Gradients - From Terminal Text Effects

Terminal.Gui/Drawing/FillPair.cs

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+namespace Terminal.Gui;
+
+/// <summary>
+///     Describes a pair of <see cref="IFill"/> which cooperate in creating
+///     <see cref="Attribute"/>. One gives foreground color while other gives background.
+/// </summary>
+public class FillPair
+{
+    /// <summary>
+    ///     Creates a new instance using the provided fills for foreground and background
+    ///     color when assembling <see cref="Attribute"/>.
+    /// </summary>
+    /// <param name="fore"></param>
+    /// <param name="back"></param>
+    public FillPair (IFill fore, IFill back)
+    {
+        Foreground = fore;
+        Background = back;
+    }
+
+    /// <summary>
+    ///     The fill which provides point based foreground color.
+    /// </summary>
+    public IFill Foreground { get; init; }
+
+    /// <summary>
+    ///     The fill which provides point based background color.
+    /// </summary>
+    public IFill Background { get; init; }
+
+    /// <summary>
+    ///     Returns the color pair (foreground+background) to use when rendering
+    ///     a rune at the given <paramref name="point"/>.
+    /// </summary>
+    /// <param name="point"></param>
+    /// <returns></returns>
+    public Attribute GetAttribute (Point point)
+    {
+        return new (Foreground.GetColor (point), Background.GetColor (point));
+    }
+}

