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

using System;
#if WPF
using System.Windows;
using System.Windows.Media;
#elif UWP
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Media;
#elif WINUI
using Windows.Foundation;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Media;
#elif AVALONIA
using Avalonia;
using Avalonia.Layout;
using Avalonia.Media;
#endif

namespace MapControl;

public partial class PushpinBorder
{
    public Size ArrowSize
    {
        get => (Size)GetValue(ArrowSizeProperty);
        set => SetValue(ArrowSizeProperty, value);
    }

    public double BorderWidth
    {
        get => (double)GetValue(BorderWidthProperty);
        set => SetValue(BorderWidthProperty, value);
    }

    protected virtual Geometry BuildGeometry()
    {
        var width = Math.Floor(ActualWidth);
        var height = Math.Floor(ActualHeight);
        var x1 = BorderWidth / 2d;
        var y1 = BorderWidth / 2d;
        var x2 = width - x1;
        var y3 = height - y1;
        var y2 = y3 - ArrowSize.Height;
        var aw = ArrowSize.Width;
        var r1 = CornerRadius.TopLeft;
        var r2 = CornerRadius.TopRight;
        var r3 = CornerRadius.BottomRight;
        var r4 = CornerRadius.BottomLeft;

        var figure = new PathFigure
        {
            StartPoint = new Point(x1, y1 + r1),
            IsClosed = true,
            IsFilled = true
        };

        figure.ArcTo(x1 + r1, y1, r1);
        figure.LineTo(x2 - r2, y1);
        figure.ArcTo(x2, y1 + r2, r2);

        if (HorizontalAlignment == HorizontalAlignment.Right)
        {
            figure.LineTo(x2, y3);
            figure.LineTo(x2 - aw, y2);
        }
        else
        {
            figure.LineTo(x2, y2 - r3);
            figure.ArcTo(x2 - r3, y2, r3);
        }

        if (HorizontalAlignment == HorizontalAlignment.Center)
        {
            var c = width / 2d;
            figure.LineTo(c + aw / 2d, y2);
            figure.LineTo(c, y3);
            figure.LineTo(c - aw / 2d, y2);
        }

        if (HorizontalAlignment == HorizontalAlignment.Left || HorizontalAlignment == HorizontalAlignment.Stretch)
        {
            figure.LineTo(x1 + aw, y2);
            figure.LineTo(x1, y3);
        }
        else
        {
            figure.LineTo(x1 + r4, y2);
            figure.ArcTo(x1, y2 - r4, r4);
        }

        var geometry = new PathGeometry();
        geometry.Figures.Add(figure);

        return geometry;
    }
}

internal static class PathFigureExtensions
{
    public static void LineTo(this PathFigure figure, double x, double y)
    {
        figure.Segments.Add(new LineSegment
        {
            Point = new Point(x, y)
        });
    }

    public static void ArcTo(this PathFigure figure, double x, double y, double r)
    {
        if (r > 0d)
        {
            figure.Segments.Add(new ArcSegment
            {
                Point = new Point(x, y),
                Size = new Size(r, r),
                SweepDirection = SweepDirection.Clockwise
            });
        }
    }
}