TextBlockWithShadow

TextBlockWithShadow.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Layout;
using Avalonia.Media;
using Avalonia.Media.Immutable;
using Avalonia.Media.TextFormatting;

namespace MyApp
{
    public class TextBlockWithShadow : TextBlock
    {
        private TextLayout? _shadowLayout;

        public static StyledProperty<IBrush?> ShadowBrushProperty =
            AvaloniaProperty.Register<TextBlockWithShadow, IBrush?>(nameof(ShadowBrush), new ImmutableSolidColorBrush(Colors.Black, 0.44));

        public IBrush? ShadowBrush
        {
            get => GetValue(ShadowBrushProperty);
            set => SetValue(ShadowBrushProperty, value);
        }

        public static StyledProperty<double> ShadowXOffsetProperty =
            AvaloniaProperty.Register<TextBlockWithShadow, double>(nameof(ShadowXOffset));

        public double ShadowXOffset
        {
            get => GetValue(ShadowXOffsetProperty);
            set => SetValue(ShadowXOffsetProperty, value);
        }

        public static StyledProperty<double> ShadowYOffsetProperty =
            AvaloniaProperty.Register<TextBlockWithShadow, double>(nameof(ShadowYOffset), 2);

        public double ShadowYOffset
        {
            get => GetValue(ShadowYOffsetProperty);
            set => SetValue(ShadowYOffsetProperty, value);
        }

        public override void Render(DrawingContext context)
        {
            var background = Background;

            if (background != null)
            {
                context.FillRectangle(background, new Rect(Bounds.Size));
            }

            if (TextLayout is null)
            {
                return;
            }

            var textAlignment = TextAlignment;

            var width = Bounds.Size.Width;

            var offsetX = 0.0;

            switch (textAlignment)
            {
                case TextAlignment.Center:
                    offsetX = (width - TextLayout.Size.Width) / 2;
                    break;

                case TextAlignment.Right:
                    offsetX = width - TextLayout.Size.Width;
                    break;
            }

            var padding = Padding;

            var top = padding.Top;
            var textSize = TextLayout.Size;

            if (Bounds.Height < textSize.Height)
            {
                switch (VerticalAlignment)
                {
                    case VerticalAlignment.Center:
                        top += (Bounds.Height - textSize.Height) / 2;
                        break;

                    case VerticalAlignment.Bottom:
                        top += (Bounds.Height - textSize.Height);
                        break;
                }
            }

            using (context.PushPostTransform(Matrix.CreateTranslation(padding.Left + offsetX + ShadowXOffset, top + ShadowYOffset)))
            {
                _shadowLayout?.Draw(context);
            }
            using (context.PushPostTransform(Matrix.CreateTranslation(padding.Left + offsetX, top)))
            {
                TextLayout.Draw(context);
            }
        }

        protected override TextLayout? CreateTextLayout(Size constraint, string text)
        {
            var layout = base.CreateTextLayout(constraint, text);
            if (layout is null)
            {
                _shadowLayout = null;
                return null;
            }

            _shadowLayout = new TextLayout(
                text ?? string.Empty,
                new Typeface(FontFamily, FontStyle, FontWeight),
                FontSize,
                ShadowBrush,
                TextAlignment,
                TextWrapping,
                TextTrimming,
                TextDecorations,
                constraint.Width,
                constraint.Height,
                maxLines: MaxLines,
                lineHeight: LineHeight);
            return layout;
        }
    }
}

Usage.xaml

      <local:TextBlockWithShadow Text="HELLO WORLD"
                                 FontSize="60"
                                 ShadowBrush="Green"
                                 ShadowYOffset="10"
                                 ShadowXOffset="10" />