Apply stroke to a textblock in WPF

Below is my more idiomatically WPF, full-featured take on this. It supports pretty much everything you’d expect, including:

• all font related properties including stretch and style
• text alignment (left, right, center, justify)
• text wrapping
• text trimming
• text decorations (underline, strike through etcetera)

Here’s a simple example of what can be achieved with it:

<local:OutlinedTextBlock FontFamily="Verdana" FontSize="20pt" FontWeight="ExtraBold" TextWrapping="Wrap" StrokeThickness="1" Stroke="{StaticResource TextStroke}" Fill="{StaticResource TextFill}">
    Neque porro quisquam est qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit
</local:OutlinedTextBlock>

Which results in:

Here’s the code for the control:

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows;
using System.Windows.Documents;
using System.Windows.Markup;
using System.Windows.Media;

[ContentProperty("Text")]
public class OutlinedTextBlock : FrameworkElement
{
    public static readonly DependencyProperty FillProperty = DependencyProperty.Register(
        "Fill",
        typeof(Brush),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(Brushes.Black, FrameworkPropertyMetadataOptions.AffectsRender));

    public static readonly DependencyProperty StrokeProperty = DependencyProperty.Register(
        "Stroke",
        typeof(Brush),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(Brushes.Black, FrameworkPropertyMetadataOptions.AffectsRender));

    public static readonly DependencyProperty StrokeThicknessProperty = DependencyProperty.Register(
        "StrokeThickness",
        typeof(double),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(1d, FrameworkPropertyMetadataOptions.AffectsRender));

    public static readonly DependencyProperty FontFamilyProperty = TextElement.FontFamilyProperty.AddOwner(
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty FontSizeProperty = TextElement.FontSizeProperty.AddOwner(
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty FontStretchProperty = TextElement.FontStretchProperty.AddOwner(
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty FontStyleProperty = TextElement.FontStyleProperty.AddOwner(
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty FontWeightProperty = TextElement.FontWeightProperty.AddOwner(
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty TextProperty = DependencyProperty.Register(
        "Text",
        typeof(string),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextInvalidated));

    public static readonly DependencyProperty TextAlignmentProperty = DependencyProperty.Register(
        "TextAlignment",
        typeof(TextAlignment),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty TextDecorationsProperty = DependencyProperty.Register(
        "TextDecorations",
        typeof(TextDecorationCollection),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty TextTrimmingProperty = DependencyProperty.Register(
        "TextTrimming",
        typeof(TextTrimming),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(OnFormattedTextUpdated));

    public static readonly DependencyProperty TextWrappingProperty = DependencyProperty.Register(
        "TextWrapping",
        typeof(TextWrapping),
        typeof(OutlinedTextBlock),
        new FrameworkPropertyMetadata(TextWrapping.NoWrap, OnFormattedTextUpdated));

    private FormattedText formattedText;
    private Geometry textGeometry;

    public OutlinedTextBlock()
    {
        this.TextDecorations = new TextDecorationCollection();
    }

    public Brush Fill
    {
        get { return (Brush)GetValue(FillProperty); }
        set { SetValue(FillProperty, value); }
    }

    public FontFamily FontFamily
    {
        get { return (FontFamily)GetValue(FontFamilyProperty); }
        set { SetValue(FontFamilyProperty, value); }
    }

    [TypeConverter(typeof(FontSizeConverter))]
    public double FontSize
    {
        get { return (double)GetValue(FontSizeProperty); }
        set { SetValue(FontSizeProperty, value); }
    }

    public FontStretch FontStretch
    {
        get { return (FontStretch)GetValue(FontStretchProperty); }
        set { SetValue(FontStretchProperty, value); }
    }

    public FontStyle FontStyle
    {
        get { return (FontStyle)GetValue(FontStyleProperty); }
        set { SetValue(FontStyleProperty, value); }
    }

    public FontWeight FontWeight
    {
        get { return (FontWeight)GetValue(FontWeightProperty); }
        set { SetValue(FontWeightProperty, value); }
    }

    public Brush Stroke
    {
        get { return (Brush)GetValue(StrokeProperty); }
        set { SetValue(StrokeProperty, value); }
    }

    public double StrokeThickness
    {
        get { return (double)GetValue(StrokeThicknessProperty); }
        set { SetValue(StrokeThicknessProperty, value); }
    }

