BlazorMouseAdapter.cs

using System.Drawing;
using Gondwana.Blazor.Rendering;
using Gondwana.Input.Keyboard;
using Gondwana.Input.Mouse;
using BrowserMouseEventArgs = Microsoft.AspNetCore.Components.Web.MouseEventArgs;
using BrowserWheelEventArgs = Microsoft.AspNetCore.Components.Web.WheelEventArgs;
using GondwanaMouseButton = Gondwana.Input.Mouse.MouseButton;
 
namespace Gondwana.Blazor.Input.Mouse;

public sealed class BlazorMouseAdapter : IMouseAdapter, IDisposable
{
    private readonly BlazorRenderSurfaceComponentBase _component;
    private readonly HashSet<GondwanaMouseButton> _pressed = new();
    private readonly object _pressedLock = new();
    private PointF _currentPosition;
    private KeyboardModifierState _modifiers;
    private int _scrollDelta;

    public Point CurrentPosition => _component.ToScreenPx(_currentPosition.X, _currentPosition.Y);

    public HashSet<GondwanaMouseButton> PressedButtons
    {
        get
        {
            lock (_pressedLock)
                return new HashSet<GondwanaMouseButton>(_pressed);
        }
    }

    public KeyboardModifierState CurrentKeyboardModifiers => _modifiers;

    public int ScrollDelta => Interlocked.Exchange(ref _scrollDelta, 0);

    public BlazorMouseAdapter(BlazorBitmapRenderSurfaceComponent component)
        : this((BlazorRenderSurfaceComponentBase)component)
    {
    }

    public BlazorMouseAdapter(BlazorRenderSurfaceComponentBase component)
    {
        ArgumentNullException.ThrowIfNull(component);
        _component = component;
 
        _component.MouseDown += OnMouseDown;
        _component.MouseUp += OnMouseUp;
        _component.MouseMove += OnMouseMove;
        _component.Wheel += OnWheel;
    }
 
    private void OnMouseDown(BrowserMouseEventArgs e)
    {
        lock (_pressedLock)
            _pressed.Add(MapButton(e.Button));
        UpdatePosition(e);
    }
 
    private void OnMouseUp(BrowserMouseEventArgs e)
    {
        lock (_pressedLock)
            _pressed.Remove(MapButton(e.Button));
        UpdatePosition(e);
    }
 
    private void OnMouseMove(BrowserMouseEventArgs e) => UpdatePosition(e);
 
    private void OnWheel(BrowserWheelEventArgs e)
    {
        // Browser DeltaY: positive = scroll down. Negate to match the convention used by other
        // Gondwana adapters (positive = scroll up / scroll away from user).
        Interlocked.Add(ref _scrollDelta, (int)(-e.DeltaY));
    }
 
    private void UpdatePosition(BrowserMouseEventArgs e)
    {
        _currentPosition = new PointF((float)e.OffsetX, (float)e.OffsetY);
 
        _modifiers = KeyboardModifierState.None;
        if (e.ShiftKey) _modifiers |= KeyboardModifierState.Shift;
        if (e.CtrlKey) _modifiers |= KeyboardModifierState.Ctrl;
        if (e.AltKey) _modifiers |= KeyboardModifierState.Alt;
    }
 
    private static GondwanaMouseButton MapButton(long button) => button switch
    {
        0 => GondwanaMouseButton.Left,
        1 => GondwanaMouseButton.Middle,
        2 => GondwanaMouseButton.Right,
        _ => GondwanaMouseButton.None
    };

    public void Dispose()
    {
        _component.MouseDown -= OnMouseDown;
        _component.MouseUp -= OnMouseUp;
        _component.MouseMove -= OnMouseMove;
        _component.Wheel -= OnWheel;
    }
}