annotations/Azaion.Annotator/Extensions/CanvasExtensions.cs

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

namespace Azaion.Annotator.Extensions;

public static class CanvasExtensions
{
    public static readonly DependencyProperty PercentPositionProperty =
        DependencyProperty.RegisterAttached("PercentPosition", typeof(Point), typeof(CanvasExtensions), 
            new PropertyMetadata(new Point(0, 0), OnPercentPositionChanged));
    
    public static readonly DependencyProperty PercentSizeProperty =
        DependencyProperty.RegisterAttached("PercentSize", typeof(Point), typeof(CanvasExtensions), 
            new PropertyMetadata(new Point(0, 0), OnPercentSizeChanged));

    private static void OnPercentSizeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        
    }
    
    public static void SetPercentPosition(DependencyObject obj, Point value) => obj.SetValue(PercentPositionProperty, value);
    
    private static void OnPercentPositionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (!(d is FrameworkElement element)) return;
        if (!(VisualTreeHelper.GetParent(element) is Canvas canvas)) return;

        canvas.SizeChanged += (s, arg) =>
        {
            var percentPosition = (Point)element.GetValue(PercentPositionProperty);
            var xPosition = percentPosition.X * canvas.ActualWidth - element.ActualWidth / 2;
            var yPosition = percentPosition.Y * canvas.ActualHeight - element.ActualHeight / 2;
            Canvas.SetLeft(element, xPosition);
            Canvas.SetTop(element, yPosition);
        };
    }
}