Fixes #1265 - Adds Sixel rendering support

Terminal.Gui/Application/Application.Driver.cs

@@ -26,4 +26,6 @@
     /// </remarks>
     [SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
     public static string ForceDriver { get; set; } = string.Empty;
+
+    public static string Sixel;
 }

Terminal.Gui/ConsoleDrivers/NetDriver.cs

@@ -1020,6 +1020,19 @@ public override void UpdateScreen ()
                 SetCursorPosition (lastCol, row);
                 Console.Write (output);
             }
+
+            /*
+            // Hard-coded sixel content from the file
+            string knownGood = "\u001bP0;0;0q\"1;1;60;23#0;2;0;0;0#1;2;99;36;0#2;2;96;40;0#3;2;98;39;0#4;2;95;42;0#5;2;93;46;0#6;2;91;50;0#7;2;92;49;0#8;2;94;44;0#9;2;0;100;7#10;2;87;56;0#11;2;86;58;0#12;2;84;61;0#13;2;85;60;0#14;2;90;52;0#15;2;91;50;0#16;2;88;54;0#17;2;81;65;0#18;2;80;67;0#19;2;82;64;0#20;2;78;71;0#21;2;79;70;0#22;2;76;74;0#23;2;75;76;0#24;2;75;76;0#25;2;75;76;0#26;2;73;78;0#27;2;73;78;0#28;2;74;77;0#29;2;74;77;0#30;2;74;77;0#31;2;75;77;0#32;2;74;78;0#33;2;74;78;0#34;2;74;77;0#35;2;72;80;0#36;2;71;81;0#37;2;72;81;0#38;2;71;81;0#39;2;72;81;0#40;2;73;78;0#41;2;73;78;0#42;2;73;79;0#43;2;73;79;0#44;2;73;80;0#45;2;73;79;0#46;2;72;80;0#47;2;73;80;0#48;2;72;80;0#49;2;73;79;0#50;2;69;85;0#51;2;68;86;0#52;2;69;86;0#53;2;68;86;0#54;2;69;86;0#55;2;68;87;0#56;2;68;87;0#57;2;68;87;0#58;2;68;87;0#59;2;68;87;0#60;2;71;82;0#61;2;71;82;0#62;2;71;82;0#63;2;71;82;0#64;2;71;82;0#65;2;71;83;0#66;2;70;83;0#67;2;70;84;0#68;2;69;84;0#69;2;70;84;0#70;2;70;84;0#71;2;70;84;0#72;2;71;83;0#73;2;71;83;0#74;2;69;85;0#75;2;69;85;0#76;2;69;85;0#77;2;70;85;0#78;2;69;85;0#79;2;69;86;0#80;2;69;85;0#81;2;62;96;0#82;2;62;96;0#83;2;62;96;0#84;2;62;97;0#85;2;62;97;0#86;2;62;96;0#87;2;61;98;0#88;2;62;97;0#89;2;61;98;0#90;2;62;98;0#91;2;62;97;0#92;2;61;98;0#93;2;62;98;0#94;2;61;98;0#95;2;60;99;0#96;2;61;99;0#97;2;60;99;0#98;2;61;99;0#99;2;60;100;0#100;2;60;100;0#101;2;60;100;0#102;2;62;98;0#103;2;65;90;0#104;2;67;88;0#105;2;67;89;0#106;2;67;89;0#107;2;67;89;0#108;2;67;89;0#109;2;67;88;0#110;2;68;88;0#111