Fix BaselineAlignment (#16276)

* Implement remaining BaselineAlignment variants

* Adjust BaselineOffset calculation

* Draw all shaped runs at the baseline

* Random change please revert

* Revert change

src/Avalonia.Base/Media/TextDecoration.cs

@@ -182,18 +182,18 @@ namespace Avalonia.Media
                     break;
             }
 
-            var origin = new Point();
+            var origin = baselineOrigin;
 
             switch (Location)
             {
-                case TextDecorationLocation.Baseline:
+                case TextDecorationLocation.Overline:
-                    origin += glyphRun.BaselineOrigin;
+                    origin += new Point(0, textMetrics.Ascent);
                     break;
                 case TextDecorationLocation.Strikethrough:
-                    origin += new Point(baselineOrigin.X, baselineOrigin.Y + textMetrics.StrikethroughPosition);
+                    origin += new Point(0, textMetrics.StrikethroughPosition);
                     break;
                 case TextDecorationLocation.Underline:
-                    origin += new Point(baselineOrigin.X, baselineOrigin.Y + textMetrics.UnderlinePosition);
+                    origin += new Point(0, textMetrics.UnderlinePosition);
                     break;
             }
 
@@ -255,7 +255,10 @@ namespace Avalonia.Media
                 }
             }
 
-            drawingContext.DrawLine(pen, origin, origin + new Point(glyphRun.Metrics.Width, 0));
+            var p1 = origin;
+            var p2 = p1 + new Point(glyphRun.Metrics.Width, 0);
+
+            drawingContext.DrawLine(pen, p1, p2);
         }
     }
 }

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

@@ -64,7 +64,7 @@ namespace Avalonia.Media.TextFormatting
 
                 if (Properties.BackgroundBrush != null)
                 {
-                    drawingContext.DrawRectangle(Properties.BackgroundBrush, null, GlyphRun.Bounds);
+                    drawingContext.DrawRectangle(Properties.BackgroundBrush, null, GlyphRun.Bounds.Translate(new Vector(0, -Baseline)));
                 }
 
                 drawingContext.DrawGlyphRun(Properties.ForegroundBrush, GlyphRun);
@@ -204,7 +204,8 @@ namespace Avalonia.Media.TextFormatting
                 ShapedBuffer.FontRenderingEmSize,
                 Text,
                 ShapedBuffer,
-                biDiLevel: BidiLevel);
+                biDiLevel: BidiLevel,
+                baselineOrigin: new Point());
         }
 
         public void Dispose()

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

@@ -115,18 +115,19 @@ namespace Avalonia.Media.TextFormatting
 
             switch (baselineAlignment)
             {
+                case BaselineAlignment.Baseline:
+                    return textLine.Baseline;
                 case BaselineAlignment.Top:
-                    return 0;
+                case BaselineAlignment.TextTop:
+                    return textLine.Baseline - textLine.Extent + textRun.Size.Height / 2;
                 case BaselineAlignment.Center:
-                    return textLine.Height / 2 - textRun.Size.Height / 2;
+                    return textLine.Height / 2 + baseline - textRun.Size.Height / 2;
+                case BaselineAlignment.Subscript:
                 case BaselineAlignment.Bottom:
-                    return textLine.Height - textRun.Size.Height;
-                case BaselineAlignment.Baseline:
-                case BaselineAlignment.TextTop:
                 case BaselineAlignment.TextBottom:
-                case BaselineAlignment.Subscript:
+                    return textLine.Height - textRun.Size.Height + baseline;
                 case BaselineAlignment.Superscript:
-                    return textLine.Baseline - baseline;
+                    return baseline;
                 default:
                     throw new ArgumentOutOfRangeException(nameof(baselineAlignment), baselineAlignment, null);
             }
@@ -1143,7 +1144,6 @@ namespace Avalonia.Media.TextFormatting
             }
 
             TextRun? currentRun = null;
-            TextRun? previousRun = null;
 
             while (runIndex < _indexedTextRuns.Count)
             {
@@ -1182,7 +1182,7 @@ namespace Avalonia.Media.TextFormatting
 
