XAML-Map-Control/MapControl/Avalonia/PushpinBorder.Avalonia.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Media;
using System;
using Brush = Avalonia.Media.IBrush;

namespace MapControl
{
    public partial class PushpinBorder : Decorator
    {
        public static readonly StyledProperty<CornerRadius> CornerRadiusProperty =
            DependencyPropertyHelper.Register<PushpinBorder, CornerRadius>(nameof(CornerRadius), new CornerRadius());

        public static readonly StyledProperty<Size> ArrowSizeProperty =
            DependencyPropertyHelper.Register<PushpinBorder, Size>(nameof(ArrowSize), new Size(10d, 20d));

        public static readonly StyledProperty<double> BorderWidthProperty =
            DependencyPropertyHelper.Register<PushpinBorder, double>(nameof(BorderWidth));

        public static readonly StyledProperty<Brush> BackgroundProperty =
            DependencyPropertyHelper.Register<PushpinBorder, Brush>(nameof(Background));

        public static readonly StyledProperty<Brush> BorderBrushProperty =
            DependencyPropertyHelper.Register<PushpinBorder, Brush>(nameof(BorderBrush));

        static PushpinBorder()
        {
            AffectsMeasure<PushpinBorder>(ArrowSizeProperty, BorderWidthProperty, CornerRadiusProperty);
            AffectsRender<PushpinBorder>(BackgroundProperty, BorderBrushProperty);
        }

        public double ActualWidth => Bounds.Width;
        public double ActualHeight => Bounds.Height;

        public CornerRadius CornerRadius
        {
            get => GetValue(CornerRadiusProperty);
            set => SetValue(CornerRadiusProperty, value);
        }

        public Brush Background
        {
            get => GetValue(BackgroundProperty);
            set => SetValue(BackgroundProperty, value);
        }

        public Brush BorderBrush
        {
            get => GetValue(BorderBrushProperty);
            set => SetValue(BorderBrushProperty, value);
        }

        protected override Size MeasureOverride(Size constraint)
        {
            var width = 2d * BorderWidth + Padding.Left + Padding.Right;
            var height = 2d * BorderWidth + Padding.Top + Padding.Bottom;

            if (Child != null)
            {
                Child.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
                width += Child.DesiredSize.Width;
                height += Child.DesiredSize.Height;
            }

            var minWidth = BorderWidth + Math.Max(
                CornerRadius.TopLeft + CornerRadius.TopRight,
                CornerRadius.BottomLeft + CornerRadius.BottomRight + ArrowSize.Width);

            var minHeight = BorderWidth + Math.Max(
                CornerRadius.TopLeft + CornerRadius.BottomLeft,
                CornerRadius.TopRight + CornerRadius.BottomRight);

            return new Size(
                Math.Max(width, minWidth),
                Math.Max(height, minHeight) + ArrowSize.Height);
        }

        protected override Size ArrangeOverride(Size size)
        {
            Child?.Arrange(new Rect(
                BorderWidth + Padding.Left,
                BorderWidth + Padding.Top,
                Child.DesiredSize.Width,
                Child.DesiredSize.Height));

            return DesiredSize;
        }

        public override void Render(DrawingContext drawingContext)
        {
            var pen = new Pen
            {
                Brush = BorderBrush,
                Thickness = BorderWidth,
                LineJoin = PenLineJoin.Round
            };

            drawingContext.DrawGeometry(Background, pen, BuildGeometry());

            base.Render(drawingContext);
        }
    }
}