Terminal.Gui/Drawing/Gradient.cs

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+// This code is a C# port from python library Terminal Text Effects  https://github.com/ChrisBuilds/terminaltexteffects/
+
+namespace Terminal.Gui;
+
+/// <summary>
+///     Describes the pattern that a <see cref="Gradient"/> results in e.g. <see cref="Vertical"/>,
+///     <see cref="Horizontal"/> etc
+/// </summary>
+public enum GradientDirection
+{
+    /// <summary>
+    ///     Color varies along Y axis but is constant on X axis.
+    /// </summary>
+    Vertical,
+
+    /// <summary>
+    ///     Color varies along X axis but is constant on Y axis.
+    /// </summary>
+    Horizontal,
+
+    /// <summary>
+    ///     Color varies by distance from center (i.e. in circular ripples)
+    /// </summary>
+    Radial,
+
+    /// <summary>
+    ///     Color varies by X and Y axis (i.e. a slanted gradient)
+    /// </summary>
+    Diagonal
+}
+
+/// <summary>
+/// Describes a <see cref="Spectrum"/> of colors that can be combined
+/// to make a color gradient.  Use <see cref="BuildCoordinateColorMapping"/>
+/// to create into gradient fill area maps.
+/// </summary>
+public class Gradient
+{
+    /// <summary>
+    ///     The discrete colors that will make up the <see cref="Gradient"/>.
+    /// </summary>
+    public List<Color> Spectrum { get; }
+
+    private readonly bool _loop;
+    private readonly List<Color> _stops;
+    private readonly List<int> _steps;
+
+    /// <summary>
+    ///     Creates a new instance of the <see cref="Gradient"/> class which hosts a <see cref="Spectrum"/>
+    ///     of colors including all <paramref name="stops"/> and <paramref name="steps"/> interpolated colors
+    ///     between each corresponding pair.
+    /// </summary>
+    /// <param name="stops">The colors to use in the spectrum (N)</param>
+    /// <param name="steps">
+    ///     The number of colors to generate between each pair (must be N-1 numbers).
+    ///     If only one step is passed then it is assumed to be the same distance for all pairs.
+    /// </param>
+    /// <param name="loop">True to duplicate the first stop and step so that the gradient repeats itself</param>
+    /// <exception cref="ArgumentException"></exception>
+    public Gradient (IEnumerable<Color> stops, IEnumerable<int> steps, bool loop = false)
+    {
+        _stops = stops.ToList ();
+
+        if (_stops.Count < 1)
+        {
+            throw new ArgumentException ("At least one color stop must be provided.");
+        }
+
+        _steps = steps.ToList ();
+
+        // If multiple colors and only 1 step assume same distance applies to all steps
+        if (_stops.Count > 2 && _steps.Count == 1)
+        {
+            _steps = Enumerable.Repeat (_steps.Single (), _stops.Count () - 1).ToList ();
+        }
+
+        if (_steps.Any (step => step < 1))
+        {
+            throw new ArgumentException ("Steps must be greater than 0.");
+        }
+
+        if (_steps.Count != _stops.Count - 1)
+        {
+            throw new ArgumentException ("Number of steps must be N-1");
+        }
+
+        _loop = loop;
+        Spectrum = GenerateGradient (_steps);
+    }
+
+    /// <summary>
+    ///     Returns the color to use at the given part of the spectrum
+    /// </summary>
+    /// <param name="fraction">
+    ///     Proportion of the way through the spectrum, must be between
+    ///     0 and 1 (inclusive).  Returns the last color if <paramref name="fraction"/> is
+    ///     <see cref="double.NaN"/>.
+    /// </param>
+    /// <returns></returns>
+    /// <exception cref="ArgumentOutOfRangeException"></exception>
+    public Color GetColorAtFraction (double fraction)
+    {
+        if (double.IsNaN (fraction))
+        {
+            return Spectrum.Last ();
+        }
+
+        if (fraction is < 0 or > 1)
+        {
+            throw new ArgumentOutOfRangeException (nameof (fraction), @"Fraction must be between 0 and 1.");
+        }
+
+        var index = (int)(fraction * (Spectrum.Count - 1));
+
+        return Spectrum [index];
+    }
+
+    private List<Color> GenerateGradient (IEnumerable<int> steps)
+    {
+        List<Color> gradient = new ();
+
+        if (_stops.Count == 1)
+        {
+            for (var i = 0; i < steps.Sum (); i++)
+            {
+                gradient.Add (_stops [0]);
+            }
+
+            return gradient;
+        }
+
+        List<Color> stopsToUse = _stops.ToList ();
+        List<int> stepsToUse = _steps.ToList ();
+
+        if (_loop)
+        {
+            stopsToUse.Add (_stops [0]);
+            stepsToUse.Add (_steps.First ());
+        }
+
+        var colorPairs = stopsToUse.Zip (stopsToUse.Skip (1), (start, end) => new { start, end });
+        List<int> stepsList = stepsToUse;
+
+        foreach ((var colorPair, int thesteps) in colorPairs.Zip (stepsList, (pair, step) => (pair, step)))
+        {
+            gradient.AddRange (InterpolateColors (colorPair.start, colorPair.end, thesteps));
+        }
+
+        return gradient;
+    }
+
+    private static IEnumerable<Color> InterpolateColors (Color start, Color end, int steps)
+    {
+        for (var step = 0; step < steps; step++)
+        {
+            double fraction = (double)step / steps;
+            var r = (int)(start.R + fraction * (end.R - start.R));
+            var g = (int)(start.G + fraction * (end.G - start.G));
+            var b = (int)(start.B + fraction * (end.B - start.B));
+
+            yield return new (r, g, b);
+        }
+
+        yield return end; // Ensure the last color is included
+    }
+
+    /// <summary>
+    ///     <para>
+    ///         Creates a mapping starting at 0,0 and going to <paramref name="maxRow"/> and <paramref name="maxColumn"/>
+    ///         (inclusively) using the supplied <paramref name="direction"/>.
+    ///     </para>
+    ///     <para>
+    ///         Note that this method is inclusive i.e. passing 1/1 results in 4 mapped coordinates.
+    ///     </para>
+    /// </summary>
+    /// <param name="maxRow"></param>
+    /// <param name="maxColumn"></param>
+    /// <param name="direction"></param>
+    /// <returns></returns>
+    public Dictionary<Point, Color> BuildCoordinateColorMapping (int maxRow, int maxColumn, GradientDirection direction)
+    {
+        Dictionary<Point, Color> gradientMapping = new ();
+
+        switch (direction)
+        {
+            case GradientDirection.Vertical:
+                for (var row = 0; row <= maxRow; row++)
+                {
+                    double fraction = maxRow == 0 ? 1.0 : (double)row / maxRow;
+                    Color color = GetColorAtFraction (fraction);
+
+                    for (var col = 0; col <= maxColumn; col++)
+                    {
+                        gradientMapping [new (col, row)] = color;
+                    }
+                }
+
+                break;
+
+            case GradientDirection.Horizontal:
+                for (var col = 0; col <= maxColumn; col++)
+                {
+                    double fraction = maxColumn == 0 ? 1.0 : (double)col / maxColumn;
+                    Color color = GetColorAtFraction (fraction);
+
+                    for (var row = 0; row <= maxRow; row++)
+                    {
+                        gradientMapping [new (col, row)] = color;
+                    }
+                }
+
+                break;
+
+            case GradientDirection.Radial:
+                for (var row = 0; row <= maxRow; row++)
+                {
+                    for (var col = 0; col <= maxColumn; col++)
+                    {
+                        double distanceFromCenter = FindNormalizedDistanceFromCenter (maxRow, maxColumn, new (col, row));
+                        Color color = GetColorAtFraction (distanceFromCenter);
+                        gradientMapping [new (col, row)] = color;
+                    }
+                }
+
+                break;
+
+            case GradientDirection.Diagonal:
+                for (var row = 0; row <= maxRow; row++)
+                {
+                    for (var col = 0; col <= maxColumn; col++)
+                    {
+                        double fraction = ((double)row * 2 + col) / (maxRow * 2 + maxColumn);
+                        Color color = GetColorAtFraction (fraction);
+                        gradientMapping [new (col, row)] = color;
+                    }
+                }
+
+                break;
+        }
+
+        return gradientMapping;
+    }
+
+    private static double FindNormalizedDistanceFromCenter (int maxRow, int maxColumn, Point coord)
+    {
+        double centerX = maxColumn / 2.0;
+        double centerY = maxRow / 2.0;
+        double dx = coord.X - centerX;
+        double dy = coord.Y - centerY;
+        double distance = Math.Sqrt (dx * dx + dy * dy);
+        double maxDistance = Math.Sqrt (centerX * centerX + centerY * centerY);
+
+        return distance / maxDistance;
+    }
+}

