Text processing fixes

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

@@ -10,20 +10,27 @@ public sealed class TextBounds
         /// <summary>
         /// Constructing TextBounds object
         /// </summary>
-        internal TextBounds(Rect bounds, FlowDirection flowDirection)
+        internal TextBounds(Rect bounds, FlowDirection flowDirection, IList<TextRunBounds> runBounds)
         {
             Rectangle = bounds;
             FlowDirection = flowDirection;
+            TextRunBounds = runBounds;
         }
 
         /// <summary>
         /// Bounds rectangle
         /// </summary>
-        public Rect Rectangle { get; }
+        public Rect Rectangle { get; internal set; }
 
         /// <summary>
         /// Text flow direction inside the boundary rectangle
         /// </summary>
         public FlowDirection FlowDirection { get; }
+
+        /// <summary>
+        /// Get a list of run bounding rectangles
+        /// </summary>
+        /// <returns>Array of text run bounds</returns>
+        public IList<TextRunBounds> TextRunBounds { get; }
     }
 }

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

@@ -230,7 +230,7 @@ public IEnumerable<Rect> HitTestTextRange(int start, int length)
             foreach (var textLine in TextLines)
             {
                 //Current line isn't covered.
-                if (textLine.FirstTextSourceIndex + textLine.Length <= start)
+                if (textLine.FirstTextSourceIndex + textLine.Length < start)
                 {
                     currentY += textLine.Height;
 
@@ -239,18 +239,27 @@ public IEnumerable<Rect> HitTestTextRange(int start, int length)
 
                 var textBounds = textLine.GetTextBounds(start, length);
 
-                foreach (var bounds in textBounds)
+                if(textBounds.Count > 0)
                 {
-                    Rect? last = result.Count > 0 ? result[result.Count - 1] : null;
-
-                    if (last.HasValue && MathUtilities.AreClose(last.Value.Right, bounds.Rectangle.Left) && MathUtilities.AreClose(last.Value.Top, currentY))
+                    foreach (var bounds in textBounds)
                     {
-                        result[result.Count - 1] = last.Value.WithWidth(last.Value.Width + bounds.Rectangle.Width);
+                        Rect? last = result.Count > 0 ? result[result.Count - 1] : null;
+
+                        if (last.HasValue && MathUtilities.AreClose(last.Value.Right, bounds.Rectangle.Left) && MathUtilities.AreClose(last.Value.Top, currentY))
+                        {
+                            result[result.Count - 1] = last.Value.WithWidth(last.Value.Width + bounds.Rectangle.Width);
+                        }
+                        else
+                        {
+                            result.Add(bounds.Rectangle.WithY(currentY));
+                        }
+
+                        foreach (var runBounds in bounds.TextRunBounds)
+                        {
+                            start += runBounds.Length;
+                            length -= runBounds.Length;
+                        }
                     }
-                    else
-                    {
-                        result.Add(bounds.Rectangle.WithY(currentY));
-                    }                  
                 }
 
                 if(textLine.FirstTextSourceIndex + textLine.Length >= start + length)