Only apply the font fallback to regions of missing glyphs

samples/Sandbox/MainWindow.axaml

@@ -1,29 +1,5 @@
 <Window xmlns="https://github.com/avaloniaui"
         xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
         x:Class="Sandbox.MainWindow">
-  <StackPanel>
-    <TextBox x:Name="txtBox" Text="أَبْجَدِيَّة عَرَبِيَّة" SelectionStart="19" SelectionEnd="23"/>
-    <NumericUpDown Value="{Binding #txtBox.SelectionStart, Mode=TwoWay}"/>
-    <NumericUpDown Value="{Binding #txtBox.SelectionEnd, Mode=TwoWay}"/>
-    <RichTextBlock x:Name="txtBlock" Text="أَبْجَدِيَّة عَرَبِيَّة" IsTextSelectionEnabled="True"/>
-    <NumericUpDown Value="{Binding Distance, Mode=TwoWay}"/>
-    <TextBlock Text="{Binding #txtBlock.SelectionStart}"/>
-    <TextBlock Text="{Binding #txtBlock.SelectionEnd}"/>
-    <DockPanel DockPanel.Dock="Top" LastChildFill="False">
-      <RichTextBlock Name="RichTextBlock"
-                     TextAlignment="Left"
-                     Margin="4,4,4,8"
-                     ClipToBounds="True"
-                     FontSize="30"
-                     MaxLines="3"
-                     TextWrapping="Wrap"
-                     FontWeight="DemiBold"
-                     Text="{Binding Text}"
-                     Inlines="{Binding InlineCollection, Mode=OneWay}">
-      </RichTextBlock>
-      <Button Click="Button_OnClick">Update inlines</Button>
-      <Button Click="TextButton_OnClick">Update text</Button>
-    </DockPanel>
-  </StackPanel>
- 
+    <TextBox Text="C:\привет мир\幸福\幸福"/>
 </Window>

samples/Sandbox/MainWindow.axaml.cs

@@ -13,126 +13,15 @@ namespace Sandbox
 {
     public class MainWindow : Window
     {
-        private TestViewModel _dc;
-
         public MainWindow()
         {
             this.InitializeComponent();
-            this.AttachDevTools();
-
-            var textBox = this.FindControl<TextBox>("txtBox");
-
-            textBox.TemplateApplied += TextBox_TemplateApplied;          
-        }
-
-        private void TextBox_TemplateApplied(object sender, Avalonia.Controls.Primitives.TemplateAppliedEventArgs e)
-        {
-            var textBox = sender as TextBox;
-
-            var textPresenter = e.NameScope.Find("PART_TextPresenter") as TextPresenter;
-
-            _dc = new TestViewModel(textPresenter);
-
-            DataContext = _dc;
+            this.AttachDevTools();        
         }
 
         private void InitializeComponent()
         {
             AvaloniaXamlLoader.Load(this);
         }
-
-        private void Button_OnClick(object? sender, RoutedEventArgs e)
-        {
-            _dc.InlineCollection = new InlineCollection
-        {
-            new Run(""),
-            new Run("test3") {FontWeight = Avalonia.Media.FontWeight.Bold},
-        };
-            // _dc.Text = "nununu";
-        }
-
-        private void TextButton_OnClick(object? sender, RoutedEventArgs e)
-        {
-            _dc.Text = "nununu";
-        }
-    }
-
-    public class TestViewModel : ViewModelBase
-    {
-        private readonly TextPresenter _textPresenter;
-        private double _distance = 45;
-
-        public TestViewModel(TextPresenter textPresenter)
-        {
-            _textPresenter = textPresenter;
-        }
-
-        private InlineCollection _inlineCollection;
-        private string _text;
-
-        public string Text
-        {
-            get => _text;
-            set
-            {
-                _text = value;
-                RaisePropertyChanged();
-            }
-        }
-
-        public InlineCollection InlineCollection
-        {
-            get => _inlineCollection;
-            set
-            {
-                _inlineCollection = value;
-                RaisePropertyChanged();
-            }
-        }
-
-        public double Distance 
-        { 
-            get => _distance; 
-            set
-            {
-                OnDistanceChanged(value);
-                RaisePropertyChanged();
-            }
-        }
-
-        private void OnDistanceChanged(double distance)
-        {
-            if(distance < 0)
-            {
-                distance = 0;
-            }
-
-            if(distance > _textPresenter.TextLayout.Bounds.Width)
-            {
-                distance = _textPresenter.TextLayout.Bounds.Width;
-            }
-
-            var height = _textPresenter.TextLayout.Bounds.Height;
-
-            var distanceY = height / 2;
-
-            _textPresenter.MoveCaretToPoint(new Point(distance, distanceY));
-
-            var caretIndex = _textPresenter.CaretIndex;
-
-            Debug.WriteLine(caretIndex);
-
-            _distance = distance;
-        }
-    }
-
-    public class ViewModelBase : INotifyPropertyChanged
-    {
-        public event PropertyChangedEventHandler PropertyChanged;
-
-        protected void RaisePropertyChanged([CallerMemberName]string propertyName = "")
-        {
-            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
-        }
-    }
+    }    
 }

