Add SelectionForegroundBrush to SelectableTextBlock (#13618)

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

@@ -48,7 +48,7 @@ namespace Avalonia.Media.TextFormatting
         /// <returns>
         /// The created text style run.
         /// </returns>
-        private static ValueSpan<TextRunProperties> CreateTextStyleRun(ReadOnlySpan<char> text, int firstTextSourceIndex,
+        internal static ValueSpan<TextRunProperties> CreateTextStyleRun(ReadOnlySpan<char> text, int firstTextSourceIndex,
             TextRunProperties defaultProperties, IReadOnlyList<ValueSpan<TextRunProperties>>? textModifier)
         {
             if (textModifier == null || textModifier.Count == 0)

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -105,7 +105,7 @@ namespace Avalonia.Controls.Presenters
 
         static TextPresenter()
         {
-            AffectsRender<TextPresenter>(CaretBrushProperty, SelectionBrushProperty, TextElement.ForegroundProperty);
+            AffectsRender<TextPresenter>(CaretBrushProperty, SelectionBrushProperty, SelectionForegroundBrushProperty, TextElement.ForegroundProperty);
         }
 
         public TextPresenter() { }

src/Avalonia.Controls/SelectableTextBlock.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Data;
 using System.Linq;
 using Avalonia.Controls.Documents;
 using Avalonia.Controls.Utils;
@@ -32,6 +33,9 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<IBrush?> SelectionBrushProperty =
             TextBox.SelectionBrushProperty.AddOwner<SelectableTextBlock>();
 
+        public static readonly StyledProperty<IBrush?> SelectionForegroundBrushProperty =
+            TextBox.SelectionForegroundBrushProperty.AddOwner<SelectableTextBlock>();
+
         public static readonly DirectProperty<SelectableTextBlock, bool> CanCopyProperty =
             TextBox.CanCopyProperty.AddOwner<SelectableTextBlock>(o => o.CanCopy);
 
@@ -63,6 +67,15 @@ namespace Avalonia.Controls
             set => SetValue(SelectionBrushProperty, value);
         }
 
+        /// <summary>
+        /// Gets or sets a brush that is used for the foreground of selected text
+        /// </summary>
+        public IBrush? SelectionForegroundBrush
+        {
+            get => GetValue(SelectionForegroundBrushProperty);
+            set => SetValue(SelectionForegroundBrushProperty, value);
+        }
+
         /// <summary>
         /// Gets or sets a character index for the beginning of the current selection.
         /// </summary>
@@ -167,6 +180,58 @@ namespace Avalonia.Controls
             UpdateCommandStates();
         }
 
+        protected override TextLayout CreateTextLayout(string? text)
+        {
+            var typeface = new Typeface(FontFamily, FontStyle, FontWeight, FontStretch);
+
+            var defaultProperties = new GenericTextRunProperties(
+                typeface,
+                FontSize,
+                TextDecorations,
+                Foreground);
+
+            var paragraphProperties = new GenericTextParagraphProperties(FlowDirection, TextAlignment, true, false,
+                defaultProperties, TextWrapping, LineHeight, 0, LetterSpacing)
+            {
+                LineSpacing = LineSpacing
+            };
+
+            IReadOnlyList<ValueSpan<TextRunProperties>>? textStyleOverrides = null;
+            var selectionStart = SelectionStart;
+            var selectionEnd = SelectionEnd;
+            var start = Math.Min(selectionStart, selectionEnd);
+            var length = Math.Max(selectionStart, selectionEnd) - start;
+
+            if (length > 0 && SelectionForegroundBrush != null)
+            {
+                textStyleOverrides = new[]
+                {
+                        new ValueSpan<TextRunProperties>(start, length,
+                        new GenericTextRunProperties(typeface, FontSize,
+                            foregroundBrush: SelectionForegroundBrush))
+                    };
+            }
+
+            ITextSource textSource;
+
+            if (_textRuns != null)
+            {
+                textSource = new InlinesTextSource(_textRuns, textStyleOverrides);
+            }
+            else
+            {
+                textSource = new FormattedTextSource(text ?? "", defaultProperties, textStyleOverrides);
+            }
+
+            return new TextLayout(
+                textSource,
+                paragraphProperties,
+                TextTrimming,
+                _constraint.Width,
+                _constraint.Height,
+                MaxLines);
+        }
+
         protected override void RenderTextLayout(DrawingContext context, Point origin)
         {
             var selectionStart = SelectionStart;
@@ -220,10 +285,17 @@ namespace Avalonia.Controls
         {
             base.OnPropertyChanged(change);
 
