Ability to configure font features

samples/ControlCatalog/Pages/TextBlockPage.xaml

@@ -128,6 +128,13 @@
           </Span>.
         </SelectableTextBlock>
       </Border>
+      <Border>
+        <TextBlock FontFamily="Times New Roman">
+          <Run Text="ABC" FontFeatures="+c2sc, +smcp"/>
+          <Run Text="DEF"/>
+          <Run Text="0123" FontFeatures="frac"/>
+        </TextBlock> 
+      </Border>
     </WrapPanel>
   </StackPanel>
 </UserControl>

src/Avalonia.Base/Media/FontFeature.cs

@@ -0,0 +1,153 @@
+using System.Globalization;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace Avalonia.Media;
+
+/// <summary>
+/// Font feature
+/// </summary>
+public record FontFeature
+{
+    private const int DefaultValue = 1;
+    private const int InfinityEnd = -1;
+
+    private static readonly Regex s_featureRegex = new Regex(
+        @"^\s*(?<Value>[+-])?\s*(?<Tag>\w{4})\s*(\[\s*(?<Start>\d+)?(\s*(?<Separator>:)\s*)?(?<End>\d+)?\s*\])?\s*(?(Value)()|(=\s*(?<Value>\d+|on|off)))?\s*$", 
+        RegexOptions.Compiled | RegexOptions.ExplicitCapture);
+
+    /// <summary>Gets or sets the tag.</summary>
+    public string Tag
+    {
+        get;
+        init;
+    }
+
+    /// <summary>Gets or sets the value.</summary>
+    public int Value
+    {
+        get;
+        init;
+    }
+
+    /// <summary>Gets or sets the start.</summary>
+    public int Start
+    {
+        get;
+        init;
+    }
+
+    /// <summary>Gets or sets the end.</summary>
+    public int End
+    {
+        get;
+        init;
+    }
+
+    /// <summary>
+    /// Creates an instance of FontFeature.
+    /// </summary>
+    public FontFeature()
+    {
+        Tag = string.Empty;
+        Value = DefaultValue;
+        Start = 0;
+        End = InfinityEnd;
+    }
+
+    /// <summary>
+    /// Parses a string to return a <see cref="FontFeature"/>.
+    /// Syntax is the following:
+    ///  
+    ///     Syntax 	        Value 	Start 	End 	 
+    ///     Setting value: 	  	  	  	 
+    ///     kern 	        1 	    0 	    ∞ 	    Turn feature on
+    ///     +kern 	        1 	    0 	    ∞ 	    Turn feature on
+    ///     -kern 	        0 	    0 	    ∞ 	    Turn feature off
+    ///     kern=0 	        0 	    0 	    ∞ 	    Turn feature off
+    ///     kern=1 	        1 	    0 	    ∞ 	    Turn feature on
+    ///     aalt=2 	        2 	    0 	    ∞ 	    Choose 2nd alternate
+    ///     Setting index: 	  	  	  	 
+    ///     kern[] 	        1 	    0 	    ∞ 	    Turn feature on
+    ///     kern[:] 	    1 	    0 	    ∞ 	    Turn feature on
+    ///     kern[5:] 	    1 	    5 	    ∞ 	    Turn feature on, partial
+    ///     kern[:5] 	    1 	    0 	    5 	    Turn feature on, partial
+    ///     kern[3:5] 	    1 	    3 	    5 	    Turn feature on, range
+    ///     kern[3] 	    1 	    3 	    3+1 	Turn feature on, single char
+    ///     Mixing it all: 	  	  	  	 
+    ///     aalt[3:5]=2 	2 	    3 	    5 	    Turn 2nd alternate on for range
+    /// 
+    /// </summary>
+    /// <param name="s">The string.</param>
+    /// <returns>The <see cref="FontFeature"/>.</returns>
+    // ReSharper disable once UnusedMember.Global
+    public static FontFeature Parse(string s)
+    {
+        var match = s_featureRegex.Match(s);
+
+        if (!match.Success)
+        {
+            return new FontFeature();
+        }
+
+        var hasSeparator = match.Groups["Separator"].Value == ":";
+        var hasStart = int.TryParse(match.Groups["Start"].Value, NumberStyles.None, CultureInfo.InvariantCulture, out var start);
+        var hasEnd = int.TryParse(match.Groups["End"].Value, NumberStyles.None, CultureInfo.InvariantCulture, out var end);
+
+        var stringValue = match.Groups["Value"].Value;
+        if (stringValue == "-" || stringValue.ToUpperInvariant() == "OFF")
+            stringValue = "0";
+        if (stringValue == "+" || stringValue.ToUpperInvariant() == "ON")
+            stringValue = "1";
+
+        var result = new FontFeature
+        {
+            Tag = match.Groups["Tag"].Value,
+            Start = hasStart ? start : 0,
+            End = hasEnd ? end : hasStart && !hasSeparator ? (start + 1) : InfinityEnd,
+            Value = int.TryParse(stringValue, NumberStyles.None, CultureInfo.InvariantCulture, out var value) ? value : DefaultValue,
+        };
+
+        return result;
+    }
+
+    /// <summary>
+    /// Gets a string representation of the <see cref="FontFeature"/>.
+    /// </summary>
+    /// <returns>The string representation.</returns>
+    public override string ToString()
+    {
+        var result = new StringBuilder(128);
+
+        if (Value == 0)
+            result.Append('-');
+        result.Append(Tag ?? string.Empty);
+
+        if (Start != 0 || End != InfinityEnd)
+        {
+            result.Append('[');
+
+            if (Start > 0)
+                result.Append(Start.ToString(CultureInfo.InvariantCulture));
+
+            if (End != Start + 1) 
+            {
+                result.Append(':');
+                if (End != InfinityEnd)
+                    result.Append(End.ToString(CultureInfo.InvariantCulture));
+            }
+
+            result.Append(']');
+        }
+
+        if (Value is DefaultValue or 0)
+        {
+            return result.ToString();
+        }
+
+        result.Append('=');
+        result.Append(Value.ToString(CultureInfo.InvariantCulture));
+
+        return result.ToString();
+    }
+}

