Add specific colorizer (#21)

README.md

@@ -43,6 +43,18 @@
    var wcg = new WordCloudGenerator<SKBitmap>(wordCloud, engine, layout, colorizer);
    ```
 
+   You can also use `SpecificColorizer` to colorize specific words with chosen colors:
+
+   ```cs
+   var colorizer = new SpecificColorizer(
+       new Dictionary<string, Color>
+       {
+           ["KnowledgePicker"] = Color.FromArgb(0x0f3057),
+           ["WordCloud"] = Color.FromArgb(0xe25a5a)
+       },
+       fallback: new RandomColorizer()); // fallback argument is optional
+   ```
+
 5. Now we can *arrange* the topic cloud:
 
    ```cs

src/KnowledgePicker.WordCloud/Coloring/IColorizer.cs

@@ -1,11 +1,18 @@
+using KnowledgePicker.WordCloud.Primitives;
+using System.Drawing;
+
 namespace KnowledgePicker.WordCloud.Coloring
 {
     public interface IColorizer
     {
         /// <summary>
-        /// Gets the hex string color for text.
+        /// Gets color for the specified <paramref name="item"/>.
         /// </summary>
-        /// <returns>Hex string color in format #RRGGBB.</returns>
-        string GetColorAsHex();
+        /// <param name="item">The item being colored.</param>
+        /// <returns>
+        /// Can return <see langword="null"/> to use the default color
+        /// (<see cref="WordCloudInput.TextColor"/>).
+        /// </returns>
+        Color? GetColor(LayoutItem item);
     }
 }

src/KnowledgePicker.WordCloud/Coloring/RandomColorizer.cs

@@ -1,5 +1,5 @@
+using KnowledgePicker.WordCloud.Primitives;
 using System;
-using System.Diagnostics.CodeAnalysis;
 using System.Drawing;
 
 namespace KnowledgePicker.WordCloud.Coloring
@@ -11,38 +11,22 @@ public class RandomColorizer : IColorizer
     {
         private readonly Random random;
 
-        public RandomColorizer() : this(Environment.TickCount) { }
-
-        public RandomColorizer(int seed)
+        public RandomColorizer()
         {
-            random = new Random(seed);
+            random = new Random();
         }
 
-        /// <summary>
-        /// Gets a random color.
-        /// </summary>
-        [SuppressMessage("Security", "CA5394:Do not use insecure randomness")]
-        private Color GetRandomColor()
-        {
-            return Color.FromArgb(random.Next(0, 255), random.Next(0, 255), random.Next(0, 255));
-        }
-
-        /// <summary>
-        /// Converts Color to hex string.
-        /// </summary>
-        private static string ConvertToHexString(Color c)
+        public RandomColorizer(int seed)
         {
-            return $"#{c.R:X2}{c.G:X2}{c.B:X2}";
+            random = new Random(seed);
         }
 
-        /// <summary>
-        /// Gets the randon RGB color as a hex string.
-        /// </summary>
-        public string GetColorAsHex()
+        public Color? GetColor(LayoutItem item)
         {
-            Color c = GetRandomColor();
-            return ConvertToHexString(c);
+            return Color.FromArgb(
+                random.Next(0, 255),
+                random.Next(0, 255),
+                random.Next(0, 255));
         }
-
     }
 }

src/KnowledgePicker.WordCloud/Coloring/SpecificColorizer.cs

@@ -0,0 +1,32 @@
+using KnowledgePicker.WordCloud.Primitives;
+using System.Collections.Generic;
+using System.Drawing;
+
+namespace KnowledgePicker.WordCloud.Coloring
+{
+    /// <summary>
+    /// Colors specific words with provided colors.
+    /// </summary>
+    public class SpecificColorizer : IColorizer
+    {
+        private readonly IReadOnlyDictionary<string, Color> mapping;
+        private readonly IColorizer? fallback;
+
+        public SpecificColorizer(
+            IReadOnlyDictionary<string, Color> mapping,
+            IColorizer? fallback = null)
+        {
+            this.mapping = mapping;
+            this.fallback = fallback;
+        }
+
+        public Color? GetColor(LayoutItem item)
+        {
+            if (mapping.TryGetValue(item.Entry.Word, out var color))
+            {
+                return color;
+            }
+            return fallback?.GetColor(item);
+        }
+    }
+}

