Avalonia/samples/ControlCatalog/Pages/PointerContactsTab.cs

#nullable enable
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;

using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Media;
using Avalonia.Media.Immutable;

namespace ControlCatalog.Pages;

public class PointerContactsTab : Control
{
    class PointerInfo
    {
        public Point Point { get; set; }
        public Color Color { get; set; }
    }

    private static Color[] AllColors = new[]
    {
            Colors.Aqua,
            Colors.Beige,
            Colors.Chartreuse,
            Colors.Coral,
            Colors.Fuchsia,
            Colors.Crimson,
            Colors.Lavender,
            Colors.Orange,
            Colors.Orchid,
            Colors.ForestGreen,
            Colors.SteelBlue,
            Colors.PapayaWhip,
            Colors.PaleVioletRed,
            Colors.Goldenrod,
            Colors.Maroon,
            Colors.Moccasin,
            Colors.Navy,
            Colors.Wheat,
            Colors.Violet,
            Colors.Sienna,
            Colors.Indigo,
            Colors.Honeydew
        };

    private Dictionary<IPointer, PointerInfo> _pointers = new Dictionary<IPointer, PointerInfo>();

    public PointerContactsTab()
    {
        ClipToBounds = true;
    }

    void UpdatePointer(PointerEventArgs e)
    {
        if (!_pointers.TryGetValue(e.Pointer, out var info))
        {
            if (e.RoutedEvent == PointerMovedEvent)
                return;
            var colors = AllColors.Except(_pointers.Values.Select(c => c.Color)).ToArray();
            var color = colors[new Random().Next(0, colors.Length - 1)];
            _pointers[e.Pointer] = info = new PointerInfo { Color = color };
        }

        info.Point = e.GetPosition(this);
        InvalidateVisual();
    }

    protected override void OnPointerPressed(PointerPressedEventArgs e)
    {
        UpdatePointer(e);
        e.Pointer.Capture(this);
        e.Handled = true;
        base.OnPointerPressed(e);
    }

    protected override void OnPointerMoved(PointerEventArgs e)
    {
        UpdatePointer(e);
        e.Handled = true;
        base.OnPointerMoved(e);
    }

    protected override void OnPointerReleased(PointerReleasedEventArgs e)
    {
        _pointers.Remove(e.Pointer);
        e.Handled = true;
        InvalidateVisual();
    }

    protected override void OnPointerCaptureLost(PointerCaptureLostEventArgs e)
    {
        _pointers.Remove(e.Pointer);
        InvalidateVisual();
    }

    public override void Render(DrawingContext context)
    {
        context.FillRectangle(Brushes.Transparent, new Rect(default, Bounds.Size));
        foreach (var pt in _pointers.Values)
        {
            var brush = new ImmutableSolidColorBrush(pt.Color);

            context.DrawEllipse(brush, null, pt.Point, 75, 75);
        }
    }
}