XAML-Map-Control/MapControl/MapScale.cs

// XAML Map Control - http://xamlmapcontrol.codeplex.com/
// © 2015 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

using System;
using System.Globalization;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace MapControl
{
    /// <summary>
    /// Draws a map scale overlay.
    /// </summary>
    public class MapScale : MapOverlay
    {
        public static readonly DependencyProperty PaddingProperty = Control.PaddingProperty.AddOwner(
            typeof(MapScale), new FrameworkPropertyMetadata(new Thickness(2d)));

        private double length;
        private Size size;

        static MapScale()
        {
            IsHitTestVisibleProperty.OverrideMetadata(
                typeof(MapScale), new FrameworkPropertyMetadata(false));

            MinWidthProperty.OverrideMetadata(
                typeof(MapScale), new FrameworkPropertyMetadata(100d));

            HorizontalAlignmentProperty.OverrideMetadata(
                typeof(MapScale), new FrameworkPropertyMetadata(HorizontalAlignment.Right));

            VerticalAlignmentProperty.OverrideMetadata(
                typeof(MapScale), new FrameworkPropertyMetadata(VerticalAlignment.Bottom));

            StrokeStartLineCapProperty.OverrideMetadata(
                typeof(MapScale), new FrameworkPropertyMetadata(PenLineCap.Round));

            StrokeEndLineCapProperty.OverrideMetadata(
                typeof(MapScale), new FrameworkPropertyMetadata(PenLineCap.Round));
        }

        public Thickness Padding
        {
            get { return (Thickness)GetValue(PaddingProperty); }
            set { SetValue(PaddingProperty, value); }
        }

        protected override Size MeasureOverride(Size availableSize)
        {
            if (ParentMap != null && ParentMap.CenterScale > 0d)
            {
                length = MinWidth / ParentMap.CenterScale;
                var magnitude = Math.Pow(10d, Math.Floor(Math.Log10(length)));

                if (length / magnitude < 2d)
                {
                    length = 2d * magnitude;
                }
                else if (length / magnitude < 5d)
                {
                    length = 5d * magnitude;
                }
                else
                {
                    length = 10d * magnitude;
                }

                size.Width = length * ParentMap.CenterScale + StrokeThickness + Padding.Left + Padding.Right;
                size.Height = FontSize * FontFamily.LineSpacing + StrokeThickness + Padding.Top + Padding.Bottom;
            }
            else
            {
                size.Width = size.Height = 0d;
            }

            return size;
        }

        protected override void OnRender(DrawingContext drawingContext)
        {
            if (ParentMap != null)
            {
                var x1 = Padding.Left + StrokeThickness / 2d;
                var x2 = size.Width - Padding.Right - StrokeThickness / 2d;
                var y1 = size.Height / 2d;
                var y2 = size.Height - Padding.Bottom - StrokeThickness / 2d;
                var text = new FormattedText(
                    length >= 1000d ? string.Format("{0:0} km", length / 1000d) : string.Format("{0:0} m", length),
                    CultureInfo.InvariantCulture, FlowDirection.LeftToRight, Typeface, FontSize, Foreground);

                drawingContext.DrawRectangle(Background ?? ParentMap.Background, null, new Rect(size));
                drawingContext.DrawLine(Pen, new Point(x1, y1), new Point(x1, y2));
                drawingContext.DrawLine(Pen, new Point(x2, y1), new Point(x2, y2));
                drawingContext.DrawLine(Pen, new Point(x1, y2), new Point(x2, y2));
                drawingContext.DrawText(text, new Point((size.Width - text.Width) / 2d, 0d));
            }
        }

        protected override void OnViewportChanged()
        {
            InvalidateMeasure();
        }
    }
}