Avalonia/samples/ControlCatalog/Pages/PointersPage.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reactive.Linq;
using System.Runtime.InteropServices;
using System.Threading;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Layout;
using Avalonia.Media;
using Avalonia.Media.Immutable;
using Avalonia.Threading;
using Avalonia.VisualTree;

namespace ControlCatalog.Pages;

public class PointersPage : Decorator
{
    public PointersPage()
    {
        Child = new TabControl
        {
            Items = new[]
            {
                new TabItem() { Header = "Contacts", Content = new PointerContactsTab() },
                new TabItem() { Header = "IntermediatePoints", Content = new PointerIntermediatePointsTab() }
            }
        };
    }
    
    
    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);
            }
        }
    }

    public class PointerIntermediatePointsTab : Decorator
    {
        public PointerIntermediatePointsTab()
        {
            this[TextBlock.ForegroundProperty] = Brushes.Black;
            var slider = new Slider
            {
                Margin = new Thickness(5),
                Minimum = 0,
                Maximum = 500
            };

            var status = new TextBlock()
            {
                HorizontalAlignment = HorizontalAlignment.Left,
                VerticalAlignment = VerticalAlignment.Top,
            };
            Child = new Grid
            {
                Children =
                {
                    new PointerCanvas(slider, status),
                    new Border
                    {
                        Background = Brushes.LightYellow,
                        Child = new StackPanel
                        {
                            Children =
                            {
                                new StackPanel
                                {
                                    Orientation = Orientation.Horizontal,
                                    Children =
                                    {
                                        new TextBlock { Text = "Thread sleep:" },
                                        new TextBlock()
                                        {
                                            [!TextBlock.TextProperty] =slider.GetObservable(Slider.ValueProperty)
                                                .Select(x=>x.ToString()).ToBinding()
                                        }
                                    }
                                },
                                slider
                            }
                        },

                        HorizontalAlignment = HorizontalAlignment.Right,
                        VerticalAlignment = VerticalAlignment.Top,
                        Width = 300,
                        Height = 60
                    },
                    status
                }
            };
        }

        class PointerCanvas : Control
        {
            private readonly Slider _slider;
            private readonly TextBlock _status;
            private int _events;
            private Stopwatch _stopwatch = Stopwatch.StartNew();
            private Dictionary<int, PointerPoints> _pointers = new();
            class PointerPoints
            {
                struct CanvasPoint
                {
                    public IBrush Brush;
                    public Point Point;
                    public double Radius;
                }

                readonly CanvasPoint[] _points = new CanvasPoint[1000];
                int _index;
                
                public  void Render(DrawingContext context)
                {
                    
                    CanvasPoint? prev = null;
                    for (var c = 0; c < _points.Length; c++)
                    {
                        var i = (c + _index) % _points.Length;
                        var pt = _points[i];
                        if (prev.HasValue && prev.Value.Brush != null && pt.Brush != null)
                            context.DrawLine(new Pen(Brushes.Black), prev.Value.Point, pt.Point);
                        prev = pt;
                        if (pt.Brush != null)
                            context.DrawEllipse(pt.Brush, null, pt.Point, pt.Radius, pt.Radius);

                    }

                }

                void AddPoint(Point pt, IBrush brush, double radius)
                {
                    _points[_index] = new CanvasPoint { Point = pt, Brush = brush, Radius = radius };
                    _index = (_index + 1) % _points.Length;
                }

                public void HandleEvent(PointerEventArgs e, Visual v)
                {
                    e.Handled = true;
                    if (e.RoutedEvent == PointerPressedEvent)
                        AddPoint(e.GetPosition(v), Brushes.Green, 10);
                    else if (e.RoutedEvent == PointerReleasedEvent)
                        AddPoint(e.GetPosition(v), Brushes.Red, 10);
                    else
                    {
                        var pts = e.GetIntermediatePoints(v);
                        for (var c = 0; c < pts.Count; c++)
                        {
                            var pt = pts[c];
                            AddPoint(pt.Position, c == pts.Count - 1 ? Brushes.Blue : Brushes.Black,
                                c == pts.Count - 1 ? 5 : 2);
                        }
                    }
                }
            }
            
            public PointerCanvas(Slider slider, TextBlock status)
            {
                _slider = slider;
                _status = status;
                DispatcherTimer.Run(() =>
                {
                    if (_stopwatch.Elapsed.TotalSeconds > 1)
                    {
                        _status.Text = "Events per second: " + (_events / _stopwatch.Elapsed.TotalSeconds);
                        _stopwatch.Restart();
                        _events = 0;
                    }

                    return this.GetVisualRoot() != null;
                }, TimeSpan.FromMilliseconds(10));
            }


            void HandleEvent(PointerEventArgs e)
            {
                _events++;
                Thread.Sleep((int)_slider.Value);
                InvalidateVisual();

                if (e.RoutedEvent == PointerReleasedEvent && e.Pointer.Type == PointerType.Touch)
                {
                    _pointers.Remove(e.Pointer.Id);
                    return;
                }

                if (!_pointers.TryGetValue(e.Pointer.Id, out var pt))
                    _pointers[e.Pointer.Id] = pt = new PointerPoints();
                pt.HandleEvent(e, this);
                
                
            }
            
            public override void Render(DrawingContext context)
            {
                context.FillRectangle(Brushes.White, Bounds);
                foreach(var pt in _pointers.Values)
                    pt.Render(context);
                base.Render(context);
            }

            protected override void OnPointerPressed(PointerPressedEventArgs e)
            {
                if (e.ClickCount == 2)
                {
                    _pointers.Clear();
                    InvalidateVisual();
                    return;
                }
                
                HandleEvent(e);
                base.OnPointerPressed(e);
            }

            protected override void OnPointerMoved(PointerEventArgs e)
            {
                HandleEvent(e);
                base.OnPointerMoved(e);
            }

            protected override void OnPointerReleased(PointerReleasedEventArgs e)
            {
                HandleEvent(e);
                base.OnPointerReleased(e);
            }
        }
    
    }
}