Terminal.Gui/Drawing/GradientFill.cs

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+namespace Terminal.Gui;
+
+/// <summary>
+///     Implementation of <see cref="IFill"/> that uses a color gradient (including
+///     radial, diagonal etc.).
+/// </summary>
+public class GradientFill : IFill
+{
+    private readonly Dictionary<Point, Color> _map;
+
+    /// <summary>
+    ///     Creates a new instance of the <see cref="GradientFill"/> class that can return
+    ///     color for any point in the given <paramref name="area"/> using the provided
+    ///     <paramref name="gradient"/> and <paramref name="direction"/>.
+    /// </summary>
+    /// <param name="area"></param>
+    /// <param name="gradient"></param>
+    /// <param name="direction"></param>
+    public GradientFill (Rectangle area, Gradient gradient, GradientDirection direction)
+    {
+        _map = gradient.BuildCoordinateColorMapping (area.Height - 1, area.Width - 1, direction)
+                       .ToDictionary (
+                                      kvp => new Point (kvp.Key.X + area.X, kvp.Key.Y + area.Y),
+                                      kvp => kvp.Value);
+    }
+
+    /// <summary>
+    ///     Returns the color to use for the given <paramref name="point"/> or Black if it
+    ///     lies outside the prepared gradient area (see constructor).
+    /// </summary>
+    /// <param name="point"></param>
+    /// <returns></returns>
+    public Color GetColor (Point point)
+    {
+        if (_map.TryGetValue (point, out Color color))
+        {
+            return color;
+        }
+
+        return new (0, 0); // Default to black if point not found
+    }
+}

Terminal.Gui/Drawing/IFill.cs

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+namespace Terminal.Gui;
+
+/// <summary>
+///     Describes an area fill (e.g. solid color or gradient).
+/// </summary>
+public interface IFill
+{
+    /// <summary>
+    ///     Returns the color that should be used at the given point
+    /// </summary>
+    /// <param name="point"></param>
+    /// <returns></returns>
+    Color GetColor (Point point);
+}