Fix TextAlignment="DetectFromContent"

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

@@ -273,6 +273,11 @@ public double WidthIncludingTrailingWhitespace
             }
         }
 
+        /// <summary>
+        /// Get minimum width of all text lines that can be layouted horizontally without trimming or wrapping.
+        /// </summary>
+        internal double MinTextWidth => _metrics.MinTextWidth;
+
         /// <summary>
         /// Draws the text layout.
         /// </summary>
@@ -544,21 +549,13 @@ private TextLine[] CreateTextLines()
         {
             var objectPool = FormattingObjectPool.Instance;
 
-            var lineStartOfLongestLine = double.MaxValue;
-            var origin = new Point();
             var first = true;
 
-            double accBlackBoxLeft, accBlackBoxTop, accBlackBoxRight, accBlackBoxBottom;
-
-            accBlackBoxLeft = accBlackBoxTop = double.MaxValue;
-            accBlackBoxRight = accBlackBoxBottom = double.MinValue;
-
             if (MathUtilities.IsZero(MaxWidth) || MathUtilities.IsZero(MaxHeight))
             {
                 var textLine = TextFormatterImpl.CreateEmptyTextLine(0, double.PositiveInfinity, _paragraphProperties);
 
-                UpdateMetrics(textLine, ref lineStartOfLongestLine, ref origin, ref first,
-                    ref accBlackBoxLeft, ref accBlackBoxTop, ref accBlackBoxRight, ref accBlackBoxBottom);
+                UpdateMetrics(textLine, ref first);
 
                 return new TextLine[] { textLine };
             }
@@ -576,7 +573,7 @@ private TextLine[] CreateTextLines()
                 while (true)
                 {
                     var textLine = textFormatter.FormatLine(_textSource, _textSourceLength, MaxWidth,
-                        _paragraphProperties, previousLine?.TextLineBreak);
+                        _paragraphProperties, previousLine?.TextLineBreak) as TextLineImpl;
 
                     if (textLine is null)
                     {
@@ -587,8 +584,7 @@ private TextLine[] CreateTextLines()
 
                             textLines.Add(emptyTextLine);
 
-                            UpdateMetrics(emptyTextLine, ref lineStartOfLongestLine, ref origin, ref first,
-                                ref accBlackBoxLeft, ref accBlackBoxTop, ref accBlackBoxRight, ref accBlackBoxBottom);
+                            UpdateMetrics(emptyTextLine, ref first);
                         }
 
                         break;
@@ -615,13 +611,12 @@ private TextLine[] CreateTextLines()
 
                     if (hasOverflowed && _textTrimming != TextTrimming.None)
                     {
-                        textLine = textLine.Collapse(GetCollapsingProperties(MaxWidth));
+                        textLine = (TextLineImpl)textLine.Collapse(GetCollapsingProperties(MaxWidth));
                     }
 
                     textLines.Add(textLine);
 
-                    UpdateMetrics(textLine, ref lineStartOfLongestLine, ref origin, ref first,
-                        ref accBlackBoxLeft, ref accBlackBoxTop, ref accBlackBoxRight, ref accBlackBoxBottom);
+                    UpdateMetrics(textLine, ref first);
 
                     previousLine = textLine;
 
@@ -648,8 +643,7 @@ private TextLine[] CreateTextLines()
 
                     textLines.Add(textLine);
 
-                    UpdateMetrics(textLine, ref lineStartOfLongestLine, ref origin, ref first,
-                        ref accBlackBoxLeft, ref accBlackBoxTop, ref accBlackBoxRight, ref accBlackBoxBottom);
+                    UpdateMetrics(textLine, ref first);
                 }
 
                 if (_paragraphProperties.TextAlignment == TextAlignment.Justify)
@@ -683,44 +677,27 @@ private TextLine[] CreateTextLines()
             }
         }
 