                             break;
                         }
-                    case TextRun:
+                    case not null:
                         {
                             if(direction == LogicalDirection.Forward)
                             {
@@ -1212,8 +1212,6 @@ namespace Avalonia.Media.TextFormatting
                 }
 
                 runIndex++;
-
-                previousRun = currentRun;
             }
 
             return currentRun;
@@ -1242,61 +1240,57 @@ namespace Avalonia.Media.TextFormatting
                 switch (_textRuns[index])
                 {
                     case ShapedTextRun textRun:
-                        {
+                    {
-                            var textMetrics = textRun.TextMetrics;
+                        var textMetrics = textRun.TextMetrics;
-                            var glyphRun = textRun.GlyphRun;
+                        var glyphRun = textRun.GlyphRun;
-                            var runBounds = glyphRun.InkBounds.WithX(widthIncludingWhitespace + glyphRun.InkBounds.X);
+                        var runBounds = glyphRun.InkBounds.WithX(widthIncludingWhitespace + glyphRun.InkBounds.X);
 
-                            bounds = bounds.Union(runBounds);
+                        bounds = bounds.Union(runBounds);
 
-                            if (fontRenderingEmSize < textMetrics.FontRenderingEmSize)
+                        if (ascent > textMetrics.Ascent)
-                            {
+                        {
-                                fontRenderingEmSize = textMetrics.FontRenderingEmSize;
+                            ascent = textMetrics.Ascent;
+                        }
 
-                                if (ascent > textMetrics.Ascent)
+                        if (descent < textMetrics.Descent)
-                                {
+                        {
-                                    ascent = textMetrics.Ascent;
+                            descent = textMetrics.Descent;
-                                }
+                        }
 
-                                if (descent < textMetrics.Descent)
+                        if (lineGap < textMetrics.LineGap)
-                                {
+                        {
-                                    descent = textMetrics.Descent;
+                            lineGap = textMetrics.LineGap;
-                                }
+                        }
 
-                                if (lineGap < textMetrics.LineGap)
+                        if (descent - ascent + lineGap > height)
-                                {
+                        {
-                                    lineGap = textMetrics.LineGap;
+                            height = descent - ascent + lineGap;
-                                }
+                        }
 
-                                if (descent - ascent + lineGap > height)
-                                {
-                                    height = descent - ascent + lineGap;
-                                }
-                            }
 
-                            widthIncludingWhitespace += textRun.Size.Width;
+                        widthIncludingWhitespace += textRun.Size.Width;
 
-                            break;
+                        break;
-                        }
+                    }
 
                     case DrawableTextRun drawableTextRun:
+                    {
+                        widthIncludingWhitespace += drawableTextRun.Size.Width;
+
+                        if (drawableTextRun.Size.Height > height)
                         {
-                            widthIncludingWhitespace += drawableTextRun.Size.Width;
+                            height = drawableTextRun.Size.Height;
+                        }
 
-                            if (drawableTextRun.Size.Height > height)
+                        //Adjust current ascent so drawables and text align at the bottom edge of the line.
-                            {
+                        var offset = Math.Max(0, drawableTextRun.Baseline + ascent - descent);
-                                height = drawableTextRun.Size.Height;
-                            }
-                          
-                            //Adjust current ascent so drawables and text align at the bottom edge of the line.
-                            var offset = Math.Max(0, drawableTextRun.Baseline + ascent - descent);
 
-                            ascent -= offset;
+                        ascent -= offset;
 
-                            bounds = bounds.Union(new Rect(new Point(bounds.Right, 0), drawableTextRun.Size));
+                        bounds = bounds.Union(new Rect(new Point(bounds.Right, 0), drawableTextRun.Size));
 
-                            break;
+                        break;
-                        }
+                    }
                 }
             }
 

tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLayoutTests.cs

@@ -1123,7 +1123,7 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
 
                 var rect = textLayout.HitTestTextPosition(text.Length);
 
-                Assert.Equal(14.0625, rect.Top);
+                Assert.Equal(16.32, rect.Top);
             }
         }