;2;67;88;0#112;2;66;89;0#113;2;66;90;0#114;2;66;90;0#115;2;67;89;0#116;2;66;90;0#117;2;66;90;0#118;2;66;91;0#119;2;67;89;0#120;2;65;91;0#121;2;65;91;0#122;2;65;92;0#123;2;65;92;0#124;2;64;93;0#125;2;64;94;0#126;2;64;94;0#127;2;64;93;0#128;2;65;93;0#129;2;64;93;0#130;2;64;93;0#131;2;65;92;0#132;2;66;91;0#133;2;63;95;0#134;2;64;94;0#135;2;64;94;0#136;2;64;95;0#137;2;63;95;0#138;2;63;95;0#139;2;63;95;0#140;2;64;95;0#141;2;63;96;0#142;2;63;96;0#143;2;64;95;0#144;2;75;75;0#4~{w#7??B^}o#14F^_#10BFo_#13F~o#19?BN{#0{Ez|llJ}KsSsKw#37@FW#70BEw_#107?@Mo#121B]w#135@Mw#88BMo_$#8?BCo#6???@#15Nw_#16^{w#11N^w#12?N~{o#17BB#9wCAQQs?oGGGo#45F{o#65F{_#55?@Fw_#132?C#129@Co#141@Eo#87@#98N^~~$#5??BN~{_#18!17?@#22!5?@BB_#32B#26B#48?AG_#74?@F[o#110EO#120??_#124BMo#83@Ko$#23!33?B#72!7?W#52?AG#112?@Nw-#4@F^~w#5FN{o#15?F]o#16N~[_#13?D~w_#19@?{wo#18?Gw_#20Gw#22www_#32Fo_#37DMo#72C_#52@W_#110G_#121@Nw_#83?@^w_$#2EW_#8?Fwo#7BN~w_#10???b]o#12??F^}{#9@@AAAB?@AAA@#23[w#45F]o#65@Mo#74B]_#107@FWo#129?FW_#88??F[_$#3w_#14!9?@No#11??@Ny#0!4?BAEDDDCFEDDDEB#26?G#48@Io#70@J[_#55F]o#112FMo#135?BN}_#87?AO$#17!26?Gwo#21?Wo#124!21?CO#98???@N-#0MIyAyYmggWowGggwGgggGggG}I}wGgggWgggGw}A}??wKuyYYU{wGw?wG}I}$#1o_#4?@@@#8@A#7?@FFE#14?BE#10?BF#11F#13FFC#19?@@@C#18?@F#21FC#22?BFFE#23@#32@?o#37AA#70?@#74@@#55@#110@#107BE#121@F}#124@#135F#141@#83@#88@$#3@O#5!5?DFEG#15?@FC#16@FC#12!4?BF#17???BFE#20??BFC#144??@#45??@Nw#65@B#112!6?@C#129?@E$#9?CC{CcOOO_??oOO?oOOOoOOo?s??oOOO_OOOo??{!4?oGCccg??o???o?s$#2?@@#48!39?DC#120!8?A-#1^^OO#3OO#2O#4OOO#8O#5OO#7O^O#15O#14OO#10??O#11OO#13OO#12OOO#19OWO#18?OO#21O#20OO#22OOO#23O#32O#26O#45WO#48O#65OO#70O#74OO#55O#110O#112@O#121OO#129O#135O$#0??NGNK!4INNGN?NGN?NGNNGNGNNGN?NGGIIGNNGNNHNCLJJJGNFKJIJGNGN$#9???F?B!4D??F???F???F??F?F??F???FFDDF??F??E?BACCCF??BCCCF?F$#16!18?NOO#17!9?F?O#52!18?G#107??O-\u001b\\";
+
+            Application.Sixel = knownGood;
+            */
+
+            if (!string.IsNullOrWhiteSpace(Application.Sixel))
+            {
+                Console.SetCursorPosition (0,0);
+                Console.Write (Application.Sixel);
+            }
         }
 