    public string Text
    {
        get { return (string)GetValue(TextProperty); }
        set { SetValue(TextProperty, value); }
    }

    public TextAlignment TextAlignment
    {
        get { return (TextAlignment)GetValue(TextAlignmentProperty); }
        set { SetValue(TextAlignmentProperty, value); }
    }

    public TextDecorationCollection TextDecorations
    {
        get { return (TextDecorationCollection)this.GetValue(TextDecorationsProperty); }
        set { this.SetValue(TextDecorationsProperty, value); }
    }

    public TextTrimming TextTrimming
    {
        get { return (TextTrimming)GetValue(TextTrimmingProperty); }
        set { SetValue(TextTrimmingProperty, value); }
    }

    public TextWrapping TextWrapping
    {
        get { return (TextWrapping)GetValue(TextWrappingProperty); }
        set { SetValue(TextWrappingProperty, value); }
    }

    protected override void OnRender(DrawingContext drawingContext)
    {
        this.EnsureGeometry();

        drawingContext.DrawGeometry(this.Fill, new Pen(this.Stroke, this.StrokeThickness), this.textGeometry);
    }

    protected override Size MeasureOverride(Size availableSize)
    {
        this.EnsureFormattedText();

        // constrain the formatted text according to the available size
        // the Math.Min call is important - without this constraint (which seems arbitrary, but is the maximum allowable text width), things blow up when availableSize is infinite in both directions
        // the Math.Max call is to ensure we don't hit zero, which will cause MaxTextHeight to throw
        this.formattedText.MaxTextWidth = Math.Min(3579139, availableSize.Width);
        this.formattedText.MaxTextHeight = Math.Max(0.0001d, availableSize.Height);

        // return the desired size
        return new Size(this.formattedText.Width, this.formattedText.Height);
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        this.EnsureFormattedText();

        // update the formatted text with the final size
        this.formattedText.MaxTextWidth = finalSize.Width;
        this.formattedText.MaxTextHeight = finalSize.Height;

        // need to re-generate the geometry now that the dimensions have changed
        this.textGeometry = null;

        return finalSize;
    }

    private static void OnFormattedTextInvalidated(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var outlinedTextBlock = (OutlinedTextBlock)dependencyObject;
        outlinedTextBlock.formattedText = null;
        outlinedTextBlock.textGeometry = null;

        outlinedTextBlock.InvalidateMeasure();
        outlinedTextBlock.InvalidateVisual();
    }

    private static void OnFormattedTextUpdated(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var outlinedTextBlock = (OutlinedTextBlock)dependencyObject;
        outlinedTextBlock.UpdateFormattedText();
        outlinedTextBlock.textGeometry = null;

        outlinedTextBlock.InvalidateMeasure();
        outlinedTextBlock.InvalidateVisual();
    }

    private void EnsureFormattedText()
    {
        if (this.formattedText != null || this.Text == null)
        {
            return;
        }

        this.formattedText = new FormattedText(
            this.Text,
            CultureInfo.CurrentUICulture,
            this.FlowDirection,
            new Typeface(this.FontFamily, this.FontStyle, this.FontWeight, FontStretches.Normal),
            this.FontSize,
            Brushes.Black);

        this.UpdateFormattedText();
    }

    private void UpdateFormattedText()
    {
        if (this.formattedText == null)
        {
            return;
        }

        this.formattedText.MaxLineCount = this.TextWrapping == TextWrapping.NoWrap ? 1 : int.MaxValue;
        this.formattedText.TextAlignment = this.TextAlignment;
        this.formattedText.Trimming = this.TextTrimming;

        this.formattedText.SetFontSize(this.FontSize);
        this.formattedText.SetFontStyle(this.FontStyle);
        this.formattedText.SetFontWeight(this.FontWeight);
        this.formattedText.SetFontFamily(this.FontFamily);
        this.formattedText.SetFontStretch(this.FontStretch);
        this.formattedText.SetTextDecorations(this.TextDecorations);
    }

    private void EnsureGeometry()
    {
        if (this.textGeometry != null)
        {
            return;
        }

        this.EnsureFormattedText();
        this.textGeometry = this.formattedText.BuildGeometry(new Point(0, 0));
    }
}