Fix text rendering where TextAlignment != Left.

The renderer was using the wrong bounds for text where `TextAlignment != Left` as seen in #1625. To fix this, change `FormattedTextImpl.Size` to `Bounds`, which returns a rect that takes into account the text alignment and similarly change `FormattedText.Measure` to return a `Rect` instead of a `Size.

Fixes #1625.

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -275,7 +275,7 @@ namespace Avalonia.Controls.Presenters
                     Typeface = new Typeface(FontFamily, FontSize, FontStyle, FontWeight),
                     TextAlignment = TextAlignment,
                     Constraint = availableSize,
-                }.Measure();
+                }.Measure().Size;
             }
         }
 

src/Avalonia.Controls/TextBlock.cs

@@ -396,7 +396,7 @@ namespace Avalonia.Controls
                     FormattedText.Constraint = Size.Infinity;
                 }
 
-                return FormattedText.Measure();
+                return FormattedText.Measure().Size;
             }
 
             return new Size();

src/Avalonia.Visuals/Media/FormattedText.cs

@@ -159,13 +159,10 @@ namespace Avalonia.Media
         }
 
         /// <summary>
-        /// Gets the size of the text, taking <see cref="Constraint"/> into account.
+        /// Gets the bounds of the text, taking <see cref="Constraint"/> into account.
         /// </summary>
-        /// <returns>The bounds box of the text.</returns>
-        public Size Measure()
-        {
-            return PlatformImpl.Size;
-        }
+        /// <returns>The bounds of the text.</returns>
+        public Rect Measure() => PlatformImpl.Bounds;
 
         private void Set<T>(ref T field, T value)
         {

src/Avalonia.Visuals/Platform/IFormattedTextImpl.cs

@@ -1,6 +1,7 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System;
 using System.Collections.Generic;
 using Avalonia.Media;
 
@@ -17,9 +18,9 @@ namespace Avalonia.Platform
         Size Constraint { get; }
 
         /// <summary>
-        /// The measured size of the text.
+        /// The measured bounds of the text.
         /// </summary>
-        Size Size { get; }
+        Rect Bounds{ get; }
 
         /// <summary>
         /// Gets the text.

src/Avalonia.Visuals/Rendering/SceneGraph/TextNode.cs

@@ -27,7 +27,7 @@ namespace Avalonia.Rendering.SceneGraph
             Point origin,
             IFormattedTextImpl text,
             IDictionary<IVisual, Scene> childScenes = null)
-            : base(new Rect(origin, text.Size), transform, null)
+            : base(text.Bounds, transform, null)
         {
             Transform = transform;
             Foreground = foreground?.ToImmutable();

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -218,7 +218,7 @@ namespace Avalonia.Skia
         /// <inheritdoc />
         public void DrawText(IBrush foreground, Point origin, IFormattedTextImpl text)
         {
-            using (var paint = CreatePaint(foreground, text.Size))
+            using (var paint = CreatePaint(foreground, text.Bounds.Size))
             {
                 var textImpl = (FormattedTextImpl) text;
                 textImpl.Draw(this, Canvas, origin.ToSKPoint(), paint, _canTextUseLcdRendering);

src/Skia/Avalonia.Skia/FormattedTextImpl.cs

@@ -89,7 +89,7 @@ namespace Avalonia.Skia
 
         public Size Constraint => _constraint;
 
-        public Size Size => _size;
+        public Rect Bounds => _bounds;
 
         public IEnumerable<FormattedTextLine> GetLines()
         {
@@ -135,7 +135,7 @@ namespace Avalonia.Skia
                 };
             }
 