src/Avalonia.Base/Media/FontFeatureCollection.cs

@@ -0,0 +1,10 @@
+using Avalonia.Collections;
+
+namespace Avalonia.Media;
+
+/// <summary>
+/// List of font feature settings
+/// </summary>
+public class FontFeatureCollection : AvaloniaList<FontFeature>
+{
+}

src/Avalonia.Base/Media/FormattedText.cs

@@ -3,6 +3,7 @@
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Globalization;
+using System.Linq;
 using Avalonia.Media.TextFormatting;
 using Avalonia.Utilities;
 
@@ -50,6 +51,7 @@ public class FormattedText
         /// <param name="typeface">Type face used to display text.</param>
         /// <param name="emSize">Font em size in visual units (1/96 of an inch).</param>
         /// <param name="foreground">Foreground brush used to render text.</param>
+        /// <param name="features">Optional list of turned on/off features.</param>
         public FormattedText(
             string textToFormat,
             CultureInfo culture,
@@ -183,6 +185,7 @@ public void SetForegroundBrush(IBrush? foregroundBrush, int startIndex, int coun
 
                 var newProps = new GenericTextRunProperties(
                     runProps.Typeface,
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     runProps.TextDecorations,
                     foregroundBrush,
@@ -197,6 +200,62 @@ public void SetForegroundBrush(IBrush? foregroundBrush, int startIndex, int coun
             }
         }
 