-        private void UpdateMetrics(
-            TextLine currentLine,
-            ref double lineStartOfLongestLine,
-            ref Point origin,
-            ref bool first,
-            ref double accBlackBoxLeft,
-            ref double accBlackBoxTop,
-            ref double accBlackBoxRight,
-            ref double accBlackBoxBottom)
+        private void UpdateMetrics(TextLineImpl currentLine, ref bool first)
         {
-            var blackBoxLeft = origin.X + currentLine.Start + currentLine.OverhangLeading;
-            var blackBoxRight = origin.X + currentLine.Start + currentLine.Width - currentLine.OverhangTrailing;
-            var blackBoxBottom = origin.Y + currentLine.Height + currentLine.OverhangAfter;
-            var blackBoxTop = blackBoxBottom - currentLine.Extent;
+            _metrics.InkBounds = _metrics.InkBounds.Union(new Rect(new Point(0, _metrics.Bounds.Bottom) + currentLine.InkBounds.Position, currentLine.InkBounds.Size));
+            _metrics.Bounds = _metrics.Bounds.Union(new Rect(new Point(0, _metrics.Bounds.Bottom) + currentLine.Bounds.Position, currentLine.Bounds.Size));
 
-            accBlackBoxLeft = Math.Min(accBlackBoxLeft, blackBoxLeft);
-            accBlackBoxRight = Math.Max(accBlackBoxRight, blackBoxRight);
-            accBlackBoxBottom = Math.Max(accBlackBoxBottom, blackBoxBottom);
-            accBlackBoxTop = Math.Min(accBlackBoxTop, blackBoxTop);
+            _metrics.MinTextWidth = Math.Max(_metrics.MinTextWidth, currentLine.Bounds.Width);
+            _metrics.MinTextWidth = Math.Max(_metrics.MinTextWidth, currentLine.InkBounds.Width);
 
-            _metrics.OverhangAfter = currentLine.OverhangAfter;
-
-            _metrics.Height += currentLine.Height;
-            _metrics.Width = Math.Max(_metrics.Width, currentLine.Width);
-            _metrics.WidthIncludingTrailingWhitespace = Math.Max(_metrics.WidthIncludingTrailingWhitespace, currentLine.WidthIncludingTrailingWhitespace);
-            lineStartOfLongestLine = Math.Min(lineStartOfLongestLine, currentLine.Start);
-
-            _metrics.Extent = accBlackBoxBottom - accBlackBoxTop;
-            _metrics.OverhangLeading = accBlackBoxLeft - lineStartOfLongestLine;
-            _metrics.OverhangTrailing = _metrics.Width - (accBlackBoxRight - lineStartOfLongestLine);
+            _metrics.Height = _metrics.Bounds.Height;
+            _metrics.Width = _metrics.InkBounds.Width;
+            _metrics.WidthIncludingTrailingWhitespace = _metrics.Bounds.Width;
+            _metrics.Extent = _metrics.InkBounds.Height;
+            _metrics.OverhangLeading = Math.Max(0, _metrics.Bounds.Left - _metrics.InkBounds.Left);
+            _metrics.OverhangTrailing = Math.Max(0, _metrics.InkBounds.Right - _metrics.Bounds.Right);
+            _metrics.OverhangAfter = Math.Max(0, _metrics.InkBounds.Bottom - _metrics.Bounds.Bottom);
 
             if (first)
             {
                 _metrics.Baseline = currentLine.Baseline;
                 first = false;
             }
-
-            origin = origin.WithY(origin.Y + currentLine.Height);
         }
 
         /// <summary>
@@ -764,6 +741,11 @@ private class CachedMetrics
             // horizontal bounding box metrics
             public double OverhangLeading;
             public double OverhangTrailing;
+
+            public Rect Bounds;
+            public Rect InkBounds;
+
+            public double MinTextWidth;
         }
     }
 }

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

@@ -18,6 +18,9 @@ internal class TextLineImpl : TextLine
         private TextLineBreak? _textLineBreak;
         private readonly FlowDirection _resolvedFlowDirection;
 