-            bool end = point.X > _size.Width || point.Y > _lines.Sum(l => l.Height);
+            bool end = point.X > _bounds.Width || point.Y > _lines.Sum(l => l.Height);
 
             return new TextHitTestResult()
             {
@@ -323,7 +323,7 @@ namespace Avalonia.Skia
         private Size _constraint = new Size(double.PositiveInfinity, double.PositiveInfinity);
         private float _lineHeight = 0;
         private float _lineOffset = 0;
-        private Size _size;
+        private Rect _bounds;
         private List<AvaloniaFormattedTextLine> _skiaLines;
 
         private static void ApplyWrapperTo(ref SKPaint current, DrawingContextImpl.PaintWrapper wrapper,
@@ -639,12 +639,26 @@ namespace Avalonia.Skia
             if (_skiaLines.Count == 0)
             {
                 _lines.Add(new FormattedTextLine(0, _lineHeight));
-                _size = new Size(0, _lineHeight);
+                _bounds = new Rect(0, 0, 0, _lineHeight);
             }
             else
             {
                 var lastLine = _skiaLines[_skiaLines.Count - 1];
-                _size = new Size(maxX, lastLine.Top + lastLine.Height);
+                _bounds = new Rect(0, 0, maxX, lastLine.Top + lastLine.Height);
+
+                switch (_paint.TextAlign)
+                {
+                    case SKTextAlign.Center:
+                        _bounds = new Rect(Constraint).CenterRect(_bounds);
+                        break;
+                    case SKTextAlign.Right:
+                        _bounds = new Rect(
+                            Constraint.Width - _bounds.Width,
+                            0,
+                            _bounds.Width,
+                            _bounds.Height);
+                        break;
+                }
             }
         }
 
@@ -660,7 +674,7 @@ namespace Avalonia.Skia
             {
                 double width = Constraint.Width > 0 && !double.IsPositiveInfinity(Constraint.Width) ?
                                 Constraint.Width :
-                                _size.Width;
+                                _bounds.Width;
 
                 switch (align)
                 {

src/Windows/Avalonia.Direct2D1/Media/DrawingContextImpl.cs

@@ -274,7 +274,7 @@ namespace Avalonia.Direct2D1.Media
             {
                 var impl = (FormattedTextImpl)text;
 
-                using (var brush = CreateBrush(foreground, impl.Size))
+                using (var brush = CreateBrush(foreground, impl.Bounds.Size))
                 using (var renderer = new AvaloniaTextRenderer(this, _deviceContext, brush.PlatformBrush))
                 {
                     if (brush.PlatformBrush != null)

src/Windows/Avalonia.Direct2D1/Media/FormattedTextImpl.cs

@@ -45,12 +45,12 @@ namespace Avalonia.Direct2D1.Media
                 }
             }
 
-            Size = Measure();
+            Bounds = Measure();
         }
 
         public Size Constraint => new Size(TextLayout.MaxWidth, TextLayout.MaxHeight);
 
-        public Size Size { get; }
+        public Rect Bounds { get; }
 
         public string Text { get; }
 
@@ -104,7 +104,7 @@ namespace Avalonia.Direct2D1.Media
             }
         }
 
-        private Size Measure()
+        private Rect Measure()
         {
             var metrics = TextLayout.Metrics;
 
@@ -115,7 +115,11 @@ namespace Avalonia.Direct2D1.Media
                 width = metrics.Width;
             }
 
-            return new Size(width, TextLayout.Metrics.Height);
+            return new Rect(
+                TextLayout.Metrics.Left,
+                TextLayout.Metrics.Top,
+                width,
+                TextLayout.Metrics.Height);
         }
     }
 }

tests/Avalonia.Layout.UnitTests/FullLayoutTests.cs

@@ -146,7 +146,7 @@ namespace Avalonia.Layout.UnitTests
 
             public string Text { get; }
 
-            public Size Size => new Size();
+            public Rect Bounds => Rect.Empty;
 
             public void Dispose()
             {

tests/Avalonia.RenderTests/Media/FormattedTextImplTests.cs

@@ -100,7 +100,7 @@ namespace Avalonia.Direct2D1.RenderTests.Media
         public void Should_Measure_String_Correctly(string input, double fontSize, double expWidth, double expHeight)
         {
             var fmt = Create(input, fontSize);
-            var size = fmt.Size;
+            var size = fmt.Bounds.Size;
 
             Assert.Equal(expWidth, size.Width, 2);
             Assert.Equal(expHeight, size.Height, 2);
@@ -265,4 +265,4 @@ namespace Avalonia.Direct2D1.RenderTests.Media
             }
         }
     }
-}
+}