+        /// <summary>
+        /// Sets or changes the font features for the text object 
+        /// </summary>
+        /// <param name="fontFeatures">Feature collection</param>
+        public void SetFontFeatures(FontFeatureCollection? fontFeatures)
+        {
+            SetFontFeatures(fontFeatures, 0, _text.Length);
+        }
+
+        /// <summary>
+        /// Sets or changes the font features for the text object 
+        /// </summary>
+        /// <param name="fontFeatures">Feature collection</param>
+        /// <param name="startIndex">The start index of initial character to apply the change to.</param>
+        /// <param name="count">The number of characters the change should be applied to.</param>
+        public void SetFontFeatures(FontFeatureCollection? fontFeatures, int startIndex, int count)
+        {
+            var limit = ValidateRange(startIndex, count);
+            for (var i = startIndex; i < limit;)
+            {
+                var formatRider = new SpanRider(_formatRuns, _latestPosition, i);
+                i = Math.Min(limit, i + formatRider.Length);
+
+#pragma warning disable 6506
+                // Presharp warns that runProps is not validated, but it can never be null 
+                // because the rider is already checked to be in range
+
+                if (!(formatRider.CurrentElement is GenericTextRunProperties runProps))
+                {
+                    throw new NotSupportedException($"{nameof(runProps)} can not be null.");
+                }
+
+                if ((fontFeatures == null && runProps.FontFeatures == null) ||
+                    (fontFeatures != null && runProps.FontFeatures != null && 
+                     fontFeatures.SequenceEqual(runProps.FontFeatures)))
+                {
+                    continue;
+                }
+
+                var newProps = new GenericTextRunProperties(
+                    runProps.Typeface,
+                    fontFeatures,
+                    runProps.FontRenderingEmSize,
+                    runProps.TextDecorations,
+                    runProps.ForegroundBrush,
+                    runProps.BackgroundBrush,
+                    runProps.BaselineAlignment,
+                    runProps.CultureInfo
+                );
+
+#pragma warning restore 6506
+                _latestPosition = _formatRuns.SetValue(formatRider.CurrentPosition, i - formatRider.CurrentPosition,
+                    newProps, formatRider.SpanPosition);
+            }
+        }
+
         /// <summary>
         /// Sets or changes the font family for the text object 
         /// </summary>
@@ -270,6 +329,7 @@ public void SetFontFamily(FontFamily fontFamily, int startIndex, int count)
 
                 var newProps = new GenericTextRunProperties(
                     new Typeface(fontFamily, oldTypeface.Style, oldTypeface.Weight),
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     runProps.TextDecorations,
                     runProps.ForegroundBrush,
@@ -329,6 +389,7 @@ public void SetFontSize(double emSize, int startIndex, int count)
 
                 var newProps = new GenericTextRunProperties(
                     runProps.Typeface,
+                    runProps.FontFeatures,
                     emSize,
                     runProps.TextDecorations,
                     runProps.ForegroundBrush,
@@ -391,6 +452,7 @@ public void SetCulture(CultureInfo culture, int startIndex, int count)
 
                 var newProps = new GenericTextRunProperties(
                     runProps.Typeface,
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     runProps.TextDecorations,
                     runProps.ForegroundBrush,
@@ -450,6 +512,7 @@ public void SetFontWeight(FontWeight weight, int startIndex, int count)
 
                 var newProps = new GenericTextRunProperties(
                     new Typeface(oldTypeface.FontFamily, oldTypeface.Style, weight),
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     runProps.TextDecorations,
                     runProps.ForegroundBrush,
@@ -506,6 +569,7 @@ public void SetFontStyle(FontStyle style, int startIndex, int count)
 
                 var newProps = new GenericTextRunProperties(
                     new Typeface(oldTypeface.FontFamily, style, oldTypeface.Weight),
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     runProps.TextDecorations,
                     runProps.ForegroundBrush,
@@ -562,6 +626,7 @@ public void SetFontTypeface(Typeface typeface, int startIndex, int count)
 
                 var newProps = new GenericTextRunProperties(
                     typeface,
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     runProps.TextDecorations,
                     runProps.ForegroundBrush,
@@ -619,6 +684,7 @@ public void SetTextDecorations(TextDecorationCollection textDecorations, int sta
 