+        private Rect _inkBounds;
+        private Rect _bounds;
+
         public TextLineImpl(TextRun[] textRuns, int firstTextSourceIndex, int length, double paragraphWidth,
             TextParagraphProperties paragraphProperties, FlowDirection resolvedFlowDirection = FlowDirection.LeftToRight,
             TextLineBreak? lineBreak = null, bool hasCollapsed = false)
@@ -85,10 +88,20 @@ public TextLineImpl(TextRun[] textRuns, int firstTextSourceIndex, int length, do
         /// <inheritdoc/>
         public override double WidthIncludingTrailingWhitespace => _textLineMetrics.WidthIncludingTrailingWhitespace;
 
+        /// <summary>
+        /// Get the logical text bounds.
+        /// </summary>
+        internal Rect Bounds => _bounds;
+
+        /// <summary>
+        /// Get the bounding box that is covered with black pixels.
+        /// </summary>
+        internal Rect InkBounds => _inkBounds;
+
         /// <inheritdoc/>
         public override void Draw(DrawingContext drawingContext, Point lineOrigin)
         {
-            var (currentX, currentY) = lineOrigin + new Point(Start, 0);
+            var (currentX, currentY) = lineOrigin + new Point(Start, 0);           
 
             foreach (var textRun in _textRuns)
             {
@@ -1377,6 +1390,10 @@ private TextLineMetrics CreateLineMetrics()
 
             var start = GetParagraphOffsetX(width, widthIncludingWhitespace);
 
+            _inkBounds = new Rect(bounds.Position + new Point(start, 0), bounds.Size);
+
+            _bounds = new Rect(start, 0, widthIncludingWhitespace, height);
+
             return new TextLineMetrics
             {
                 HasOverflowed = hasOverflowed,

src/Avalonia.Controls/TextBlock.cs

@@ -740,9 +740,7 @@ protected override Size MeasureOverride(Size availableSize)
             //This implicitly recreated the TextLayout with a new constraint if we previously reset it.
             var textLayout = TextLayout;
 
-            var width = textLayout.OverhangLeading + textLayout.WidthIncludingTrailingWhitespace + textLayout.OverhangTrailing;
-
-            var size = LayoutHelper.RoundLayoutSizeUp(new Size(width, textLayout.Height).Inflate(padding), 1, 1);
+            var size = LayoutHelper.RoundLayoutSizeUp(new Size(textLayout.MinTextWidth, textLayout.Height).Inflate(padding), 1, 1);
 
             return size;
         }

tests/Avalonia.Controls.UnitTests/TextBlockTests.cs

@@ -1,11 +1,12 @@
-using System;
+using System;
 using Avalonia.Controls.Documents;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
 using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.UnitTests;
 using Xunit;
+using static System.Net.Mime.MediaTypeNames;
 
 namespace Avalonia.Controls.UnitTests
 {
@@ -48,6 +49,29 @@ public void Calling_Measure_Should_Update_TextLayout()
             }
         }
 
+        [Fact]
+        public void Should_Measure_MinTextWith()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var textBlock = new TextBlock
+                {
+                    Text = "Hello
שלום
Really really really really long line",
+                    HorizontalAlignment = HorizontalAlignment.Center,
+                    TextAlignment = TextAlignment.DetectFromContent,
+                    TextWrapping = TextWrapping.Wrap
+                };
+
+                textBlock.Measure(new Size(1920, 1080));
+
+                var textLayout = textBlock.TextLayout;
+
+                var constraint = LayoutHelper.RoundLayoutSizeUp(new Size(textLayout.MinTextWidth, textLayout.Height), 1, 1);
+
+                Assert.Equal(textBlock.DesiredSize, constraint);
+            }
+        }
+
         [Fact]
         public void Calling_Arrange_With_Different_Size_Should_Update_Constraint_And_TextLayout()
         {