AvaloniaTouchInputAdapter.cs

using System.Collections.Concurrent;
using System.Drawing;
using Avalonia.Controls;
using Avalonia.Input;
using Gondwana.Input.Touch;
using Microsoft.Extensions.Logging;
 
namespace Gondwana.Avalonia.Input.Touch;

public sealed class AvaloniaTouchInputAdapter : ITouchAdapter, IDisposable
{
    private readonly Control _control;
    private readonly bool _emulateMouse;
    private readonly Dictionary<int, TouchPoint> _activeTouches = new();
    private TouchPoint[] _activeTouchesSnapshot = Array.Empty<TouchPoint>();
    private readonly ConcurrentQueue<TouchPoint> _pendingBegins = new();
    private readonly ConcurrentQueue<TouchPoint> _pendingEnds = new();
    private bool _isDisposed;

    public IReadOnlyList<TouchPoint> ActiveTouches => _activeTouchesSnapshot;

    public AvaloniaTouchInputAdapter(Control control, bool emulateMouse = false)
    {
        _control = control ?? throw new ArgumentNullException(nameof(control));
        _emulateMouse = emulateMouse;
 
        _control.PointerPressed += OnPointerPressed;
        _control.PointerMoved += OnPointerMoved;
        _control.PointerReleased += OnPointerReleased;
        _control.PointerCaptureLost += OnPointerCaptureLost;
 
        Engine.Logger.LogInformation("AvaloniaTouchInputAdapter initialized.");
    }
 
    private void OnPointerPressed(object? sender, PointerPressedEventArgs e)
    {
        if (e.Pointer.Type == PointerType.Mouse && !_emulateMouse)
            return;
 
        // For mouse pointers, only emulate touch for the primary (left) button.
        // Right- and middle-clicks should not generate touch events.
        if (e.Pointer.Type == PointerType.Mouse &&
            !e.GetCurrentPoint(sender as Control).Properties.IsLeftButtonPressed)
            return;
 
        var id = GetTouchId(e.Pointer);
        var pos = GetPosition(e, sender as Control);
        var point = new TouchPoint(id, pos, TouchPhase.Began);
 
        _activeTouches[id] = point;
        RebuildSnapshot();
        _pendingBegins.Enqueue(point);
    }
 
    private void OnPointerMoved(object? sender, PointerEventArgs e)
    {
        if (e.Pointer.Type == PointerType.Mouse && !_emulateMouse)
            return;
 
        var id = GetTouchId(e.Pointer);
 
        // Only track movement for contacts that are already active (i.e., button/finger is held).
        // On desktop, PointerMoved fires even without a button down; skip those.
        if (!_activeTouches.ContainsKey(id))
            return;
 
        var pos = GetPosition(e, sender as Control);
        var point = new TouchPoint(id, pos, TouchPhase.Moved);
 
        _activeTouches[id] = point;
        RebuildSnapshot();
    }
 
    private void OnPointerReleased(object? sender, PointerReleasedEventArgs e)
    {
        if (e.Pointer.Type == PointerType.Mouse && !_emulateMouse)
            return;
 
        var id = GetTouchId(e.Pointer);
 
        if (!_activeTouches.ContainsKey(id))
            return;
 
        var pos = GetPosition(e, sender as Control);
        var point = new TouchPoint(id, pos, TouchPhase.Ended);
 
        _activeTouches.Remove(id);
        RebuildSnapshot();
        _pendingEnds.Enqueue(point);
    }
 
    private void OnPointerCaptureLost(object? sender, PointerCaptureLostEventArgs e)
    {
        if (e.Pointer.Type == PointerType.Mouse && !_emulateMouse)
            return;
 
        // The system cancelled the pointer (e.g. incoming call on Android).
        var id = GetTouchId(e.Pointer);
 
        if (!_activeTouches.TryGetValue(id, out var existing))
            return;
 
        var point = new TouchPoint(existing.Id, existing.Position, TouchPhase.Cancelled);
        _activeTouches.Remove(id);
        RebuildSnapshot();
        _pendingEnds.Enqueue(point);
    }

    public IReadOnlyList<TouchPoint> ConsumeBeganTouches()
    {
        if (_pendingBegins.IsEmpty)
            return Array.Empty<TouchPoint>();
 
        var snapshot = new List<TouchPoint>(_pendingBegins.Count);
        while (_pendingBegins.TryDequeue(out var point))
            snapshot.Add(point);
        return snapshot;
    }

    public IReadOnlyList<TouchPoint> ConsumeEndedTouches()
    {
        if (_pendingEnds.IsEmpty)
            return Array.Empty<TouchPoint>();
 
        var snapshot = new List<TouchPoint>(_pendingEnds.Count);
        while (_pendingEnds.TryDequeue(out var point))
            snapshot.Add(point);
        return snapshot;
    }
 
    private void RebuildSnapshot()
    {
        _activeTouchesSnapshot = _activeTouches.Values.ToArray();
    }

    private static int GetTouchId(IPointer pointer)
        => pointer.Type == PointerType.Mouse ? 0 : (int)pointer.Id;
 
    private static Point GetPosition(PointerEventArgs e, Control? relativeTo)
    {
        var pos = e.GetPosition(relativeTo);
        return PointerCoordinates.ToScreenPx(relativeTo, new PointF((float)pos.X, (float)pos.Y));
    }

    public void Dispose()
    {
        if (_isDisposed) return;
        _isDisposed = true;
 
        _control.PointerPressed -= OnPointerPressed;
        _control.PointerMoved -= OnPointerMoved;
        _control.PointerReleased -= OnPointerReleased;
        _control.PointerCaptureLost -= OnPointerCaptureLost;
 
        Engine.Logger.LogInformation("AvaloniaTouchInputAdapter disposed.");
    }
}