-            if (change.Property == SelectionStartProperty || change.Property == SelectionEndProperty)
+            if (change.Property == SelectionStartProperty || 
+                change.Property == SelectionEndProperty)
             {
                 RaisePropertyChanged(SelectedTextProperty, "", "");
                 UpdateCommandStates();
+                InvalidateTextLayout();
+            }
+
+            if(change.Property == SelectionForegroundBrushProperty)
+            {
+                InvalidateTextLayout();
             }
         }
 

src/Avalonia.Controls/TextBlock.cs

@@ -7,6 +7,7 @@ using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.Media.TextFormatting;
 using Avalonia.Metadata;
+using Avalonia.Utilities;
 
 namespace Avalonia.Controls
 {
@@ -155,8 +156,8 @@ namespace Avalonia.Controls
                 nameof(Inlines), t => t.Inlines, (t, v) => t.Inlines = v);
 
         private TextLayout? _textLayout;
-        private Size _constraint;
-        private IReadOnlyList<TextRun>? _textRuns;
+        protected Size _constraint;
+        protected IReadOnlyList<TextRun>? _textRuns;
         private InlineCollection? _inlines;
 
         /// <summary>
@@ -846,7 +847,7 @@ namespace Avalonia.Controls
             InvalidateTextLayout();
         }
 
-        private readonly record struct SimpleTextSource : ITextSource
+        protected readonly record struct SimpleTextSource : ITextSource
         {
             private readonly string _text;
             private readonly TextRunProperties _defaultProperties;
@@ -875,13 +876,17 @@ namespace Avalonia.Controls
             }
         }
 
-        private readonly struct InlinesTextSource : ITextSource
+#pragma warning disable CA1815 // Equals und Gleichheitsoperator für Werttypen außer Kraft setzen
+        protected readonly struct InlinesTextSource : ITextSource
+#pragma warning restore CA1815 // Equals und Gleichheitsoperator für Werttypen außer Kraft setzen
         {
             private readonly IReadOnlyList<TextRun> _textRuns;
+            private readonly IReadOnlyList<ValueSpan<TextRunProperties>>? _textModifier;
 
-            public InlinesTextSource(IReadOnlyList<TextRun> textRuns)
+            public InlinesTextSource(IReadOnlyList<TextRun> textRuns, IReadOnlyList<ValueSpan<TextRunProperties>>? textModifier = null)
             {
                 _textRuns = textRuns;
+                _textModifier = textModifier;
             }
 
             public IReadOnlyList<TextRun> TextRuns => _textRuns;
@@ -904,11 +909,13 @@ namespace Avalonia.Controls
                         continue;
                     }
 
-                    if (textRun is TextCharacters)
+                    if (textRun is TextCharacters textCharacters)
                     {
                         var skip = Math.Max(0, textSourceIndex - currentPosition);
 
-                        return new TextCharacters(textRun.Text.Slice(skip), textRun.Properties!);
+                        var textStyleRun = FormattedTextSource.CreateTextStyleRun(textRun.Text.Slice(skip).Span, textSourceIndex, textCharacters.Properties, _textModifier);
+
+                        return new TextCharacters(textRun.Text.Slice(skip, textStyleRun.Length), textStyleRun.Value);
                     }
 
                     return textRun;
@@ -916,6 +923,6 @@ namespace Avalonia.Controls
 
                 return new TextEndOfParagraph();
             }
-        }
+         }
     }
 }