Correctly measure TextBlocks.

Perspex.Direct2D1/TextService.cs

@@ -7,6 +7,7 @@
 namespace Perspex.Direct2D1
 {
     using System;
+    using System.Linq;
     using Perspex.Media;
     using Perspex.Platform;
     using SharpDX.DirectWrite;
@@ -28,46 +29,60 @@ namespace Perspex.Direct2D1
                 (float)text.FontSize);
         }
 
-        public TextLayout GetTextLayout(Factory factory, FormattedText text)
+        public TextLayout GetTextLayout(Factory factory, FormattedText text, Size constraint)
         {
             return new TextLayout(
                 factory,
                 text.Text,
                 GetTextFormat(factory, text),
-                float.MaxValue,
-                float.MaxValue);
+                (float)constraint.Width,
+                (float)constraint.Height);
         }
 
-        public int GetCaretIndex(FormattedText text, Point point)
+        public int GetCaretIndex(FormattedText text, Point point, Size constraint)
         {
-            TextLayout layout = GetTextLayout(this.factory, text);
-            SharpDX.Bool isTrailingHit;
-            SharpDX.Bool isInside;
+            using (TextLayout layout = GetTextLayout(this.factory, text, constraint))
+            {
+                SharpDX.Bool isTrailingHit;
+                SharpDX.Bool isInside;
 
-            HitTestMetrics result = layout.HitTestPoint(
-                (float)point.X,
-                (float)point.Y,
-                out isTrailingHit,
-                out isInside);
+                HitTestMetrics result = layout.HitTestPoint(
+                    (float)point.X,
+                    (float)point.Y,
+                    out isTrailingHit,
+                    out isInside);
 
-            return result.TextPosition + (isTrailingHit ? 1 : 0);
+                return result.TextPosition + (isTrailingHit ? 1 : 0);
+            }
         }
 
-        public Point GetCaretPosition(FormattedText text, int caretIndex)
+        public Point GetCaretPosition(FormattedText text, int caretIndex, Size constraint)
         {
-            TextLayout layout = GetTextLayout(this.factory, text);
-            float x;
-            float y;
-            layout.HitTestTextPosition(caretIndex, false, out x, out y);
-            return new Point(x, y);
+            using (TextLayout layout = GetTextLayout(this.factory, text, constraint))
+            {
+                float x;
+                float y;
+                layout.HitTestTextPosition(caretIndex, false, out x, out y);
+                return new Point(x, y);
+            }
         }
 
-        public Size Measure(FormattedText text)
+        public double[] GetLineHeights(FormattedText text, Size constraint)
         {
-            TextLayout layout = GetTextLayout(this.factory, text);
-            return new Size(
-                layout.Metrics.WidthIncludingTrailingWhitespace,
-                layout.Metrics.Height);
+            using (TextLayout layout = GetTextLayout(this.factory, text, constraint))
+            {
+                return layout.GetLineMetrics().Select(x => (double)x.Height).ToArray();
+            }
+        }
+
+        public Size Measure(FormattedText text, Size constraint)
+        {
+            using (TextLayout layout = GetTextLayout(this.factory, text, constraint))
+            {
+                return new Size(
+                    layout.Metrics.WidthIncludingTrailingWhitespace,
+                    layout.Metrics.Height);
+            }
         }
     }
 }

Perspex/Controls/TextBlock.cs

@@ -18,7 +18,7 @@ namespace Perspex.Controls
 
         static TextBlock()
         {
-            AffectsRender(TextProperty);
+            AffectsMeasure(TextProperty);
         }
 
         public string Text
@@ -56,7 +56,7 @@ namespace Perspex.Controls
         {
             if (!string.IsNullOrEmpty(this.Text))
             {
-                return this.FormattedText.Size;
+                return this.FormattedText.Measure(availableSize);
             }
 
             return new Size();

Perspex/Controls/TextBox.cs

@@ -126,7 +126,8 @@ namespace Perspex.Controls
             IPlatformRenderInterface platform = Locator.Current.GetService<IPlatformRenderInterface>();
             this.CaretIndex = platform.TextService.GetCaretIndex(
                 this.textBoxView.FormattedText,
-                e.GetPosition(this.textBoxView));
+                e.GetPosition(this.textBoxView),
+                this.ActualSize);
         }
     }
 }

Perspex/Controls/TextBoxView.cs

@@ -79,7 +79,11 @@ namespace Perspex.Controls
             if (this.parent.IsFocused)
             {
                 IPlatformRenderInterface platform = Locator.Current.GetService<IPlatformRenderInterface>();
-                Point caretPos = platform.TextService.GetCaretPosition(this.formattedText, this.parent.CaretIndex);
+                Point caretPos = platform.TextService.GetCaretPosition(
+                    this.formattedText, 
+                    this.parent.CaretIndex,
+                    this.ActualSize);
+                double[] lineHeights = platform.TextService.GetLineHeights(this.formattedText, this.ActualSize);
                 Brush caretBrush = Brushes.Black;
 
                 if (this.caretBlink)
@@ -87,14 +91,14 @@ namespace Perspex.Controls
                     context.DrawLine(
                         new Pen(caretBrush, 1),
                         caretPos,
-                        new Point(caretPos.X, caretPos.Y + this.FormattedText.Size.Height));
+                        new Point(caretPos.X, caretPos.Y + lineHeights[0]));
                 }
             }
         }
 
         protected override Size MeasureOverride(Size constraint)
         {
-            return new Size(this.FormattedText.Size.Width, this.FormattedText.Size.Height);
+            return this.FormattedText.Measure(constraint);
         }
 
         private FormattedText CreateFormattedText()

Perspex/Media/FormattedText.cs

@@ -17,13 +17,16 @@ namespace Perspex.Media
 
         public string Text { get; set; }
 
-        public Size Size
+        public double[] GetLineHeights(Size constraint)
         {
-            get
-            {
-                IPlatformRenderInterface factory = Locator.Current.GetService<IPlatformRenderInterface>();
-                return factory.TextService.Measure(this);
-            }
+            IPlatformRenderInterface factory = Locator.Current.GetService<IPlatformRenderInterface>();
+            return factory.TextService.GetLineHeights(this, constraint);
+        }
+
+        public Size Measure(Size constraint)
+        {
+            IPlatformRenderInterface factory = Locator.Current.GetService<IPlatformRenderInterface>();
+            return factory.TextService.Measure(this, constraint);
         }
     }
 }

Perspex/Platform/ITextService.cs

@@ -10,10 +10,12 @@ namespace Perspex.Platform
 
     public interface ITextService
     {
-        Size Measure(FormattedText text);
+        int GetCaretIndex(FormattedText text, Point point, Size constraint);
 
-        int GetCaretIndex(FormattedText text, Point point);
+        Point GetCaretPosition(FormattedText text, int caretIndex, Size constraint);
 
-        Point GetCaretPosition(FormattedText text, int caretIndex);
+        double[] GetLineHeights(FormattedText text, Size constraint);
+
+        Size Measure(FormattedText text, Size constraint);
     }
 }