         SetCursorPosition (0, 0);

Terminal.Gui/Drawing/Quant/CIE76ColorDistance.cs

@@ -0,0 +1,17 @@
+namespace Terminal.Gui;
+
+/// <summary>
+/// This is the simplest method to measure color difference in the CIE Lab color space. The Euclidean distance in Lab
+/// space is more aligned with human perception than RGB space, as Lab attempts to model how humans perceive color differences.
+/// </summary>
+public class CIE76ColorDistance : LabColorDistance
+{
+    public override double CalculateDistance (Color c1, Color c2)
+    {
+        var lab1 = RgbToLab (c1);
+        var lab2 = RgbToLab (c2);
+
+        // Euclidean distance in Lab color space
+        return Math.Sqrt (Math.Pow (lab1.L - lab2.L, 2) + Math.Pow (lab1.A - lab2.A, 2) + Math.Pow (lab1.B - lab2.B, 2));
+    }
+}

Terminal.Gui/Drawing/Quant/CIE94ColorDistance.cs

@@ -0,0 +1,45 @@
+namespace Terminal.Gui;
+
+/// <summary>
+/// CIE94 improves on CIE76 by introducing adjustments for chroma (color intensity) and lightness.
+/// This algorithm considers human visual perception more accurately by scaling differences in lightness and chroma.
+/// It is better but slower than <see cref="CIE76ColorDistance"/>.
+/// </summary>
+public class CIE94ColorDistance : LabColorDistance
+{
+    // Constants for CIE94 formula (can be modified for different use cases like textiles or graphics)
+    private const double kL = 1.0;
+    private const double kC = 1.0;
+    private const double kH = 1.0;
+
+    public override double CalculateDistance (Color first, Color second)
+    {
+        var lab1 = RgbToLab (first);
+        var lab2 = RgbToLab (second);
+
+        // Delta L, A, B
+        double deltaL = lab1.L - lab2.L;
+        double deltaA = lab1.A - lab2.A;
+        double deltaB = lab1.B - lab2.B;
+
+        // Chroma values for both colors
+        double c1 = Math.Sqrt (lab1.A * lab1.A + lab1.B * lab1.B);
+        double c2 = Math.Sqrt (lab2.A * lab2.A + lab2.B * lab2.B);
+        double deltaC = c1 - c2;
+
+        // Delta H (calculated indirectly)
+        double deltaH = Math.Sqrt (Math.Pow (deltaA, 2) + Math.Pow (deltaB, 2) - Math.Pow (deltaC, 2));
+
+        // Scaling factors
+        double sL = 1.0;
+        double sC = 1.0 + 0.045 * c1;
+        double sH = 1.0 + 0.015 * c1;
+
+        // CIE94 color difference formula
+        return Math.Sqrt (
+                          Math.Pow (deltaL / (kL * sL), 2) +
+                          Math.Pow (deltaC / (kC * sC), 2) +
+                          Math.Pow (deltaH / (kH * sH), 2)
+                         );
+    }
+}

Terminal.Gui/Drawing/Quant/ColorQuantizer.cs

@@ -0,0 +1,70 @@
+
+
+namespace Terminal.Gui;
+
+/// <summary>
+/// Translates colors in an image into a Palette of up to 256 colors.
+/// </summary>
+public class ColorQuantizer
+{
+    /// <summary>
+    /// Gets the current colors in the palette based on the last call to
+    /// <see cref="BuildPalette"/>.
+    /// </summary>
+    public IReadOnlyCollection<Color> Palette { get; private set; } = new List<Color> ();
+
+    /// <summary>
+    /// Gets or sets the maximum number of colors to put into the <see cref="Palette"/>.
+    /// Defaults to 256 (the maximum for sixel images).
+    /// </summary>
+    public int MaxColors { get; set; } = 256;
+
+    /// <summary>
+    /// Gets or sets the algorithm used to map novel colors into existing
+    /// palette colors (closest match). Defaults to <see cref="CIE94ColorDistance"/>
+    /// </summary>
+    public IColorDistance DistanceAlgorithm { get; set; } = new CIE94ColorDistance ();
+
+    /// <summary>
+    /// Gets or sets the algorithm used to build the <see cref="Palette"/>.
+    /// </summary>
+    public IPaletteBuilder PaletteBuildingAlgorithm { get; set; } = new MedianCutPaletteBuilder (new EuclideanColorDistance ()) ;
+
+    public void BuildPalette (Color [,] pixels)
+    {
+        List<Color> allColors = new List<Color> ();
+        int width = pixels.GetLength (0);
+        int height = pixels.GetLength (1);
+
+        for (int x = 0; x < width; x++)
+        {
+            for (int y = 0; y < height; y++)
+            {
+                allColors.Add (pixels [x, y]);
+            }
+        }
+
+        Palette = PaletteBuildingAlgorithm.BuildPalette (allColors, MaxColors);
+    }
+
+    public int GetNearestColor (Color toTranslate)
+    {
+        // Simple nearest color matching based on DistanceAlgorithm
+        double minDistance = double.MaxValue;
+        int nearestIndex = 0;
+
+        for (var index = 0; index < Palette.Count; index++)
+        {
+            Color color = Palette.ElementAt (index);
+            double distance = DistanceAlgorithm.CalculateDistance (color, toTranslate);
+
+            if (distance < minDistance)
+            {
+                minDistance = distance;
+                nearestIndex = index;
+            }
+        }
+
+        return nearestIndex;
+    }
+}