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

@@ -38,7 +38,7 @@ namespace Avalonia.Media.TextFormatting
         /// Gets a list of <see cref="ShapeableTextCharacters"/>.
         /// </summary>
         /// <returns>The shapeable text characters.</returns>
-        internal IReadOnlyList<ShapeableTextCharacters> GetShapeableCharacters(ReadOnlySlice<char> runText, sbyte biDiLevel, 
+        internal IReadOnlyList<ShapeableTextCharacters> GetShapeableCharacters(ReadOnlySlice<char> runText, sbyte biDiLevel,
             ref TextRunProperties? previousProperties)
         {
             var shapeableCharacters = new List<ShapeableTextCharacters>(2);
@@ -65,7 +65,7 @@ namespace Avalonia.Media.TextFormatting
         /// <param name="biDiLevel">The bidi level of the run.</param>
         /// <param name="previousProperties"></param>
         /// <returns>A list of shapeable text runs.</returns>
-        private static ShapeableTextCharacters CreateShapeableRun(ReadOnlySlice<char> text, 
+        private static ShapeableTextCharacters CreateShapeableRun(ReadOnlySlice<char> text,
             TextRunProperties defaultProperties, sbyte biDiLevel, ref TextRunProperties? previousProperties)
         {
             var defaultTypeface = defaultProperties.Typeface;
@@ -76,7 +76,7 @@ namespace Avalonia.Media.TextFormatting
             {
                 if (script == Script.Common && previousTypeface is not null)
                 {
-                    if(TryGetShapeableLength(text, previousTypeface.Value, defaultTypeface, out var fallbackCount, out _))
+                    if (TryGetShapeableLength(text, previousTypeface.Value, defaultTypeface, out var fallbackCount, out _))
                     {
                         return new ShapeableTextCharacters(text.Take(fallbackCount),
                             defaultProperties.WithTypeface(previousTypeface.Value), biDiLevel);
@@ -86,10 +86,10 @@ namespace Avalonia.Media.TextFormatting
                 return new ShapeableTextCharacters(text.Take(count), defaultProperties.WithTypeface(currentTypeface),
                     biDiLevel);
             }
-            
+
             if (previousTypeface is not null)
             {
-                if(TryGetShapeableLength(text, previousTypeface.Value, defaultTypeface, out count, out _))
+                if (TryGetShapeableLength(text, previousTypeface.Value, defaultTypeface, out count, out _))
                 {
                     return new ShapeableTextCharacters(text.Take(count),
                         defaultProperties.WithTypeface(previousTypeface.Value), biDiLevel);
@@ -106,12 +106,12 @@ namespace Avalonia.Media.TextFormatting
                 {
                     continue;
                 }
-                
+
                 codepoint = codepointEnumerator.Current;
-                    
+
                 break;
             }
-            
+
             //ToDo: Fix FontFamily fallback
             var matchFound =
                 FontManager.Current.TryMatchCharacter(codepoint, defaultTypeface.Style, defaultTypeface.Weight,
@@ -157,14 +157,14 @@ namespace Avalonia.Media.TextFormatting
         /// <param name="script"></param>
         /// <returns></returns>
         protected static bool TryGetShapeableLength(
-            ReadOnlySlice<char> text, 
-            Typeface typeface, 
+            ReadOnlySlice<char> text,
+            Typeface typeface,
             Typeface? defaultTypeface,
             out int length,
             out Script script)
         {
             length = 0;
-            script = Script.Unknown;         
+            script = Script.Unknown;
 
             if (text.Length == 0)
             {
@@ -182,7 +182,7 @@ namespace Avalonia.Media.TextFormatting
 
                 var currentScript = currentGrapheme.FirstCodepoint.Script;
 
-                if (currentScript != Script.Common && defaultFont != null && defaultFont.TryGetGlyph(currentGrapheme.FirstCodepoint, out _))
+                if (defaultFont != null && defaultFont.TryGetGlyph(currentGrapheme.FirstCodepoint, out _))
                 {
                     break;
                 }
@@ -192,7 +192,7 @@ namespace Avalonia.Media.TextFormatting
                 {
                     break;
                 }
-                
+
                 if (currentScript != script)
                 {
                     if (script is Script.Unknown || currentScript != Script.Common &&

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -498,13 +498,13 @@ namespace Avalonia.Controls.Presenters
 
             IReadOnlyList<ValueSpan<TextRunProperties>>? textStyleOverrides = null;
 
-            if (length > 0)
+            if (length > 0 && SelectionForegroundBrush != null)
             {
                 textStyleOverrides = new[]
                 {
                     new ValueSpan<TextRunProperties>(start, length,
                         new GenericTextRunProperties(typeface, FontSize,
-                            foregroundBrush: SelectionForegroundBrush ?? Brushes.Red))
+                            foregroundBrush: SelectionForegroundBrush))
                 };
             }
 

src/Avalonia.Controls/TextBox.cs

@@ -1245,8 +1245,6 @@ namespace Avalonia.Controls
 
                 var caretIndex = hit.TextPosition;
 
-                Debug.WriteLine($"TextPos: {caretIndex}, X: {point.X}");
-
                 var text = Text;
 
                 if (text != null && _wordSelectionStart >= 0)