                 var newProps = new GenericTextRunProperties(
                     runProps.Typeface,
+                    runProps.FontFeatures,
                     runProps.FontRenderingEmSize,
                     textDecorations,
                     runProps.ForegroundBrush,

src/Avalonia.Base/Media/TextFormatting/GenericTextRunProperties.cs

@@ -1,4 +1,6 @@
-using System.Globalization;
+using System;
+using System.Collections.Generic;
+using System.Globalization;
 
 namespace Avalonia.Media.TextFormatting
 {
@@ -9,9 +11,25 @@ public class GenericTextRunProperties : TextRunProperties
     {
         private const double DefaultFontRenderingEmSize = 12;
 
+        // TODO12: Remove in 12.0.0 and make fontFeatures parameter in main ctor optional
         public GenericTextRunProperties(Typeface typeface, double fontRenderingEmSize = DefaultFontRenderingEmSize,
             TextDecorationCollection? textDecorations = null, IBrush? foregroundBrush = null,
             IBrush? backgroundBrush = null, BaselineAlignment baselineAlignment = BaselineAlignment.Baseline,
+            CultureInfo? cultureInfo = null) : 
+            this(typeface, null, fontRenderingEmSize, textDecorations, foregroundBrush,
+            backgroundBrush, baselineAlignment, cultureInfo)
+        {
+        }
+
+        // TODO12:Change signature in 12.0.0
+        public GenericTextRunProperties(
+            Typeface typeface, 
+            FontFeatureCollection? fontFeatures, 
+            double fontRenderingEmSize = DefaultFontRenderingEmSize,
+            TextDecorationCollection? textDecorations = null,
+            IBrush? foregroundBrush = null,
+            IBrush? backgroundBrush = null,
+            BaselineAlignment baselineAlignment = BaselineAlignment.Baseline,
             CultureInfo? cultureInfo = null)
         {
             Typeface = typeface;
@@ -21,6 +39,7 @@ public GenericTextRunProperties(Typeface typeface, double fontRenderingEmSize =
             BackgroundBrush = backgroundBrush;
             BaselineAlignment = baselineAlignment;
             CultureInfo = cultureInfo;
+            FontFeatures = fontFeatures;
         }
 
         /// <inheritdoc />
@@ -38,6 +57,9 @@ public GenericTextRunProperties(Typeface typeface, double fontRenderingEmSize =
         /// <inheritdoc />
         public override IBrush? BackgroundBrush { get; }
 
+        /// <inheritdoc />
+        public override FontFeatureCollection? FontFeatures { get; }
+
         /// <inheritdoc />
         public override BaselineAlignment BaselineAlignment { get; }
 

src/Avalonia.Base/Media/TextFormatting/TextFormatterImpl.cs

@@ -272,7 +272,7 @@ private static RentedList<TextRun> ShapeTextRuns(IReadOnlyList<TextRun> textRuns
                                 }
 
                                 var shaperOptions = new TextShaperOptions(
-                                    properties.CachedGlyphTypeface,
+                                    properties.CachedGlyphTypeface, properties.FontFeatures,
                                     properties.FontRenderingEmSize, shapeableRun.BidiLevel, properties.CultureInfo,
                                     paragraphProperties.DefaultIncrementalTab, paragraphProperties.LetterSpacing);
 
@@ -976,7 +976,8 @@ internal static ShapedTextRun CreateSymbol(TextRun textRun, FlowDirection flowDi
 
             var cultureInfo = textRun.Properties.CultureInfo;
 
-            var shaperOptions = new TextShaperOptions(glyphTypeface, fontRenderingEmSize, (sbyte)flowDirection, cultureInfo);
+            var shaperOptions = new TextShaperOptions(glyphTypeface, textRun.Properties.FontFeatures, 
+                fontRenderingEmSize, (sbyte)flowDirection, cultureInfo);
 
             var shapedBuffer = textShaper.ShapeText(textRun.Text, shaperOptions);