src/KnowledgePicker.WordCloud/Drawing/SkGraphicEngine.cs

@@ -10,16 +10,17 @@ namespace KnowledgePicker.WordCloud.Drawing
     public sealed class SkGraphicEngine : IGraphicEngine<SKBitmap>
     {
         private readonly SKCanvas canvas;
+        private readonly SKColor defaultColor;
         private readonly SKPaint textPaint;
         private readonly WordCloudInput wordCloud;
-        private readonly bool ownsTextPaint;
         private bool bitmapExtracted;
 
         private SkGraphicEngine(ISizer sizer, WordCloudInput wordCloud,
             SKPaint textPaint)
         {
             Sizer = sizer;
             this.wordCloud = wordCloud;
+            defaultColor = textPaint.Color;
             this.textPaint = textPaint;
             Bitmap = new SKBitmap(wordCloud.Width, wordCloud.Height);
             canvas = new SKCanvas(Bitmap);
@@ -31,13 +32,13 @@ public SkGraphicEngine(ISizer sizer, WordCloudInput wordCloud,
             Sizer = sizer;
             Bitmap = new SKBitmap(wordCloud.Width, wordCloud.Height);
             canvas = new SKCanvas(Bitmap);
+            defaultColor = SKColor.Parse(wordCloud.TextColor);
             textPaint = new SKPaint
             {
-                Color = SKColor.Parse(wordCloud.TextColor),
+                Color = defaultColor,
                 Typeface = font,
                 IsAntialias = antialias
             };
-            ownsTextPaint = true;
             this.wordCloud = wordCloud;
         }
 
@@ -60,14 +61,22 @@ public void Draw(PointD location, RectangleD measured, string text, int count, s
             // https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/graphics/skiasharp/basics/text.
             textPaint.TextSize = (float)Sizer.GetFontSize(count);
             if (colorHex != null)
+            {
                 textPaint.Color = SKColor.Parse(colorHex);
+            }
+            else
+            {
+                textPaint.Color = defaultColor;
+            }
             canvas.DrawText(text, (float)(location.X - measured.Left),
                 (float)(location.Y - measured.Top), textPaint);
         }
 
         public IGraphicEngine<SKBitmap> Clone()
         {
-            return new SkGraphicEngine(Sizer, wordCloud, textPaint);
+            var clonedTextPaint = textPaint.Clone();
+            clonedTextPaint.Color = defaultColor;
+            return new SkGraphicEngine(Sizer, wordCloud, clonedTextPaint);
         }
 
         public SKBitmap ExtractBitmap()
@@ -78,10 +87,7 @@ public SKBitmap ExtractBitmap()
 
         public void Dispose()
         {
-            if (ownsTextPaint)
-            {
-                textPaint.Dispose();
-            }
+            textPaint.Dispose();
             canvas.Dispose();
             if (!bitmapExtracted)
             {

src/KnowledgePicker.WordCloud/KnowledgePicker.WordCloud.csproj

@@ -30,4 +30,8 @@
     <PackageReference Include="SkiaSharp" Version="2.88.3" />
   </ItemGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="KnowledgePicker.WordCloud.Tests" />
+  </ItemGroup>
+
 </Project>

src/KnowledgePicker.WordCloud/Utilities/ColorUtil.cs

@@ -0,0 +1,15 @@
+using System.Drawing;
+
+namespace KnowledgePicker.WordCloud.Utilities
+{
+    internal static class ColorUtil
+    {
+        /// <summary>
+        /// Converts <see cref="Color"/> to hex string.
+        /// </summary>
+        public static string ToHexString(this Color c)
+        {
+            return $"#{c.R:X2}{c.G:X2}{c.B:X2}";
+        }
+    }
+}

src/KnowledgePicker.WordCloud/WordCloudGenerator.cs

@@ -2,6 +2,7 @@
 using KnowledgePicker.WordCloud.Drawing;
 using KnowledgePicker.WordCloud.Layouts;
 using KnowledgePicker.WordCloud.Primitives;
+using KnowledgePicker.WordCloud.Utilities;
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -76,7 +77,14 @@ public TBitmap Draw()
             {
                 // Draw words.
                 foreach (var item in items)
-                    engine.Draw(item.Location, item.Measured, item.Entry.Word, item.Entry.Count, colorizer?.GetColorAsHex());
+                {
+                    engine.Draw(
+                        item.Location,
+                        item.Measured,
+                        item.Entry.Word,
+                        item.Entry.Count,
+                        colorizer?.GetColor(item)?.ToHexString());
+                }
                 return engine.ExtractBitmap();
             });
         }