Terminal.Gui/Drawing/Quant/EuclideanColorDistance.cs

@@ -0,0 +1,16 @@
+namespace Terminal.Gui;
+
+/// <summary>
+/// Calculates the distance between two colors using Euclidean distance in 3D RGB space.
+/// This measures the straight-line distance between the two points representing the colors.
+/// </summary>
+public class EuclideanColorDistance : IColorDistance
+{
+    public double CalculateDistance (Color c1, Color c2)
+    {
+        int rDiff = c1.R - c2.R;
+        int gDiff = c1.G - c2.G;
+        int bDiff = c1.B - c2.B;
+        return Math.Sqrt (rDiff * rDiff + gDiff * gDiff + bDiff * bDiff);
+    }
+}

Terminal.Gui/Drawing/Quant/IColorDistance.cs

@@ -0,0 +1,18 @@
+namespace Terminal.Gui;
+
+/// <summary>
+/// Interface for algorithms that compute the relative distance between pairs of colors.
+/// This is used for color matching to a limited palette, such as in Sixel rendering.
+/// </summary>
+public interface IColorDistance
+{
+    /// <summary>
+    /// Computes a similarity metric between two <see cref="Color"/> instances.
+    /// A larger value indicates more dissimilar colors, while a smaller value indicates more similar colors.
+    /// The metric is internally consistent for the given algorithm.
+    /// </summary>
+    /// <param name="c1">The first color.</param>
+    /// <param name="c2">The second color.</param>
+    /// <returns>A numeric value representing the distance between the two colors.</returns>
+    double CalculateDistance (Color c1, Color c2);
+}

Terminal.Gui/Drawing/Quant/IPaletteBuilder.cs

@@ -0,0 +1,17 @@
+namespace Terminal.Gui;
+
+/// <summary>
+/// Builds a palette of a given size for a given set of input colors.
+/// </summary>
+public interface IPaletteBuilder
+{
+    /// <summary>
+    /// Reduce the number of <paramref name="colors"/> to <paramref name="maxColors"/> (or less)
+    /// using an appropriate selection algorithm.
+    /// </summary>
+    /// <param name="colors">Color of every pixel in the image. Contains duplication in order
+    /// to support algorithms that weigh how common a color is.</param>
+    /// <param name="maxColors">The maximum number of colours that should be represented.</param>
+    /// <returns></returns>
+    List<Color> BuildPalette (List<Color> colors, int maxColors);
+}

Terminal.Gui/Drawing/Quant/LabColorDistance.cs

@@ -0,0 +1,52 @@
+using ColorHelper;
+
+namespace Terminal.Gui;
+
+public abstract class LabColorDistance : IColorDistance
+{
+    // Reference white point for D65 illuminant (can be moved to constants)
+    private const double RefX = 95.047;
+    private const double RefY = 100.000;
+    private const double RefZ = 108.883;
+
+    // Conversion from RGB to Lab
+    protected LabColor RgbToLab (Color c)
+    {
+        var xyz = ColorHelper.ColorConverter.RgbToXyz (new RGB (c.R, c.G, c.B));
+
+        // Normalize XYZ values by reference white point
+        double x = xyz.X / RefX;
+        double y = xyz.Y / RefY;
+        double z = xyz.Z / RefZ;
+
+        // Apply the nonlinear transformation for Lab
+        x = x > 0.008856 ? Math.Pow (x, 1.0 / 3.0) : 7.787 * x + 16.0 / 116.0;
+        y = y > 0.008856 ? Math.Pow (y, 1.0 / 3.0) : 7.787 * y + 16.0 / 116.0;
+        z = z > 0.008856 ? Math.Pow (z, 1.0 / 3.0) : 7.787 * z + 16.0 / 116.0;
+
+        // Calculate Lab values
+        double l = 116.0 * y - 16.0;
+        double a = 500.0 * (x - y);
+        double b = 200.0 * (y - z);
+
+        return new LabColor (l, a, b);
+    }
+
+    // LabColor class encapsulating L, A, and B values
+    protected class LabColor
+    {
+        public double L { get; }
+        public double A { get; }
+        public double B { get; }
+
+        public LabColor (double l, double a, double b)
+        {
+            L = l;
+            A = a;
+            B = b;
+        }
+    }
+
+    /// <inheritdoc />
+    public abstract double CalculateDistance (Color c1, Color c2);
+}