names.
+    /// </summary>
+    /// <returns></returns>
+    public static IEnumerable<string> GetW3CColorNames ()
+    {
+        foreach (DictionaryEntry entry in _resourceManager.GetResourceSet (CultureInfo.CurrentCulture, true, true)!)
+        {
+            string keyName = entry.Key.ToString () ?? string.Empty;
+
+            if (entry.Value is string colorName && keyName.StartsWith ('#'))
+            {
+                yield return colorName;
+            }
+        }
+    }
+
+    /// <summary>
+    ///     Parses <paramref name="name"/> and returns <paramref name="color"/> if name is a W3C standard named color.
+    /// </summary>
+    /// <param name="name">The name to parse.</param>
+    /// <param name="color">If successful, the color.</param>
+    /// <returns><see langword="true"/> if <paramref name="name"/> was parsed successfully.</returns>
+    public static bool TryParseW3CColorName (string name, out Color color)
+    {
+        // Iterate through all resource entries to find the matching color name
+        foreach (DictionaryEntry entry in _resourceManager.GetResourceSet (CultureInfo.CurrentCulture, true, true)!)
+        {
+            if (entry.Value is string colorName && colorName.Equals (name, StringComparison.OrdinalIgnoreCase))
+            {
+                // Parse the key to extract the color components
+                string key = entry.Key.ToString () ?? string.Empty;
+
+                if (key.StartsWith ("#") && key.Length == 7)
+                {
+                    if (int.TryParse (key.Substring (1, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out int r)
+                        && int.TryParse (key.Substring (3, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out int g)
+                        && int.TryParse (key.Substring (5, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out int b))
+                    {
+                        color = new (r, g, b);
+
+                        return true;
+                    }
+                }
+            }
+        }
+
+        color = default (Color);
+
+        return false;
+    }
+}

Terminal.Gui/Drawing/IColorNameResolver.cs

@@ -0,0 +1,34 @@
+namespace Terminal.Gui;
+
+/// <summary>
+///     When implemented by a class, allows mapping <see cref="Color"/> to
+///     human understandable name (e.g. w3c color names) and vice versa.
+/// </summary>
+public interface IColorNameResolver
+{
+    /// <summary>
+    ///     Returns the names of all known colors.
+    /// </summary>
+    /// <returns></returns>
+    IEnumerable<string> GetColorNames ();
+
+    /// <summary>
+    ///     Returns <see langword="true"/> if <paramref name="color"/> is a recognized
+    ///     color. In which case <paramref name="name"/> will be the name of the color and
+    ///     return value will be true otherwise false.
+    /// </summary>
+    /// <param name="color"></param>
+    /// <param name="name"></param>
+    /// <returns></returns>
+    bool TryNameColor (Color color, out string name);
+
+    /// <summary>
+    ///     Returns <see langword="true"/> if <paramref name="name"/> is a recognized
+    ///     color. In which case <paramref name="color"/> will be the color the name corresponds
+    ///     to otherwise returns false.
+    /// </summary>
+    /// <param name="name"></param>
+    /// <param name="color"></param>
+    /// <returns></returns>
+    bool TryParseColor (string name, out Color color);
+}

Terminal.Gui/Drawing/W3CColors.cs

@@ -0,0 +1,24 @@
+namespace Terminal.Gui;
+
+/// <summary>
+///     Helper class that resolves w3c color names to their hex values
+///     Based on https://www.w3schools.com/colors/color_tryit.asp
+/// </summary>
+public class W3CColors : IColorNameResolver
+{
+    /// <inheritdoc/>
+    public IEnumerable<string> GetColorNames () { return ColorStrings.GetW3CColorNames (); }
+
+    /// <inheritdoc/>
+    public bool TryParseColor (string name, out Color color) { return ColorStrings.TryParseW3CColorName (name, out color); }
+
+    /// <inheritdoc/>
+    public bool TryNameColor (Color color, out string name)
+    {
+        string answer = ColorStrings.GetW3CColorName (color);
+
+        name = answer ?? string.Empty;
+
+        return answer != null;
+    }
+}